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This so-called Kessler effect could in theory happen if a space debris collision sets off a chain reaction, with the resulting debris cloud making an entire orbital path unsafe for many years.Almost 60 years of rocket launches, explosions and collisions have left 300 000 pieces of space junk larger…

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A four-armed robotic junk collector will be launched into space by the European Space Agency in what it says will be the first mission to remove an item of debris from orbit.

The ClearSpace-1 mission, scheduled for launch in 2025, will cost €120m and will grab a single piece of junk. But the agency hopes the mission will pave the way for a wide-reaching clear-up operation, with Esa's director general calling for new rules that would compel those who launch satellites to take responsibility for removing them from orbit once they are retired from use.

"Imagine how dangerous sailing the high seas would be if all the ships ever lost in history were still drifting on top of the water," said Jan Wörner, Esa's director general. "That is the current situation in orbit, and it cannot be allowed to continue."

In the past 60 years, thousands of tonnes of junk has accumulated around the Earth, including old rocket parts, about 3,500 defunct satellites and an estimated 750,000 smaller fragments, some from collisions between larger bits of junk. The fragments are typically circulating with a velocity of 20,000km/h (12,500mph).

Unless a clear-up operation is mounted, the chances of collisions will escalate as thousands more satellites are put into orbit.

Funding for the mission was agreed at Space19+, ESA's misterial council, which took place in Seville, Spain, at the end of November. The mission will be run by a consortium led by a Swiss startup called Clearspace.

The target for ClearSpace-1 is a piece of junk called Vespa, which was left in an orbit around 800km above the Earth by ESA's Vega launcher in 2013. Vespa weighs 100kg - around the size of a small satellite - and was selected because it has a simple shape and sturdy construction, which make it unlikely to fragment when it is grabbed.

The "chaser" ClearSpace space probe will be launched into the target orbit where it will track down Vespa, grab it using a quartet of robotic arms and drag it out of orbit, with Vespa and the chaser both burning up in the atmosphere on the way down to Earth.

A future ambition is to create a clear-up robot that could eject junk into the atmosphere, before continuing to capture and de-orbit other pieces of junk.

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European Space Agency to launch space debris collector in 2025

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A four-armed robotic junk collector will be launched into space by the European Space Agency in what it says will be the first mission to remove an item of debris from orbit. The ClearSpace-1 mission, scheduled for launch in 2025, will cost €120m and will grab a single piece of junk.

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An artist rendering shows how a ClearSpace spacecraft would remove a large piece of debris from space. (ClearSpace)

The Pentagon wants to clean up space. Well, not all of it. But at least the increasingly polluted region in low Earth orbit, where thousands of bits of debris, spent rocket stages and dead satellites whiz uncontrollably, like so much flotsam.
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All of that junk from decades of space travel is not just unseemly but also poses serious risks to all sorts of satellites, including those the Pentagon and intelligence agencies use for national security. But tidying up space is far more difficult than cleaning a freeway or even an ocean. For one, objects in orbit are traveling incredibly fast - about 17,500 mph, or about five miles a second. Some of them are tumbling violently, making them difficult to grab. And it's expensive to launch a spacecraft capable of sidling up to a piece of space garbage, grabbing it and tugging it out of orbit so it can burn up in the atmosphere.

Still, the Defense Department, as well as other government agencies, has grown convinced that as Earth's orbit becomes more crowded - and dirty - something needs to be done. Even something as small as a screw acts like a bullet in space and can cause enormous damage.

Pieces of debris have cracked a window on the International Space Station. Last year, a micrometeorite shot right through the station's robotic arm, leaving a bullet-size hole. The Defense Department does not want that to happen to one of the satellites it uses for missile defense, or spying, or guiding precision munitions with GPS.

Recently, it has launched a program, called Orbital Prime, under the U.S. Space Force that will give companies seed money to develop the technology needed to clean up space. In the first round of the program, companies can win awards of $250,000, with as much as $1.5 million in a second round of funding. The program will culminate with a test demonstration in orbit.

In a video posted online advertising the program, Gen. David Thompson, the Space Force's vice chief of space operations, said the Pentagon tracks more than 40,000 objects in space the size of a fist or larger. But he said there are at least 10 times as many smaller objects in orbit that the Pentagon can't reliably track.

"This debris and associated congestion threaten the long-term sustainability of the space domain," he said. "It demands action."

The long-simmering issue again burst into the spotlight late last year after Russia blew up a dead satellite with a missile, creating a massive debris cloud that threatened the people on the International Space Station. The crew - which included two Russian cosmonauts, four Americans and one European astronaut - were forced to board their spacecraft and wait to see if the station got hit and whether they would have to flee for Earth. NASA Administrator Bill Nelson called it "reckless and dangerous" and said he was "outraged by this irresponsible and destabilizing action."

One of the concerns is that the more debris there is in space, the more it could proliferate - debris creating more debris.

Astroscale is one of the companies that intends to participate in the Space Force's Orbital Prime program. Headquartered in Japan, the company, which has a U.S. office in Denver, is developing a spacecraft it hopes would be able to meet a tumbling object in space, mimic its spin and then grab it using a magnet. It is also working with the Japanese space agency to rendezvous and inspect a spent Japanese rocket stage. A separate mission, to be completed by the space agency, would remove the stage from orbit.

The missions are not easy. On a test this week, the company ran into trouble. Its spacecraft successfully released an object in space, but there was a problem, or an "anomaly," once it attempted to navigate toward it. "For the safety of the mission we have decided not to proceed with the capture attempt until the anomalies are resolved," the company said in a statement Wednesday.

Still, it remained optimistic that a vibrant space economy is dependent on it being clean.

"We want the space economy to grow," said Ron Lopez, president and managing director of Astroscale U.S. "We want to be an enabler of that. And we want to make sure that we're doing that longterm and that environment is there for future generations."

The issue also has gotten the attention of the White House. Its Office of Science and Technology Policy recently sought input from space industry leaders on what to do about the problem.

Speaker after speaker said that governments around the world need to fund these efforts to help create a market for companies to operate. They also said that it had become an imperative for the governments largely responsible for the problem in the first place.

"If the U.S. Navy had had a derelict ship sitting in sovereign waters, creating a safety hazard, the U.S. Navy would go out and grab that ship," said Doug Loverro, a former top Pentagon and NASA space official. "And I'm not sure why we don't see the same responsibility for government for their derelict ships and their derelict bodies that are in space today."

Or, as James Lowenthal, a professor of astronomy at Smith College in Massachusetts, put it: "Just as we rely on the government to protect the air we breathe and the water we drink, we have to rely on the government to protect the resource and the global commons of low Earth orbit."

Europe and Britain have also begun to work toward cleaning up debris - a move that's long overdue, space industry experts say. ClearSpace, a Swiss company, has a contract with the European Space Agency to remove a large piece of debris - a symbol that the issue is finally being addressed. It proposes using a spacecraft with large arms that would grapple the debris like a Venus' flytrap.

"This is why we're here. Because we think change is possible," said Luc Piguet, ClearSpace's co-founder and chief executive. "And we think we can build a space industry that operates with a different model, where maintenance is just a normal part of it."

But others say the effort will need to grow and involve international collaboration since most of the debris was generated by the United States, Russia and China. If governments don't band together to act soon, there will eventually be collisions - or conjunctions, as they're called - further polluting space. And although the Pentagon tracks objects in space and can warn satellite operators of a high likelihood of a collision, it does not have the authority to force anyone to move their satellite. In the meantime, the number of close calls has climbed. But a miss doesn't get much attention.

There are "lots of near-misses, and people are able to go: 'Not a big deal. See, we're resilient,' " said Darren McKnight, a senior technical fellow at LeoLabs, a company that tracks space objects. "No, you were lucky. And the statistics will catch up with you. And you will roll the dice, and they will come up snake eyes one of these times."

McKnight has worked with a consortium of scientists from all over the world to identify the 50 most dangerous large objects - U.S., Russian and Chinese spent satellites and rocket stages - that have the greatest chance of colliding with other bits of debris.

"They literally are the size of a yellow school bus," he said. "The only difference is they have no brakes, they have no steering wheel, and they're going 15,000 miles per hour." There are 18 spent Russian rocket stages "within a small altitude band, and we call that the bad neighborhood."

That neighborhood is about 500 miles high, cluttered with large objects that will stay aloft for years, perhaps even many decades - each turn around Earth presenting another chance for a collision. Cleaning it up is a big and difficult job, one that McKnight thinks the United States, Russia and China should collaborate on.

"It will take leadership," he said. And a willingness to look past grievances on the ground. But ultimately a partnership would be necessary and is in all of the countries' interest: "Why can't we cooperatively clean up what we cooperatively messed up?"

correction

Previous versions of this article incorrectly said Smith College is in Michigan. It is in Massachusetts. This post has been corrected.

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The Pentagon is looking for garbage collectors in space

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The Pentagon wants to clean up space. Well, not all of it. But at least the increasingly polluted region in low Earth orbit, where thousands of bits of debris, spent rocket stages and dead satellites whiz uncontrollably, like so much flotsam. Tech is not your friend. We are.

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This site may earn affiliate commissions from the links on this page. Terms of use.

Humans have gotten rather good at launching things into orbit, but we don't always bother to bring them back down when we're done with them. This has led to a problem with accumulating space junk, which can be serious hazards for future space missions. Japan has launched the Kounotori 6 spacecraft on its way to the International Space Station, but this cargo vessel has a dual purpose. It has been equipped with an electromagnetic tether designed to drag space junk out of orbit.

ESA scientists estimate there are hundreds of thousands of individual pieces of highly dangerous space debris above Earth thanks to human activity. As of a few years ago, there were around 670,000 objects between 1 and 10 cm and 29,000 objects larger than 10cm. There are also millions of small objects under 1 cm across, and these can still have enough energy to cause damage to spacecraft and satellites if they collide at high enough relative velocities.

So, space is a bit of a junk heap. So why aren't we more careful about bringing things back into the atmosphere when we're done with them? Money. Once an object is in a stable orbit, you need to expend energy to slow it down (i.e. burning retrograde) until it hits the atmosphere. That means you'd need to equip most satellites and probes with engines and extra fuel, which isn't usually considered a priority. Thus, Japan is experimenting with Kounotori 6 as a way to clean up after everyone.

Kounotori 6 has a 2,300-foot electrodynamic tether (EDT), which could one day be used to send space junk back into the atmosphere where it can burn up safely. The EDT has a 44 pound weight at the end to simulate a piece of space junk that needs to be dragged out of orbit. Electrons from the ambient plasma surrounding Earth are pulled in by the tether and emitted by the vehicle. This provides a small amount of thrust that can be used to de-orbit the object (along with the vehicle) without expensive engines and fuel tanks. The Japanese Space Agency calls this a "current drive."

The test version attached to Kounotori 6 isn't long enough to drag the spacecraft out of orbit. It's going to be used to test the current drive for a week before the cargo mission to the ISS continues. The tether will be jettisoned before Kounotori 6 approaches the station. There are plans for future versions of the EDT that are 16,400 and 32,800 feet long, which should produce enough thrust to drag larger objects out of orbit.

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Japanese spacecraft will test space junk collector on its way to the ISS - ExtremeTech

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This site may earn affiliate commissions from the links on this page. Terms of use. Humans have gotten rather good at launching things into orbit, but we don't always bother to bring them back down when we're done with them. This has led to a problem with accumulating space junk, which can be serious hazards for future space missions.

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Author links open overlay panel Ghada Sokar a Decebal Constantin Mocanu a b Mykola Pechenizkiy a

Show more

Abstract

The continual learning (CL) paradigm aims to enable neural networks to learn tasks continually in a sequential fashion. The fundamental challenge in this learning paradigm is catastrophic forgetting previously learned tasks when the model is optimized for a new task, especially when their data is not accessible. Current architectural-based methods aim at alleviating the catastrophic forgetting problem but at the expense of expanding the capacity of the model. Regularization-based methods maintain a fixed model capacity; however, previous studies showed the huge performance degradation of these methods when the task identity is not available during inference (e.g. class incremental learning scenario). In this work, we propose a novel architectural-based method referred as SpaceNet1 for class incremental learning scenario where we utilize the available fixed capacity of the model intelligently. SpaceNet trains sparse deep neural networks from scratch in an adaptive way that compresses the sparse connections of each task in a compact number of neurons. The adaptive training of the sparse connections results in sparse representations that reduce the interference between the tasks. Experimental results show the robustness of our proposed method against catastrophic forgetting old tasks and the efficiency of SpaceNet in utilizing the available capacity of the model, leaving space for more tasks to be learned. In particular, when SpaceNet is tested on the well-known benchmarks for CL: split MNIST, split Fashion-MNIST, CIFAR-10/100, and iCIFAR100, it outperforms regularization-based methods by a big performance gap. Moreover, it achieves better performance than architectural-based methods without model expansion and achieves comparable results with rehearsal-based methods, while offering a huge memory reduction.

Keywords

Class incremental learning

Ghada Sokar is a Ph.D. student at the Department of Mathematics and Computer Science, Eindhoven University of Technology, the Netherlands. She is mainly working on continual learning. Her current research interests are continual lifelong learning, few-shot learning, and sparse neural networks. She is also a teaching assistant at Eindhoven University of Technology. She contributes to different machine learning courses. Previously, she was a research scientist at Mentor Graphic, Egypt.

Decebal Constantin Mocanu is an Assistant Professor in Artificial Intelligence and Machine Learning at University of Twente, the Netherlands; Guest Assistant Professor at Eindhoven University of Technology (TU/e); and an alumni member of TU/e Young Academy of Engineering. During his PhD (graduated June 2017 at TU/e) and after that, Decebal worked on connections and nodes importance in complex networks, communication networks, memory-free online learning, transfer and multitask learning, reinforcement learning, continual learning, sparse and scalable artificial neural networks. He introduced the concepts of generative replay and sparse training. His short-term research interest is to conceive scalable deep artificial neural network models and their corresponding learning algorithms using principles from network science, evolutionary computing, optimization, and neuroscience.

Mykola Pechenizkiy is Full Professor and Chair of the Data Mining research group that is part of the Data and Artificial Intelligence cluster at the Department of Mathematics and Computer Science, Eindhoven University of Technology, the Netherlands. His core expertise and research interests are in predictive analytics and knowledge discovery from evolving data, and in their application to real-world problems in industry, medicine and education. He has been a principal investigator of several nationally funded and industry funded projects that being inspired by challenges of the real-world applications aim at developing foundations for next generation of informed and responsible predictive analytics. Over the past decade he has co-authored more than 100 peer-reviewed publications. He serves on several program committees and editorial boards of leading data mining and AI conferences (AAAI, ECMLPKDD, IJCAI) and journals (Data Mining and Knowledge Discovery, Machine Leaning).

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SpaceNet: Make Free Space for Continual Learning

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Author links open overlay panel Ghada Sokar Person a Envelope Decebal Constantin Mocanu a b Mykola Pechenizkiy a Show more The continual learning (CL) paradigm aims to enable neural networks to learn tasks continually in a sequential fashion.

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If a team of astronomers has its way, the International Space Station will be outfitted with a spiffy laser-wielding telescope. No, no, hold on---it's not to kill aliens or rebel civilizations. It's to clean up a huge mess.

If anything rivals the human drive for exploration, it is the apparent need to leave a spectacular plume of trash in our wake. In space, the problem is becoming acute. Decades of discarded satellites and unchecked collisions have left some 3,000 tons of debris in orbit. That's roughly 15 blue whales, 600 elephants, or 1,500 cars.

Mankind's slovenly ways threaten our continued use of space-based satellites, which have become a core component of modern technological infrastructure. You've probably used those satellites dozens of ways so far today. Have you sent a text? Watched TV? Used GPS? Checked the weather? If you'd like to keep doing these things, astronomers will soon need to find a way of tidying up low Earth orbit. In that region, between 100 and 1,250 miles above the planet, mere flecks of paint (of which there are many) travel with sufficient force to sever electrical wires, dent spacecraft, and kill astronauts.

Lasers could be the saviors in operation Orbital Clean House. A team of astronomers at Japan's RIKEN, a network of basic-research laboratories, have proposed adding debris-zapping capabilities to a telescope they are already developing for the ISS. They plan to start on a small scale, with a laser no more powerful than the pointer you use to play with your cat. In time, the power could be increased to become a proper laser cannon. (Yes, dear reader, a laser cannon.)

If the notion of lasers in space sounds slightly terrifying, you're not alone. "The problem with it is mostly political," says Don Kessler, who spent more than 30 years at NASA's Johnson Space Center. "Everyone is afraid you are going to weaponize space." Kessler began the field of studying orbital debris and lends his name to "Kessler syndrome," a scenario in which colliding debris begins a cascade of increasing debris and destruction.

If you can take out a derelict satellite or rocket body, you also have the ability to kill a working satellite. And given how important satellites are to militaries, an attack could prompt a war. But if astronomers are going to put a laser cannon anywhere above Earth, the ISS would be the place to do it. Bolting the proposed laser to the ostensibly neutral space station---which already must make frequent maneuvers to avoid larger, tracked pieces of debris---might be a way to make a scientifically sound idea politically sound as well.

For the team at RIKEN, the proposed laser cannon is a way to not only clean up their beloved orbits but also make their telescope, the Extreme Universe Space Observatory, more practically relevant, says project scientist Marco Casolino. With its wide field of view and the ability to register even the quickest flashes of light, the scope would be well suited for spotting debris as it whizzes past the ISS.

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The Mad Plan to Clean Up Space Junk With a Laser Cannon

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If a team of astronomers has its way, the International Space Station will be outfitted with a spiffy laser-wielding telescope. No, no, hold on---it's not to kill aliens or rebel civilizations. It's to clean up a huge mess. If anything rivals the human drive for exploration, it is the apparent need to leave a spectacular plume of trash in our wake.

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It's not this.

China's space broom isn't the Death Star super laser. It's an orbiting satellite with a laser only powerful enough to heat up pieces of space junk, so that they change course burn up in the atmosphere.

In a recent article in scientific journal Optik, a faculty member at China's Air Force Engineering University proposed building a laser-armed satellite, a "broom" to do battle with the pernicious problem of space debris.

Laser-armed satellites, naturally, generate a lot of attention, and so the proposal of Quan Wen and his co-authors has made its way into several splashy headlines. But it's more than hype. The concept addresses a real (and growing) problem: there's something like 17,852 artificial objects orbiting earth (PDF), and an estimated 300,000-plus pieces of space debris larger than a marble. At the fast orbital velocities up in space, even large craft like the International Space Station have to maneuver out of the way of small objects to avoid catastrophic damage.

Quan's research looks at the efficacy of a hypothetical laser operating near the infrared spectrum. It would blast away targeted space debris for a couple minutes, at a rate of twenty bursts of laserfire a second. That amount of energy would be sufficient to vaporize part of the object's mass. Contrary to public imagination, space laser brooms like the one proposed don't actually vaporize space debris, but rather "burn off" a chunk. This would create sufficient kinetic force from the chemical combustion to change the object's orbit. With that change in direction, the debris will quickly reenter the atmosphere and burn up. Because of atmospheric distortion, it's much more effective to zap space debris with a satellite than, say, a ground-based laser.

Of course, for now it's all theory. The laser broom would need to be actually mounted on a satellite and lofted into orbit to test its true efficacy. And even then, it'd still face some legal grey areas (technically speaking, space debris are still the property of owners of the satellites they originated from, which is very, very difficult to track) as well as major suspicion about the idea of implementing a weapon-like technology up in space.

Like many others, China's space program has both civilian and military applications. (The AoLong 1 satellite, for example, has a robotic arm for mechanically de-orbiting space debris that has has potential as an anti-satellite sabotage technology.) And so there's an obvious question: can the space laser broom be an anti-satellite weapon? It's certainly possible, though a cost-effective laser broom would need to be small-just big enough to take care of small debris. To quickly deal serious damage to enemy spacecraft, one would need a much larger space laser weapon; perhaps an orbital battlemoon?
Peter Warren Singer is a strategist and senior fellow at the New America Foundation. He has been named by Defense News as one of the 100 most influential people in defense issues. He was also dubbed an official "Mad Scientist" for the U.S. Army's Training and Doctrine Command. Jeffrey is a national security professional in the greater D.C. area.
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Space’s Trash Collector? A Japanese Entrepreneur Wants the Job (Published 2016)

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Net to catch space debris around Earth is successfully deployed

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Scientists are trying to clean up the tens of thousands of pieces of junk in space.

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https://www.cnn.com/2017/06/13/tech/space-sweepers-astroscale-japan/index.html

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Magsat ( Magnetic field Satellite, Applications Explorer Mission-C or AEM-C or Explorer 61) was a NASA/ USGS (United States Geological Survey) spacecraft, launched on 30 October 1979. The mission was to map the Earth's magnetic field, the satellite had two magnetometers. The scalar ( cesium vapor) and vector magnetometers gave Magsat a capability beyond that of any previous spacecraft. Extended by a telescoping boom, the magnetometers were distanced from the magnetic field created by the satellite and its electronics. The satellite carried two magnetometers, a three-axis fluxgate magnetometer for determining the strength and direction of magnetic fields, and an ion-vapor/vector magnetometer for determining the magnetic field caused by the vector magnetometer itself. Magsat is considered to be one of the more important Science/Earth orbiting satellites launched; the data it accumulated is still being used, particularly in linking new satellite data to past observations.

The Magsat project was a joint NASA/USGS effort to measure near-Earth magnetic fields on a global basis. Objectives included obtaining an accurate description of the Earth's magnetic field, obtaining data for use in the update and refinement of world and regional magnetic charts, compilation of a global crustal magnetic anomaly map, and interpretation of that map in terms of geologic/geophysical models of the Earth's crust.

The Explorer 61 was launched into a low, near-polar, orbit by the Scout vehicle. The basic spacecraft was made up of two distinct parts: the instrument module that contained a vector and a scalar magnetometer and their unique supporting gear; and the base module that contained the necessary data-handling, power, communications, command, and attitude-control subsystems to support the instrument module. The base module complete with its subsystems was composed of residual Small Astronomy Satellite (SAS-C) hardware. The magnetometers were deployed after launch to a position 6 m (20 ft) behind the spacecraft. At this distance, the influence of magnetic materials from the instrument and base module (chiefly from the star cameras) was less than 1 mT. Sixteen complete vector magnetic field measurements and eight scalar measurements were obtained every second.

On 30 October 1979, Magsat was launched from pad SLC-5 at Vandenberg Air Force Base in California on a Scout G-1 bearing 96.80° in a dusk to dawn orbit. The spacecraft was placed in an orbit with a perigee of 351.90 km (218.66 mi) and an apogee of 578.40 km (359.40 mi). After reaching orbit, its telescoping boom was extended outward by 6 m (20 ft). Two star cameras were used to define the position of the spacecraft relative to Earth. The orbit allowed the satellite to map a majority of the Earth's surfaces except the geographic poles.

After launch the payload was brought to an orbit of 96.75° facing the Sun as the Earth rotated underneath. It was kept in a close Earth orbit, with vector magnetometers capable of sensing magnetic fields closer to Earth's surface. The data collected by this satellite allowed a 3D-mapping of the Earth's magnetic interior as never seen before. In combination with a later satellite, Ørsted, it has been an essential component for explaining the current declining state of the Earth's magnetic field.

According to a Johns Hopkins University / Applied Physics Laboratory (JHU/APL) report, and archival NASA source documentation (Johns Hopkins APL Technical Digest, July-September 1980, Vol. 1, No. 3), the Magsat spacecraft utilized two RCA 1802 microprocessors running at a 2- MHz clock speed in a redundant setup. A stored memory of 2.8 kilobytes in PROMs with 1 kilobytes of random-access memory (RAM) provided the program and working space for the microprocessor. Other integrated circuits chips of the CDP 1800 family of circuits were also used, including the CDP 1852 interface circuit and the CDP 1822 1K x 1 RAM, as well as Harris CMOS 6611A PROMs.

Three families of circuits were considered for the computer system design: two NMOS families (the Motorola 6800 and Intel 8080 microprocessors) and the RCA CDP1802 CMOS microprocessor. The 1802 was chosen based on various criteria, including the 1802 CMOS technology being power efficient by two orders of magnitude compared to the NMOS microprocessors, compatibility with the existing power supply of the satellite and the low-power requirements of CMOS, the radiation hardening of the 1802 and lack thereof in the 6800 and 8080, and other 1802-based functioning and features. Software for the project was developed with an in-house APL-generated 1802 cross-assembler running on IBM 360/ 370 mainframe computers.

Scalar Magnetometer

The scalar magnetometer had two dual-cell, cesium-vapor sensor heads whose output frequency was proportional to the total magnetic field. With this sensor configuration, only two small diamond-shaped dead zones existed. These lay along the orbit normal (the East-West direction) for the orbit and attitude chosen for this mission and a direction in which the magnetic field was never oriented. The scalar magnetometer's basic accuracy was on the order of 0.5 nT. A period count system converted the magnetometer output frequency to a digital word acceptable to the spacecraft telemetry system. This digital data had a resolution and accuracy of between 0.5 and 1.0 nT in the range 1.5E4 to 6.4E4 nT. Most of the time, noise on the spacecraft resulted in operation of only one sensor at a time. Eight total magnetic field strength measurements were obtained every second.

Vector Magnetometer

The vector magnetometer consisted of three fluxgate sensing elements aligned along orthogonal axes. The output of each vector sensor was converted to a digital word by an analog-to-digital converter. The outputs of all these axes were sampled essentially at the same time. Sixteen vectors were measured per second. Each vector measurement had a resolution of better than 1 nT and an absolute accuracy of better than 6 nT rms when referenced to a geocentric coordinate system. The measurement range was ± 6.4E4 nT.

Magsat was not without problems. One of the biggest is that the motion of a metallic object tends to create a magnetic field. One study after the mission found a nonlinear fluxgate response when exposed to fields greater than 5000 mT. The applied field had to be transverse to the axis of the magnetometer. The design was improved by creating a feedback relay over a spherical design. This was the design used on later spacecraft, as the Ørsted satellite. This configuration magnetometer was also later used on the magnetometer of the Jupiter orbiter Juno, which arrived at the planet Jupiter in the 2010s.

The satellite decayed from orbit on 11 June 1980.

^

^ "History of Vector Magnetometers in Space". Archived from the original on 20 May 2012.

^

Mobley F, Eckard L, Fountain G, and Ousley G. - ^ MAGSAT - A new satellite to survey the Earth's magnetic field 1980 IEEE Transactions on Magnetics 16 (5): 758-760

^ Vandenberg AFB Launch History. The Space Archive

^ Hulot G., Eymin C., Langlais B., Mandea M., Olsen N. (April 2002). "Small-scale structure of the geodynamo inferred from Ørsted and Magsat satellite data". Nature. 416 (6881): 620-623. Bibcode:2002Natur.416..620H. doi:10.1038/416620a. PMID 11948347. S2CID 4426588.

^ NASA AND USGS MAGNETIC DATABASE "ROCKS" THE WORLD NASA This article incorporates text from this source, which is in the public domain.

^ Lew, Ark L. (February 1980). "Space Programs - The Microprocessor-Based MAGSAT Command System" (PDF).

^ "Johns Hopkins APL Technical Digest July-September 1980, Vol. 1, No. 3" (PDF). Johns Hopkins. NASA Archives. This article incorporates text from this source, which is in the public domain.

^

^

Acuna, M. H., MAGSAT - Vector Magnetometer Absolute Sensor Alignment Determination. September 1981 NASA technical Memorandum 79648 Goddard Space Flight Center, NASA ^ This article incorporates text from this source, which is in the public domain.

^ Primdahl, F., H. Luhr and E. K. Lauridsen, The Effect of Large Uncompensated Transverse Fields on the Fluxgate Magnetic Sensor Output, Danish Space Research Institute Report 1-92, 1992

^ [1] This article incorporates text from this source, which is in the public domain.

Langel R, Ousley G, Berbert J, Murphy J, and Settle M. ^ The MAGSAT Mission GEOPHYSICAL RESEARCH LETTERS, VOL. 9, NO. 4, PAGES 243-245, 1982

Media related to Magsat at Wikimedia Commons

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Magsat ( Magnetic field Satellite, Applications Explorer Mission-C or AEM-C or Explorer 61) was a NASA/ USGS (United States Geological Survey) spacecraft, launched on 30 October 1979. The mission was to map the Earth's magnetic field, the satellite had two magnetometers. The scalar ( cesium vapor) and vector magnetometers gave Magsat a capability beyond that of any previous spacecraft.

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Collector satellite:The collecting satellite would convert solar energy into electrical energy, powering a microwave transmitter or laser emitter, and transmit this energy to a collector (or microwave rectenna) on Earth's surface.

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Collector satellite:The collecting satellite would convert solar energy into electrical energy, powering a microwave transmitter or laser emitter, and transmit this energy to a collector (or microwave rectenna) on Earth's surface.

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Fishing in space: Nets could snag space junk

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Removing old satellites from orbit may one day happen in much the same way a fisherman scoops up schools of fish.

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Could We Use Magnets To Clear Up Our Space Junk?

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Magnets work just as well in space as on Earth, so could we make use of them to help collect space debris? What problems would that have?

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23.24 | The Tethered Satellite in Figure 23.12 has a mass of 525 kg and is at the end of a 20.0 km

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yotube Electro Dynamic Tether - Google Search

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Search instead for yotube Electro Dynamic Tether

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To Clean Up Space Junk, Some People Grabbed a Net and Harpoon

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The latest efforts to corral space debris employ a wide-ranging bag of tricks including orbital fishing gear, tiny thrusters, and “space feathers.”

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Space

Space debris can damage spacecrafts of damage space stations due to the high speed at which it travels. Image: UNSPLASH/NASA

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Should we be worried about space debris? Scientists explain

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Space Space debris can damage spacecrafts of damage space stations due to the high speed at which it travels. Image: UNSPLASH/NASA Stay up to date: Space Follow Space debris consists of discarded launch vehicles or parts of a spacecraft, which float around hundreds of miles above Earth.

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All you need to know about the proposed giant magnetic fishing net to collect space debris

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yotube Electro Dynamic Tether - Google Search

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SENER Aeroespacial trabaja en el proyecto de innovación ‘Electrodynamic Tether technology for passive consumable-less deorbit kit’ para ...

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Even tho teams have managed to try and remove the junk, it's not going as smoothly as people think, and because of that its going to be an ongoing struggle but using space nets turned out to capture lots of space debris throughout unlike other solutions.

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Even tho teams have managed to try and remove the junk, it's not going as smoothly as people think, and because of that its going to be an ongoing struggle but using space nets turned out to capture lots of space debris throughout unlike other solutions.

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How 4 NASA Satellites Will Study Magnetic Fields of Earth & Sun (Infographic)

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(Image credit: By Karl Tate, Infographics Artist) NASA's Magnetic Multiscale mission, or MMS, consists of a fleet of four identical satellites studies three phenomena in Earth's magnetosphere: magnetic reconnection, energetic particle acceleration, and turbulence. These processes occur everywhere in the universe but can only be effectively studied close to Earth.

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Finally, somebody's doing something about Earth's orbital trash problem.

A European satellite designed to test different methods of "active debris removal" is scheduled to launch to the space station on a SpaceX Dragon cargo ship on April 2. It will be the first in-space test of technologies to collect and remove large pieces of orbital junk, a growing threat that has long concerned the world's space agencies. A Japanese experiment in space trash removal, called KITE, had to be scrapped last year when the spacecraft's tether failed to deploy.

The $18.5 million RemoveDEBRIS satellite due to launch on Monday was funded half by the European Commission, and half by a consortium of 10 companies, including the spacecraft's builder, Surrey Satellite Technology in England, and Airbus, which contributed the net and harpoon mechanisms to be evaluated in the tests.

If the schedule holds, the 220-pound RemoveDEBRIS satellite will be pushed out of the station's Japanese module airlock in late May to begin a series of experiments. About the size of a dorm room refrigerator, it will be the largest satellite ever launched from the station.

In the first test, a CubeSat released from the main spacecraft will maneuver to a distance of more than 20 feet, where it will unfurl a balloon (to provide a bigger target). A net similar to the kind used in commercial fishing will then be deployed from the main spacecraft to capture the CubeSat. Atmospheric drag should cause the netted CubeSat to burn up in the atmosphere in a matter of weeks, according to Guglielmo Aglietti, Director of the Surrey Space Centre at the University of Surrey, and the principal investigator for RemoveDEBRIS.

For the second test, another CubeSat will be released to fly at a distance from the main spacecraft, where a camera and LIDAR will observe it to assess how well future trash-collecting satellites could judge the position and speed of a piece of debris.

Then, to test a different method of snaring space trash, a standoff target-made of representative satellite materials-will be shot with a harpoon connected to a tether. Finally, a large sail will be unfurled from the main satellite to increase its atmospheric drag and cause it to burn up during re-entry, about a year and a half later. The project investigators expect to have all their tests wrapped up by the end of this year, says Aglietti.

If everything works as hoped, the technologies tested on RemoveDEBRIS will be incorporated into planning for the e.deborbit mission planned for launch around 2024. That project, expected to cost some $400 million, aims to capture and de-orbit the eight-ton Envisat spacecraft. RemoveDEBRIS is just a first step toward the much more ambitious goal of removing the largest dead satellites from orbit. Those are the biggest threats, since a hit from some other bit of speeding space junk could turn any of them into thousands of new pieces of debris. And with 7,500 tons of garbage already circling the Earth, that's an accident global space managers would dearly like to prevent.

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SpaceX Cargo Ship Will Carry First Test of Space Debris Cleanup

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Finally, somebody's doing something about Earth's orbital trash problem. A European satellite designed to test different methods of "active debris removal" is scheduled to launch to the space station on a SpaceX Dragon cargo ship on April 2.

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https://www.planetary.org/articles/what-is-solar-sailing

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China Proposes Orbiting Laser to Combat Space Junk

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It’s not an anti-satellite weapon. At all. Of course not.

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Students are about to send a tiny satellite - the size of a loaf of bread - to space.

The nanosatellite will be a test run for a propulsion method that will use Earth's magnetic field to generate thrust and allow small satellites to maintain low earth orbit.

Staying in Orbit Is a Challenge

About 60% of satellites are in low earth orbit. They typically use thrusters to boost themselves higher, so they don't fall off course or back to Earth. But currently, this isn't an option for CubeSats. These nanosatellites are so small they can't efficiently carry fuel, thrusters, or propellant.

There is enough drag in the thin upper atmosphere to slow the tiny satellites down. Eventually, they will drop toward Earth and begin to break apart. If they haven't decayed yet, they will burn up upon reentry - just months or even days after they first reached their orbit.

"These smaller spacecraft just don't last very long, maybe even days to weeks, or a few months, dependent upon how high they are," said Brian Gilchrist, a professor of electrical engineering and computer science at the University of Michigan.

But a satellite designed and built by 250 University of Michigan students (primarily undergraduates) could maintain low earth orbit without fuel. The team plans to explore the feasibility of their new propulsion system this weekend, on a tag-a-long mission to space with Virgin Orbit.

How it Works

Once in space, the students plan to keep the tiny satellite, named MiTEE-1 (Miniature Tether Electrodynamics Experiment-1), in low earth orbit without thrusters of propellant. Instead, it uses the Earth's electromagnetism to provide propulsion.

Solar panels affixed to two CubeSats generate electricity, which passes through a connecting wire. As the CubeSat orbits Earth, the ionosphere completes the circuit. When a wire conducts electrical current in a magnetic field, it exerts a force on the wire - boosting the CubeSat higher into orbit.

It will only generate a small amount of force, but the team hopes it will be enough to compensate for the atmosphere's drag and keep the small satellite orbiting.

If successful, these tiny, low-cost satellites could stay in low earth orbit longer and accomplish important missions on a budget - like testing new technology, collecting data, monitoring storms or natural disasters. They could even operate in swarms.

Next Steps

The MiTEE-1 gives students first-hand experience in space exploration, but this is only the beginning. The first mission is designed to measure the amount of current that the satellite can draw from the ionosphere in various conditions, and calculate if it will be enough to maintain low earth orbit.

Next, they will build a second MiTEE satellite to demonstrate the electric propulsion system in operation.
We'd love to hear from you! If you have a comment about this article or if you have a tip for a future Freethink story, please email us at [email protected]

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Tiny satellite uses Earth's magnetic field to generate thrust

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Students are about to send a tiny satellite - the size of a loaf of bread - to space. The nanosatellite will be a test run for a propulsion method that will use Earth's magnetic field to generate thrust and allow small satellites to maintain low earth orbit.

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A computer-generated image representing the locations, but not relative sizes, of space debris as could be seen from high Earth orbit (HEO). The two main debris fields are the ring of objects in geosynchronous Earth orbit (GEO) and the cloud of objects in low Earth orbit (LEO).

Space debris (also known as space junk, space pollution, space waste, space trash, space garbage, or cosmic debris) are defunct human-made objects in space - principally in Earth orbit - which no longer serve a useful function. These include derelict spacecraft - nonfunctional spacecraft and abandoned launch vehicle stages - mission-related debris, and particularly numerous in Earth orbit, fragmentation debris from the breakup of derelict rocket bodies and spacecraft. In addition to derelict human-made objects left in orbit, other examples of space debris include fragments from their disintegration, erosion and collisions or even paint flecks, solidified liquids expelled from spacecraft, and unburned particles from solid rocket motors. Space debris represents a risk to spacecraft.

Space debris is typically a negative externality - it creates an external cost on others from the initial action to launch or use a spacecraft in near-Earth orbit - a cost that is typically not taken into account nor fully accounted for in the cost by the launcher or payload owner.

Several spacecraft, both crewed and uncrewed, have been damaged or destroyed by space debris. The measurement, mitigation, and potential removal of debris are conducted by some participants in the space industry.

As of November 2022, the US Space Surveillance Network reported 25,857 artificial objects in orbit above the Earth, including 5,465 operational satellites. However, these are just the objects large enough to be tracked and in an orbit that makes tracking possible. Satellite debris that is in a Molniya orbit, such as the Kosmos Oko series, might be too high above the northern hemisphere to be tracked. As of January 2019, more than 128 million pieces of debris smaller than 1 cm (0.4 in), about 900,000 pieces of debris 1-10 cm, and around 34,000 of pieces larger than 10 cm (3.9 in) were estimated to be in orbit around the Earth. When the smallest objects of artificial space debris (paint flecks, solid rocket exhaust particles, etc.) are grouped with micrometeoroids, they are together sometimes referred to by space agencies as MMOD (Micrometeoroid and Orbital Debris). Collisions with debris have become a hazard to spacecraft; the smallest objects cause damage akin to sandblasting, especially to solar panels and optics like telescopes or star trackers that cannot easily be protected by a ballistic shield.

Below 2,000 km (1,200 mi) Earth- altitude, pieces of debris are denser than meteoroids; most are dust from solid rocket motors, surface erosion debris like paint flakes, and frozen coolant from Soviet nuclear-powered satellites. For comparison, the International Space Station orbits in the 300-400 kilometres (190-250 mi) range, while the two most recent large debris events - the 2007 Chinese antisat weapon test and the 2009 satellite collision - occurred at 800 to 900 kilometres (500 to 560 mi) altitude. The ISS has Whipple shielding to resist damage from small MMOD; however, known debris with a collision chance over 1/10,000 are avoided by maneuvering the station.

Space debris began to accumulate in Earth orbit immediately with the first launch of an artificial satellite Sputnik 1 into orbit in October 1957. But even before that humans might have produced ejecta that became space debris, as in the August 1957 Pascal B test. Going back even earlier, there was natural ejecta from Earth in orbit.

After the launch of Sputnik, the North American Aerospace Defense Command (NORAD) began compiling a database (the Space Object Catalog) of all known rocket launches and objects reaching orbit: satellites, protective shields and upper-stages of launch vehicles. NASA later published modified versions of the database in two-line element set, and beginning in the early 1980s the CelesTrak bulletin board system re-published them.

Gabbard diagram of almost 300 pieces of debris from the disintegration of the five-month-old third stage of the Chinese Long March 4 booster on 11 March 2000

The trackers (NORAD) who fed the database were aware of other objects in orbit, many of which were the result of in-orbit explosions. Some were deliberately caused during the 1960s anti-satellite weapon (ASAT) testing, and others were the result of rocket stages blowing up in orbit as leftover propellant expanded and ruptured their tanks. To improve tracking, NORAD employee John Gabbard kept a more detailed database of as many objects as he could identify.

Studying the explosions, in March 1971, Gabbard developed a technique for predicting the orbital paths of their products, and Gabbard diagrams (or plots) are now widely used. These studies were used to improve the modeling of orbital evolution and decay.

When the NORAD database became publicly available during the 1970s, techniques developed for the asteroid-belt were applied to the study to the database of known artificial satellite Earth objects.

Baker-Nunn cameras were widely used to study space debris.

In addition to approaches to debris reduction where time and natural gravitational/atmospheric effects help to clear space debris, or a variety of technological approaches that have been proposed (with most not implemented) to reduce space debris, a number of scholars have observed that institutional factors - political, legal, economic, and cultural "rules of the game" - are the greatest impediment to the cleanup of near-Earth space. By 2014, there was little commercial incentive to reduce space debris, since the cost of dealing with it is not assigned to the entity producing it, but rather falls on all users of the space environment, and rely on human society as a whole that benefits from space technologies and knowledge. A number of suggestions for improving institutions so as to increase the incentives to reduce space debris have been made. These include government mandates to create incentives, as well as companies coming to see economic benefit to reducing debris more aggressively than existing government standard practices. In 1979 NASA founded the Orbital Debris Program to research mitigation measures for space debris in Earth orbit.

During the 1980s, NASA and other U.S. groups attempted to limit the growth of debris. One trial solution was implemented by McDonnell Douglas in 1981 for the Delta launch vehicle by having the booster move away from its payload and vent any propellant remaining in its tanks. This eliminated one source for pressure buildup in the tanks which had previously caused them to explode and create additional orbital debris. Other countries were slower to adopt this measure and, due especially to a number of launches by the Soviet Union, the problem grew throughout the decade.

A new battery of studies followed as NASA, NORAD, and others attempted to better understand the orbital environment, with each adjusting the number of pieces of debris in the critical-mass zone upward. Although in 1981 (when Schefter's article was published) the number of objects was estimated at 5,000, new detectors in the Ground-based Electro-Optical Deep Space Surveillance system found new objects. By the late 1990s, it was thought that most of the 28,000 launched objects had already decayed and about 8,500 remained in orbit. By 2005 this was adjusted upward to 13,000 objects, and a 2006 study increased the number to 19,000 as a result of an ASAT and a satellite collision. In 2011, NASA said that 22,000 objects were being tracked.

A 2006 NASA model suggested that if no new launches took place the environment would retain the then-known population until about 2055, when it would increase on its own. Richard Crowther of Britain's Defence Evaluation and Research Agency said in 2002 that he believed the cascade would begin about 2015. The National Academy of Sciences, summarizing the professional view, noted widespread agreement that two bands of LEO space - 900 to 1,000 km (620 mi) and 1,500 km (930 mi) - were already past critical density.

In the 2009 European Air and Space Conference, University of Southampton researcher Hugh Lewis predicted that the threat from space debris would rise 50 percent in the next decade and quadruple in the next 50 years. As of 2009, more than 13,000 close calls were tracked weekly.

A 2011 report by the U.S. National Research Council warned NASA that the amount of orbiting space debris was at a critical level. According to some computer models, the amount of space debris "has reached a tipping point, with enough currently in orbit to continually collide and create even more debris, raising the risk of spacecraft failures." The report called for international regulations limiting debris and research of disposal methods.

Objects in Earth orbit including fragmentation debris. November 2020 NASA:ODPO

By mid-1994 there had been 68 breakups or debris "anomalous events" involving satellites launched by the former Soviet Union/Russia and 18 similar events had been discovered involving rocket bodies and other propulsion-related operational debris.[40]

As of 2009, 19,000 debris over 5 cm (2 in) were tracked by United States Space Surveillance Network.[16]

As of July 2013, estimates of more than 170 million debris smaller than 1 cm (0.4 in), about 670,000 debris 1-10 cm, and approximately 29,000 larger pieces of debris are in orbit.[41]

As of July 2016, nearly 18,000 artificial objects are orbiting above Earth,[42] including 1,419 operational satellites.[43]

As of October 2019, nearly 20,000 artificial objects in orbit above the Earth,[9] including 2,218 operational satellites.[10]

As of January 2019 there were estimated to be over 128 million pieces of debris smaller than 1 cm (0.39 in), and approximately 900,000 pieces between 1 and 10 cm. The count of large debris (defined as 10 cm across or larger) was 34,000 in 2019, and at least 37,000 by June 2023. The technical measurement cut-off is c. 3 mm (0.12 in).

As of 2020, there were 8,000 metric tons of debris in orbit, a figure that is expected to increase.

Satellite hit by a space debris; animation by ESA

In the orbits nearest to Earth - less than 2,000 km (1,200 mi) orbital altitude, referred to as low-Earth orbit (LEO) - there have traditionally been few "universal orbits" that keep a number of spacecraft in particular rings (in contrast to GEO, a single orbit that is widely used by over 500 satellites). This is beginning to change in 2019, and several companies have begun to deploy the early phases of satellite internet constellations, which will have many universal orbits in LEO with 30 to 50 satellites per orbital plane and altitude. Traditionally, the most populated LEO orbits have been a number of sun-synchronous satellites that keep a constant angle between the Sun and the orbital plane, making Earth observation easier with consistent sun angle and lighting. Sun-synchronous orbits are polar, meaning they cross over the polar regions. LEO satellites orbit in many planes, typically up to 15 times a day, causing frequent approaches between objects. The density of satellites - both active and derelict - is much higher in LEO.

Orbits are affected by gravitational perturbations (which in LEO include unevenness of the Earth's gravitational field due to variations in the density of the planet), and collisions can occur from any direction. The average impact speed of collisions in Low Earth Orbit is 10 km/s with maximums reaching above 14 km/s due to orbital eccentricity. The 2009 satellite collision occurred at a closing speed of 11.7 km/s (26,000 mph), creating over 2,000 large debris fragments. These debris cross many other orbits and increase debris collision risk.

It is theorized that a sufficiently large collision of spacecraft could potentially lead to a cascade effect, or even make some particular low Earth orbits effectively unusable for long term use by orbiting satellites, a phenomenon known as the Kessler syndrome. The theoretical effect is projected to be a theoretical runaway chain reaction of collisions that could occur, exponentially increasing the number and density of space debris in low-Earth orbit, and has been hypothesized to ensue beyond some critical density.

Crewed space missions are mostly at 400 km (250 mi) altitude and below, where air drag helps clear zones of fragments. The upper atmosphere is not a fixed density at any particular orbital altitude; it varies as a result of atmospheric tides and expands or contracts over longer time periods as a result of space weather. These longer-term effects can increase drag at lower altitudes; the 1990s expansion was a factor in reduced debris density. Another factor was fewer launches by Russia; the Soviet Union made most of their launches in the 1970s and 1980s.

At higher altitudes, where air drag is less significant, orbital decay takes longer. Slight atmospheric drag, lunar perturbations, Earth's gravity perturbations, solar wind and solar radiation pressure can gradually bring debris down to lower altitudes (where it decays), but at very high altitudes this may take centuries. Although high-altitude orbits are less commonly used than LEO and the onset of the problem is slower, the numbers progress toward the critical threshold more quickly.

Many communications satellites are in geostationary orbits (GEO), clustering over specific targets and sharing the same orbital path. Although velocities are low between GEO objects, when a satellite becomes derelict (such as Telstar 401) it assumes a geosynchronous orbit; its orbital inclination increases about .8° and its speed increases about 160 km/h (99 mph) per year. Impact velocity peaks at about 1.5 km/s (0.93 mi/s). Orbital perturbations cause longitude drift of the inoperable spacecraft and precession of the orbital plane. Close approaches (within 50 meters) are estimated at one per year. The collision debris pose less short-term risk than from an LEO collision, but the satellite would likely become inoperable. Large objects, such as solar-power satellites, are especially vulnerable to collisions.

Although the ITU now requires proof a satellite can be moved out of its orbital slot at the end of its lifespan, studies suggest this is insufficient. Since GEO orbit is too distant to accurately measure objects under 1 m (3 ft 3 in), the nature of the problem is not well known. Satellites could be moved to empty spots in GEO, requiring less maneuvering and making it easier to predict future motion. Satellites or boosters in other orbits, especially stranded in geostationary transfer orbit, are an additional concern due to their typically high crossing velocity.

Despite efforts to reduce risk, spacecraft collisions have occurred. The European Space Agency telecom satellite Olympus-1 was struck by a meteoroid on 11 August 1993 and eventually moved to a graveyard orbit. On 29 March 2006, the Russian Express-AM11 communications satellite was struck by an unknown object and rendered inoperable; its engineers had enough contact time with the satellite to send it into a graveyard orbit.

Vanguard 1 is expected to remain in orbit for 240 years.[66][67]

In 1958, the United States of America had launched Vanguard I into a medium Earth orbit (MEO). As of October 2009, it, the upper stage of Vanguard 1's launch rocket and associated piece of debris, are the oldest surviving artificial space objects still in orbit and are expected to be until after the year 2250. As of May 2022, the Union of Concerned Scientists listed 5,465 operational satellites from a known population of 27,000 pieces of orbital debris tracked by NORAD.

Despite the use of passivization, or prior to its standardization, many satellites and rocket bodies have exploded or broken apart on orbit. In February 2015, for example, the USAF Defense Meteorological Satellite Program Flight 13 (DMSP-F13) exploded on orbit, creating at least 149 debris objects, which were expected to remain in orbit for decades. Later that same year, NOAA-16 which had been decommissioned after an anomaly in June 2014, broke apart on orbit into at least 275 pieces. For older programs, such as the Soviet-era Meteor 2 and Kosmos satellites, design flaws resulted in numerous break-ups - at least 68 by 1994 - following decommissioning, resulting in more debris.

In addition to the accidental creation of debris, some has been made intentionally through the deliberate destruction of satellites. This has been done as a test of anti-satellite or anti-ballistic missile technology, or to prevent a sensitive satellite from being examined by a foreign power. The United States has conducted over 30 anti-satellite weapons tests (ASATs), the Soviet Union/ Russia has performed at least 27, China has performed 10 and India has performed at least one. The most recent ASATs were the Chinese interception of FY-1C, Russian trials of its PL-19 Nudol, the American interception of USA-193 and India's interception of an unstated live satellite.

A drifting thermal blanket photographed in 1998 during STS-88.

Space debris includes a glove lost by astronaut Ed White on the first American space-walk (EVA), a camera lost by Michael Collins near Gemini 10, a thermal blanket lost during STS-88, garbage bags jettisoned by Soviet cosmonauts during Mir's 15-year life, a wrench, and a toothbrush. Sunita Williams of STS-116 lost a camera during an EVA. During an STS-120 EVA to reinforce a torn solar panel, a pair of pliers was lost, and in an STS-126 EVA, Heidemarie Stefanyshyn-Piper lost a briefcase-sized tool bag.

Spent upper stage of a Delta II rocket, photographed by the XSS 10 satellite

Rocket upper stages which end up in orbit are a significant source of space debris. In characterizing the problem of space debris, it was learned that much debris was due to rocket upper stages (e.g. the Inertial Upper Stage) which end up in orbit, and break up due to decomposition of unvented unburned fuel. The first such instance involved the launch of the Transit-4a satellite in 1961. Two hours after insertion the Ablestar upper stage exploded. But even boosters that don't break apart can be a problem as a major known impact event involved an (intact) Ariane booster.

Although NASA and the United States Air Force now require upper-stage passivation, other launchers - such as the Chinese and Russian space agencies - do not. Lower stages, like the Space Shuttle's solid rocket boosters or Apollo program's Saturn IB launch vehicles, do not reach orbit.

Orbit of 2020 SO

Examples:

Two Japanese H-2A rockets rockets broke up in 2006.

A Russian Briz-M booster stage exploded in orbit over South Australia on 19 February 2007. Launched on 28 February 2006 carrying an Arabsat-4A communications satellite, it malfunctioned before it could use up its propellant. Although the explosion was captured on film by astronomers, due to the orbit path the debris cloud has been difficult to measure with radar. By 21 February 2007, over 1,000 fragments were identified. A 14 February 2007 breakup was recorded by Celestrak.

Another Briz-M broke up on 16 October 2012 after a failed 6 August Proton-M launch. The amount and size of the debris was unknown.

The second stage of the Zenit-2, called the SL-16 by western governments, along with the second stages of the Vostok and Kosmos launch vehicles, make up about 20% of the total mass of launch debris in Low Earth Orbit (LEO). An analysis that determined the 50 "statistically most concerning" debris objects in low Earth orbit determined that the top 20 were all Zenit-2 upper stages.

a Delta II rocket used to launch NASA's 1989 COBE spacecraft exploded on December 3, 2006. This occurred even though its residual fuel had already been vented to space.

In December 2020, scientists confirmed that a previously detected near-Earth object, 2020 SO, was rocket booster space junk launched in 1966 orbiting Earth and the Sun.

At least eight Delta rockets have contributed orbital debris in the sun-synchronous low earth orbit environment. The variant of the Delta upper stage that was used in the 1970's was found to be prone to in-orbit explosions. Starting in 1981, depletion burns - to get rid of excess propellant - became standard and no Delta Rocket Bodies launched after 1981 experience severe fragmentations afterward, but some of those launched prior to 1981 continued to explode. In 1991, the Delta 1975-052B fragmented, 16 years after launch, demonstrating the resilience of the propellent.

A past debris source was the testing of anti-satellite weapons (ASATs) by the U.S. and Soviet Union during the 1960s and 1970s. North American Aerospace Defense Command (NORAD) files only contained data for Soviet tests, and debris from U.S. tests were only identified later. By the time the debris problem was understood, widespread ASAT testing had ended; the U.S. Program 437 was shut down in 1975.

The U.S. restarted their ASAT programs in the 1980s with the Vought ASM-135 ASAT. A 1985 test destroyed a 1-tonne (2,200 lb) satellite orbiting at 525 km (326 mi), creating thousands of debris larger than 1 cm (0.39 in). Due to the altitude, atmospheric drag decayed the orbit of most debris within a decade. A de facto moratorium followed the test.

Known orbit planes of Fengyun-1C debris one month after the weather satellite's disintegration by the Chinese ASAT

China's government was condemned for the military implications and the amount of debris from the 2007 anti-satellite missile test, the largest single space debris incident in history (creating over 2,300 pieces golf-ball size or larger, over 35,000 1 cm (0.4 in) or larger, and one million pieces 1 mm (0.04 in) or larger). The target satellite orbited between 850 km (530 mi) and 882 km (548 mi), the portion of near-Earth space most densely populated with satellites. Since atmospheric drag is low at that altitude, the debris is slow to return to Earth, and in June 2007 NASA's Terra environmental spacecraft maneuvered to avoid impact from the debris. Dr. Brian Weeden, U.S. Air Force officer and Secure World Foundation staff member, noted that the 2007 Chinese satellite explosion created an orbital debris of more than 3,000 separate objects that then required tracking. On 20 February 2008, the U.S. launched an SM-3 missile from the USS Lake Erie to destroy a defective U.S. spy satellite thought to be carrying 450 kg (1,000 lb) of toxic hydrazine propellant. The event occurred at about 250 km (155 mi), and the resulting debris has a perigee of 250 km (155 mi) or lower. The missile was aimed to minimize the amount of debris, which (according to Pentagon Strategic Command chief Kevin Chilton) had decayed by early 2009.

On 27 March 2019, Indian Prime Minister Narendra Modi announced that India shot down one of its own LEO satellites with a ground-based missile. He stated that the operation, part of Mission Shakti, would defend the country's interests in space. Afterwards, US Air Force Space Command announced they were tracking 270 new pieces of debris but expected the number to grow as data collection continues.

The vulnerability of satellites to debris and the possibility of attacking LEO satellites to create debris clouds has triggered speculation that it is possible for countries unable to make a precision attack. An attack on a satellite of 10 t (22,000 lb) or more would heavily damage the LEO environment.

A micrometeoroid left this crater on the surface of Space Shuttle Challenger's front window on STS-7.

Space junk can be a hazard to active satellites and spacecraft. It has been theorized that Earth orbit could even become impassable if the risk of collision grows too high.

However, since the risk to spacecraft increases with exposure to high debris densities, it is more accurate to say that LEO would be rendered unusable by orbiting craft. The threat to craft passing through LEO to reach a higher orbit would be much lower owing to the very short time span of the crossing.

Uncrewed spacecraft

Although spacecraft are typically protected by Whipple shields, solar panels, which are exposed to the Sun, wear from low-mass impacts. Even small impacts can produce a cloud of plasma which is an electrical risk to the panels.

Satellites are believed to have been destroyed by micrometeorites and (small) orbital debris (MMOD). The earliest suspected loss was of Kosmos 1275, which disappeared on 24 July 1981 (a month after launch). Kosmos contained no volatile fuel, therefore, there appeared to be nothing internal to the satellite which could have caused the destructive explosion which took place. However, the case has not been proven and another hypothesis forwarded is that the battery exploded. Tracking showed it broke up, into 300 new objects.

Many impacts have been confirmed since. For example, on 24 July 1996, the French microsatellite Cerise was hit by fragments of an Ariane-1 H-10 upper-stage booster which exploded in November 1986. On 29 March 2006, the Russian Ekspress AM11 communications satellite was struck by an unknown object and rendered inoperable. On 13 October 2009, Terra suffered a single battery cell failure anomaly and a battery heater control anomaly which were subsequently considered likely the result of an MMOD strike. On 12 March 2010, Aura lost power from one-half of one of its 11 solar panels and this was also attributed to an MMOD strike. On 22 May 2013, GOES 13 was hit by an MMOD which caused it to lose track of the stars that it used to maintain an operational attitude. It took nearly a month for the spacecraft to return to operation.

The first major satellite collision occurred on 10 February 2009. The 950 kg (2,090 lb) derelict satellite Kosmos 2251 and the operational 560 kg (1,230 lb) Iridium 33 collided, 500 mi (800 km) over northern Siberia. The relative speed of impact was about 11.7 km/s (7.3 mi/s), or about 42,120 km/h (26,170 mph). Both satellites were destroyed, creating thousands of pieces of new smaller debris, with legal and political liability issues unresolved even years later. On 22 January 2013, BLITS (a Russian laser-ranging satellite) was struck by debris suspected to be from the 2007 Chinese anti-satellite missile test, changing both its orbit and rotation rate.

Satellites sometimes perform Collision Avoidance Maneuvers and satellite operators may monitor space debris as part of maneuver planning. For example, in January 2017, the European Space Agency made the decision to alter orbit of one of its three Swarm mission spacecraft, based on data from the US Joint Space Operations Center, to lower the risk of collision from Cosmos-375, a derelict Russian satellite.

Crewed spacecraft

Crewed flights are naturally particularly sensitive to the hazards that could be presented by space debris conjunctions in the orbital path of the spacecraft. Examples of occasional avoidance maneuvers, or longer-term space debris wear, have occurred in Space Shuttle missions, the MIR space station, and the International Space Station.

Space Shuttle missions

Space Shuttle Discovery's lower starboard wing and Thermal Protection System tiles, photographed on STS-114 during an R-Bar Pitch Manoeuvre where astronauts examine the TPS for any damage during ascent

From the early Space Shuttle missions, NASA used NORAD space monitoring capabilities to assess the Shuttle's orbital path for debris. In the 1980s, this used a large proportion of NORAD capacity. The first collision-avoidance maneuver occurred during STS-48 in September 1991, a seven-second thruster burn to avoid debris from the derelict satellite Kosmos 955. Similar maneuvers were initiated on missions 53, 72 and 82.

One of the earliest events to publicize the debris problem occurred on Space Shuttle Challenger's second flight, STS-7. A fleck of paint struck its front window, creating a pit over 1 mm (0.04 in) wide. On STS-59 in 1994, Endeavour's front window was pitted about half its depth. Minor debris impacts increased from 1998.

Window chipping and minor damage to thermal protection system tiles (TPS) were already common by the 1990s. The Shuttle was later flown tail-first to take a greater proportion of the debris load on the engines and rear cargo bay, which are not used in orbit or during descent, and thus are less critical for post-launch operation. When flying attached to the ISS, the two connected spacecraft were flipped around so the better-armoured station shielded the orbiter.

Space Shuttle Endeavour had a major impact on its radiator during STS-118. The entry hole is about 5.5 mm (0.22 in), and the exit hole is twice as large.

A NASA 2005 study concluded that debris accounted for approximately half of the overall risk to the Shuttle. Executive-level decision to proceed was required if the catastrophic impact was likelier than 1 in 200. On a normal (low-orbit) mission to the ISS, the risk was approximately 1 in 300, but the Hubble telescope repair mission was flown at the higher orbital altitude of 560 km (350 mi) where the risk was initially calculated at a 1-in-185 (due in part to the 2009 satellite collision). A re-analysis with better debris numbers reduced the estimated risk to 1 in 221, and the mission went ahead.

Debris incidents continued on later Shuttle missions. During STS-115 in 2006 a fragment of circuit board bored a small hole through the radiator panels in Atlantis's cargo bay. On STS-118 in 2007 debris blew a bullet-like hole through Endeavour's radiator panel.

Impact wear was notable on Mir, the Soviet space station since it remained in space for long periods with its original solar module panels.

Debris impacts on Mir's solar panels degraded their performance. The damage is most noticeable on the panel on the right, which is facing the camera with a high degree of contrast. Extensive damage to the smaller panel below is due to impact with a Progress spacecraft.

International Space Station

The ISS also uses Whipple shielding to protect its interior from minor debris. However, exterior portions (notably its solar panels) cannot be protected easily. In 1989, the ISS panels were predicted to degrade approximately 0.23% in four years due to the "sandblasting" effect of impacts with small orbital debris. An avoidance maneuver is typically performed for the ISS if "there is a greater than one-in-10,000 chance of a debris strike". As of January 2014, there have been sixteen maneuvers in the fifteen years the ISS had been in orbit. By 2019, over 1,400 meteoroid and orbital debris (MMOD) impacts had been recorded on the ISS.

As another method to reduce the risk to humans on board, ISS operational management asked the crew to shelter in the Soyuz on three occasions due to late debris-proximity warnings. In addition to the sixteen thruster firings and three Soyuz-capsule shelter orders, one attempted maneuver was not completed due to not having the several days' warning necessary to upload the maneuver timeline to the station's computer. A March 2009 event involved debris believed to be a 10 cm (3.9 in) piece of the Kosmos 1275 satellite. In 2013, the ISS operations management did not make a maneuver to avoid any debris, after making a record four debris maneuvers the previous year.

Kessler syndrome

Growth of tracked objects in orbit and related events;[137] efforts to manage outer space global commons have so far not reduced the debris or the growth of objects in orbit

The Kessler syndrome, proposed by NASA scientist Donald J. Kessler in 1978, is a theoretical scenario in which the density of objects in low Earth orbit (LEO) is high enough that collisions between objects could cause a cascade effect where each collision generates space debris that increases the likelihood of further collisions. He further theorized that one implication, if this were to occur, is that the distribution of debris in orbit could render space activities and the use of satellites in specific orbital ranges economically impractical for many generations.

The growth in the number of objects as a result of the late-1990s studies sparked debate in the space community on the nature of the problem and the earlier dire warnings. According to Kessler's 1991 derivation and 2001 updates, the LEO environment in the 1,000 km (620 mi) altitude range should be cascading. However, only one major satellite collision incident occurred: the 2009 satellite collision between Iridium 33 and Cosmos 2251. The lack of obvious short-term cascading has led to speculation that the original estimates overstated the problem. According to Kessler in 2010 however, a cascade may not be obvious until it is well advanced, which might take years.

Saudi officials inspect a crashed PAM-D module in January 2001.

Although most debris burns up in the atmosphere, larger debris objects can reach the ground intact. According to NASA, an average of one cataloged piece of debris has fallen back to Earth each day for the past 50 years. Despite their size, there has been no significant property damage from the debris. Burning up in the atmosphere may also contribute to atmospheric pollution. Numerous small cylindrical tanks from space objects have been found, designed to hold fuel or gasses.

Radar and optical detectors such as lidar are the main tools for tracking space debris. Although objects under 10 cm (4 in) have reduced orbital stability, debris as small as 1 cm can be tracked, however determining orbits to allow re-acquisition is difficult. Most debris remain unobserved. The NASA Orbital Debris Observatory tracked space debris with a 3 m (10 ft) liquid mirror transit telescope. FM Radio waves can detect debris, after reflecting off them onto a receiver. Optical tracking may be a useful early-warning system on spacecraft.

The U.S. Strategic Command keeps a catalog of known orbital objects, using ground-based radar and telescopes, and a space-based telescope (originally to distinguish from hostile missiles). The 2009 edition listed about 19,000 objects. Other data come from the ESA Space Debris Telescope, TIRA, the Goldstone, Haystack, and EISCAT radars and the Cobra Dane phased array radar, to be used in debris-environment models like the ESA Meteoroid and Space Debris Terrestrial Environment Reference (MASTER).

The Long Duration Exposure Facility (LDEF) is an important source of information on small-particle space debris.

Returned space hardware is a valuable source of information on the directional distribution and composition of the (sub-millimetre) debris flux. The LDEF satellite deployed by mission STS-41-C Challenger and retrieved by STS-32 spent 68 months in orbit to gather debris data. The EURECA satellite, deployed by STS-46 in 1992 and retrieved by STS-57 Endeavour in 1993, was also used for debris study.

The solar arrays of Hubble were returned by missions STS-61 Endeavour and STS-109 Columbia, and the impact craters studied by the ESA to validate its models. Materials returned from Mir were also studied, notably the Mir Environmental Effects Payload (which also tested materials intended for the ISS).

A debris cloud resulting from a single event is studied with scatter plots known as Gabbard diagrams, where the perigee and apogee of fragments are plotted with respect to their orbital period. Gabbard diagrams of the early debris cloud prior to the effects of perturbations, if the data were available, are reconstructed. They often include data on newly observed, as yet uncatalogued fragments. Gabbard diagrams can provide important insights into the features of the fragmentation, the direction and point of impact.

An average of about one tracked object per day has been dropping out of orbit for the past 50 years, averaging almost three objects per day at solar maximum (due to the heating and expansion of the Earth's atmosphere), but one about every three days at solar minimum, usually five and a half years later. In addition to natural atmospheric effects, corporations, academics and government agencies have proposed plans and technology to deal with space debris, but as of November 2014, most of these are theoretical, and there is no extant business plan for debris reduction.

A number of scholars have also observed that institutional factors - political, legal, economic, and cultural "rules of the game" - are the greatest impediment to the cleanup of near-Earth space. There is little commercial incentive to act, since costs are not assigned to polluters, though a number of technological solutions have been suggested. However, effects to date are limited. In the US, governmental bodies have been accused of backsliding on previous commitments to limit debris growth, "let alone tackling the more complex issues of removing orbital debris." The different methods for removal of space debris have been evaluated by the Space Generation Advisory Council, including French astrophysicist Fatoumata Kébé.

There is no international treaty minimizing space debris. However, the United Nations Committee on the Peaceful Uses of Outer Space (COPUOS) published voluntary guidelines in 2007, using a variety of earlier national regulatory attempts at developing standards for debris mitigation. As of 2008, the committee was discussing international "rules of the road" to prevent collisions between satellites. By 2013, a number of national legal regimes existed, typically instantiated in the launch licenses that are required for a launch in all spacefaring nations.

The U.S. issued a set of standard practices for civilian (NASA) and military ( DoD and USAF) orbital-debris mitigation in 2001. The standard envisioned disposal for final mission orbits in one of three ways: 1) atmospheric reentry where even with "conservative projections for solar activity, atmospheric drag will limit the lifetime to no longer than 25 years after completion of mission;" 2) maneuver to a "storage orbit:" move the spacecraft to one of four very broad parking orbit ranges (2,000-19,700 km (1,200-12,200 mi), 20,700-35,300 km (12,900-21,900 mi), above 36,100 km (22,400 mi), or out of Earth orbit completely and into any heliocentric orbit; 3) "Direct retrieval: Retrieve the structure and remove it from orbit as soon as practicable after completion of mission." The standard articulated in option 1, which is the standard applicable to most satellites and derelict upper stages launched, has come to be known as the "25-year rule". The US updated the Orbital Debris Mitigation Standard Practices (ODMSP) in December 2019, but made no change to the 25-year rule even though "[m]any in the space community believe that the timeframe should be less than 25 years." There is no consensus however on what any new timeframe might be.

In 2002, the European Space Agency (ESA) worked with an international group to promulgate a similar set of standards, also with a "25-year rule" applying to most Earth-orbit satellites and upper stages. Space agencies in Europe began to develop technical guidelines in the mid-1990s, and ASI, UKSA, CNES, DLR and ESA signed a "European Code of Conduct" in 2006, which was a predecessor standard to the ISO international standard work that would begin the following year. In 2008, ESA further developed "its own "Requirements on Space Debris Mitigation for Agency Projects" which "came into force on 1 April 2008."

Germany and France have posted bonds to safeguard the property from debris damage. The "direct retrieval" option (option no. 3 in the US "standard practices" above) has rarely been done by any spacefaring nation (exception, USAF X-37) or commercial actor since the earliest days of spaceflight due to the cost and complexity of achieving direct retrieval, but the ESA has scheduled a 2025 demonstration mission (Clearspace-1) to do this with a single small 100 kg (220 lb) derelict upper stage at a projected cost of €120 million not including the launch costs.

By 2006, the Indian Space Research Organization (ISRO) had developed a number of technical means of debris mitigation (upper stage passivation, propellant reserves for movement to graveyard orbits, etc.) for ISRO launch vehicles and satellites, and was actively contributing to inter-agency debris coordination and the efforts of the UN COPUOS committee.

In 2007, the ISO began preparing an international standard for space-debris mitigation. By 2010, ISO had published "a comprehensive set of space system engineering standards aimed at mitigating space debris. [with primary requirements] defined in the top-level standard, ISO 24113." By 2017, the standards were nearly complete. However, these standards are not binding on any party by ISO or any international jurisdiction. They are simply available for use in any of a variety of voluntary ways. They "can be adopted voluntarily by a spacecraft manufacturer or operator, or brought into effect through a commercial contract between a customer and supplier, or used as the basis for establishing a set of national regulations on space debris mitigation."

The voluntary ISO standard also adopted the "25-year rule" for the "LEO protected region" below 2,000 km (1,200 mi) altitude that has been previously (and still is, as of 2019) used by the US, ESA, and UN mitigation standards, and identifies it as "an upper limit for the amount of time that a space system shall remain in orbit after its mission is completed. Ideally, the time to deorbit should be as short as possible (i.e., much shorter than 25 years)".

Holger Krag of the European Space Agency states that as of 2017 there is no binding international regulatory framework with no progress occurring at the respective UN body in Vienna.

The continued practice of disposing of space debris on Earth in areas such as the spacecraft cemetery has raised environmental concerns. Klinger states that "the environmental geopolitics of Earth and outer space are inextricably linked by the spatial politics of privilege and sacrifice - among people, places, and institutions". Since 1971, 273 spacecraft and satellites have been directed to Point Nemo; this number includes the Mir Space Station (142 tonnes) and will include the International Space Station in 2024 (240 tonnes). In 2018, it was found that the water had 26 microplastic particles per cubic metre, meaning it is highly polluted. The prevalence of orbital debris has been likened to the terrestrial environmental phenomenon of " sacrifice zones", which are designated geographic regions with high levels of environmental degradation.

Since the 1960s, over three hundred rocket launch sites have been built globally. Among these launch sites, 17 hosted 90 launches in 2017 alone. Rocket launches affect local and global environments through the construction of necessary infrastructure, exposure of local environments to toxic residue and the dispersal of pollutants. Rockets are the only source of direct anthropogenic emissions into the stratosphere and emit ozone depleting substances such as nitrous oxide, hydrogen chloride and aluminium oxide; these substances can destroy 105 ozone molecules before depleting. Each launch showers an area concentrated within a kilometre with toxins, heavy metals, and acids. This results in localised regional acid rain, plant death, fish kills, and failed seed germination. Furthermore, studies on trace elements concentration in alligators, near NASA launch activities in Florida (USA), showed that over 50% of alligators had "greater than toxic levels" of trace elements in their liver. Similarly, research in Kazakhstan, Russia and China has found that unsymmetrical dimethylhydrazine (UDMH) has carcinogenic, mutagenic, convulsant, teratogenic, embryotoxic and DNA damaging effects on rodents living near the Baikonur Cosmodrome, Kazakhstan. It is unknown, however, at what trace concentrations these toxic effects manifest in humans or how it may bioaccumulate up the food chain. A lack of adequate resourcing to maintain safe, non-toxic environments makes these areas sacrifice zones and spaces of waste. The relative remoteness of these spaces makes them attractive launch sites, yet this "periphery" remain central to both their human and non-human inhabitants, who become "sacrificial".

An increase in anthropogenic activity in outer space has resulted in large amounts of physical pollution known as orbital debris. This has resulted in space becoming more and more congested due to this rapid increase. This increase in congestion threatens the orbital operations of nations and corporations alike. However, orbital debris also has an impact on the wider population through various means, such as potentially lethal debris falling from the sky, or orbital debris ruining night skies through light pollution. Environmental justice as described by the United States Environmental Protection Agency is the fair and meaningful involvement of all demographics in the development and implementation of environmental regulations and policies. Outer space can be seen as an environment like any other environment on Earth, making orbital debris a potential issue of environmental justice.

The idea of environmental injustice is also that the rights of those who have suffered environmental harm or have been disrupted and encroached upon by more powerful actors are protected. In the context of the space industry large space organisations and nations are the powerful actors and those who have suffered are public. Recent research shows that space exploration opens many questions about environmental justice. Environmental geopolitics of the earth and that of outer space are linked, particularly by the geopolitics of privilege from one party and sacrifice from another. They are also linked in the premise of environmental justice, this injustice can unfold on multiple scales such as emission from space launches, placement of outer space-related infrastructure and of course orbital debris in this case.

There is an argument that as well as viewing space as an environment space should also be viewed as a commons. If space is viewed as a commons then its resources need to be managed for the common good of all people. If not, then this poses a risk of injustice. By managing space as a resource that all nations have access to, and none can claim sovereignity over, outer space can be also understood as an example of a global commons. However, legally defining space as a common is challenging, as the idea of global commons is a social construct. Many space treaties include various phrases describing and defining the usage of outer space, including phrases such as "for the benefit of all people" and "shall be the providence of all mankind". However, none of these treaties provides an adequate framework for handling resources or resolving issues.

Governance frameworks for outer space have a very narrow and utilitarian view of outer space that looks at what they can gain from exploration.

Spatial density of LEO space debris by altitude, according to 2011 a NASA report to the United Nations Office for Outer Space Affairs[194]

Spatial density of space debris by altitude according to ESA MASTER-2001, without debris from the Chinese ASAT and 2009 collision events

As of the 2010s, several technical approaches to the mitigation of the growth of space debris are typically undertaken, yet no comprehensive legal regime or cost assignment structure is in place to reduce space debris in the way that terrestrial pollution has reduced since the mid-20th century.

To avoid excessive creation of artificial space debris, many - but not all - satellites launched to above-low-Earth-orbit are launched initially into elliptical orbits with perigees inside Earth's atmosphere so the orbit will quickly decay and the satellites then will destroy themselves upon reentry into the atmosphere. Other methods are used for spacecraft in higher orbits. These include passivation of the spacecraft at the end of its useful life; as well as the use of upper stages that can reignite to decelerate the stage to intentionally deorbit it, often on the first or second orbit following payload release; satellites that can, if they remain healthy for years, deorbit themselves from the lower orbits around Earth. Other satellites (such as many CubeSats) in low orbits below approximately 400 km (250 mi) orbital altitude depend on the energy-absorbing effects of the upper atmosphere to reliably deorbit a spacecraft within weeks or months.

Increasingly, spent upper stages in higher orbits - orbits for which low-delta-v deorbit is not possible, or not planned for - and architectures that support satellite passivation, at end of life are passivated at end of life. This removes any internal energy contained in the vehicle at the end of its mission or useful life. While this does not remove the debris of the now derelict rocket stage or satellite itself, it does substantially reduce the likelihood of the spacecraft destructing and creating many smaller pieces of space debris, a phenomenon that was common in many of the early generations of US and Soviet spacecraft.

Upper stage passivation (e.g. of Delta boosters) by releasing residual propellants reduces debris from orbital explosions; however even as late as 2011, not all upper stages implement this practice. SpaceX used the term "propulsive passivation" for the final maneuver of their six-hour demonstration mission ( STP-2) of the Falcon 9 second stage for the US Air Force in 2019, but did not define what all that term encompassed.

With a "one-up, one-down" launch-license policy for Earth orbits, launchers would rendezvous with, capture and de-orbit a derelict satellite from approximately the same orbital plane. Another possibility is the robotic refueling of satellites. Experiments have been flown by NASA, and SpaceX is developing large-scale on-orbit propellant transfer technology.

Another approach to debris mitigation is to explicitly design the mission architecture to always leave the rocket second-stage in an elliptical geocentric orbit with a low-perigee, thus ensuring rapid orbital decay and avoiding long-term orbital debris from spent rocket bodies. Such missions will often complete the payload placement in a final orbit by the use of low-thrust electric propulsion or with the use of a small kick stage to circularize the orbit. The kick stage itself may be designed with the excess-propellant capability to be able to self-deorbit.

Although the ITU requires geostationary satellites to move to a graveyard orbit at the end of their lives, the selected orbital areas do not sufficiently protect GEO lanes from debris. Rocket stages (or satellites) with enough propellant may make a direct, controlled de-orbit, or if this would require too much propellant, a satellite may be brought to an orbit where atmospheric drag would cause it to eventually de-orbit. This was done with the French Spot-1 satellite, reducing its atmospheric re-entry time from a projected 200 years to about 15 by lowering its altitude from 830 km (516 mi) to about 550 km (342 mi).

The Iridium constellation - 95 communication satellites launched during the five-year period between 1997 and 2002 - provides a set of data points on the limits of self-removal. The satellite operator - Iridium Communications - remained operational over the two-decade life of the satellites (albeit with a company name change through a corporate bankruptcy during the period) and, by December 2019, had "completed disposal of the last of its 65 working legacy satellites." However, this process left 30 satellites with a combined mass of (20,400 kg (45,000 lb), or nearly a third of the mass of this constellation) in LEO orbits at approximately 700 km (430 mi) altitude, where self-decay is quite slow. Of these satellites, 29 simply failed during their time in orbit and were thus unable to self-deorbit, while one - Iridium 33 - was involved in the 2009 satellite collision with the derelict Russian military satellite Kosmos-2251. No contingency plan was laid for the removal of satellites that were unable to remove themselves. In 2019, the Iridium CEO, Matt Desch, said that Iridium would be willing to pay an active-debris-removal company to deorbit its remaining first-generation satellites if it were possible for an unrealistically low cost, say "US$10,000 per deorbit, but [he] acknowledged that price would likely be far below what a debris-removal company could realistically offer. 'You know at what point [it's] a no-brainer, but [I] expect the cost is really in the millions or tens of millions, at which price I know it doesn't make sense.'"

Passive methods of increasing the orbital decay rate of spacecraft debris have been proposed. Instead of rockets, an electrodynamic tether could be attached to a spacecraft at launch; at the end of its lifetime, the tether would be rolled out to slow the spacecraft. Other proposals include a booster stage with a sail-like attachment and a large, thin, inflatable balloon envelope.

In late December 2022, ESA successfully carried out a demonstration of a breaking sail-based satellite deorbiter, , which could be used by mitigation measures and is part of ESA's Zero Debris Initiative. Around one year earlier, China also tested a drag sail.

A variety of approaches have been proposed, studied, or had ground subsystems built to use other spacecraft to remove existing space debris.

A consensus of speakers at a meeting in Brussels in October 2012, organized by the Secure World Foundation (a U.S. think tank) and the French International Relations Institute, reported that removal of the largest debris would be required to prevent the risk to spacecraft becoming unacceptable in the foreseeable future (without any addition to the inventory of dead spacecraft in LEO). To date in 2019, removal costs and legal questions about ownership and the authority to remove defunct satellites have stymied national or international action. Current space law retains ownership of all satellites with their original operators, even debris or spacecraft which are defunct or threaten active missions.

A well-studied solution uses a remotely controlled vehicle to rendezvous with, capture, and return debris to a central station. One such system is Space Infrastructure Servicing, a commercially developed refueling depot and service spacecraft for communications satellites in geosynchronous orbit originally scheduled for a 2015 launch. The SIS would be able to "push dead satellites into graveyard orbits." The Advanced Common Evolved Stage family of upper stages is being designed with a high leftover-propellant margin (for derelict capture and de-orbit) and in-space refueling capability for the high delta-v required to de-orbit heavy objects from geosynchronous orbit. A tug-like satellite to drag debris to a safe altitude for it to burn up in the atmosphere has been researched. When debris is identified the satellite creates a difference in potential between the debris and itself, then using its thrusters to move itself and the debris to a safer orbit.

A variation of this approach is for the remotely controlled vehicle to rendezvous with debris, capture it temporarily to attach a smaller de-orbit satellite and drag the debris with a tether to the desired location. The "mothership" would then tow the debris-smallsat combination for atmospheric entry or move it to a graveyard orbit. One such system is the proposed Busek ORbital DEbris Remover (ORDER), which would carry over 40 SUL (satellite on umbilical line) de-orbit satellites and propellant sufficient for their removal.

On 7 January 2010 Star, Inc. reported that it received a contract from the Space and Naval Warfare Systems Command for a feasibility study of the ElectroDynamic Debris Eliminator (EDDE) propellantless spacecraft for space-debris removal. In February 2012 the Swiss Space Center at École Polytechnique Fédérale de Lausanne announced the Clean Space One project, a nanosatellite demonstration project for matching orbit with a defunct Swiss nanosatellite, capturing it and de-orbiting together. The mission has seen several evolutions to reach a pac-man inspired capture model. In 2013, Space Sweeper with Sling-Sat (4S), a grappling satellite which captures and ejects debris was studied. In 2022, a Chinese satellite, SJ-21, grabbed an unused satellite and "threw" it into an orbit with a lower risk for it to collide.

In December 2019, the European Space Agency awarded the first contract to clean up space debris. The €120 million mission dubbed ClearSpace-1 (a spinoff from the EPFL project) is slated to launch in 2025. It aims to remove a 100 kg VEga Secondary Payload Adapter (Vespa) left by Vega flight VV02 in an 800 km (500 mi) orbit in 2013. A "chaser" will grab the junk with four robotic arms and drag it down to Earth's atmosphere where both will burn up.

The laser broom uses a ground-based laser to ablate the front of the debris, producing a rocket-like thrust that slows the object. With continued application, the debris would fall enough to be influenced by atmospheric drag. During the late 1990s, the U.S. Air Force's Project Orion was a laser-broom design. Although a test-bed device was scheduled to launch on a Space Shuttle in 2003, international agreements banning powerful laser testing in orbit limited its use to measurements. The 2003 Space Shuttle Columbia disaster postponed the project and according to Nicholas Johnson, chief scientist and program manager for NASA's Orbital Debris Program Office, "There are lots of little gotchas in the Orion final report. There's a reason why it's been sitting on the shelf for more than a decade."

The momentum of the laser-beam photons could directly impart a thrust on the debris sufficient to move small debris into new orbits out of the way of working satellites. NASA research in 2011 indicates that firing a laser beam at a piece of space junk could impart an impulse of 1 mm (0.039 in) per second, and keeping the laser on the debris for a few hours per day could alter its course by 200 m (660 ft) per day. One drawback is the potential for material degradation; the energy may break up the debris, adding to the problem. A similar proposal places the laser on a satellite in Sun-synchronous orbit, using a pulsed beam to push satellites into lower orbits to accelerate their reentry. A proposal to replace the laser with an Ion Beam Shepherd has been made, and other proposals use a foamy ball of aerogel or a spray of water, inflatable balloons, electrodynamic tethers, electroadhesion, and dedicated anti-satellite weapons.

On 28 February 2014, Japan's Japan Aerospace Exploration Agency (JAXA) launched a test "space net" satellite. The launch was an operational test only. In December 2016 the country sent a space junk collector via Kounotori 6 to the ISS by which JAXA scientists experiment to pull junk out of orbit using a tether. The system failed to extend a 700-meter tether from a space station resupply vehicle that was returning to Earth. On 6 February the mission was declared a failure and leading researcher Koichi Inoue told reporters that they "believe the tether did not get released".

The RemoveDEBRIS mission plan is to test the efficacy of several ADR technologies on mock targets in low Earth orbit. In order to complete its planned experiments the platform is equipped with a net, a harpoon, a laser ranging instrument, a dragsail, and two CubeSats (miniature research satellites). The mission was launched on 2 April 2018.

Metal processing technologies to melt space debris and transform it into other useful form factors are developed by CisLunar Industries. Their system uses electromagnetic heating to melt metal and shape it into metal wire, sheet metal, and metal fuel.

A propulsion system dubbed the Neumann Drive has been developed in Adelaide, Australia, with first sent into space in June 2023. Metal space junk is converted into fuel rods, which can be plugged into the Neumann Drive, "basically converting the solid metal propellant into plasma". The Drive will be used by American space companies which already carry nets or robotic arms to capture orbital waste. The thruster enables these satellites to return to Earth with the waste they have collected, allowing it to be melted down to make more fuel.

With the rapid development of the computer and digitalization industries, more countries and companies have engaged in space activities since the turn of the 20th century. The tragedy of the commons is an economic theory referring to a situation where maximizing self-interest through using a shared resource can finally lead to the resource degradation shared by all. Based on the theory, individuals' rational action in space will finally lead to an irrational collective result: orbits are crowded with debris. As a common-pool resource, the Earth's orbits, especially LEO and GEO that accommodate most satellites, are nonexcludable and rivalry. To address the tragedy and ensure space sustainability, many technical approaches have been developed. And in terms of governance mechanisms, the top-down centralized one is less suitable to tackle the complex debris problem due to the increasing number of space actors. Instead, much evidence has proved that polycentric form of governance developed by Elinor Ostrom can work in space.

In the process of promoting the polycentric network, there are some existing barriers needed to be dealt with.

As orbital debris is a global problem affecting both spacefaring and non-spacefaring nations, it is necessary to be handled in a worldwide context. Because of the complexity and dynamics of object movements like spacecraft, debris, meteorites, etc., many countries and regions including the United States, Europe, Russia and China have developed their space situational awareness (SSA) to avoid potential threats in space or plan actions in advance. To a certain extent, SSA plays a role in tracking space debris. In order to build a powerful SSA system, there are two prerequisites: international cooperation and exchange of information and data. However, limitations still exist in spite of the substantially improving data quality over the past decades. Some space powers are not willing to share the information that they have collected, and those, such as the U.S., that have shared the data keep parts of it secret. Instead of joining in a coordinated way, a great deal of SSA programs and national databases run parallel to each other with some overlaps, hindering the formation of a collaborative monitoring system.

Some private actors are also trying to establish SSA systems. For example, the Space Data Association (SDA) formed in 2009 is a non-governmental entity. It currently consists of 21 global satellite operators and 4 executive members: Eutelsat, Inmarsat, Intelsat and SES. SDA is a non-profit platform, aiming to avoid radio interference and space collisions through pooling data from operators independently. Researchers suggest that it is essential to establish an international center for exchanging information on space debris because SSA networks do not completely equal debris tracking systems - the former ones focus more on active and threatening objects in space. And in terms of debris populations and defunct satellites, not very much operators have provided data.

In a polycentric governance network, a resource that cannot be holistically monitored is less possible to be well managed. Both insufficient transnational cooperation and information sharing bring resistance to addressing the debris problem. There is still a long way to go before building a global network that covers complete data and has strong interconnection and interoperability.

With the commercialization of satellites and space, the private sector is getting more interested in space activities. For example, SpaceX is planning to create a network of around 12,000 small satellites that can transmit high-speed internet to any place in the world. The proportion of commercial spacecraft has increased from 4.6% in the 1980s to 55.6% in the 2010s. Despite the high participation rate of commercial entities, UN COPUOS once deliberately excluded them from having a voice in discussions unless being formally invited by a member state. Ostrom said that the involvement of all relevant stakeholders in the rule-design and implementation process is one of the critical elements of successful governance. The exclusion of private actors largely reduces the effectiveness of the committee's role in making collective-choice arrangements that reflect the interests of all space users.

The limited engagement of private actors slows down the process of addressing space debris to some degree. Ties existing between dissimilar stakeholders in the governance network offer access to diverse resources. Different competence among stakeholders can help allocate the tasks more reasonably. In that case, the expertise and experience of private operators are critical to help the world achieve space sustainability. The complementary strengths of different stakeholders enable the governance network to be more adaptable to changes and reach common goals more effectively. In recent years, many private actors have seen commercial opportunities of eliminating space debris. It is estimated that by 2022 the global market for debris monitoring and removal will generate a revenue of around $2.9 billion. For example, Astroscale has contracted with European and Japanese space agencies to develop the capacity of removing orbital debris. Despite that, they are still in small quantity compared to the number of those who have placed satellites in space. Privateer Space, a Hawaiian-based startup company started by American engineer Alex Fielding, space environmentalist Dr. Moriba Jah, and Apple co-founder Steve Wozniak, announced plans in September 2021 to launch hundreds of satellites into orbit in order to study space debris. However, the company stated it is in "stealth mode" and no such satellites have been launched.

Fortunately, the current space exploration is not completely driven by competition, and there still exists a chance for dialogues and cooperation among all stakeholders in both developed and developing countries, to reach an agreement on tackling space debris and assure an equitable and orderly exploration. Besides private actors, network governance does not necessarily exclude the states from playing a role. Instead, the different functions of states might promote the governance process. To improve the polycentric governance network of space debris, researchers suggest: encourage data-sharing among different national and organizational databases at the political level; develop shared standards for data collection systems to improve interoperability; enhance the participation of private actors through involving them in national and international discussions.

A piece of a thermal blanket that may have come from the descent stage of the Perseverance

Perseverance's backshell sitting upright on the surface of Jezero Crater

The issue of space debris has been raised as a mitigation challenge for missions around the Moon with the danger of increasing space debris around it.

In 2022, several elements of space debris were found on Mars, Perseverance's backshell was found on the surface of Jezero Crater, and a piece of a thermal blanket that may have come from the descent stage of the rover.

It is thought that on 4 March 2022, for the first time, human space debris - most likely a spent rocket body, Long March 3C third stage from the 2014 Chang'e 5 T1 mission - unintentionally hit the lunar surface, creating an unexpected double crater.

Until the End of the World (1991) is a French sci-fi drama set under the backdrop of an out-of-control Indian nuclear satellite, predicted to re-enter the atmosphere, threatening vast populated areas of the Earth.

, a 2013 survival film directed by Alfonso Cuaron, is about a disaster on a space mission caused by Kessler syndrome.

In season 1 of Love, Death & Robots (2019), episode 11, "Helping Hand", revolves around an astronaut being struck by a screw from space debris which knocks her off a satellite in orbit.

Manga and anime tells a story about a crew of Space Debris station that collects and disposes space debris.

Gleghorn, George; et al. (1995). Orbital Debris: A Technical Assessment (PDF) (Report). National Academy of Sciences. ISBN 0-309-05125-8..

Hoots, Felix; Schumacher, Paul Jr.; Glover, Robert A. (2004). "History of Analytical Orbit Modeling in the U.S. Space Surveillance System". Journal of Guidance, Control, and Dynamics. 27 (2): 174-185. Bibcode:2004JGCD...27..174H. doi:10.2514/1.9161.

Johnson, Nicholas L. (1998). "Monitoring and Controlling Debris in Space". Scientific American. 279 (2): 62-67. Bibcode:1998SciAm.279b..62J. doi:10.1038/scientificamerican0898-62. JSTOR 26070599..

Kessler, Donald (1971). "Estimate of Particle Densities and Collision Danger for Spacecraft Moving Through the Asteroid Belt". Physical Studies of Minor Planets. NASA SP-267. 267: 595-605. Bibcode:1971NASSP.267..595K..

Kessler, Donald; Cour-Palais, Burton (June 1978). "Collision Frequency of Artificial Satellites: The Creation of a Debris Belt" (PDF). Journal of Geophysical Research. 81 (A6): 2637-46. Bibcode:1978JGR....83.2637K. doi:10.1029/JA083iA06p02637. Archived from the original (PDF) on 15 May 2011..

Kessler, Donald (1981). "Sources of Orbital Debris and the Projected Environment for Future Spacecraft" (PDF). Journal of Spacecraft. 16 (4): 357-60. Bibcode:1981JSpRo..18..357K. doi:10.2514/3.57828. Archived from the original (PDF) on 14 July 2010..

Kessler, Donald (December 1991). "Collisional Cascading: The Limits of Population Growth in Low Earth Orbit" (PDF). Advances in Space Research. 11 (12): 63-66. Bibcode:1991AdSpR..11l..63K. doi:10.1016/0273-1177(91)90543-S. Archived from the original (PDF) on 14 July 2010..

Kessler, Donald; Anz-Meador, Phillip (March 2001). "Critical Number of Spacecraft in Low Earth Orbit: Using Fragmentation Data to Evaluate the Stability of the Orbital Debris Environment" (PDF). Proceedings of the Third European Conference on Space Debris. Darmstadt Germany..

Kessler, Donald (8 March 2009). The Kessler Syndrome. Western University Canada..

Liou, J.-C. (14 January 2020). "Risks from Orbital Debris and Space Situational Awareness" (PDF). IAA Conference on Space Situational Awareness. Washington, D.C..

Schefter, Jim (July 1982). "The Growing Peril of Space Debris". Popular Science. Vol. 221, no. 1. pp. 48-51 - via Google Books..

"What is Orbital Debris?", Center for Orbital and Reentry Debris Studies, Aerospace Corporation

Committee for the Assessment of NASA's Orbital Debris Programs (2011). Limiting Future Collision Risk to Spacecraft: An Assessment of NASA's Meteoroid and Orbital Debris Programs. Washington, D.C.: National Research Council. ISBN 978-0-309-21974-7.
News item summarizing the above report

Steven A. Hildreth and Allison Arnold. Threats to U.S. National Security Interests in Space: Orbital Debris Mitigation and Removal. Washington, D.C.: Congressional Research Service, 8 January 2014.

David Leonard, "The Clutter Above", Bulletin of the Atomic Scientists, July/August 2005.

Patrick McDaniel, "A Methodology for Estimating the Uncertainty in the Predicted Annual Risk to Orbiting Spacecraft from Current or Predicted Space Debris Population". National Defense University, 1997.

"Interagency Report on Orbital Debris, 1995", National Science and Technology Council, November 1995.

Nickolay Smirnov, Space Debris: Hazard Evaluation and Mitigation. Boca Raton, FL: CRC Press, 2002, ISBN 0-415-27907-0.

Richard Talcott, "How We Junked Up Outer Space", Astronomy, Volume 36, Issue 6 (June 2008), pp. 40-43.

"Technical report on space debris, 1999", United Nations, 2006. ISBN 92-1-100813-1.

Robin Biesbroek (2015). Active Debris Removal in Space: How to Clean the Earth's Environment from Space Debris. CreateSpace. ISBN 978-1-5085-2918-7.

Khatchadourian, Raffi, "The Trash Nebula: Millions of man-made artifacts are circling Earth. Will one of them cause a disaster?", 28 September 2020, pp. 44-52, 54-55. "By one estimate, there are a hundred million bits of debris that are a millimetre in size, a hundred million as small as a micron. We live in a corona of trash. [T]he problem, if ignored, could destroy all the satellites that orbit near the Earth - a loss that would be more acutely felt as humanity increasingly relied on space." (p. 47.)

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Space debris (also known as space junk, space pollution, space waste, space trash, space garbage, or cosmic debris) are defunct human-made objects in space - principally in Earth orbit - which no longer serve a useful function.

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There are almost 30,000 man-made objects orbiting Earth. Many are tiny pieces of rockets and satellites, while others just aren't used anymore. All of them pose risks to other space craft and satellites, which means at some point we're going to have to remove them - and the European Space Agency has a couple ideas how.
Produced by Matt Stuart. Additional reporting by Rebecca Harrington. Video courtesy of ESA.

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This massive net could solve a huge problem in space

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There are almost 30,000 man-made objects orbiting Earth. Many are tiny pieces of rockets and satellites, while others just aren't used anymore. All of them pose risks to other space craft and satellites, which means at some point we're going to have to remove them - and the European Space Agency has a couple ideas how.

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By

What is a satellite?

A satellite is any object that orbits something else, as, for example, the Earth orbits the sun. There are hundreds of satellites in operation. They are used for diverse purposes such as weather forecasting, television signal, amateur radio and internet communications and the Global Positioning System. They are also used to look outward at the solar system for research and data gathering purposes.

In a communications context, a satellite is a specialized wireless receiver/transmitter that is launched by a rocket and placed in orbit around the Earth.

The Soviet Union launched the first manmade satellite in 1957. Sputnik I was about the size of a basketball and transmitted a simple Morse code signal over and over. In contrast, modern satellites can receive and retransmit thousands of signals simultaneously, from simple digital data to complex television programming.

How do satellites work?

Satellites are typically launched into orbit using a rocket. They are positioned at different heights and travel different tracks around the Earth at different speeds. Once in orbit, the Earth's gravitational pull keeps the satellite from following a path straight out into space.

These devices usually have an antenna that lets them send and receive data. They also have a power source, typically a battery or solar power panels. Other equipment on a satellite depends on its purpose. They may have cameras, telescopes and sensors. The International Space Station is a complex satellite with living and working quarters for its inhabitants along with equipment for research.

The exact way a satellite works also depends on its purpose. One may collect images and other data from the solar system and transmit it back to Earth. Communication satellites capture signals sent from the Earth, increase their strength and retransmit them to receiving stations on Earth. Satellites are critical when transmitting television, radio, voice and data signals across virtually any distance.

Satellites do have transmission delays based on the distance a signal travels in its round-trip from Earth to the satellite and back to Earth. These transmission delays, also called propagation delays, are only a fraction of a second, but they can cause quality issues. Advances in technology have reduced these delays.

Why are satellites important?

Satellites serve a range of important purposes, including the following:

Earth surveillance and research. Satellites can view large parts of the Earth. This enables them to gather data and video signals quickly, typically faster than equipment at ground level. This information is used in various ways, including weather, climate and military applications.

Space data collection and research. Satellites also facilitate space exploration. Specialized systems, such as the Hubble Space Telescope, capture images of the solar system and celestial phenomena faster and more clearly than ground-based telescopes. They are not restricted by the Earth's atmosphere, which reduces the level of image clarity.

Communications. Satellites extend the reach of ground-based communications systems that typically connect with a line-of-sight signal or wireline media such as copper or fiber optic cables. They also eliminate signal blockage by fixed objects on the ground, such as mountains and tall buildings.

What are the three satellite orbit types?

There are three types of communications satellite systems. They are categorized according to the type of orbit they follow.

Geostationary orbit

A geostationary satellite orbits the Earth over the equator, approximately 22,000 miles up. At that altitude, one complete trip around the Earth relative to the sun takes 24 hours. These satellites remain over the same spot on the Earth's surface at all times. A geostationary satellite stays fixed in the sky from any point on the Earth's surface from which it can be seen. Weather satellites are usually of this type.

A geostationary satellite can "see" approximately 40% of the Earth's surface. Three such satellites, spaced at equal intervals -- 120 angular degrees apart -- can provide coverage of the entire inhabited world. A dish antenna aimed at the spot in the sky where the satellite is can access a satellite internet connection.

Low Earth orbit

A low Earth orbit ( LEO) satellite system uses a large fleet of satellites, each in a circular orbit at a constant altitude of a few hundred miles. The orbits take the satellites over, or nearly over, the geographic poles. Each revolution takes from 90 minutes to a few hours. The fleet is arranged in such a way that at least one satellite is on a line of sight from any point on the Earth's surface at any time.

The entire system operates in a manner similar to the way a cellular telephone functions. The main difference is that the transponders, or wireless receiver/transmitters, are moving rather than fixed, and are in space rather than on the Earth. A well-designed LEO system makes it possible for anyone to have a wireless internet connection from any point on the planet, using an antenna no more sophisticated than old-fashioned television "rabbit ears."

Some satellites revolve around the Earth in elliptical orbits. These ones move rapidly when they are near perigee, or their lowest altitude. They move slowly when they are near apogee, or their highest altitude. Amateur radio operators use these "birds," as these LEO satellites are also called, as well as commercial and government services. The directional antennas they use must be constantly adjusted to follow the satellite's path across the sky.

Polar orbit

Satellites in polar orbits are the third type. Their orbits traverse the north and south poles rather than align to the equator. With a geosynchronous or elliptical orbit, these satellites can view all or most of the Earth's surface, the same as equatorial satellites. They are valuable for government and military applications.

How are satellites used?

In addition to broadcasting television signals, satellites are used for an array of commercial, government and military applications. Some specific ones include the following:

Navigation satellites are used for ship-to-ship communications and position identification.

Weather satellites use sensors to monitor the Earth's weather systems and patterns. They measure visible light, reflected light and infrared radiation.

Newer LEO satellites orbit closer to the Earth than geosynchronous satellites. This makes them ideal for voice and data communications. Wi-Fi networks, internet service providers and emergency communications services use them.

Satellites are used for broadcasting applications, including sending radio and television signals to consumers.

The International Space Station is a satellite that provides many services, including research and development, Earth and space observation among other applications. One of the biggest concerns for the space station is avoiding space debris, such as abandoned satellites, pieces of rocket boosters and fragments of satellites.

Alternatives to satellite technology

The obvious alternative to satellite transmission is ground-based communications networks. These can include terrestrial facilities, such as copper wire, fiber optics and coaxial cable. Options include microwave, radio waves, free-space optics (laser) and undersea transmission systems.

Ground-level communication has many challenges, including geographical obstacles, political limitations and commercial viability. Terrestrial and satellite communications systems are often blended to build large-scale global communications networks.

Stratospheric drone technology has the potential to take over some functions of satellites. High-altitude, solar powered drones are in development that are expected fly at heights of at least 65,000 feet. Plans are for these aircrafts to stay aloft for as long as a year and take over some of the monitoring and telecommunications tasks that satellites now handle.
Satellite technology has many practical applications. See how it is helping close the digital divide.

Continue Reading About satellite

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By A satellite is any object that orbits something else, as, for example, the Earth orbits the sun. There are hundreds of satellites in operation. They are used for diverse purposes such as weather forecasting, television signal, amateur radio and internet communications and the Global Positioning System.

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Website privacy and terms. The Maanmittauslaitos.fi website uses the Siteimprove user monitoring service to analyse and develop the use of the website and traffic. In addition, the website uses the React&Share service to develop the content and collect user feedback.

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See a satellite net collect space junk | CNN Business

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A satellite successfully tested its new space-cleaning technology as part of a plan to clean up the thousands of pieces of rubbish floating around Earth's orbit.

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Derelict satellites could in future be grappled and removed from key orbits around Earth with a space tug using magnetic forces.

This same magnetic attraction or repulsion is also being considered as a safe method for multiple satellites to maintain close formations in space.

Such satellite swarms are being considered for future astronomy or Earth-observing missions - if their relative positions can stay stable they could act as a single giant telescope.

To combat space debris, interest is growing in plucking entire satellites from space. The biggest challenge is to grapple and secure such uncontrolled, rapidly tumbling objects, typically of several tonnes.

Multiple techniques are being investigated, including robotic arms, nets and harpoons.

Now researcher Emilien Fabacher of the Institut Supérieur de l'Aéronautique et de l'Espace, part of the University of Toulouse in France, has added another method to the list: magnetic grappling.

"With a satellite you want to deorbit, it's much better if you can stay at a safe distance, without needing to come into direct contact and risking damage to both chaser and target satellites," explains Emilien.

"So the idea I'm investigating is to apply magnetic forces either to attract or repel the target satellite, to shift its orbit or deorbit it entirely."

Such target satellites would not need to be specially equipped in advance. Instead, such a tug would influence target satellites using their 'magnetorquers': reliable electromagnets already carried to adjust orientation using Earth's magnetic field.

"These are standard issue aboard many low-orbiting satellites," adds Emilien.

The strong magnetic field required by the chaser satellite would be generated using superconducting wires cooled to cryogenic temperatures.

Similarly satellites could also keep multiple satellites flying in precise formation, comments Finn Ankersen, an ESA expert in rendezvous and docking, formation flight.

"This kind of contactless magnetic influence would work from about 10-15 m out, offering positioning precision within 10 cm with attitude precision 1-2º."

For his PhD research, Emilien has been researching how the resulting guidance, navigation and control techniques would work in practice, combining a rendezvous simulator with magnetic interaction models, while also taking account of the ever-changing state of Earth's own magnetosphere.

His research has been supported through ESA's Networking/Partnering Initiative, which supports work carried out by universities and research institutes on advanced technologies with potential space applications. Emilien also visited ESA's technical centre in the Netherlands, to consult with Agency experts.

Emilien recalls that the concept originally came out of discussion with ESA experts, and he was lucky enough to be in the right place at the right time to explore its feasibility: "The first surprise was that it was indeed possible, theoretically - initially we couldn't be sure, but it turns out that the physics works fine."

Thank you for liking

You have already liked this page, you can only like it once!

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Magnetic space tug could target dead satellites

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Derelict satellites could in future be grappled and removed from key orbits around Earth with a space tug using magnetic forces. This same magnetic attraction or repulsion is also being considered as a safe method for multiple satellites to maintain close formations in space.

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https://www.esa.int/Enabling_Support/Space_Engineering_Technology/Magnetic_space_tug_could_target_dead_satellites

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Derelict satellites could in future be grappled and removed from key orbits around Earth with a space tug using magnetic forces.

This same magnetic attraction or repulsion is also being considered as a safe method for multiple satellites to maintain close formations in space.

Such satellite swarms are being considered for future astronomy or Earth-observing missions - if their relative positions can stay stable they could act as a single giant telescope.

To combat space debris, interest is growing in plucking entire satellites from space. The biggest challenge is to grapple and secure such uncontrolled, rapidly tumbling objects, typically of several tonnes.

Multiple techniques are being investigated, including robotic arms, nets and harpoons.

Now researcher Emilien Fabacher of the Institut Supérieur de l'Aéronautique et de l'Espace, part of the University of Toulouse in France, has added another method to the list: magnetic grappling.

"With a satellite you want to deorbit, it's much better if you can stay at a safe distance, without needing to come into direct contact and risking damage to both chaser and target satellites," explains Emilien.

"So the idea I'm investigating is to apply magnetic forces either to attract or repel the target satellite, to shift its orbit or deorbit it entirely."

Such target satellites would not need to be specially equipped in advance. Instead, such a tug would influence target satellites using their 'magnetorquers': reliable electromagnets already carried to adjust orientation using Earth's magnetic field.

"These are standard issue aboard many low-orbiting satellites," adds Emilien.

The strong magnetic field required by the chaser satellite would be generated using superconducting wires cooled to cryogenic temperatures.

Similarly satellites could also keep multiple satellites flying in precise formation, comments Finn Ankersen, an ESA expert in rendezvous and docking, formation flight.

"This kind of contactless magnetic influence would work from about 10-15 m out, offering positioning precision within 10 cm with attitude precision 1-2º."

For his PhD research, Emilien has been researching how the resulting guidance, navigation and control techniques would work in practice, combining a rendezvous simulator with magnetic interaction models, while also taking account of the ever-changing state of Earth's own magnetosphere.

His research has been supported through ESA's Networking/Partnering Initiative, which supports work carried out by universities and research institutes on advanced technologies with potential space applications. Emilien also visited ESA's technical centre in the Netherlands, to consult with Agency experts.

Emilien recalls that the concept originally came out of discussion with ESA experts, and he was lucky enough to be in the right place at the right time to explore its feasibility: "The first surprise was that it was indeed possible, theoretically - initially we couldn't be sure, but it turns out that the physics works fine."

Thank you for liking

You have already liked this page, you can only like it once!

# data[].attributes.attachment_link.title
Magnetic space tug could target dead satellites

# data[].attributes.attachment_link.description
Derelict satellites could in future be grappled and removed from key orbits around Earth with a space tug using magnetic forces. This same magnetic attraction or repulsion is also being considered as a safe method for multiple satellites to maintain close formations in space.

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Solar sail technology will eventually play a key role in long-distance NASA missions. But just how far will these solar sails be able to take us and how fast will they get us there?

As we found out in the last section, solar sails would not initially be driven by the amount of force that is used to launch the space shuttle. NASA believes that the exploration of space is similar to the tale of the "Tortoise and the Hare," with rocket-propelled spacecraft being the hare. In this race, the rocket-propelled spacecraft will quickly jump out, moving quickly toward its destination. On the other hand, a rocketless spacecraft powered by a solar sail would begin its journey at a slow but steady pace, gradually picking up speed as the sun continues to exert force upon it. Sooner or later, no matter how fast it goes, the rocket ship will run out of power. In contrast, the solar sail craft has an endless supply of power from the sun. Additionally, the solar sail could potentially return to Earth, whereas the rocket powered vehicle would not have any propellant to bring it back.

As it continues to be pushed by sunlight, the solar sail-propelled vehicle will build up speeds that rocket powered vehicles would never be able to achieve. Such a vehicle would eventually travel at about 56 mi/sec (90 km/sec), which would be more than 200,000 mph (324,000 kph). That speed is about 10 times faster than the space shuttle's orbital speed of 5 mi/sec (8 km/sec). To give you an idea how fast that is, you could travel from New York to Los Angeles in less than a minute with a solar sail vehicle traveling at top speed.

If NASA were to launch an interstellar probe powered by solar sails, it would take only eight years for it to catch the Voyager 1 spacecraft (the most distant spacecraft from Earth), which has been traveling for more than 20 years. By adding a laser or magnetic beam transmitter, NASA said it could push speeds to 18,600 mi/sec (30,000 km/sec), which is one-tenth the speed of light. At those speeds, interstellar travel would be an almost certainty.

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What is a solar sail? How can you use sunlight to move a spacecraft in outer space? In this article, HowStuffWorks will show you how solar sail technology works, take an in-depth look at the Cosmos-1 mission and find out what solar-sails mean for future space travel.

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A British satellite, designed to test out ways to clean up debris in space, just successfully ensnared a simulated piece of junk in orbit using a big net. On Sunday, September 16th, the vehicle, known as the RemoveDEBRIS satellite, deployed its onboard net, which then captured a nearby target probe that the vehicle had released a few seconds earlier. The demonstration shows that a simple idea like a net may be an effective way to clean up all the material orbiting Earth.

The RemoveDEBRIS satellite is meant to try out numerous different methods for cleaning up space junk, which has become a growing problem ever since we started launching rockets into orbit. Thousands of dead, uncontrollable objects linger in orbit, including defunct satellites, spent launch vehicles, and other pieces of debris that have come off other spacecraft. And all of this junk is moving fast, at upwards of 17,000 miles per hour. The more debris we have in orbit, the higher the chance that these pieces might collide at break-neck speeds, creating even more debris that could pose a threat to other spacecraft.

The more debris we have in orbit, the higher the chance that these pieces might collide

The US Department of Defense's Space Surveillance Network is currently tracking around 8,000 objects in orbit with Earth-based antennas, in order to calculate the chances of two large pieces running into one another. However, many engineers are trying to come up with ways to clean up the junk that's up there in order to make collisions even less likely. It's tough, though, since these objects are moving fast, and removing them without creating more debris is tricky. Some engineers have come up with super innovative concepts, like space lasers that can heat up spacecraft or electrified wires that could drag objects out of orbit.

However, the RemoveDEBRIS satellite, built by the Surrey Space Centre at the University of Surrey, is meant to test out much more low-key means of space debris removal. Along with experimenting with a deployable net, the satellite is also equipped with a harpoon that can spear objects, as well as a drag sail that can help slow down debris and make them fall to Earth faster. The plan is to see if these technologies can even work, before trying them out on future spacecraft that are tasked with cleaning up debris.

"We thought technologies like the harpoon or net are relatively low-cost," Guglielmo Aglietti, director of the Surrey Space Centre and principal investigator of the RemoveDEBRIS project, told The Verge in April after the satellite launched. "If we can demonstrate technologies that are affordable, there's a much higher probability this will happen."

"We thought technologies like the harpoon or net are relatively low cost."

RemoveDEBRIS launched to the International Space Station in April, on board a SpaceX Falcon 9 rocket. Then in June, the satellite was loaded into the Nanoracks Kaber Microsatellite Deployer and deployed into space. It's remained in orbit since then, and this weekend it started the first phase of its experiments.

The idea behind the net is relatively simple: capture a piece of material and then drag it down to Earth's atmosphere, where it will burn up. To see if this idea could work, RemoveDEBRIS was equipped with a small standardized satellite known as a CubeSat, which it deployed on Sunday. The tiny satellite drifted outward and then inflated a balloon to increase its overall size (in order to represent a larger, more realistic piece of debris). Once the CubeSat was more than 20 feet away, the RemoveDEBRIS vehicle then shot out its net. Masses at the edges of the net wrapped around the target to make sure it didn't break free from the snare.

The netted CubeSat should fall to Earth within a month or two, but if this concept is used in the future, ideally the net will also contain some kind of technology that could tow the debris downward. "After you grab something with a net, you want to tow your piece of debris down to bury it in the atmosphere," said Aglietti. "In our experiment, we just test the net. We're not testing the towing part."

However, RemoveDEBRIS will be testing out a way to tug debris down to Earth. It will be experimenting with something known as a drag sail, designed to slow down spacecraft in orbit. In low Earth orbit, where much of this debris resides, there are still small particles from our planet's atmosphere that are constantly bombarding objects. These particles slightly push on spacecraft, bumping them out of orbit and dragging them down to Earth. And the more surface area a spacecraft has, the more it gets bombarded by these particles. So increasing the area of a vehicle with a sail, for instance, helps to knock it down to Earth more quickly.

In the months ahead, RemoveDEBRIS will try out its onboard harpoon

In the months ahead, RemoveDEBRIS will deploy a thin sail that will do exactly this and ultimately take the satellite out of orbit. But before that happens, the vehicle will first try out its onboard harpoon. Soon, RemoveDEBRIS will deploy a flat target that will extend outward from the spacecraft. Quickly afterward, it will fire its harpoon and attempt to strike the target. The test is meant to demonstrate another way of capturing spacecraft.

Additionally, RemoveDEBRIS is equipped with special cameras and LIDAR technology that could also be used to image space debris and help with navigation. It's all meant to show that these tools could be used to clean up real defunct satellites someday.

"If the demonstration is successful, we will learn a lot of useful stuff," Aglietti said. "Then the idea is there will be real missions to capture a real piece of debris." Such space junk-capturing satellites will need to have thrusters on board so that they can catch up with the fast-moving debris. But Aglietti hopes RemoveDEBRIS will inspire confidence that these methods are practical. "We think it will be a good stepping stone to prove that the building blocks of space debris removal are viable," he said.

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Satellite uses giant net to practice capturing space junk

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A British satellite, designed to test out ways to clean up debris in space, just successfully ensnared a simulated piece of junk in orbit using a big net. On Sunday, September 16th, the vehicle, known as the RemoveDEBRIS satellite, deployed its onboard net, which then captured a nearby target probe that the vehicle had released a few seconds earlier.

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A New Idea for Cleaning Up Space Debris: Magnets

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Prof. Jake J. Abbott is leading a team that has discovered a way to manipulate orbiting debris with spinning magnets.

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a space net in space and how it would work 

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A tether deployed from a rocket stage.

Today's scientists are already hard at work on new ideas for spaceflight in the future. New technology is being developed to help propel spacecraft into Earth orbit -- and beyond. NASA researchers are studying ways to create more powerful and more efficient rockets. Engineers are considering things such as energy beamed from the ground, ions, and plasma as possible concepts for next-generation engines. Next to all of these super-high-tech ideas, one spaceflight possibility sounds remarkably simple -- string.

Needless to say, if it's going to help propel spacecraft and satellites into higher Earth orbits, and beyond, it has to be some high-tech string. More accurately, the technology is called space tethers. A tether is essentially just something used to tie one object to another. On Earth, tethers are generally used to keep something in place. In space, however, tethers could serve several useful purposes.

One of the uses being examined would be to move satellites into higher orbit, or even to help send spacecraft out into the solar system. This would be done using a process known as momentum exchange. The system would involve placing a satellite in orbit that would be used to boost other objects further from Earth. This satellite would consist of a tether with a grappling mechanism on one end that could "grab" the items being boosted. On the other end of the tether would be a counter mass, which would serve to keep the tether taut. The tether itself could be tens to hundreds of kilometers in length. Researchers are still looking into what materials would make the best space tethers. In fact, one possibility is based on fishing line! The tether will have to be able to resist the corrosion caused by atomic oxygen in the upper reaches of Earth's atmosphere, as well as damage from micrometeoroids.

A tether hangs from an orbiting satellite.

When the new satellite or space probe is launched, the spinning tether system captures it and essentially "flings" it farther from Earth. Using a method such as this would greatly reduce the altitude to which an object would have to be launched initially. This, in turn, would cut down on the needed power of the rocket used to launch it, which, of course, would reduce the cost of the launch. Researchers believe that satellites could be placed in a geosynchronous orbit for as little as one-half of the current launch cost.

Of course, nothing good is ever free, and that includes placing satellites into better orbits. The system is called momentum exchange because it does just that -- exchanges momentum from the orbiting tether to the boosted satellite or probe. That means that the tether loses momentum, and falls closer to the Earth as the other object moves further from it. Without a way to reboost the tether satellite, it could only perform the momentum exchange technique a very limited number of times before dropping into Earth's atmosphere. That's where another use of space tethers comes in.

Another technology NASA researchers are developing is the Electrodynamic Tether (EDT). As the long wire of an EDT passes through Earth's magnetic field, it sets up a voltage along the tether. This voltage makes electrons flow down the tether, like water flowing down a pipe. If the tether has the right systems to allow it to collect and emit electrons, then an electrical current (the flow of electrons) will move through the tether. Any time an electrical current flows in a magnetic field, there is a force. This may sound strange, but it is the same principle that makes every electric motor on Earth work, from the motor in a blender to the motor that spins your CDs.

Another view of a momentum exchange tether.

Current naturally flowing through the tether can be used by spacecraft for power. But again, we don't get something for nothing. The force created by that flowing current slows the spacecraft down and takes energy out of its orbit. Eventually, the object would re-enter Earth's atmosphere, where, without heat shielding, it would burn up. Such a system could be used to prevent space junk from accumulating in orbit. When a satellite reached the end of its useful life span, it could deploy a tether that would slow it down until it disintegrated in the atmosphere, clearing the way for new satellites to be placed in that orbit.

If we want to boost satellites up to higher orbits, we have to force the current to flow through the tether in the direction opposite the way it wants to go. To do this, we need energy, which can be collected from the Sun using solar panels. When a tether forces current in the direction opposite from the direction it wants to go, it's like pumping water up a pipe. The force on the tether from "pumping" current adds energy to the orbit of the tether and boosts it into a higher orbit. In fact, some NASA researchers believe that by using a tether like this, the orbit of the International Space Station could be continuously reboosted, countering the effect of atmospheric drag without requiring any additional propellant.

Artist's conception of a tether used in jovian exploration.

The same electrodynamic tether technology would be used to reboost the momentum-exchange tether after each use. It would use energy collected from solar panels to drive electrical current through the tether in the right direction to add energy to its orbit and reboost it for another use. In fact, the type of tether they are developing is called a Momentum-Exchange/Electrodynamic Reboost tether.

Experiments conducted in space involving EDT tether concepts have met with limited success when the materials used proved incapable of handling the strains of the current and space exposure. However, those experiments did prove that it is possible to generate a current using a space tether. The next test of the tether concepts for NASA will be the Propulsive Small Expendable Deployer System (ProSEDS) experiment, planned for launch in 2004. The ProSEDS experiment will be launched from an expendable rocket, and will deploy a 15-kilometer (9.3-mile) tether about the width of dental floss. The experiment is designed to use EDT technology to drag the Delta rocket stage from which it deployed back into Earth's atmosphere, where it would burn up.

If successful, ProSEDS will demonstrate that it is possible to use tether technology to help eliminate space junk, and will open the door for more advanced space tether applications. That's not bad for a long piece of high-tech string!

Courtesy of NASA's Aerospace Technology Enterprise/NASAexplores

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NASA - National Aeronautics and Space Administration

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A tether deployed from a rocket stage. Today's scientists are already hard at work on new ideas for spaceflight in the future. New technology is being developed to help propel spacecraft into Earth orbit -- and beyond. NASA researchers are studying ways to create more powerful and more efficient rockets.

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https://science.nasa.gov/missions/tss

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Orbit: Low-Earth Orbit
TSS-1:
TSS consisted of a satellite, tether, and a tether deployment/retrieval system which remained on the Space Shuttle. The space tether experiment was a joint project between NASA and the Italian Space Agency, designed to study the electrodynamics of a tether system in the ionosphere, the region of the upper atmosphere populated by charged particles - electrons and ions. TSS-1 was also meant to test and develop the capability for future tether applications on the Shuttle and Space Station.

The TSS satellite - a gumball-like spacecraft with a 1.6-meter diameter - was deployed from the US Space Shuttle and remained connected by a conducting tether. The shuttle dragged the tether across the Earth's magnetic field, thus producing one part of a dynamo circuit. The experiment intended to determine whether this system could produce electric power, generating current to run equipment aboard the space shuttle.

Because of a technical problem (a protruding bolt in the deploying mechanism), TSS-1 could not fully deploy to its 12.5-mile extent; instead it was only released to 840 feet.
TSS-1R:
TSS-1R was a reflight of the TSS-1 satellite that had been flown on the Space Shuttle

mission STS-46 in July 1992. Like TSS-1, the TSS-1R mission aimed to test the TSS system, and

examine the electromagnetic interaction between the TSS and the ambient space plasma.

Five hours after deployment began on February 25, 1996, with 12.24 miles (of 12.5 miles planned) tether released, the tether cable suddenly snapped near the top of the deployment boom. The malfunction was later attributed to an electrical discharge through fractured insulation. Unrestrained, the TSS satellite shot away into higher orbit. TSS instruments were reactivated and produced data for three days until batter power ran out.

Despite the malfunctions, the TSS missions were able to supply useful data. Currents measured during deployment were at least three times greater than predicted by analytical models, and the amount of power generated was directly proportional to the current. Scientists were also able to examine ionized shock wave and plasma waves around the satellite, and how gas from the satellites' thrusters interacts with the ionosphere.

Top of Page | Back to Missions

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Orbit: Low-Earth Orbit TSS-1: TSS consisted of a satellite, tether, and a tether deployment/retrieval system which remained on the Space Shuttle. The space tether experiment was a joint project between NASA and the Italian Space Agency, designed to study the electrodynamics of a tether system in the ionosphere, the region of the upper atmosphere populated by charged particles - electrons and ions.

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Sunlight pushes gently on spacecraft with large, lightweight, mirrored solar sails. They enable travel throughout the solar system and beyond without rocket propellant. SolarSailWiki covers everything from the science of light pressure, what they can do for us, to technologies and missions of the future.

Please help SolarSailWiki become a comprehensive source of solar sail information. Ask for an account by sending an email to admin at solarsails dot info.

Solar Sailing

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NASA to Launch World's Largest Solar Sail in 2014

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Sunlight pushes gently on spacecraft with large, lightweight, mirrored solar sails. They enable travel throughout the solar system and beyond without rocket propellant. SolarSailWiki covers everything from the science of light pressure, what they can do for us, to technologies and missions of the future.

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Hundreds of years ago, early discoverers used the Sun as a compass. Turns out the light of the Sun can do more than just guide us; it can actually propel us farther and faster into the vast realm of space than we've ever been able to go. With new solar sail technology, scientists are finding a way to convert light energy from the Sun into a lightweight, propellant-free source of propulsion for spacecraft.

Artist's concept of Columbus' Santa Maria and a solar sail (Click on image for larger version)

"The idea of solar sails has been around for about 100 years, but our structural technology has just now gotten to the point where we are ready to perform some missions using this type of propulsion," said Hoppy Price, solar sail technology lead engineer at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "Solar sails are now being considered for interstellar travel because they don't have to carry any fuel to operate and can be propelled by sunlight and high-powered lasers."

Solar sails are energy efficient, inexpensive to make and can greatly reduce a spacecraft's weight. Typically, spacecraft use rockets that apply short powerful thrusts to the spacecraft, which then coasts to its destination. Solar sails replace these heavier rockets, yet still increase spacecraft speed.

Artist's concept of solar sail (Click on image for larger version)

Solar sails are composed of large, flat, smooth sheets of ultra-thin film supported by lightweight structures. A highly reflective material covers the side that faces the Sun. The result is a huge mirror, at least the size of a football field. These mirrors reflect continuous sunlight and transfer the momentum from photons to an object in order to propel it.

The inspiration for this technology came from 17th-century astronomer Johannes Kepler, who deduced that winds blew objects about in space after he observed comet tails blown by what appeared to be a solar breeze. Kepler suggested that eventually ships might navigate through space using sails that could catch this wind. He was wrong about the winds, as they do not exist in the vacuum that is space. But his eyes did not fool him; he saw the gentle pressure of solar light particles (photons) on dust particles released by the comet as it was in orbit. On Earth, frictional forces in the atmosphere are too large, making it hard to observe this pressure. It can, however, be observed and used to advantage in space.

To harness this natural force, physicists looked to Newton's law, which states that any object under the influence of unbalanced forces will undergo a net acceleration of its motion. They also realized that the power exerted by the Sun, albeit a very tiny force, is persistent. Over weeks and months, the gentle acceleration provided by the Sun could eventually make a spacecraft reach speeds fast enough to cover the distance between Los Angeles and New York in less than one minute, five times faster than the Voyager and Pioneer spacecraft now zooming through the outer solar system.

Artist's concept of solar sail near Earth (Click on image for larger version)

Researchers figured they had to design a craft that combined the forces acting upon it in a way that produces a net acceleration in the desired direction of travel. They came up with solar sails, not to be confused with "solar cells," the technology that uses solar panels to convert sunlight into electricity.

"NASA has a technology program now underway to develop flight-ready solar sails," Price said. "We expect to test them on the ground in 2005 and fly science missions with them a few years later."

If successful, future flight missions may use solar sails to achieve a number of objectives related to this type of propulsion, including increased opportunities to change or correct the path of any given mission. Small kite-sized sails several meters in diameter might adjust the orbit and stability of spacecraft, while super-sized sails (1,000,000 square meters or 250 acres), with possible assistance of laser or microwave transmitters, might help achieve interstellar travel.

Artist's concept of interstellar solar sail

Solar sails have been proposed for use on an interstellar probe that might launch as early as 2015. In that case, a sail nearly half-a-kilometer (1640 feet) wide would allow the probe to travel fast enough to surpass the distance covered by Voyager 1, currently the most distant spacecraft from Earth, by 2023. In only eight years, the probe would cover the same distance Voyager 1 traveled in more than four decades.

More information:
Solar sails home page
Related animations

Charli Schuler
NASA Jet Propulsion Laboratory

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NASA - National Aeronautics and Space Administration

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Hundreds of years ago, early discoverers used the Sun as a compass. Turns out the light of the Sun can do more than just guide us; it can actually propel us farther and faster into the vast realm of space than we've ever been able to go.

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The motion of the long conducting wire of a tethered satellite across the geomagnetic field creates an emf of about 0.1-0.2 V/m along the length of th...

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Last month, a private satellite tracking company spotted a Chinese spacecraft apparently grabbing and throwing a dead satellite away into a "graveyard" orbit.

Something out of a Star Wars movie occurred in Earth's orbit last month.

A Chinese satellite was spotted in late January grabbing another long-dead satellite and days later throwing it into a "graveyard" orbit 300 km away, where objects are less likely to hit spacecraft.

These rare events were presented by Dr. Brien Flewelling in a webinar hosted by the Center of Strategic and International Studies and Secure World Foundation last month. Flewelling is the chief space situational awareness architect of ExoAnalytic Solutions, a private U.S. company that tracks the position of satellites using a large global network of optic telescopes.

The Chinese SJ-21 satellite was seen on January 22 changing its usual place in the sky to approach decommissioned satellite Compass-G2. A few days later, SJ-21 attached to G2, altering its orbit.

Chinese officials haven't yet confirmed that the apparent space tug occurred.

Over the course of the next few days, the spacecraft couple started dancing westward, ExoAnalytic's video footage showed. By January 26, the two satellites separated, and G2 was kicked into oblivion.

The Compass-G2, or BeiDou-2 G2, is a spacecraft from China's BeiDou-2 Navigation Satellite System that failed shortly after launching in 2009. For more than 10 years, the metal carcass has been wandering around Earth alongside millions of other pieces of space trash.

SJ-21, which launched in October 2021, has now returned to a geostationary orbit (GEO) just above the Congo Basin. GEO happens when a satellite orbits Earth over the equator at the same speed the planet rotates.

From the Earth's point of view, satellites in GEO seem to be standing still, barring a wobble or two. This type of orbit is sometimes called a Clarke orbit, named after British sci-fi writer Arthur C. Clarke. He popularized the idea of GEO in a 1945 paper promising to revolutionize telecommunications.

Less than two decades later, the first geostationary satellite was launched.

China's space tug: A service or a threat?

There's nothing wrong with throwing out the trash - many other countries have launched or are currently developing technologies to clear space junk.

Japan launched its ELSA-d mission in March 2021, designed to test space debris capturing and removal technologies. The European Space Agency plans to launch its own trash removal mission in 2025.

However, despite the seeming ubiquity of efforts to develop and implement space junk disposal technology, some U.S. officials have expressed worry over Chinese trash disposal satellites like the SJ-21.

James Dickinson, commander of the US Space Command said in April 2021 that technology like China's SJ-21 "could be used in a future system for grappling other satellites."

But is there a real threat?

In its 2021 counterspace report, the Secure World Foundation said that there is strong evidence that both China and Russia are working to develop technology with "counterspace capabilities" - the ability to destruct space systems.

However, the report said, Chinese official statements have remained "consistently aligned to the peaceful purposes of outer space" and there is no proof that they have facilitated any destructive or counterspace operations.

A 2021 report by the Chinese Aerospace Studies Institute (CASI), a United States Air Force think tank maintained that SJ-21's use will likely be restricted to testing methods of space garbage disposal.

Space maintenance

The CASI report concluded that SJ-21 is most likely one of China's On-Orbit Servicing, Assembly, and Manufacturing (OSAM) satellites.

Many space agencies have been developing OSAM missions for decades. These could be, for example, spacecraft designed for refueling or repairing existing satellites - or disposing of space waste.

Since the beginning of space activities in the '60s, more than 6,000 launches have delivered over 50,000 objects in orbit, according to the US Space Surveillance Network. More than 30,000 artificial objects are orbiting our planet, of which only about 5,000 are functioning, according to the ESA's Space Debris Office.

And that's just counting the objects large enough to be tracked. The US, Russia, China and India have all blown satellites in space generating huge amounts of new smaller debris.

ESA numbers show that more than 300 million smaller objects are flying through space at incredible speeds of up to 30,000 km/h, almost 5 times the speed of the fastest bullet.

The ESA started testing OSAM projects in 1990 with the GSV (the Geostationary Servicing Vehicle) program, which was intended to grab and repair broken satellites in GEO.

The famous and successful optics repair of the Hubble Space Telescope in December 1993 is another example of an OSAM mission at work.

NASA has plans for several more OSAM missions, including OSAM-1 and OSAM-2. The latter is designed to 3D print components in space, with the hope of one day being able to build, directly in space, parts too big to fit inside any rocket.

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Chinese 'space cleaner' throws old satellite away - DW - 02/09/2022

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Last month, a private satellite tracking company spotted a Chinese spacecraft apparently grabbing and throwing a dead satellite away into a "graveyard" orbit. Something out of a Star Wars movie occurred in Earth's orbit last month.

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Paris (AFP) August 16, 2000 - NASA is to test a laser "broom" capable of removing debris in the path of the International Space Station (ISS), on a space shuttle mission in 2003, the British magazine New Scientist reports in its Saturday issue.
The broom, dubbed Project Orion, is designed to stop objects between one and 10 centimeters (0.4 to 4 inches) in diameter, which could puncture holes in the hull of the ISS.

If a clean up system is not put in place soon, NASA scientists say there is a one in 10 chance an object will damage the ISS during the next 10 years.

The increased amount of space junk has become a problem for the ISS and for other space missions. The station is equipped to deal with items smaller than one centimeter, while controllers on the ground can spot anything larger than ten centimeters and give the crew advance warning.

But intermediate objects could cause significant damage.

"The result could be much worse, like the difference between a single bullet and a shotgun blast," Jonathan Campbell, a scientist at the Marshall Space Flight Center in the US city of Huntsville, told New Scientist.

He said a clean-up operation would cost 200 million dollars (220 million euros) and take two years.

Campbell said a laser pulse could lock onto a piece of debris, slow it down and then sweep it out of the path of the ISS. Researchers are now experimenting with tracking objects from the ground.

One terrestial obstacle to the project is international treaties barring laser weapons in space.

John Pike at the Federation of American Scientists in Washington told the magazine that although NASA's plans were above reproach "other countries have plenty of reasons to be suspicious."

Copyright 2000 AFP. All rights reserved. The material on this page is provided by AFP and may not be published, broadcast, rewritten or redistributed.

Orbital Debris Research at NASA-Johnson Space Center

Space Debris Research Program at U.S. Air Force Research Lab

Hypervelocity Impact Technology Facility

Space Debris Activities at ESA/ESOC
Vienna, VA - September 27, 1999 - SM&A Corporation has released its Space Environmental Analysis Tool (SEAT), a software tool used by spacecraft designers, analysts, and operators to evaluate the effects of the space environment on their spacecraft, and was developed as an add-on module for Analytical Graphics's Satellite Tool Kit (STK).
Space Debris, ESA, Mission Analysis Section at ESOC

DebrisWeb

Space Debris Research at DERA, U.K.

NASA LDEF Archive System

Center for Orbital and Reentry Debris Studies
TECH SPACE
Your SEAT To The Space Environment

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NASA Hopes Laser Broom Will Help Clean Up Space Debris

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Paris (AFP) August 16, 2000 - NASA is to test a laser "broom" capable of removing debris in the path of the International Space Station (ISS), on a space shuttle mission in 2003, the British magazine New Scientist reports in its Saturday issue.The broom, dubbed Project Orion, is designed to stop objects between one and 10 centimeters (0.4 to 4 inches) in diameter, which could puncture holes in the hull of the ISS.

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team have managed to demonstrate how clearing up the thousands of tonnes of space junk currently swirling around our planet might actually be possible. While the latest demonstration worked, the project is still in its test phase. The box was actually ejected from the satellite itself, to simulate a piece of space debris tumbling around the planet. 

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team have managed to demonstrate how clearing up the thousands of tonnes of space junk currently swirling around our planet might actually be possible. While the latest demonstration worked, the project is still in its test phase. The box was actually ejected from the satellite itself, to simulate a piece of space debris tumbling around the planet. 

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The momentum of light could be enough to avert collisions in space.

Scientists in the United States have devised a new way to avoid collisions among space debris, and possibly even reduce the amount of debris in orbit. The method uses a medium-powered, ground-based laser to nudge the debris off course - but some are concerned that the laser could be used as a weapon.

Debris orbiting Earth is a mounting problem. Two years ago, a satellite owned by the communications provider Iridium, based in McLean, Virginia, smashed into a defunct Russian satellite at ten times the speed of a rifle bullet, putting an end to the 'big sky' theory that assumed space was too vast for chance collisions. That incident alone created more than 1,700 pieces of debris, raising the total amount by nearly 20%.

Space analysts are particularly concerned about the possible onset of Kessler syndrome, when enough debris is present to make collisions so likely there would be an avalanche effect that would leave the Earth's orbit uninhabitable for satellites.

Scientists at NASA have considered using a ground-based laser to mitigate debris collisions before. However, in their 'laser broom' concept, a powerful, megawatt-class laser would vaporize the surface of a piece of debris that is heading for another, causing the debris to recoil out of harm's way. But critics argued that the laser could be used as a weapon, as it could easily damage an enemy's active satellites. Indeed, both the United States and China have in the past 15 years been accused of testing the ability of ground-based lasers to 'dazzle' satellites and render them inoperable.

Now, James Mason, a NASA contractor at the Universities Space Research Association in Moffett Field, California, and his colleagues have come up with a variation on the laser broom concept that they claim is unlikely to be useful as a weapon. In a paper uploaded to the arXiv preprint server, Mason and colleagues suggest using a medium-powered laser of 5-10 kilowatts to illuminate debris with light a few times more intense than sunlight, imparting just enough momentum to nudge the debris off course. "We think this scheme is potentially one of the least-threatening ways to solve a problem that has to be addressed," says Mason.

In the researchers' proposal, a piece of debris that has a high risk of collision would be tracked by another laser and a telescope. As the debris comes over the horizon, technicians would switch on the main laser and illuminate the debris until it reaches its highest point. If the debris isn't nudged far enough to avoid a collision the first time, the technicians would repeat the procedure for several days until the collision risk becomes negligible.

With just one laser facility, Mason's group says, the number of debris collisions could be almost halved. What's more, by mitigating the number of collisions, the amount of debris would lessen as it slowly burns up in Earth's atmosphere. And that would avoid the onset of Kessler syndrome, the researchers say.

All the experts in space debris contacted by Nature said that the new proposal is feasible, but still has problems. "It'll be ineffective against dense objects that are too heavy to move," says William Priedhorsky of Los Alamos National Laboratory in New Mexico. "To use a medical analogy, they propose not to cure the disease, but to manage it."

And some are concerned that the laser could still be used to push enemy satellites out of orbit. Christophe Bonnal, a debris expert at the French space agency CNES, doesn't buy the researchers' claim that the laser's power would be too low for anti-satellite uses. "Let's be logical," he says. "If the power is low, you'll have no effect on the debris."

But Hugh Lewis, an engineer at the Southampton University, UK, "cautiously" welcomes the idea. "Any method that aims to address the growing debris problem should be taken seriously, I think," he says.

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Lasers could nudge space debris aside - Nature

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The momentum of light could be enough to avert collisions in space. Scientists in the United States have devised a new way to avoid collisions among space debris, and possibly even reduce the amount of debris in orbit.

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Decades of space exploration have left a shroud of space junk enveloping Earth. They're much more than a minor inconvenience-functional satellites, space shuttles that ferry astronauts back and forth and the International Space Station (ISS) all have to dodge and weave through the detritus. Earlier this year, a gaping hole was discovered in a 58-feet-long arm of the ISS, thought to be caused by an object too tiny to track. The incident came just eight months after the ISS sidestepped another, larger piece of debris. Earth's debris field now includes 27,000 cataloged objects-from paint chips to spent rocket stages-all which threaten to damage spacefaring investments that cost millions of dollars.

"It's probably the one of the most important environmental problems of our time," says Hugh Lewis, an astronautical engineer at the University of Southampton in the United Kingdom. Like climate change, he says that the issue of space debris stems from humans polluting and abusing a common resource, in this case, the environment of space. "It's a technological problem we've created, ... driven by our own choices."

To combat this issue, Astroscale Inc., a private Japan-headquartered company, has devised several commercial spacecrafts tasked with decluttering space. The company is on track to deliver the world's first garbage truck for removing defunct satellites in 2024, and today announced its prototype completed its first demonstration in space. Although experts say that one active debris remover isn't enough to solve the problem, it is an important move toward protecting valuable equipment in space, including satellites that aid with everything from weather forecasts to GPS navigation.

"Those services are under threat," says Lewis. "That threat is the destruction of the satellites, or the disruption to the services because we have to maneuver the satellites to avoid the space debris."

Astroscale's efforts are one of the first, tiny steps towards cleaning up debris. Its flagship mission is ELSA, short for "end-of-life services by Astroscale." ELSA will drag satellites that are no longer operating down from high altitudes to the planet's natural incinerator: the oxygen-rich atmosphere at lower Earth orbits. Both the space-cleaner and satellite will burn up here before they hit the surface of the Earth. In March this year, Astroscale launched its prototype ELSA-d (d stands for demonstration) to test its proximity capture technology. It contains two satellites: a chaser and a target that will proxy as a hunk of wreckage. Each satellite is equipped with a magnetic docking plate so that the chaser can latch onto its target.

The satellite pair successfully performed the first of four catch-and-release demos for debris disposal today. In this first test, the chaser validated its magnetic capture system by separating with the target then snagging it at close range. All the while, on-the-ground mission control recalibrated ELSA-d's sensors and verified its operational procedures. In the coming months, ELSA-d will undergo challenges of increasing complexity, from the chaser snagging prey that's drifting away to pursuing a freely tumbling target and plucking it from its flightpath. ELSA-d's fourth and final test will represent a full-service mission, in which the chaser inspects the target at close range and allows its human operators to make a go-no-go decision on the cleanup. In a fiery finale, both target and catcher will head down to lower Earth orbit to burn up in the atmosphere.

"Once those technologies are demonstrated and the global community sees that [ELSA] is a really big step towards active debris removal and end-of-life services, they're going to embrace this as more of a reality," says Mike Lindsay, Astroscale's chief technology officer. "Hopefully they'll incorporate that possibility into their own plans" as they prepare the next generation of satellites, he adds.

Just like any other mission, Astroscale's endeavor carries a potential risk of failure, but "all things being equal, I have no reason to believe that their demonstration won't be successful," says Moriba Jah, an astrodynamicist and space environmentalist at the University of Texas, Austin who wasn't involved in the ELSA project. Although a single vehicle can't make an immediate difference in a decades-long problem, he opines that ELSA-d is a small but important first step. "We need to start doing something," he says. "It's going to take many helpful things to actually start making a difference."

While Astroscale is optimistic that a string of successful demonstrations will attract new clients, its cleanup program still hinges on space entities opting to pay for its services. No international entity or law mandates space users clean up after themselves when their satellites litter, and so space has become a junkyard for failed experiments. Earth's inky backyard is a classic example of the tragedy of the commons, whereby a joint ownership of a good between multiple countries incentivizes everyone to exploit it and no one to take care of it. While the Inter-Agency Space Debris Coordination Committee has prepared a set of international guidelines for managing space debris and minimizing pollution in future missions, no enforcement mechanism is in place to ensure members adhere to it.

Moreover, ELSA is only built to clean up objects weighing less than one metric ton, or roughly 2,200 pounds, that have magnets placed on them. But the most damaging objects in space are the large rocket boosters jettisoned in the late 1900s to early 2000s. These objects are wildcards; their speeds, trajectories and positions are challenging to parse, complicating any practical plan for their disposal. They're also supersized, weighing nearly ten metric tons each. Not only are they too big to currently be collected, they also may not entirely burn up in the atmosphere if they hurl towards Earth.

Still, Astroscale's space sweeper services are crucial for chipping away at a gargantuan problem as it focuses on the smaller, newer satellites that will be launched as mega constellations. Companies like SpaceX and Amazon plan to deploy satellites by the thousands over the next few years, and ELSA could collect these satellites when they inevitably glitch. If ELSA's demonstrations are successful, Astroscale hopes that private companies will take the initiative to install magnetic plates on their satellites and contract its services to dispose of their derelict satellites. One company is already on board: the U.K.-based company OneWeb. The organization has fitted its latest satellites with ELSA-compatible docking plates. Moreover, OneWeb awarded Astroscale $3.3-million in funding earlier this year to prepare the debris-removal technology for the real-deal: ELSA-m. The commercial version of the space garbage collector, ELSA-m will retrieve multiple retired satellites in a single mission, a move that will significantly reduce costs.

Lindsay predicts that the market for active space debris removal will be strong. "People are going to be much more ready to pay for this service and remove objects that they see as threats... because they need to protect their investments, their assets in space."

"Developing the technology is critical," says Jah, but he's also skeptical, because the global community has yet to put a number on the value of removing any one object in space. As such, Astroscale can't advertise how much exactly clients are getting out of its end-of-life services, and customers have no basis to evaluate how much the services are worth to them. While morally laudable, "cleaning up debris for the sake of cleaning it, there's no solid business case to that," says Jah. Technological development for active debris removal takes time, and so does the push to convince regulatory bodies to standardize the definitions of each debris object's hazard-a number Jah calls the "space traffic footprint." He adds, "these things need to be pursued in parallel."

The cheapest and easiest solution to curb the debris dilemma is not to create debris in the first place, says Marlon Sorge, a principal engineer and aerodynamicist at Aerospace Corporation in El Segundo, California who wasn't involved in Astroscale's projects. Spacecraft-launching entities need to reduce the chances their missions fail, because these dead objects only end up as junk and add to the growing debris problem. Active debris removal such as the Astroscale's offerings should be a back-up to the mitigation plans that all space firms need to prioritize.

"If you don't do the mitigation, the rest of it won't make a difference," says Sorge.

The normal failure rate of satellites can soar as high as 40 percent, depending on the type. Even a failure rate as low as 2.5 percent, as SpaceX's satellite constellation Starlink boasts, will still translate to thousands of dead objects circling the sky in the years to come. So, that level of compliance still needs improvement, says Sorge. "But making your satellites so reliable that you never have to have any dead satellites is also not realistic," he adds, "which is where the active debris removal comes in."

While companies dream up solutions, the public can still help. Sorge says that individuals recognize the severity of space debris more readily now than three decades ago when he first started in the field. Lewis, Jah and Sorge all agree that public support can nudge the direction of public policy. A fussier public can make the case to the government to enforce good behavior among space users by mandating all space entities to clean space up after themselves after every mission. Experts say consumers should factor space sustainability into everyday purchasing decisions by questioning whether service providers with dealings in space take concrete action towards debris prevention and removal. These tiny steps could indirectly influence the leaders of the space industry to reduce space pollution.

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Can the World's First Space Sweeper Make a Dent in Orbiting Debris?

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Decades of space exploration have left a shroud of space junk enveloping Earth. They're much more than a minor inconvenience-functional satellites, space shuttles that ferry astronauts back and forth and the International Space Station (ISS) all have to dodge and weave through the detritus.

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Abstract

Summary An array of 55,000 40-foot antennas can generate from the rays of the Sun enough electrical power to replace 50 The economic potential is huge. There are new industries that will only grow and there are different ways to collect solar energy, including wind power. The energy sources we rely on for the most part are finite - fossil fuels, coal, oil and natural gas are all limited in supply. The cost will only continue to rise as demand increases. The time of global economic crossover between the EU, Asia Pacific and North America is coming within less than five years. The biggest opportunity for solar energy entrepreneurs would seem to be in municipal contracting where 1500 40-foot stacking antennas can be hooked into a grid to power an entire city. The antenna can generate 45 kilowatts of energy, enough to satisfy the electrical needs 7x24 of ten to twenty homes. It is possible to design and build 35-by-80-foot pedestals that track the sun from morning until night to provide full efficiency. A normal solar cell looks in the sky for only four or five hours of direct sunlight. Fabrication of these pedestals would sell for USD 50, 000-70,000 each. The solar heat collected by the antennas can be bounced into a Stirling engine, creating electricity at a focal point. Water can be heated by running through that focal point. In addition, salt water passing through the focal point can be desalinated, and since the antenna can generate up to 2,000 degrees of heat at the focal point. The salt water passing through the focal point turns to steam, which separates the salt and allows the steam to be turned into fresh drinking water. Collector energy can be retained in betavoltaics which uses semiconductors to capture energy from radioactive materials and turn it into usable electricity for automobiles. In a new battery, the silicon wafers in the battery are etched with a network of deep pores. These pores vastly increase the exposure surface area of the silicon, allowing it to absorb more energy and making the antenna collector 20 times more efficient than planar designs. A tracking pedestal powered by betavoltaics can follow the sun. With a 500-sun photovoltaic cell underneath a Fresnal lens magnifies and distributes the sun's energy at 500 times. Primary results and the main conclusions This idea is revolutionary and utilizes satellite tracking abilities to follow the sun, maintaining a constant energy source that can reach 700 to 800 degrees. This technology will have many applications, from instant fresh water in the form of steam to the use of fiber optics to filter natural light through a building. With the direction of the oil and energy costs continuing to spiral upward, there has been recent emphasis on alternative energy that is transmitted from space. Satellite antenna manufacturers can move quickly to production and create a revolution in sustainable energy that was never thought of before. The efforts of the United States, Russia, China, and India to colonize the Moon and Mars would be greatly enhanced by use of satellite solar collectors and betavoltaics electrical energy technologies for the colonies' habitats. Introduction This study was undertaken for the Global environment is in a crisis. The rich oil producing countries of Russia, Saudi Arabia, Venezuela, and Africa, have been at war to gain monopoly power and to restrict the space based explorations of the solar system. The physics of solar energy transmission to electrical mechanical energy is unique in improving the economies of the entire community of Nations. It is easy to produce satellite antennas, thus, satellite antennas can now be used as solar panels which can generate free power from the sun by converting sunlight to electricity. Solar Panels require no moving parts; have zero emissions, and no maintenance. These antennas will revolutionize the use of solar rays from the sun to benefit a global grid. These "collectors of free energy" are able to harness solar energy for thermal heating, desalination, lighting, and electricity. Further, * Clean energy means jobs. For example, the American Solar Energy Society released a report that the 8.5 million Americans working in the energy efficiency and renewable energy industries today can grow to 40 million jobs by 2020 (estimated at 200 million globally). * The EU, Asia Pacific, and North America need carbon-free, local, renewable energy now to fuel their economies. * The solution to global warming can be found in the transition to a sustainable energy economy. Methods and Materials This satellite collector study was undertaken using research methodology using primary and secondary research which began with the Science and Environmental Policy Project, Institute for Energy Research, Hoover Institution, Stanford University and the University of Michigan. The study on using betavoltiacs was conducted by a multi-disciplinary team included researchers from the University of Rochester, the University of Toronto, the Rochester Institute of Technology, and BetaBatt Inc of Houston, Texas and was supported by grants from the NSF Small Business Innovation Research (SBIR) program. Results Less than 2 Discussion Our planet is heading towards a catastrophe unless emissions of greenhouse gas in space and in the earth's atmosphere are substantially reduced. The results of this study are significant for it demonstrates that existing technologies found in the space technologies are being side-stepped in order to support the antiquated land-based energy systems that have focused on oil and gas, wind power, atomic, and water power. All along, the solar system has all the answers to lessen global warming and to create cheap energy that is free of the bureaucracies of global governments.

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Satellite Collectors of Solar Energy for Earth and Colonized Planet Habitats

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Summary An array of 55,000 40-foot antennas can generate from the rays of the Sun enough electrical power to replace 50 The economic potential is huge. There are new industries that will only grow and there are different ways to collect solar energy, including wind power.

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This satellite will clean up space junk with a net gun

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This was designed by European Space Agency. It's part of e.Deorbit, a program created to remove space debris. http://m.esa.int/ESA https://www.youtube.com/user/ESA https://www.facebook.com/EuropeanSpaceAgency https://twitter.com/esa

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https://www.aeroespacial.sener/en/products/et-pack-deorbit-electrodynamic-tether-technology

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SENER Aeroespacial and the Universidad Carlos III de Madrid (UC3M) colaborates in the development of E.T. PACK, an autonomous deorbit device or "kit" based on electrodynamic tether technology to eliminate space debris.

The small kit will be mounted on satellites in the future. Once activated from the ground, the kit will deploy an electrodynamic tether that will interact passively with the Earth's magnetosphere, producing a drag force that will cause the satellite to re-enter the Earth's atmosphere and burn up.

The electrodynamic tether, a very thin aluminum tape of about a couple of centimeters wide and a couple of kilometers long, uses the ionospheric plasma and the geomagnetic field to generate an electrical current that, thanks to an electrodynamic effect, gives rise to a force known as Lorentz drag. This force deorbits the satellite and produces the re-entry, thus contributing to the sustainable use of the outer space.

Laboratory to integrate the deorbit device

As part of the project, SENER Aerospace and UC3M have set up a laboratory, located in SENER's facilities in Tres Cantos (Madrid, Spain), which will be used to integrate the avionics system into the deorbit device that is currently under development.

The first complete prototype of the equipment will be ready by late 2022 and it is expeted to mature it in a later project that will end with an in-orbit demonstration by late 2024. The goal is to have the system operational in 2025..

E.T.PACK is a FET-OPEN project funded with €3million by the European Commission. E.T.PACK consortium includes UC3M (Coordinator), SENER Aeroespacial, the universities of Padua (Italy) and Dresden (Germany), the Fraunhofer Institute (Germany) and the Spanish company Advanced Thermal Devices. E.T.PACK has also received support from the Government of the Community of Madrid through one of its Industrial Doctorates.

E.T.PACK, a sustainable solution to put an end to space debris

At present, no country requires companies to the deorbit their satellite at the end of life. The system proposed by E.T.PACK aims to reverse this trend by providing a light, low-cost and highly effective system. The deorbiting kit will be able to communicate with the ground, stabilize a satellite of mass up to 1,000 kg and control the deorbiting maneuver to prevent collisions with other objects.

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E.T.PACK: an autonomous deorbit device based on electrodynamic tether technology

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SENER Aeroespacial and the Universidad Carlos III de Madrid (UC3M) colaborates in the development of E.T. PACK, an autonomous deorbit device or "kit" based on electrodynamic tether technology to eliminate space debris. The small kit will be mounted on satellites in the future.

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How Solar Sails Are Remaking Space Exploration

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Power generation can be realized in space when current is induced on a bare electrodynamic tether system. The performance of power generation is discussed based on a debris mitigation mission by numerical simulation in the paper. A Li-ion battery subsystem is used to complete the energy conversion-harvest and supply the energy. The battery can provide 10-300 W average electric power continuously during several hundred hour mission time. The energy conversion efficiency ranges from 1% to a maximum value 30%. With constant power consumption on board, the battery operation generally experiences a discharging phase, a charging phase, and a stable phase. The first two phases determine the mission risk coefficient. The heating problem in the stable phase cannot be ignored. The optimization of battery design and tether design should be considered for each debris mitigation mission. An extra control circuit or small battery voltage with large capacity for battery design is suggested to eliminate the stable phase. Wide or long tether designs are more appropriate for mission with high or low power demands on board, respectively. The power generation is affected by the system mass and the mission orbit parameters.

1. Introduction

The bare electrodynamic tether is a promising device with which to expand the range of a space mission [ 1]. It utilizes a bare conductive tether and an electron emission device to complete the charge exchange with the space plasma. The concept of "bare" was first introduced by Sanmartin et al. [ 2] to avoid the problem of electron collection limitations. The bare conductive tether is used as the anode to absorb electrons and is much more efficient and easier to implement than previous strategies such as anodic plasma contactors or spherical collectors. As the bare electrodynamic tether enables a large current, it can complete many space missions better in LEO (Low Earth Orbit) with high specific impulse and non-or-less propellant consumption when compared to traditional systems [ 3, 4].

When external energy is applied to the tether to change the direction of induced current, the tether works in thruster mode: the Lorentz force component has the same direction as the tether velocity which can be used for orbit raising and drag compensation [ 5], but more attention has been paid to the passive mode (or generator mode). The bare electrodynamic tether can produce the induced current and significant drag, leading to two impressive functions: power can be generated on board by a load and the system can transfer to a lower orbit. There has been great interest in the latter since the tether was introduced. Due to the characteristics of simplicity, light weight, and no external energy requirement, it is considered to be a potential active debris removal system for unusable satellites and upper stages in LEO [ 6, 7]. Much work has been done to better understand the system design [ 8, 9], electron collection [ 10], stability problems [ 11- 13], system survivability [ 14, 15], and mission performance [ 16, 17].

Although Sanmartin et al. [ 2] proposed that a bare electrodynamic tether can generate power as far back as 1993, related research mainly appeared after 2000. With the increasing demand for electric power on board, power generation by bare electrodynamic tether was gradually taken seriously as the energy can be harvested at any time. Much of the research [ 2, 18- 20] focused on the theoretical analysis of power generation performance to estimate the power and efficiency and to suggest the optimization method thereof. The performance of the power generation system will be influenced by the equivalent resistance of each part and the plasma parameters; however, the plasma parameters change during tether operation, so the theoretical formula is usually applicable for point analysis. Numerical simulation with a specific environmental model should be employed to show the long-term performance in terms of power generation. The power and efficiency vary because of the changeable plasma parameters; nevertheless, simulations show that the bare electrodynamic tether was typically efficient for space mission around Jupiter [ 21] and was a viable device with regard to meeting different power requirements on board [ 22]. The ProSEDS (Propulsive Small Expendable Deployed System) mission [ 23] proved that there is no principle problem of power generation from the tether in engineering applications, although the project was later cancelled.

For most published research on energy analysis, there remain some debatable problems: first, the energy storage subsystem model was not accurate, and generally, it was simplified to a constant resistance. This made it convenient to analyse when all parts can be transformed to a uniform parameter, but it is impractical. A normal energy storage subsystem may be thought of in terms of its voltage-current characteristic and maximum capacity. A supercapacitor [ 24] is more common by contrast. Second, power generation suffers from orbit height reduction which is intolerable for most commercial uses when the tether system is designed merely as a generator. Relevant measures have been proposed by Sanmartin et al. [ 20] and Hoyt [ 25] which, however, directly increase system complexity and control difficulty. It is more reasonable to adopt the approach of Sanjurjo-Rivo and Peláez [ 26] and McTernan et al. [ 27] who combine the debris mitigation mission and the power generation function. Third, all of the energy analysis was based on maximization of the total cumulative amount; in fact, the energy is harvested and consumed constantly, which means that the energy may not be fully utilized. The dynamic operation of the energy storage subsystem is of practical significance. Fourth, the influence of tether design and orbit parameters on power generation remains unclear. The equivalent resistance of the energy storage subsystem is usually changed. Theoretical formulae can indeed give estimates under different conditions, but long-term results are unavailable. To make the power generation more practical, these problems cannot be ignored, and they are all considered in the present research.

In this study, the power generation analysis of bare electrodynamic tether is based on a debris mitigation mission. Due to the long mission time (usually weeks or months), a large amount of energy is required to maintain the operation of the electrical appliances on board. Compared with common power sources, this energy source is simple, economical, and sustained. In the numerical simulation, a Li-ion battery system is used as the energy storage subsystem to harvest energy from the tether and provide power for the system at the same time. The battery subsystem is directly connected to the tether. The dynamic behaviour is calculated to assess the working performance in certain situations. Figures and data will show the ability of this power generation system. Furthermore, optimization of the battery design and tether design is discussed. The performance of the system under different mission requirements (mainly system mass and orbit parameters) is also studied.

2. System Model and Numerical Simulation Settings

2.1. Physical Process of Power Generation by the Tether System

When the system begins to perform the orbit transfer mission and generate electrical power, the bare tether (of km in length) is spread out at a low initial velocity from the mother spacecraft (Figure 1). Exploiting the braking system and the gravity gradient, the long, thin, tether finally reaches a steady state in which it is fully straightened, and the vector coincides with the local vertical location. The long conductive tether keeps cutting the geomagnetic induction line at a high speed (typically 8 km/s), creating a considerable induced electromotive force which can be as high as 0.15 V/m. To produce the induced current, a bare tether and a plasma contactor, both of which will be explained later, are applied. Due to the potential difference resulting from the induced electromotive force, the bare tether can collect electrons at a positive potential to the local space plasma potential while the plasma contactor will emit electrons absorbed at a negative potential in a self-consistent manner. Then, power generation is achieved when the induced current flows through the energy storage system. Meanwhile, the Lorenz force whose direction is opposite to the system velocity is created by the current and geomagnetic field, completing the orbit transfer mission.

2.2. Simulation Process and System Components Embodied

The simulation process (Figure 2) consists of five parts: initialization, system state determination, tether current distribution and movement calculation, energy storage system operation, and a result. After initialization, the simulation begins to cycle in timed steps. According to the present information pertaining to the tether system, the current and the force on tether can be calculated so that the performance of the power generation can be analysed. Meanwhile, the system updates its location which makes the current in, and force on, the tether changes. The simulation cycle continues until the termination condition is met.

The system is simplified to a combination of a mother spacecraft, a cathodic contactor, a battery system, a bare tether, and an end mass, in turn. The mother spacecraft is a point mass at one end of the tether. The battery system and cathodic contactor are treated as a single massless device but with unique characteristics. The bare tether is regarded as a line with a certain mass distribution and definite shape. The end mass is also a point mass at the other end of the tether. All parts are well connected, both physically and electrically.

2.3. System State Determination

The system state is determined by time, position, and environment. Coordinated Universal Time (UTC) is the time system used to describe orbit propagation. Classical orbital elements in the Earth Centred Inertial (ECI) (Figure 3) coordinate system [ 28] are employed to furnish detailed information pertaining to the orbit parameters. Six elements can be converted from, and to, the system centre of mass velocity v and position r, including semimajor axis eccentricity inclination longitude of the ascending node argument of periapsis and true anomaly The six elements can only be used to describe the movement of the system centre of mass: the velocity and position of other parts in the tether are all inferred therefrom.

The space environment around Earth is complex and changeable. Most parameters vary with time and position. The plasma parameters are obtained from the International Reference Ionosphere (IRI) model [ 29]. For a given location, time, and date, IRI provides monthly averages of the plasma parameters in the ionospheric altitude range. For example, the plasma density can be as high as in sunshine while as low as in an eclipse at 500 km height. The geomagnetic field information is provided by the World Magnetic Model (WMM) [ 30]. From the model, three direction component intensity of the geomagnetic field can be obtained. The total intensity ranges from  nT to  nT. The NRLMSISE-00 model [ 31] gives the atmosphere total mass density from which the atmospheric drag may be calculated. The air mass density is of the order of 10-14 or 10-13 kg∙m-3 in the given conditions. All the results showed above are at a height of 500 km and at UTC 2010.01.01.12.00.00.

2.4. Tether Current Distribution and Movement Calculation

The current distribution on tether is self-regulated according to the ability of electron collection and emission of the system. Electron collection is realized by the bare tether, and the electron emission is completed by the plasma contactor. Figure 4 shows the general voltage and current distribution along a bare tether [ 32]. The tether is so long that it will experience variable conditions in different positions. It can be divided into many short segments (each of length d each of which has its own potential, current, velocity, and local plasma and geomagnetic field parameters.

For a tether with length d, the collected current d can be described as Equation ( 1) [ 2] on the hypothesis of the orbital motion limited theory:

The tether potential is caused by the current flowing through the tether resistance while the plasma potential can be regarded as a function of induced electromotive force and is related to the position distribution of the tether [ 2]: where is the value of vector at the local tether part. For a certain system position, the distribution of is a known quantity. The plasma potential at the end mass point is usually set to be zero so that the distribution is obtained:

The current at the end mass point and the other end point yield:

The plasma contactor is located at the other end point where the electrons are emitted as well as the energy storage system is located before the plasma contactor. The potential distribution at this point is then written as:

In the simulation, hollow cathode plasma contactor (HCPC) [ 33] is employed as the electron emission device. According to the available data from the experiment conducted in our laboratory, we obtain:

Equations ( 1)-( 7) delineate the current distribution as a nonlinear boundary value problem. The MATLAB™ in-built function "bvp4c" is used to solve the BVP problem by finite iteration. The Lorentz force can be calculated once the current distribution is clear:

The force caused by the ambient electric field is not considered as it is usually negligible [ 24].

The atmospheric drag is: where the direction of vector is the normal of tether windward side and the value is the equivalent area thereof. The drag coefficient is set to 1.

The whole system is regarded as a centre of mass when describing the movement which means that the libration on the long tether is ignored. The kinetic equation of the system is: where contains all the forces except gravity force. In the simulation, only the Lorentz force and atmospheric drag are included. Other perturbations are ignored as the mission time is relatively short.

2.5. Energy Storage System

In primary design, a Li-ion battery system is used. The power generation strategy relies on the positive electrode being directly connected to the plasma contactor while the negative one is connected to the bare tether. Figure 5 shows the inner circuit which consists of the battery module, stabilizing circuit, and protection circuit.

The energy storage system can generate and supply electrical power to the battery module and provide energy to maintain on-board electrical appliances. The battery module can also maintain a relatively stable voltage. The protection circuit is used to avoid overcharging of the battery module. For simplification, the voltage of the whole battery system is treated as a constant during operation. The efficiency of power generation for the battery module under different and changeable current draw is supposed to be 100%. The performance of the power generation can be represented by:

The dynamic operation of the battery system is also reviewed. The battery capacity is set to be 10 A∙h. The working performance under a constant electric consumption on board is described by SOC (State of Charge), showed in Equation ( 12) and DOD (Depth of Discharge), showed in Equation ( 13). where is the current flowing through the battery module. When current flows into the battery, it is a positive value; otherwise, it is negative. The battery system has four working modes: (1) if and tether current flows into the battery module and stabilizing circuit; (2) if and tether current flows into the protection circuit and stabilizing circuit; (3) if tether current flows into the stabilizing circuit only; and (4) if extra tether current will flow from the battery module into the stabilizing circuit to make up the power deficit.

2.6. Energy Distribution on the Tether System

The electric power generated arises from the orbital energy of the spacecraft. The orbital energy is the sum of the gravitational potential energy and the kinetic energy of the spacecraft:

This will be constant if there is only gravitational force acting thereon. When the tether system begins its orbit transfer and power generation, the Lorentz force and atmospheric drag lead to an energy change, and the change is equal to the work done thereby:

The orbital energy is then transferred to electrical energy and frictional heating energy, respectively (Figure 6) [ 24]. Electrical energy is reflected by the current induced on the tether. It is distributed to four parts: the tether anode, tether ohm resistance, battery system, and tether cathode. Energy dissipated on the tether anode is used to absorb the ions and electrons while the tether cathode is employed to emit electrons. Meanwhile, part of the electrical energy is lost to ohmic Joule heat . The energy stored by the battery system is an energy recovery strategy that can power the electrical appliance. Therefore, the performance of the power generation is mainly determined by the tether current and the equivalent volt-ampere characteristics of other parts. Lastly, a small part of the orbital energy is transferred to frictional heating energy caused by aerodynamic drag.

3. Results and Analysis

As shown in Figure 7, to verify the HCPC model with variable voltage (AC mode in Figure 7) and code, a comparison was made with a research by Sánchez-Arriaga et al. [ 34] on the influence of different constant bias voltages (0, 20, and 40 V in Figure 7). The deorbiting mission ranges from 800 to 500 km in altitude, and the dimensions of the tether are 3 km, 4 cm, and 50  μ m, respectively. The deorbiting durations under different inclinations are not significantly different from that of the constant voltages, and the growth pattern for the duration is also similar to that of the reference.

Table 1 shows the basic parameter settings. The resistivity and mass density are values representative of aluminium which is the preferred material used for such tethers at present. Other parameters may be changed based on this table in the following variable parameter research.

The accuracy of the result is affected by the time step length: a short time step can make the result closer to reality, but it requires more computing resources. In the simulation, an appropriate time step should be set as the maximum time step when using the Runge-Kutta-Fehlberg 4/5 method. Table 2 shows the total energy that can be harvested by the battery subsystem and the orbit transfer time for different time steps. Actually, the deviations are acceptable, given they are all less than 1%. For higher resolution in describing SOC, 90 s is chosen for all calculations.

3.1. Dynamic Characteristic of the Battery Subsystem

For the battery subsystem is directly connected to the tether, it should work all the time to ensure the current loop on the tether and operation of the system throughout the mission. Figure 8 demonstrates the dynamic behaviour of the battery subsystem under the conditions set by the basic input parameters. The power consumption of the electrical appliances on board is set to be 39.7 W which is the maximum value that the battery subsystem can afford. The initial electric quantity is 10 A∙h while the whole energy power consumed is about 350 A∙h. At the beginning of the mission, the plasma, in high orbit, cannot induce enough current in the tether, so the average power harvested by the battery subsystem (nearly 36 W) is lower than the total power required. Due to the lack of energy, the battery begins to provide energy to the system, especially at night (in the shadow of the Earth). Although sometimes the power harvested exceeds the power demanded, the battery system mainly works in discharge mode. The SOC decreases until it reaches the maximum DOD at normalized time 0.41. After that, the average power increases as the plasma density increases in low orbit. The battery system begins to work mainly in charging mode, and the SOC increases. In the last part of the mission, the power that can be harvested is much greater than the power consumption. The battery is full for most of the time, while the excess electrical energy has to be consumed in the protection circuit. In the mission, the tether is ohm-dominant so that the energy dissipated on the tether (78.18%) is much larger than that stored in the battery subsystem (2.61%). The energy conversion efficiency (the ratio of to ) is small, but the battery subsystem can provide the required power. For this application, the average harvested power, or maximum available power, is more important (these are 40.5 W and 39.7 W, respectively). The effect of the atmospheric drag accounts for 6.46% of the orbital energy change such that it reduces the mission time.

The dynamic variation curve of the SOC of the battery subsystem looks like a "valley." It reaches the maximum DOD only once and does not have typical charging-discharging cycles (it is charged and discharged to certain SOC values several times). As explained, the process can be divided into three periods of time: discharging phase I, charging phase II, and stable phase III. The initial stored electrical power in the battery is used to help pass through phase I which determines the success of the mission. If sufficient, the battery can enter its charging phase and then the stable phase which means that the mission can be completed. Generally, a well-designed battery subsystem will at least experience all of phase I and most of phase II which represents achievement of its maximum capability. The phrase "well-designed" suggests that the battery characteristics and should match debris mitigation requirements (tether parameters, orbit parameters, and power consumption ); otherwise, it will be problematic with regard to the battery subsystem.

3.2. Differences with the Strategy Employed in ProSEDS

Regardless of the power consumption on board, the same bare electrodynamic tether system can complete the debris mitigation mission under different conditions, as long as the mission time can be accepted by the user; however, the flexibility of the battery subsystem is much lower than that of the tether. Figure 9(a) shows the working performance of the battery subsystem at different power consumption levels. A smaller power consumption leads to a low DOD. The duration of the discharging and charging regions decreases as the power consumption decreases as the difference between demand power and harvested energy is reduced. The behaviour of the stable region is opposite to that in regions I and II. The low power consumption means a large stable region; however, the presence of this stable region implies that the energy harvested by the battery system is not all transferred to useful ends (battery module or electrical appliances): the longer the stable region, the worse the utilization rate. The ratios of useful energy (including consumed on board and stored in the battery) to total energy which has been harvested by the battery are 0.738, 0.860, 0.934, and 0.976 when the power consumption is 30 W, 35 W, 38 W, and 39.7 W, respectively. A large amount of energy should be dissipated in the protection circuit of the battery subsystem in the form of Joule heat, leading to a critical problem which has not been considered in previous energy analysis of tether systems. Figure 9(b) shows the cumulative time for a certain wasted power range in which the battery system will suffer. The value of waste power can be higher than 24 W, and the cumulative time is considerable. To radiate the heat generated at such a high power and for a long period, a special structural design or electronic components are required. If not, the performance and lifetime of the battery subsystem will be impaired.

The battery subsystem is directly connected to the tether so that it cannot be cut-off to stop the energy harvesting in the stable region. This is the most basic difference when compared with the strategy employed in ProSEDS [ 23]. In ProSEDS, high-voltage relays were placed between the tether and the battery system and tether and contactor (Figure 10(a)). If necessary, the battery subsystem can be disconnected from the tether main circuit, and the current in the tether can flow through another line, directly reducing the heating power. Figure 10(b) illustrates the dynamic behaviour at constant power consumption under the hypothesis that the mode transition points are and The tether fails to complete the mission when is 39.7 W (the maximum power drops to 38.3 W). When is large, the SOC change also looks like a "valley" at the beginning of the mission. In other situations, the battery works as normal. In these cases, the number of mode conversion is no more than 10 times. Mode conversion frequency mainly depends on the ratio of energy harvested to that consumed. The impressive advantage of this strategy is that the system can complete the mission with a wide range of power demand without heating problems. The concern is that the relays need extra energy and are potential failure points. By comparison, the advantage of our direct connection strategy is that a relatively stable voltage drop can be maintained along one end of the tether, avoiding potential dynamic oscillation due to change in current transient.

3.3. Battery Performance of Different Battery Parameters

As mentioned above, the design of the battery subsystem should match the mission parameters. The available power for electrical appliances is mainly determined by both and . determines the maximum energy that the battery system can harvest, while determines the proportion of the energy which can be actually used. is more important as it is directly proportional to the power so that past research only focuses on it or the equivalent resistance. Figures 11(a) and 11(b) show the battery performance for different (normalized to the value in Table 1). The energy conversion efficiency for the battery subsystem is nearly linearly proportional to the battery voltage; however, the high battery voltage makes the voltage of the tether anode small (Figure 4), leading to a small tether current which further results in long mission time (shown in Figure 11(c)). Due to the decreasing tether current, the average power increases gradually to a maximum (about 260 W here) with the energy conversion efficiency rising to nearly 30%. If the voltage increases further, the average power will instead decrease [ 24, 25], which was not calculated in our simulation. It is worth mentioning that there should be a limitation on the battery voltage selection. Once it exceeds the minimum of the induced electromotive force on tether, the whole system will repeatedly suffer no current situations. From Figure 11(d), the maximum proposed voltage is no more than 600 V (a normalized value of about 14).

By contrast, does not affect the amount of power generation: it determines the actual available power supply for the appliances, but its effect on available power is not as obvious as that of . Despite this, it is necessary for power supply optimization. Figure 12 shows the maximum available power and waste power in different battery parameters. For a given power requirement (from those electrical appliances on board), several combinations of battery parameters can realize the demand: a larger battery voltage means less system mass; however, the maximum waste power on board limits such design; large battery capacity can reduce the waste power but that makes the system heavy and also directly decreases the economy (the ratio of battery capacity to total power consumed by on-board electrical appliances). Therefore, the trade-off between battery system mass and maximum waste power should be considered. From Figure 12, small battery voltage with sufficient capacity is preferred. For the conditions given in Table 1, when is 40 W, a battery voltage at 1 with a battery capacity of 1.4 is a better choice. Meanwhile, a higher output makes the DOD lower which means a lower task risk. If the power requirement is too high (>60 W), optimization of the tether structure design is recommended.

3.4. Energy Harvesting Performance of Different Input Parameters

Table 3 lists battery performances under different tether parameters. The tether mass is set to be a constant. In condition 1, the changes in maximum available power, deorbiting time, and energy conversion efficiency are all about 10% when the tether cross-section perimeter is about 5 mm, 10 mm, and 20 mm. A large perimeter means a high tether current, which leads to a higher maximum power, less deorbiting time, and a lower energy efficiency. It is suggested to increase the perimeter to generate more available power with less heating. The changes in condition 2 suggest the opposite. A long tether leads to a higher thrust, although the current is reduced because of the perimeter. The first three indices in Table 3 can change by as much as 66%, 40%, and 100%, respectively, when the tether length is 20 km, 10 km, and 5 km. This implies that a long tether design is more appropriate for missions with a low on-board power demand.

The debris mass (the mass of mother spacecraft) is changed to half or twice the basic value in Table 4. A smaller debris mass naturally means a shorter mission time which is proportional to the mass. The ability to harvest energy from the orbit is little affected by the debris mass because the current in, and force on, the tether changes little. The energy conversion efficiency of the battery system is nearly the same which means that the maximum available power should be almost the same, but as the burden of electrical power needed to make up the energy deficit is reduced by a shorter discharging section, the maximum available power is increased when the mass is reduced.

As shown in Table 5, the performance of the battery system changes regularly when the orbital parameters change. The low semimajor axis brings a higher plasma density, while the low inclination mainly means a higher plasma density with higher effective geomagnetic field intensity (the part which is perpendicular to the system velocity). When the semimajor axis and inclination are low, the current induced in the tether is large, so the maximum power is large, and the mission time is reduced. The ratio of maximum power to maximum waste power decreases as the semimajor axis and inclination increase: if the inclination is too high (greater than 60°), the maximum power drops to an extremely low value such that a battery system with a high battery voltage will be required.

4. Conclusions

(1) A numerical model is developed to calculate the power generation performance of a bare electrodynamic tether based on a Li-ion battery subsystem debris mitigation in space. The basic working performance, power generation strategy analysis, battery optimization, and applicability of the tether system are all discussed (2) Four parameters can be used to describe the performance of the power generation: mission time, energy conversion efficiency, maximum available power, and maximum waste power. The first three are used to view the mitigation mission and the performance in power generation, while the last is employed to discuss the applicability of the battery system (3) Generally, the SOC of the battery works as a "valley": this is unavoidable because of the large variation in space plasma parameters during orbit transfer. In the last part of the mission (in some cases), the power harvested will be much larger than that demanded. The excess energy should be dissipated for the battery subsystem cannot be cut off from the current loop, leading to a heating problem in the battery system. The extent of the problem is represented by maximum waste power. Extra control circuit which help the battery subsystem cut off from the tether can avoid the heating problem (4) The battery voltage directly determines magnitude of the maximum power while the battery capacity affects the final available value and waste power. It is suggested to find a combination of a low battery voltage and a large battery capacity for the battery design to avoid the heating problem; however, this choice will lead to the mass of the battery system increasing so that the trade-off between mass and waste power should be considered (5) A wide tether can increase the maximum available power in an efficient manner, while a long, thin, tether is more advantageous for low power-requirement missions. The debris mass does not have a significant effect on battery performance except with regard to the required mission time. A high semimajor axis and a high inclination of orbit increase the mission time, and the maximum available power is lower therewith

Nomenclature

Data Availability

The data used to support the findings of this study are available from the corresponding author upon request.

Conflicts of Interest

The authors declare that there is no conflict of interest regarding the publication of this paper.

Acknowledgments

This work was supported by the advanced research project in manned space (grant number 0130).

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Power Generation on a Bare Electrodynamic Tether during Debris Mitigation in Space

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Power generation can be realized in space when current is induced on a bare electrodynamic tether system. The performance of power generation is discussed based on a debris mitigation mission by numerical simulation in the paper. A Li-ion battery subsystem is used to complete the energy conversion—harvest and supply the energy.

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Building CubeSats to test electrodynamic tethering in space with MiTEE

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Satellite Snatchers in Space - Space Junk & Fishing Nets

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how a space net works and what each part does !!!

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Electrodynamic tethers speed up satellite reentry timelines - SpaceNews

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SAN FRANCISCO - Tethers Unlimited's Terminator Tape lowered a cubesat into Earth's atmosphere in eight months, while a nearly identical satellite without a 70-meter conductive tail is expected to remain in orbit for more than a decade.

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A satellite is about to demonstrate a new way of capturing space junk with magnets for the first time. With the frequency of space launches dramatically increasing in recent years, the potential for a disastrous collision above Earth is continually growing. Now, Japanese orbital clean-up company Astroscale is testing a potential solution.

The firm's End-of-Life Services by Astroscale demonstration mission is scheduled to lift off on 20 March aboard a Russian Soyuz rocket. It consists of two spacecraft: a small "client" satellite and a larger "servicer" satellite, or "chaser". The smaller satellite is equipped with a magnetic plate which allows the chaser to dock with it.

The two stacked spacecraft will perform three tests once in orbit, each of which will involve the servicer satellite releasing and then recapturing the client satellite. The first test will be the simplest, with the client satellite drifting a short distance away and then being recaptured. In the second test, the servicer satellite will set the client satellite tumbling before catching up with it and matching its motion to grab it.

Finally, if those two tests go well, the chaser will live up to its name by letting the client satellite float a few hundred metres away before finding it and attaching to it. All of these tests will be performed autonomously, with little to no human input once they are set in motion.

"These kinds of demonstrations have never been done before in space - they are very different to, say, an astronaut controlling a robotic arm on the International Space Station," says Jason Forshaw at Astroscale UK. "This is more of an autonomous mission." At the end of the tests, both spacecraft will burn up in Earth's atmosphere.

If companies wanted to use this capability, they would have to attach a magnetic plate to their satellites so they could be captured later. Because of the growing space debris problem, many countries now require firms to have a way to bring back their satellites once they run out of fuel or fail, so this could be a fairly simple contingency plan, Forshaw says. Right now, each chaser can only nab one satellite, but Astroscale is working on a version that could drag three or four out of orbit at once.
Sign up to our free Launchpad newsletter for a voyage across the galaxy and beyond, every Friday

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Satellite that can clean up space junk with a magnet about to launch

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A satellite is about to demonstrate a new way of capturing space junk with magnets for the first time. With the frequency of space launches dramatically increasing in recent years, the potential for a disastrous collision above Earth is continually growing. Now, Japanese orbital clean-up company Astroscale is testing a potential solution.

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https://www.npr.org/sections/thetwo-way/2016/12/09/505020386/japan-sends-long-electric-whip-into-orbit-to-tame-space-junk

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Solar sails (also called light sails or photon sails) are a method of spacecraft propulsion using radiation pressure exerted by sunlight on large mirrors. A number of spaceflight missions to test solar propulsion and navigation have been proposed since the 1980s. The first spacecraft to make use of the technology was IKAROS, launched in 2010.

A useful analogy to solar sailing may be a sailing boat; the light exerting a force on the mirrors is akin to a sail being blown by the wind. High-energy laser beams could be used as an alternative light source to exert much greater force than would be possible using sunlight, a concept known as beam sailing. Solar sail craft offer the possibility of low-cost operations combined with long operating lifetimes. Since they have few moving parts and use no propellant, they can potentially be used numerous times for delivery of payloads.

Solar sails use a phenomenon that has a proven, measured effect on astrodynamics. Solar pressure affects all spacecraft, whether in interplanetary space or in orbit around a planet or small body. A typical spacecraft going to Mars, for example, will be displaced thousands of kilometers by solar pressure, so the effects must be accounted for in trajectory planning, which has been done since the time of the earliest interplanetary spacecraft of the 1960s. Solar pressure also affects the orientation of a spacecraft, a factor that must be included in spacecraft design.

The total force exerted on an 800 by 800 metre solar sail, for example, is about 5 newtons (1.1 lbf) at Earth's distance from the Sun, making it a low-thrust propulsion system, similar to spacecraft propelled by electric engines, but as it uses no propellant, that force is exerted almost constantly and the collective effect over time is great enough to be considered a potential manner of propelling spacecraft.

James Clerk Maxwell, in 1861-1864, published his theory of electromagnetic fields and radiation, which shows that light has momentum and thus can exert pressure on objects. Maxwell's equations provide the theoretical foundation for sailing with light pressure. So by 1864, the physics community and beyond knew sunlight carried momentum that would exert a pressure on objects.

Jules Verne, in From the Earth to the Moon, published in 1865, wrote "there will some day appear velocities far greater than these [of the planets and the projectile], of which light or electricity will probably be the mechanical agent ... we shall one day travel to the moon, the planets, and the stars." This is possibly the first published recognition that light could move ships through space.

Pyotr Lebedev was first to successfully demonstrate light pressure, which he did in 1899 with a torsional balance; Ernest Nichols and Gordon Hull conducted a similar independent experiment in 1901 using a Nichols radiometer.

Carl Sagan, in the 1970s, popularized the idea of sailing on light using a giant structure which would reflect photons in one direction, creating momentum. He brought up his ideas in college lectures, books, and television shows. He was fixated on quickly launching this spacecraft in time to perform a rendezvous with Halley's Comet. Unfortunately, the mission didn't take place in time and he would never live to finally see it through.[citation needed ]

Many people believe that spacecraft using solar sails are pushed by the Solar winds just as sailboats and sailing ships are pushed by the winds across the waters on Earth. But Solar radiation exerts a pressure on the sail due to reflection and a small fraction that is absorbed.

The momentum of a photon or an entire flux is given by Einstein's relation:

where p is the momentum, E is the energy (of the photon or flux), and c is the speed of light. Specifically the momentum of a photon depends on its wavelength

Solar radiation pressure can be related to the irradiance ( solar constant) value of 1361 W/m 2 at 1 AU (Earth-Sun distance), as revised in 2011:

perfect absorbance: F = 4.54 μN per square metre (4.54 μPa) in the direction of the incident beam (an inelastic collision)

perfect reflectance: F = 9.08 μN per square metre (9.08 μPa) in the direction normal to surface (an elastic collision)

An ideal sail is flat and has 100% specular reflection. An actual sail will have an overall efficiency of about 90%, about 8.17 μN/m 2, due to curvature (billow), wrinkles, absorbance, re-radiation from front and back, non-specular effects, and other factors.

The force on a sail and the actual acceleration of the craft vary by the inverse square of distance from the Sun (unless extremely close to the Sun), and by the square of the cosine of the angle between the sail force vector and the radial from the Sun, so

where R is distance from the Sun in AU. An actual square sail can be modeled as:

Note that the force and acceleration approach zero generally around θ = 60° rather than 90° as one might expect with an ideal sail.

If some of the energy is absorbed, the absorbed energy will heat the sail, which re-radiates that energy from the front and rear surfaces, depending on the emissivity of those two surfaces.

Sail loading (areal density) is an important parameter, which is the total mass divided by the sail area, expressed in g/m 2. It is represented by the Greek letter σ.

A sail craft has a characteristic acceleration, a c, which it would experience at 1 AU when facing the Sun. Note this value accounts for both the incident and reflected momentums. Using the value from above of 9.08 μN per square metre of radiation pressure at 1 AU, a c is related to areal density by:

Assuming 90% efficiency, a c = 8.17 / σ mm/s 2

The lightness number, λ, is the dimensionless ratio of maximum vehicle acceleration divided by the Sun's local gravity. Using the values at 1 AU:

The lightness number is also independent of distance from the Sun because both gravity and light pressure fall off as the inverse square of the distance from the Sun. Therefore, this number defines the types of orbit maneuvers that are possible for a given vessel.

The table presents some example values. Payloads are not included. The first two are from the detailed design effort at JPL in the 1970s. The third, the lattice sailer, might represent about the best possible performance level. The dimensions for square and lattice sails are edges. The dimension for heliogyro is blade tip to blade tip.

An active attitude control system (ACS) is essential for a sail craft to achieve and maintain a desired orientation. The required sail orientation changes slowly (often less than 1 degree per day) in interplanetary space, but much more rapidly in a planetary orbit. The ACS must be capable of meeting these orientation requirements. Attitude control is achieved by a relative shift between the craft's center of pressure and its center of mass. This can be achieved with control vanes, movement of individual sails, movement of a control mass, or altering reflectivity.

Holding a constant attitude requires that the ACS maintain a net torque of zero on the craft. The total force and torque on a sail, or set of sails, is not constant along a trajectory. The force changes with solar distance and sail angle, which changes the billow in the sail and deflects some elements of the supporting structure, resulting in changes in the sail force and torque.

Sail temperature also changes with solar distance and sail angle, which changes sail dimensions. The radiant heat from the sail changes the temperature of the supporting structure. Both factors affect total force and torque.

To hold the desired attitude the ACS must compensate for all of these changes.

In Earth orbit, solar pressure and drag pressure are typically equal at an altitude of about 800 km, which means that a sail craft would have to operate above that altitude. Sail craft must operate in orbits where their turn rates are compatible with the orbits, which is generally a concern only for spinning disk configurations.

Sail operating temperatures are a function of solar distance, sail angle, reflectivity, and front and back emissivities. A sail can be used only where its temperature is kept within its material limits. Generally, a sail can be used rather close to the Sun, around 0.25 AU, or even closer if carefully designed for those conditions.

For trips within the inner Solar System, they can deliver loads and then return to Earth for subsequent voyages, operating as an interplanetary shuttle. For Mars in particular, the craft could provide economical means of routinely supplying operations on the planet according to Jerome Wright, "The cost of launching the necessary conventional propellants from Earth are enormous for manned missions. Use of sailing ships could potentially save more than $10 billion in mission costs."

Solar sail craft can approach the Sun to deliver observation payloads or to take up station keeping orbits. They can operate at 0.25 AU or closer. They can reach high orbital inclinations, including polar.

Minimum transfer times to the outer planets benefit from using an indirect transfer (solar swing-by). However, this method results in high arrival speeds. Slower transfers have lower arrival speeds.

The minimum transfer time to Jupiter for of 1 mm/s 2 with no departure velocity relative to Earth is 2 years when using an indirect transfer (solar swing-by). The arrival speed ( V) is close to 17 km/s. For Saturn, the minimum trip time is 3.3 years, with an arrival speed of nearly 19 km/s.

Oort Cloud/Sun's inner gravity focus

The Sun's inner gravitational focus point lies at minimum distance of 550 AU from the Sun, and is the point to which light from distant objects is focused by gravity as a result of it passing by the Sun. This is thus the distant point to which solar gravity will cause the region of deep space on the other side of the Sun to be focused, thus serving effectively as a very large telescope objective lens.

It has been proposed that an inflated sail, made of beryllium, that starts at 0.05 AU from the Sun would gain an initial acceleration of 36.4 m/s 2, and reach a speed of 0.00264c (about 950 km/s) in less than a day. Such proximity to the Sun could prove to be impractical in the near term due to the structural degradation of beryllium at high temperatures, diffusion of hydrogen at high temperatures as well as an electrostatic gradient, generated by the ionization of beryllium from the solar wind, posing a burst risk. A revised perihelion of 0.1 AU would reduce the aforementioned temperature and solar flux exposure. Such a sail would take "Two and a half years to reach the heliopause, six and a half years to reach the Sun's inner gravitational focus, with arrival at the inner Oort Cloud in no more than thirty years." "Such a mission could perform useful astrophysical observations en route, explore gravitational focusing techniques, and image Oort Cloud objects while exploring particles and fields in that region that are of galactic rather than solar origin."

Robert L. Forward has commented that a solar sail could be used to modify the orbit of a satellite about the Earth. In the limit, a sail could be used to "hover" a satellite above one pole of the Earth. Spacecraft fitted with solar sails could also be placed in close orbits such that they are stationary with respect to either the Sun or the Earth, a type of satellite named by Forward a " statite". This is possible because the propulsion provided by the sail offsets the gravitational attraction of the Sun. Such an orbit could be useful for studying the properties of the Sun for long durations.[citation needed ] Likewise a solar sail-equipped spacecraft could also remain on station nearly above the polar solar terminator of a planet such as the Earth by tilting the sail at the appropriate angle needed to counteract the planet's gravity.[citation needed ]

In his book The Case for Mars, Robert Zubrin points out that the reflected sunlight from a large statite, placed near the polar terminator of the planet Mars, could be focused on one of the Martian polar ice caps to significantly warm the planet's atmosphere. Such a statite could be made from asteroid material.

The MESSENGER probe orbiting Mercury used light pressure on its solar panels to perform fine trajectory corrections on the way to Mercury. By changing the angle of the solar panels relative to the Sun, the amount of solar radiation pressure was varied to adjust the spacecraft trajectory more delicately than possible with thrusters. Minor errors are greatly amplified by gravity assist maneuvers, so using radiation pressure to make very small corrections saved large amounts of propellant.

In the 1970s, Robert Forward proposed two beam-powered propulsion schemes using either lasers or masers to push giant sails to a significant fraction of the speed of light.

In the science fiction novel Rocheworld, Forward described a light sail propelled by super lasers. As the starship neared its destination, the outer portion of the sail would detach. The outer sail would then refocus and reflect the lasers back onto a smaller, inner sail. This would provide braking thrust to stop the ship in the destination star system.

Both methods pose monumental engineering challenges. The lasers would have to operate for years continuously at gigawatt strength. Forward's solution to this requires enormous solar panel arrays to be built at or near the planet Mercury. A planet-sized mirror or fresnel lens would need to be located at several dozen astronomical units from the Sun to keep the lasers focused on the sail. The giant braking sail would have to act as a precision mirror to focus the braking beam onto the inner "deceleration" sail.

A potentially easier approach would be to use a maser to drive a "solar sail" composed of a mesh of wires with the same spacing as the wavelength of the microwaves directed at the sail, since the manipulation of microwave radiation is somewhat easier than the manipulation of visible light. The hypothetical " Starwisp" interstellar probe design would use microwaves, rather than visible light, to push it. Masers spread out more rapidly than optical lasers owing to their longer wavelength, and so would not have as great an effective range.

Masers could also be used to power a painted solar sail, a conventional sail coated with a layer of chemicals designed to evaporate when struck by microwave radiation. The momentum generated by this evaporation could significantly increase the thrust generated by solar sails, as a form of lightweight ablative laser propulsion.

Another more physically realistic approach would be to use the light from the Sun to accelerate. The ship would first drop into an orbit making a close pass to the Sun, to maximize the solar energy input on the sail, then it would begin to accelerate away from the system using the light from the Sun. Acceleration will drop approximately as the inverse square of the distance from the Sun, and beyond some distance, the ship would no longer receive enough light to accelerate it significantly, but would maintain the final velocity attained. When nearing the target star, the ship could turn its sails toward it and begin to use the outward pressure of the destination star to decelerate. Rockets could augment the solar thrust.

Similar solar sailing launch and capture were suggested for directed panspermia to expand life in other solar system. Velocities of 0.05% the speed of light could be obtained by solar sails carrying 10 kg payloads, using thin solar sail vehicles with effective areal densities of 0.1 g/m 2 with thin sails of 0.1 µm thickness and sizes on the order of one square kilometer. Alternatively, swarms of 1 mm capsules could be launched on solar sails with radii of 42 cm, each carrying 10,000 capsules of a hundred million extremophile microorganisms to seed life in diverse target environments.

Theoretical studies suggest relativistic speeds if the solar sail harnesses a supernova.

Small solar sails have been proposed to accelerate the deorbiting of small artificial satellites from Earth orbits. Satellites in low Earth orbit can use a combination of solar pressure on the sail and increased atmospheric drag to accelerate satellite reentry. A de-orbit sail developed at Cranfield University is part of the UK satellite TechDemoSat-1, launched in 2014, and is expected to be deployed at the end of the satellite's five-year useful life. The sail's purpose is to bring the satellite out of orbit over a period of about 25 years. In July 2015 British 3U CubeSat called DeorbitSail was launched into space with the purpose of testing 16 m 2 deorbit structure, but eventually it failed to deploy it. There is also a student 2U CubeSat mission called PW-Sat2 planned to launch in 2017 that will test 4 m 2 deorbit sail. In June 2017 a second British 3U CubeSat called InflateSail deployed a 10 m 2 deorbit sail at an altitude of 500 kilometers (310 mi). In June 2017 the 3U Cubesat URSAMAIOR has been launched in low Earth orbit to test the deorbiting system ARTICA developed by Spacemind. The device, which occupies only 0.4 U of the cubesat, shall deploy a sail of 2.1 m 2 to deorbit the satellite at the end of the operational life

IKAROS, launched in 2010, was the first practical solar sail vehicle. As of 2015, it was still under thrust, proving the practicality of a solar sail for long-duration missions. It is spin-deployed, with tip-masses in the corners of its square sail. The sail is made of thin polyimide film, coated with evaporated aluminium. It steers with electrically controlled liquid crystal panels. The sail slowly spins, and these panels turn on and off to control the attitude of the vehicle. When on, they diffuse light, reducing the momentum transfer to that part of the sail. When off, the sail reflects more light, transferring more momentum. In that way, they turn the sail. Thin-film solar cells are also integrated into the sail, powering the spacecraft. The design is very reliable, because spin deployment, which is preferable for large sails, simplified the mechanisms to unfold the sail and the LCD panels have no moving parts.

Parachutes have very low mass, but a parachute is not a workable configuration for a solar sail. Analysis shows that a parachute configuration would collapse from the forces exerted by shroud lines, since radiation pressure does not behave like aerodynamic pressure, and would not act to keep the parachute open.

JPL's reference design was called the "heliogyro". It had plastic-film blades deployed from rollers and held out by centrifugal forces as it rotated. The spacecraft's attitude and direction were to be completely controlled by changing the angle of the blades in various ways, similar to the cyclic and collective pitch of a helicopter. Although the design had no mass advantage over a square sail, it remained attractive because the method of deploying the sail was simpler than a strut-based design. The CubeSail (UltraSail) is an active project aiming to deploy a heliogyro sail.

Heliogyro design is similar to the blades on a helicopter. The design is faster to manufacture due to lightweight centrifugal stiffening of sails. Also, they are highly efficient in cost and velocity because the blades are lightweight and long. Unlike the square and spinning disk designs, heliogyro is easier to deploy because the blades are compacted on a reel. The blades roll out when they are deploying after the ejection from the spacecraft. As the heliogyro travels through space the system spins around because of the centrifugal acceleration. Finally, payloads for the space flights are placed in the center of gravity to even out the distribution of weight to ensure stable flight.

JPL also investigated "ring sails" (Spinning Disk Sail in the above diagram), panels attached to the edge of a rotating spacecraft. The panels would have slight gaps, about one to five percent of the total area. Lines would connect the edge of one sail to the other. Masses in the middles of these lines would pull the sails taut against the coning caused by the radiation pressure. JPL researchers said that this might be an attractive sail design for large manned structures. The inner ring, in particular, might be made to have artificial gravity roughly equal to the gravity on the surface of Mars.

A solar sail can serve a dual function as a high-gain antenna. Designs differ, but most modify the metalization pattern to create a holographic monochromatic lens or mirror in the radio frequencies of interest, including visible light.

Pekka Janhunen from FMI has invented a type of solar sail called the electric solar wind sail. Mechanically it has little in common with the traditional solar sail design. The sails are replaced with straightened conducting tethers (wires) placed radially around the host ship. The wires are electrically charged to create an electric field around the wires. The electric field extends a few tens of metres into the plasma of the surrounding solar wind. The solar electrons are reflected by the electric field (like the photons on a traditional solar sail). The radius of the sail is from the electric field rather than the actual wire itself, making the sail lighter. The craft can also be steered by regulating the electric charge of the wires. A practical electric sail would have 50-100 straightened wires with a length of about 20 km each.[citation needed ]

Electric solar wind sails can adjust their electrostatic fields and sail attitudes.

All these designs maneuver, though the mechanisms are different.

Magnetic sails bend the path of the charged protons that are in the solar wind. By changing the sails' attitudes, and the size of the magnetic fields, they can change the amount and direction of the thrust.

The most common material in current designs is a thin layer of aluminum coating on a polymer (plastic) sheet, such as aluminized 2 µm Kapton film. The polymer provides mechanical support as well as flexibility, while the thin metal layer provides the reflectivity. Such material resists the heat of a pass close to the Sun and still remains reasonably strong. The aluminum reflecting film is on the Sun side. The sails of were made of aluminized PET film ( Mylar).

Eric Drexler developed a concept for a sail in which the polymer was removed. He proposed very high thrust-to-mass solar sails, and made prototypes of the sail material. His sail would use panels of thin aluminium film (30 to 100 nanometres thick) supported by a tensile structure. The sail would rotate and would have to be continually under thrust. He made and handled samples of the film in the laboratory, but the material was too delicate to survive folding, launch, and deployment. The design planned to rely on space-based production of the film panels, joining them to a deploy-able tension structure. Sails in this class would offer high area per unit mass and hence accelerations up to "fifty times higher" than designs based on deploy-able plastic films. The material developed for the Drexler solar sail was a thin aluminium film with a baseline thickness of 0.1 µm, to be fabricated by vapor deposition in a space-based system. Drexler used a similar process to prepare films on the ground. As anticipated, these films demonstrated adequate strength and robustness for handling in the laboratory and for use in space, but not for folding, launch, and deployment.

Research by Geoffrey Landis in 1998-1999, funded by the NASA Institute for Advanced Concepts, showed that various materials such as alumina for laser lightsails and carbon fiber for microwave pushed lightsails were superior sail materials to the previously standard aluminium or Kapton films.

In 2000, Energy Science Laboratories developed a new carbon fiber material that might be useful for solar sails. The material is over 200 times thicker than conventional solar sail designs, but it is so porous that it has the same mass. The rigidity and durability of this material could make solar sails that are significantly sturdier than plastic films. The material could self-deploy and should withstand higher temperatures.

There has been some theoretical speculation about using molecular manufacturing techniques to create advanced, strong, hyper-light sail material, based on nanotube mesh weaves, where the weave "spaces" are less than half the wavelength of light impinging on the sail. While such materials have so far only been produced in laboratory conditions, and the means for manufacturing such material on an industrial scale are not yet available, such materials could mass less than 0.1 g/m 2, making them lighter than any current sail material by a factor of at least 30. For comparison, 5 micrometre thick Mylar sail material mass 7 g/m 2, aluminized Kapton films have a mass as much as 12 g/m 2, and Energy Science Laboratories' new carbon fiber material masses 3 g/m 2.

The least dense metal is lithium, about 5 times less dense than aluminium. Fresh, unoxidized surfaces are reflective. At a thickness of 20 nm, lithium has an area density of 0.011 g/m 2. A high-performance sail could be made of lithium alone at 20 nm (no emission layer). It would have to be fabricated in space and not used to approach the Sun. In the limit, a sail craft might be constructed with a total areal density of around 0.02 g/m 2, giving it a lightness number of 67 and a c of about 400 mm/s 2. Magnesium and beryllium are also potential materials for high-performance sails. These 3 metals can be alloyed with each other and with aluminium.

Aluminium is the common choice for the reflection layer. It typically has a thickness of at least 20 nm, with a reflectivity of 0.88 to 0.90. Chromium is a good choice for the emission layer on the face away from the Sun. It can readily provide emissivity values of 0.63 to 0.73 for thicknesses from 5 to 20 nm on plastic film. Usable emissivity values are empirical because thin-film effects dominate; bulk emissivity values do not hold up in these cases because material thickness is much thinner than the emitted wavelengths.

Sails are fabricated on Earth on long tables where ribbons are unrolled and joined to create the sails. Sail material needed to have as little weight as possible because it would require the use of the shuttle to carry the craft into orbit. Thus, these sails are packed, launched, and unfurled in space.

In the future, fabrication could take place in orbit inside large frames that support the sail. This would result in lower mass sails and elimination of the risk of deployment failure.

Sailing operations are simplest in interplanetary orbits, where altitude changes are done at low rates. For outward bound trajectories, the sail force vector is oriented forward of the Sun line, which increases orbital energy and angular momentum, resulting in the craft moving farther from the Sun. For inward trajectories, the sail force vector is oriented behind the Sun line, which decreases orbital energy and angular momentum, resulting in the craft moving in toward the Sun. It is worth noting that only the Sun's gravity pulls the craft toward the Sun-there is no analog to a sailboat's tacking to windward. To change orbital inclination, the force vector is turned out of the plane of the velocity vector.

In orbits around planets or other bodies, the sail is oriented so that its force vector has a component along the velocity vector, either in the direction of motion for an outward spiral, or against the direction of motion for an inward spiral.

Trajectory optimizations can often require intervals of reduced or zero thrust. This can be achieved by rolling the craft around the Sun line with the sail set at an appropriate angle to reduce or remove the thrust.

A close solar passage can be used to increase a craft's energy. The increased radiation pressure combines with the efficacy of being deep in the Sun's gravity well to substantially increase the energy for runs to the outer Solar System. The optimal approach to the Sun is done by increasing the orbital eccentricity while keeping the energy level as high as practical. The minimum approach distance is a function of sail angle, thermal properties of the sail and other structure, load effects on structure, and sail optical characteristics (reflectivity and emissivity). A close passage can result in substantial optical degradation. Required turn rates can increase substantially for a close passage. A sail craft arriving at a star can use a close passage to reduce energy, which also applies to a sail craft on a return trip from the outer Solar System.

A lunar swing-by can have important benefits for trajectories leaving from or arriving at Earth. This can reduce trip times, especially in cases where the sail is heavily loaded. A swing-by can also be used to obtain favorable departure or arrival directions relative to Earth.

A planetary swing-by could also be employed similar to what is done with coasting spacecraft, but good alignments might not exist due to the requirements for overall optimization of the trajectory.

Mission

Laser Power

Vehicle Mass

Acceleration

Sail Diameter

Maximum Velocity (% of the speed of light)

1. Flyby - Alpha Centauri, 40 years

2. Rendezvous - Alpha Centauri, 41 years

3. Manned - Epsilon Eridani, 51 years (including 5 years exploring star system)

Interstellar travel catalog to use photogravitational assists for a full stop.

Successive assists at α Cen A and B could allow travel times to 75 yr to both stars.

Lightsail has a nominal mass-to-surface ratio (σnom) of 8.6×10−4 gram m−2 for a nominal graphene-class sail.

Area of the Lightsail, about 105 m2 = (316 m)2

Velocity up to 37,300 km s−1 (12.5% c)

Attitude (orientation) control

Both the Mariner 10 mission, which flew by the planets Mercury and Venus, and the MESSENGER mission to Mercury demonstrated the use of solar pressure as a method of attitude control in order to conserve attitude-control propellant.

Hayabusa also used solar pressure on its solar paddles as a method of attitude control to compensate for broken reaction wheels and chemical thruster.

MTSAT-1R ( Multi-Functional Transport Satellite)'s solar sail counteracts the torque produced by sunlight pressure on the solar array. The trim tab on the solar array makes small adjustments to the torque balance.

NASA has successfully tested deployment technologies on small scale sails in vacuum chambers.

On February 4, 1993, the Znamya 2, a 20-meter wide aluminized-mylar reflector, was successfully deployed from the Russian Mir space station. Although the deployment succeeded, propulsion was not demonstrated. A second test, Znamya 2.5, failed to deploy properly.

In 1999, a full-scale deployment of a solar sail was tested on the ground at DLR/ESA in Cologne.

A joint private project between Planetary Society, Cosmos Studios and Russian Academy of Science in 2001 made a suborbital prototype test, which failed because of rocket failure.

A 15-meter-diameter solar sail (SSP, solar sail sub payload, soraseiru sabupeiro-do) was launched together with ASTRO-F on a M-V rocket on February 21, 2006, and made it to orbit. It deployed from the stage, but opened incompletely.

On 21 May 2010, Japan Aerospace Exploration Agency (JAXA) launched the world's first interplanetary solar sail spacecraft " IKAROS" () to Venus. Using a new solar-photon propulsion method, it was the first true solar sail spacecraft fully propelled by sunlight, and was the first spacecraft to succeed in solar sail flight.

Until 2010, no solar sails had been successfully used in space as primary propulsion systems. On 21 May 2010, the Japan Aerospace Exploration Agency (JAXA) launched the IKAROS (Interplanetary Kite-craft Accelerated by Radiation Of the Sun) spacecraft, which deployed a 200 m 2 polyimide experimental solar sail on June 10. In July, the next phase for the demonstration of acceleration by radiation began. On 9 July 2010, it was verified that IKAROS collected radiation from the Sun and began photon acceleration by the orbit determination of IKAROS by range-and-range-rate (RARR) that is newly calculated in addition to the data of the relativization accelerating speed of IKAROS between IKAROS and the Earth that has been taken since before the Doppler effect was utilized. The data showed that IKAROS appears to have been solar-sailing since 3 June when it deployed the sail.

IKAROS has a diagonal spinning square sail 14×14 m (196 m 2) made of a 7.5-micrometre (0.0075 mm) thick sheet of polyimide. The polyimide sheet had a mass of about 10 grams per square metre. A thin-film solar array is embedded in the sail. Eight LCD panels are embedded in the sail, whose reflectance can be adjusted for attitude control. IKAROS spent six months traveling to Venus, and then began a three-year journey to the far side of the Sun.

A team from the NASA Marshall Space Flight Center (Marshall), along with a team from the NASA Ames Research Center, developed a solar sail mission called NanoSail-D, which was lost in a launch failure aboard a Falcon 1 rocket on 3 August 2008. The second backup version, NanoSail-D2, also sometimes called simply NanoSail-D, was launched with FASTSAT on a Minotaur IV on November 19, 2010, becoming NASA's first solar sail deployed in low earth orbit. The objectives of the mission were to test sail deployment technologies, and to gather data about the use of solar sails as a simple, "passive" means of de-orbiting dead satellites and space debris. The NanoSail-D structure was made of aluminium and plastic, with the spacecraft massing less than 10 pounds (4.5 kg). The sail has about 100 square feet (9.3 m 2) of light-catching surface. After some initial problems with deployment, the solar sail was deployed and over the course of its 240-day mission reportedly produced a "wealth of data" concerning the use of solar sails as passive deorbit devices.

On June 21, 2005, a joint private project between Planetary Society, Cosmos Studios and Russian Academy of Science launched a prototype sail Cosmos 1 from a submarine in the Barents Sea, but the Volna rocket failed, and the spacecraft failed to reach orbit. They intended to use the sail to gradually raise the spacecraft to a higher Earth orbit over a mission duration of one month. The launch attempt sparked public interest according to Louis Friedman. Despite the failed launch attempt of Cosmos 1, The Planetary Society received applause for their efforts from the space community and sparked a rekindled interest in solar sail technology.

On Carl Sagan's 75th birthday (November 9, 2009) the Planetary Society announced plans to make three further attempts, dubbed LightSail-1, -2, and -3. The new design will use a 32 m 2 Mylar sail, deployed in four triangular segments like NanoSail-D. The launch configuration is a 3U CubeSat format, and as of 2015, it was scheduled as a secondary payload for a 2016 launch on the first SpaceX Falcon Heavy launch.

Despite the losses of Cosmos 1 and NanoSail-D (which were due to failure of their launchers), scientists and engineers around the world remain encouraged and continue to work on solar sails. While most direct applications created so far intend to use the sails as inexpensive modes of cargo transport, some scientists are investigating the possibility of using solar sails as a means of transporting humans. This goal is strongly related to the management of very large (i.e. well above 1 km 2) surfaces in space and the sail making advancements. Development of solar sails for manned space flight is still in its infancy.

A technology demonstration sail craft, dubbed Sunjammer, was in development with the intent to prove the viability and value of sailing technology. Sunjammer had a square sail, 124 feet (38 meters) wide on each side (total area 13,000 sq ft or 1,208 sq m). It would have traveled from the Sun-Earth Lagrangian point 900,000 miles from Earth (1.5 million km) to a distance of 1,864,114 miles (3 million kilometers). The demonstration was expected to launch on a Falcon 9 in January 2015. It would have been a secondary payload, released after the placement of the DSCOVR climate satellite at the L1 point. Citing a lack of confidence in the ability of its contractor L'Garde to deliver, the mission was cancelled in October 2014.

As of December 2013, the European Space Agency (ESA) has a proposed deorbit sail, named " Gossamer", that would be intended to be used to accelerate the deorbiting of small (less than 700 kilograms (1,500 lb)) artificial satellites from low Earth orbits. The launch mass is 2 kilograms (4.4 lb) with a launch volume of only 15×15×25 centimetres (0.49×0.49×0.82 ft). Once deployed, the sail would expand to 5 by 5 metres (16 ft × 16 ft) and would use a combination of solar pressure on the sail and increased atmospheric drag to accelerate satellite reentry.

The Near-Earth Asteroid Scout (NEA Scout) is a mission being jointly developed by NASA's Marshall Space Flight Center (MSFC) and the Jet Propulsion Laboratory (JPL), consisting of a controllable low-cost CubeSat solar sail spacecraft capable of encountering near-Earth asteroids (NEA). Four 7 m (23 ft) booms would deploy, unfurling the 83 m 2 (890 sq ft) aluminized polyimide solar sail. In 2015, NASA announced it had selected NEA Scout to launch as one of several secondary payloads aboard Artemis 1, the first flight of the agency's heavy-lift SLS launch vehicle.

OKEANOS (Outsized Kite-craft for Exploration and Astronautics in the Outer Solar System) was a proposed mission concept by Japan's JAXA to Jupiter's Trojan asteroids using a hybrid solar sail for propulsion; the sail would have been covered with thin solar panels to power an ion engine. In-situ analysis of the collected samples would have been performed by either direct contact or using a lander carrying a high-resolution mass spectrometer. A lander and a sample-return to Earth were options under study. The OKEANOS Jupiter Trojan Asteroid Explorer was a finalist for Japan's ISAS' 2nd Large-class mission to be launched in the late 2020s. However, it was not selected.

The well-funded Breakthrough Starshot project announced on April 12, 2016, aims to develop a fleet of 1000 light sail nanocraft carrying miniature cameras, propelled by ground-based lasers and send them to Alpha Centauri at 20% the speed of light. The trip would take 20 years.

In August 2019, NASA awarded the Solar Cruiser team $400,000 for nine-month mission concept studies. The spacecraft would have a 1,672 m 2 (18,000 sq ft) solar sail and would orbit the Sun in a polar orbit, while the coronagraph instrument would enable simultaneous measurements of the Sun's magnetic field structure and velocity of coronal mass ejections. If selected for development, it would launch in 2024.

A similar technology was the theme in the Star Trek: Deep Space Nine episode, Explorers. In the episode, Lightships are described as an ancient technology used by Bajorans to travel beyond their solar system by using light from the Bajoran sun and specially constructed sails to propel them through space ("Explorers". Star Trek: Deep Space Nine. Season 3. Episode 22.).[non-primary source needed ] In the 2002 Star Wars film Attack of the Clones the main villain Count Dooku was seen using a spacecraft with solar sails.

G. Vulpetti, Fast Solar Sailing: Astrodynamics of Special Sailcraft Trajectories, ;;Space Technology Library Vol. 30, Springer, August 2012, (Hardcover) https://www.springer.com/engineering/mechanical+engineering/book/978-94-007-4776-0, (Kindle-edition), ASIN: B00A9YGY4I

G. Vulpetti, L. Johnson, G. L. Matloff, Solar Sails: A Novel Approach to Interplanetary Flight, Springer, August 2008, ISBN 978-0-387-34404-1

J. L. Wright, Space Sailing, Gordon and Breach Science Publishers, London, 1992; Wright was involved with JPL's effort to use a solar sail for a rendezvous with Halley's comet.

NASA/CR 2002-211730, Chapter IV- presents an optimized escape trajectory via the H-reversal sailing mode

G. Vulpetti, The Sailcraft Splitting Concept, JBIS, Vol. 59, pp. 48-53, February 2006

G. L. Matloff, Deep-Space Probes: To the Outer Solar System and Beyond, 2nd ed., Springer-Praxis, UK, 2005, ISBN 978-3-540-24772-2

T. Taylor, D. Robinson, T. Moton, T. C. Powell, G. Matloff, and J. Hall, "Solar Sail Propulsion Systems Integration and Analysis (for Option Period)", Final Report for NASA/MSFC, Contract No. H-35191D Option Period, Teledyne Brown Engineering Inc., Huntsville, AL, May 11, 2004

G. Vulpetti, "Sailcraft Trajectory Options for the Interstellar Probe: Mathematical Theory and Numerical Results", the Chapter IV of NASA/CR-2002-211730, The Interstellar Probe (ISP): Pre-Perihelion Trajectories and Application of Holography, June 2002

G. Vulpetti, Sailcraft-Based Mission to The Solar Gravitational Lens, STAIF-2000, Albuquerque (New Mexico, USA), 30 January - 3 February 2000

G. Vulpetti, "General 3D H-Reversal Trajectories for High-Speed Sailcraft", Acta Astronautica, Vol. 44, No. 1, pp. 67-73, 1999

C. R. McInnes, Solar Sailing: Technology, Dynamics, and Mission Applications, Springer-Praxis Publishing Ltd, Chichester, UK, 1999, ISBN 978-3-540-21062-7

Genta, G., and Brusa, E., "The AURORA Project: a New Sail Layout", Acta Astronautica, 44, No. 2-4, pp. 141-146 (1999)

S. Scaglione and G. Vulpetti, "The Aurora Project: Removal of Plastic Substrate to Obtain an All-Metal Solar Sail", special issue of Acta Astronautica, vol. 44, No. 2-4, pp. 147-150, 1999

"Deflecting Asteroids" by Gregory L. Matloff, IEEE Spectrum, April 2012

Planetary Society's solar sailing project

The Solar Photon Sail Comes of Age by Gregory L. Matloff

NASA Mission Site for NanoSail-D

NanoSail-D mission: Dana Coulter, "NASA to Attempt Historic Solar Sail Deployment", NASA, June 28, 2008

Far-out Pathways to Space: Solar Sails from NASA

Solar Sails Comprehensive collection of solar sail information and references, maintained by Benjamin Diedrich. Good diagrams showing how light sailors must tack.

U3P Multilingual site with news and flight simulators

ISAS Deployed Solar Sail Film in Space

Suggestion of a solar sail with roller reefing, hybrid propulsion and a central docking and payload station.

Interview with NASA's JPL about solar sail technology and missions

Website with technical pdf-files about solar-sailing, including NASA report and lectures at Aerospace Engineering School of Rome University

Advanced Solar- and Laser-pushed Lightsail Concepts

Andrews, D. G. (2003). "Interstellar Transportation using Today's Physics" (PDF). AIAA Paper 2003-4691. Archived from the original (PDF) on 2006-03-11.

www.aibep.org: Official site of American Institute of Beamed Energy Propulsion

Space Sailing Sailing ship concepts, operations, and history of concept

Bernd Dachwald's Website Broad information on sail propulsion and missions

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Solar sails (also called light sails or photon sails) are a method of spacecraft propulsion using radiation pressure exerted by sunlight on large mirrors. A number of spaceflight missions to test solar propulsion and navigation have been proposed since the 1980s. The first spacecraft to make use of the technology was IKAROS, launched in 2010.

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https://arxiv.org/pdf/2109.02623.pdf

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A cable that's as long as six football fields has been launched into orbit - and when it's deployed, it'll test an idea to knock out orbital debris. Japan's space agency sent the electrodynamic tether into space along with supplies for the International Space Station.

Reels aboard the Japan Aerospace Exploration Agency's Kounotori 6 craft will deploy the 700-meter (2,296 feet) tether, essentially unspooling a clothesline in space that could help clean up the roughly 20,000 pieces of potentially hazardous space debris that are tracked by systems on Earth.

Those pieces of junk are dangerous enough on their own - but they can also generate thousands more smaller pieces of debris if they collide, creating even more risk to the space station and satellites orbiting the Earth.

With the official acronym of EDT (for electrodynamic tether), the Kounotori's cable "is a promising candidate to deorbit the debris objects at low cost," JAXA says.

As illustrated by a video, the Japanese agency's plan is to use the electrified tether - counter-weighted by a 20 kilogram (44-pound) end mass - to slow down and redirect space junk into a safe but fiery reentry into the atmosphere.

According to the video, the tether will be able to change its position relative to the Kounotori craft by the use of force that's generated by an electric current and the Earth's magnetic field. The video also depicts the tether being attached to a large piece of debris so the space trash can be guided down into a destructive reentry.

Space debris has been seen as a problem for years - back in 2011, the National Research Council said the number of items had reached "tipping point" in terms of the dangers they posed to astronauts and spacecraft.

As we reported last year, "According to the Royal Institution in London, there are about 20,000 pieces of tracked space debris, ranging from larger than an apple to as big as a school bus. (There are far more objects smaller than that, including millions of pieces of debris too tiny to track, according to NASA.)"

There's a good chance we could see video of the new JAXA system being tested: Deployment of the tether will be monitored by cameras aboard the Kounotori.

According to JAXA, the Kounotori is scheduled to dock at the International Space Station on Dec. 14; the tether won't be unleashed until the Kounotori leaves the space station bearing a new cargo of waste - with the entire craft destined to burn up on reentry.

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Japan Sends Long Electric Whip Into Orbit, To Tame Space Junk

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A cable that's as long as six football fields has been launched into orbit - and when it's deployed, it'll test an idea to knock out orbital debris. Japan's space agency sent the electrodynamic tether into space along with supplies for the International Space Station.

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A laser broom is a proposed ground-based laser beam-powered propulsion system whose purpose is to sweep space debris out of the path of other artificial satellites such as the International Space Station. It would heat one side of an object enough to change its orbit and make it hit the atmosphere sooner. Space researchers have proposed that a laser broom may help mitigate Kessler syndrome, a theoretical runaway cascade of collision events between orbiting objects.

Space-based laser broom systems using a laser mounted on a satellite or space station have also been proposed.

Lasers are designed to target debris between one and ten centimetres (0.4-3.9 in) in diameter. Collisions with such debris are common of such high velocity that considerable damage and numerous secondary fragments are the results. The laser broom is intended to be used at high enough power to penetrate through the atmosphere with enough remaining power to ablate material from the target. The ablating material imparts a small thrust that lowers its orbital perigee into the upper atmosphere, thereby increasing drag so that its remaining orbital life is short. The laser would operate in pulsed mode to avoid self-shielding of the target by the ablated plasma. The power levels of lasers in this concept are well below the power levels in concepts for more rapidly effective anti-satellite weapons.

Research into this area demonstrates the precise physics involved, which shows that space debris orientation is significantly relevant to resultant trajectory of the ablated object.

Using a laser guide star and adaptive optics, a sufficiently large ground-based laser (1 megajoule pulsed HF laser) can deorbit dozens of objects per day at a reasonable cost.

The Space Shuttle routinely showed evidence of "tiny" impacts upon post-flight inspection.

Orion was a proposed ground-based laser broom project in the 1990s, estimated to cost $500 million.

A space-based laser also called "Project Orion" was planned to be installed on the International Space Station in 2003. In 2015, Japanese researchers proposed adding laser broom capabilities to the Extreme Universe Space Observatory telescope, to be launched to the ISS in 2017.

In 2014, the European CLEANSPACE project published a report studying a global architecture of debris tracking and removal laser stations.

2000 Earth Orbital Debris - NASA Research on Satellite and Spacecraft Effects by World Spaceflight News, CD-ROM: 862 pages ISBN 1-893472-28-0

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A laser broom is a proposed ground-based laser beam-powered propulsion system whose purpose is to sweep space debris out of the path of other artificial satellites such as the International Space Station. It would heat one side of an object enough to change its orbit and make it hit the atmosphere sooner.

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Starlink is the name of a satellite network that the private spaceflight company SpaceX is developing to provide low-cost internet to remote locations. While SpaceX eventually hopes to have as many as 12,000 satellites in this so-called megaconstellation, the size and scale of the project have flustered astronomers and amateur skywatchers, who fear that the bright, orbiting objects will interfere with observations of the universe.

The initial plan

SpaceX's satellite internet proposal was announced in January 2015. Though it wasn't given a name at the time, CEO Elon Musk said that the company had filed documents with international regulators to place about 4,000 satellites in low Earth orbit.

"We're really talking about something which is, in the long term, like rebuilding the internet in space," Musk said during a speech in Seattle when revealing the project.

Musk's initial estimate of the number of satellites soon grew, as he hoped to capture a part of the estimated $1 trillion worldwide internet connectivity market to help achieve his Mars colonization vision. The U.S. Federal Communications Commission (FCC) has granted SpaceX permission to fly 12,000 satellites and perhaps as many as 30,000 eventually.

To put that into perspective, only about 2,000 artificial satellites currently orbit Earth, and only 9,000 have ever been launched in all of history, according to the United Nations Office for Outer Space Affairs.

SpaceX launched its first two Starlink test craft, named TinTinA and TinTinB, in 2018. The mission went smoothly. Based on initial data, the company asked regulators for its fleet to be allowed to operate at lower altitudes than originally planned, and the FCC agreed.

The first 60 Starlink satellites were launched on May 23, 2019, aboard a SpaceX Falcon 9 rocket. The satellites successfully reached their operational altitude of 340 miles (550 kilometers) - low enough to get pulled down to Earth by atmospheric drag in a few years so that they don't become space junk once they die.

(Image credit: SpaceX)

Each Starlink satellite weighs 500 lbs. (227 kilograms) and is roughly the size of a table, according to Sky & Telescope magazine.

Rather sending internet signals through electric cables, which must be physically laid down to reach far-flung places, satellite internet works by beaming information through the vacuum of space, where it travels 47% faster than in fiber-optic cable, Business Insider reported.

Current satellite internet works using large spacecraft that orbit 22,236 miles (35,786 km) above a particular spot on the Earth. But at that distance, there are generally significant time delays in sending and receiving data. By being closer to our planet and networking together, Starlink's satellites are meant to carry large amounts of information rapidly to any point on Earth, even over the oceans and in extremely hard-to-reach places where fiber-optic cables would be expensive to lay down.

Musk said the Starlink network would be able to provide "minor" internet coverage after 400 spacecraft were up and running, and "moderate" coverage after about 800 satellites became operational.

Within days of the first launch, skywatchers spotted a linear pearl string of lights as the satellites whizzed overhead in the early morning. Web-based guides showed others how to track down the spectacular display.

"This was quite an amazing sight, and I was shouting 'Owowowow!' when the bright 'train' of objects entered into view," Netherlands-based satellite tracker Marco Langbroek previously told Space.com via email. "They were brighter than I had anticipated."

That brightness was a surprise to almost everyone, including both SpaceX and the astronomical community. Researchers began to panic and shared photos of satellite streaks in their data, such as this one from the Lowell Observatory in Arizona.

They expressed particular concerns about future images from highly sensitive telescopes such as the Vera Rubin Observatory (formerly known as the Large Synoptic Survey Telescope), which will study the entire universe in exquisite detail and is expected to come online in 2022. Radio astronomers are also planning for interference from Starlink's radio-based antennas.
Related: In photos: SpaceX launches third batch of 60 Starlink satellites to orbit
The International Astronomical Union expressed concerns in a statement released in June 2019. "Satellite constellations can pose a significant or debilitating threat to important existing and future astronomical infrastructures, and we urge their designers and deployers as well as policy-makers to work with the astronomical community in a concerted effort to analyse and understand the impact of satellite constellations," the statement said.

SpaceX received more backlash in September 2019, when the European Space Agency (ESA) announced that it had directed its Aeolus satellite to undertake evasive maneuvers and avoid crashing into "Starlink 44," one of the first 60 satellites in the megaconstellation. The agency took action after learning from the U.S. military that the probability of a collision was 1 in 1,000 - 10 times higher than ESA's threshold for conducting a collision-avoidance maneuver.

What SpaceX plans to do

SpaceX has stated that it will work with organizations and space agencies to mitigate the impacts of its megaconstellation and has continued its deployment of Starlink. The company launched a second batch of satellites in November 2019 and a third in January 2020, and it expects to begin broadband internet service by the end of 2020.

SpaceX has tried to assuage astronomers' concerns over Starlink's effect on the night sky. In the January 2020 batch, one Starlink satellite, called DarkSat, was painted in an experimental partially black coating designed to reduce its brightness.

"SpaceX is absolutely committed to finding a way forward so our Starlink project doesn't impede the value of the research you all are undertaking," Patricia Cooper, SpaceX's vice president of satellite government affairs, told astronomers at a January 2020 meeting of the American Astronomical Society in Honolulu, Nature reported.

But the huge numbers of satellites in megaconstellations from SpaceX and other private space companies, such as OneWeb, suggest that these issues will continue, and advocates have called for greater regulations from government agencies.
Additional resources:
"Here is a gift for the leaders of the world, a task more non-partisan than any other which has come before: protect our skies," stargazer Arwen Rimmer wrote in The Space Review, a weekly online publication devoted to essays and commentary about space, in early 2020.

Watch this video describing the Starlink satellite project, from SpaceX.

Read how astrophysicist Ethan Siegel thinks SpaceX can fix the damage Starlink satellites are causing to astronomy, published in Forbes.

Follow the #starlink hashtag on Twitter to catch the latest news and opinions about Starlink.

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Starlink: SpaceX's satellite internet project

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Starlink is the name of a satellite network that the private spaceflight company SpaceX is developing to provide low-cost internet to remote locations. While SpaceX eventually hopes to have as many as 12,000 satellites in this so-called megaconstellation, the size and scale of the project have flustered astronomers and amateur skywatchers, who fear that the bright, orbiting objects will interfere with observations of the universe.

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Kilometer-Long Space Tether Tests Fuel-Free Propulsion

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The U.S. space mission aims to demonstrate technology that could someday help clean up space junk

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Magnet Technology Used To Clean Up Space Junk

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