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NASA looks to solar sails as a way to power future missions

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Spacecraft equipped with solar sails could be powered with a resource that is both abundant and virtually inexhaustible: sunlight.

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Astroscale's ELSA-d Mission: "Test Capture" Success

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Future satellites could deploy solar sails to help take down pieces of space junk floating around Earth and a tiny new spacecraft hopes to make it possible.

A British satellite the size of a shoe box is slated to launch next year to test how a solar sail can act as an atmospheric brake and end its mission in a fiery plunge. If successful, the one-year mission could help lead to bigger, better solar sail spacecraft capable of trawling the space around Earth for dangerous space junk, mission planners said.

Just having a cheap, reliable method of ending a spacecraft's life could go a long way toward limiting the size of the space debris cloud surrounding Earth. Even space shuttle missions and the International Space Station must occasionally dodge space junk, which has collectively grown to more than 6,000 tons of debris leftover from 50 years of abandoning spacecraft.

Most satellites rely upon propellant-based maneuvering thrusters that may or may not still function at mission's end - and that's not even considering the launch expense of carrying all that propellant mass. By contrast, the CubeSail would simply unfurl a 16-square-foot (5-square-meter) sail. Launch of the 6.6-pound (3-kg) sail is set for late 2011.

"Using the sail as a 'propellantless' deorbiting system will allow the extra mass gained to be used for payloads or to extend the lifetime of a satellite further," said Vaios Lappas, an aerospace engineer at the University of Surrey in the UK.

Such a sail would rely upon force of sunlight, and allow scientists to test solar sailing as a space propulsion alternative to other space engines which must carry their own propellant. It also represents a much cheaper and possibly more reliable fallback technology.

Tiny satellite, big mission
CubeSail could piggyback-launch with other missions as a small nanosatellite. It will aim for an altitude of 435 to 497 miles (700 to 800 km) and enter a sun-synchronous orbit so that it can match the motion of the sun across the sky, according to Lappas.

Yet no spacecraft has flown with a solar sail as its main means of propulsion, in part because of launch failures that crippled efforts by the California-based Planetary Society and NASA. Japan successfully deployed solar sails in 2004, but did not try to use them for controlled flight.

That has led the University of Surrey team - backed by the European aerospace company Astrium - to try and ensure mission success based on the mantra of simplicity.

"We are keeping our design as simple as possible using well known materials, components and a simple design based on self-deploying booms coiled around a simple roller mechanism," Lappas told SPACE.com.

Taking down space junk
Success might lead to future CubeSail designs that can attach to existing pieces of space junk and take them down, so that space-faring nations can finally begin cleaning up some of the orbital mess.

"Protecting our planet and environment is key for sustainable growth," Lappas said.

At last estimate, there are than 20,000 pieces of space trash in orbit, according to the Space Surveillance Network. But tackling the space littering problem will likely require a nanosatellite to approach a tumbling piece of space junk travelling at high speed, researchers said.

The CubeSail team has already begun figuring out low-cost technologies that could convert small satellites into space debris cleaners, Lappas noted. But for now, satellites with a mass up to 1,100 pounds (500 kg) might soon use the CubeSail design to end themselves more cheaply and efficiently.

"We are working on using carbon-made booms with increased strength and lighter mass for larger sails," Lappas said.

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Future satellites could deploy solar sails to help take down pieces of space junk floating around Earth and a tiny new spacecraft hopes to make it possible. A British satellite the size of a shoe box is slated to launch next year to test how a solar sail can act as an atmospheric brake and end its mission in a fiery plunge.

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Last year, the European Space Agency's Sentinel-1A satellite collided with a tiny chunk of debris. Fortunately, the resulting damage to its solar panel turned out to be minor. But it got lucky. If the piece of space trash had been slightly larger, it could have shattered the entire panel, according to Holger Krag, head of the agency's Space Debris Office who spoke about the incident at this past spring's 7th European Conference on Space Debris.

Earth's orbit is littered with bolts, flecks of paint, dead satellites, and other leftovers from past missions. More than 500,000 pieces of space debris hurtle around our planet at speeds up to 17,500 miles per hour. Space trash is accumulating, and scientists fear that collisions will become more common, creating even more debris. This could trigger a domino effect where bits of shrapnel crash into other objects, creating more and more projectiles to clutter low Earth orbit.

"If that ever happens it will make space unusable essentially, and we're pretty close to that," says Jason Derleth, program executive of the NASA Innovative Advanced Concepts (NIAC) Program.

Some researchers want to take action now, before the problem inevitably grows. This past spring, the NIAC awarded researchers at The Aerospace Corporation in El Segundo, California $500,000 to continue development of an unusual-looking spacecraft that's meant to mop up small pieces of space debris; almost like a space vacuum cleaner. Called Brane Crafts, the tiny ships are about a yard across and thinner than a human hair. Each one would wrap around a chunk of debris and yank it down to into the atmosphere, where it would heat up and eventually be incinerated about 155 miles above the Earth's surface.

"You can essentially think of it as one giant piece of saran wrap covered with thrusters, and you can curl it however you want," Derleth says.

Each Brane Craft, its creators hope, will be incredibly lightweight and fuel-efficient. That means it could be ideal for more than just cleaning up space junk. One day, these tiny ships could be sent to visit asteroids, moons, and other planets.
On the prowl
To create Brane Craft, developers had to think beyond conventional spacecraft as they aren't really suited to chase down space debris. "Trying to catch something that's going that fast is really, really hard," Derleth says. "Docking with a piece of debris means you have to match that orbit exactly."

To rendezvous with a piece of debris that is literally traveling faster than a speeding bullet, dispose of it, and then hunt down the next piece of trash would also call for immense amounts of fuel, making it extremely costly.

"The Brane Craft idea is to take a spacecraft and reduce it to its absolute minimum mass," says Siegfried Janson, a senior scientist at The Aerospace Corporation. Currently, it can cost around $250,000 to launch a CubeSat, a kind of miniaturized satellite, that is about 11 pounds, Janson says. His goal is to make spacecraft that are so light that they would cost only $5,000 each to launch.

The current design is a membrane-like ship that is three square feet in size and weighs less than a banana. Each spacecraft will be made from flexible plastic sheets 10 microns thick (our hairs tend to be up to 180 microns thick) printed with a fine film of solar cells and electronics. Liquid propellant will be stored in the 15 to 20 micron gap between these sheets.

The solar cells will power a type of engine called an electrospray thruster that uses propellant very sparingly, Janson says. The whole ship will be bendy, too. "Basically it's got thin muscles integrated into the structure," he says. These "muscles" are made from a polymer sandwiched between two metal plates that can change shape when an electric current is run through them, causing a voltage difference.

These slender spacecraft are meant to be light enough to travel to space en masse. Janson envisions a batch of 50 or more Brane Crafts "like a stack of pizzas" launched together into orbit. Once they reach the International Space Station or another point in low Earth orbit, each one could be sent directions to its target piece of debris (radar stations track more than 18,000 objects in orbit, most of which are space debris).

It might take five days for the Brane Craft to maneuver up to the debris and envelop it. The Brane Craft would then fire its thrusters to push in the opposite direction to the one the debris was traveling in. This would slow the object down, causing it to gradually sink into the atmosphere. After 10 days or so, the debris would be low enough to burn up.

Typically, the Brane Craft would be incinerated along with its quarry; the spacecraft are intended to be light and cheap enough to be sacrificed at the end of the mission.

It will still be quite some time before Brane Crafts are unleashed upon the hordes of space junk orbiting our planet. Janson estimates that the ships could be ready for launch in about 10 years. He and his team are planning to use their most recent round of NASA funding to refine their design and start testing super-thin electronics.

One challenge they still need to overcome is how to protect the spacecrafts from radiation. The razor-thin ships won't have shielding to protect their sensitive electronics from radiation. Janson and his crew are designing carbon-nanotube circuits that can survive for a month near the outer edge of low Earth orbit.

And there are drawbacks to building spaceships to be so thin. As Brane Craft closes in on a piece of debris, it will likely be clobbered by other tiny detritus. "The micro-meteorite environment in low Earth orbit is normally just a pain for spacecraft; you get little dings in your solar cells and windows," Janson says. Bits of rock or manmade trash too small to even make a dent in a rocket might puncture a Brane Craft. "We have to...design the Brane Craft to be bulletproof to these really tiny bullets."
Outward bound
To start, Janson and his crew are planning to use Brane Craft on small pieces of space debris about five to 10 centimeters in size (roughly two to four inches). The ships won't be able to get rid of bulky space junk, like used upper stages. However, if scientists predict that a collision is imminent, a group of Brane Crafts could be sent to push this debris off track.

Super-thin ships like Brane Craft aren't the only tech under construction to wrangle space debris. The European Space Agency is also considering robotic arm grippers, nets, harpoons, and tethers. Another European team is planning to launch its RemoveDebris mission in late 2017 or early 2018, which will practice capturing CubeSats with a net and harpoon. Aeroscale, a satellite services company based in Singapore, is planning to capture debris using magnets. And researchers at Stanford University and NASA's Jet Propulsion Laboratory in Pasadena, California have designed a gripper inspired by gecko feet that could latch onto satellites and other large debris.

Researchers have even considered zapping debris with a ground-based laser. "You can slow things down just as they come over the horizon by pointing these very high-powered lasers at them," Derleth says. This would gobble up much less energy than launching a spaceship and sending it after individual chunks of debris. However, such a laser could potentially be turned into an anti-satellite weapon.

All of these approaches will have to prove their mettle. One advantage to Brane Craft's design, though, is it's potential to be put to work far beyond Earth's orbit. Brane Craft will be so fuel-efficient that one of these tiny ships could travel all the way to Mars and back, or make multiple trips between the moon and low Earth orbit. "You can visit just about [anywhere] in the solar system," Janson says.

Brane Craft could also be used to explore and mine asteroids, he says. It would be ridiculously expensive to build thousands of conventional spacecraft and send them traveling to individual asteroids. But perhaps swarms of Brane Crafts could visit the asteroid belt between Mars and Jupiter, and return carrying samples.

Eventually, these tiny spacecraft could even help protect the Earth, Janson says. We could manufacture larger versions or mass-produce thousands of Brane Crafts and send them out to deflect incoming asteroids.

"It's a new kind of spacecraft that nobody's ever seen, and I hope people can get really creative with it," Derleth says.

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This spacecraft is thinner than a human hair and can capture space debris

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Last year, the European Space Agency's Sentinel-1A satellite collided with a tiny chunk of debris. Fortunately, the resulting damage to its solar panel turned out to be minor. But it got lucky.

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Spaceflight Now | Breaking News | NASA pursues tests of solar sail, laser communications

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Kicking off a new line of technology demonstration missions, NASA announced plans Monday to demonstrate a laser communications system, a precise atomic clock and a futuristic solar sail in space by 2016, but officials cautioned budgetary negotiations may keep the high-tech missions on the ground.

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Kilometer-Long Space Tether Tests Fuel-Free Propulsion

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Kilometer-Long Space Tether Tests Fuel-Free Propulsion

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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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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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By Robbin Laird

When I was in Australia, I had a chance to meet with the Australian company EOS which has very innovative laser tracking technologies which provide for Australia and her allies a key space tracking capability.

This technology has evolved to the point that not only can they asset with the domain knowledge on where satellites are but also working with tracking space debris and will soon have a deployed capability to use lasers to reduce the problem.

This capability was highlighted in an article in the Daily Mail which was published on March 21, 2018.
Australian military defence contractor Electro Optic Systems has developed a laser capable of pushing space debris in orbit around so collisions can be avoided. The company, under its EOS Space Systems arm based in Mt Stromlo near Canberra, will use lasers to track space junk and then another higher-powered laser to avoid impacts by nudging the debris. Professor Craig Smith, from EOS Space Systems, said researchers had developed a photon pressure laser that was 'able to nudge space debris objects around, change their orbits.' He said the next step would be to build 'bigger and bigger lasers' that were capable of pushing the debris out of orbit while avoiding breaking up the space junk into smaller pieces. 'If they get smaller they get harder and harder to track, and so they start to become invisible - but also still lethal to satellites.'
Now another innovative player in the industry has announced success in the same domain using a different approach.

According to a story released by the University of Surrey,
The RemoveDEBRIS satellite has successfully used its on-board net technology in orbit - the first demonstration in human history of active debris removal (ADR) technology.
This satellite was built by Surrey Satellite Technology.
Sir Martin Sweeting, Chief Executive of Surrey Satellite Technology Ltd commented: "SSTL's expertise in designing and building low cost, small satellite missions has been fundamental to the success of RemoveDEBRIS, a landmark technology demonstrator for Active Debris Removal missions that will begin a new era of space junk clearance in Earth's orbit."
Surrey Satellite Technology Ltd is a spin-off company from the University of Surrey and is majority owned by Airbus.

The successful mission was described in the University of Surrey article as follows:
The spacecraft began the experimental phase of its mission on Sunday 16 September, when it used a net to capture a deployed target simulating a piece of space debris. RemoveDEBRIS was designed, built and manufactured by a consortium of leading space companies and research institutions led by the Surrey Space Centre at the University of Surrey. The spacecraft is operated in orbit by engineers at Surrey Satellite Technology Ltd in Guildford, UK. The project is co-funded by the European Commission. Professor Guglielmo Aglietti, Director of the Surrey Space Centre, said: "We are absolutely delighted with the outcome of the net technology. While it might sound like a simple idea, the complexity of using a net in space to capture a piece of debris took many years of planning, engineering and coordination between the Surrey Space Centre, Airbus and our partners - but there is more work to be done. These are very exciting times for us all." Ingo Retat, Airbus RemoveDEBRIS project head, said: "To develop this net technology to capture space debris we spent 6 years testing in parabolic flights, in special drop towers and also thermal vacuum chambers. Our small team of engineers and technicians have done an amazing job moving us one step closer to clearing up low Earth orbit." In the coming months, RemoveDEBRIS will test more ADR technologies: a vision-based navigation system that uses cameras and LiDaR technology to analyse and observe potential pieces of debris; the first harpoon capture technology used in orbit; and a drag-sail that will finally bring RemoveDEBRIS into the Earth's atmosphere where it will be destroyed, bringing its mission to a close. The US Space Surveillance Network tracks 40,000 objects and it is estimated that there are more than 7,600 tonnes of 'space junk' in and around Earth's orbit - with some moving faster than a speeding bullet, approaching speeds of 30,000 miles per hour. The research leading to these results has received funding from the European Union Seventh Framework Programme [FP7/2007-2013] under grant agreement n°607099. The RemoveDEBRIS consortium consists of:

Mission and consortium coordination - Surrey Space Centre (UK)

Satellite system engineering - ArianeGroup (France)

Platform, avionics and spacecraft operations - SSTL (UK)

Harpoon - Airbus (UK)

Net - Airbus (Germany)

Vision based navigation - CSEM (Switzerland)/ INRIA/ Airbus (France)

CubeSat dispensers - Innovative Solutions in Space (Netherlands)

Target CubeSats - Surrey Space Centre (UK)/ Stellenbosch University (South Africa)

Dragsail - Surrey Space Centre (UK)

A London Times article provided further detail.

The article quoted the project leader and then went on to describe the potential use of the technology.
We are absolutely delighted," Guglielmo Aglietti, director of the Surrey Space Centre., said "The target was spinning, which we had not expected. This was a demonstration of capturing an uncompetitive target." If the net was being used for real the satellite would then tow the junk to a lower orbit, where it would burn up as it entered the Earth's atmosphere. Professor Aglietti envisages nets being used to capture large pieces of debris, such as defunct satellites.
The featured graphic was contained in The Times article and is completed by the second graphic below:

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Space Tracking and Dealing with Space Debris: The Role of Two Innovative Smaller Companies - Second Line of Defense

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By Robbin Laird When I was in Australia, I had a chance to meet with the Australian company EOS which has very innovative laser tracking technologies which provide for Australia and her allies a key space tracking capability. This technology has evolved to the point that not only can they asset with the domain knowledge [...]

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Researchers at The Australian National University (ANU) have harnessed a technique that helps telescopes see objects in the night sky more clearly to fight against dangerous and costly space debris.

"Adaptive optics is like removing the twinkle from the stars."

The researchers' work on adaptive optics - which removes the haziness caused by turbulence in the atmosphere - has been applied to a new 'guide star' laser for better identifying, tracking and safely moving space debris.

Space debris is a major threat to the $US700 billion of space infrastructure delivering vital services around the globe each day. With laser guide star adaptive optics, this infrastructure now has a new line of defense.

The optics that focus and direct the guide star laser have been developed by the ANU researchers with colleagues from Electro Optic Systems (EOS), RMIT University, Japan, and the USA as part of the Space Environment Research Centre (SERC).

EOS will now commercialize the new guide star laser technology, which could also be incorporated in tool kits to enable high-bandwidth ground to space satellite communications.

The laser beams used for tracking space junk use infrared light and aren't visible. In contrast, the new guide star laser, which is mounted on a telescope, propagates a visible orange beam into the night sky to create an artificial star that can be used to accurately measure light distortion between Earth and space.

This guiding orange light enables adaptive optics to sharpen images of space debris. It can also guide a second, more powerful infra-red laser beam through the atmosphere to precisely track space debris or even safely move them out of orbit to avoid collisions with other debris and eventually burn up in the atmosphere.

Lead researcher, Professor Celine D'Orgeville from ANU, says adaptive optics is like "removing the twinkle from the stars."

"But that's a good thing," Professor D'Orgeville said.

"Without adaptive optics, a telescope sees an object in space like a blob of light. This is because our atmosphere distorts the light traveling between the Earth and those objects.

"But with adaptive optics, these objects become easier to see and their images become a lot sharper. Essentially, adaptive optics cuts through the distortion in our atmosphere, making sure we can clearly see the incredible images our powerful telescopes capture.

"This includes small, human-made objects - like weather and communication satellites, or space junk.

"That's why this development is such an important breakthrough when it comes to our efforts to clear our night skies of the ever-increasing clutter of space debris."

The EOS guide star laser and the ANU adaptive optics systems are located at the ANU Mount Stromlo Observatory in Canberra, Australia.

The ANU researchers will now work with EOS to test the new technology and apply it to a range of other applications including laser communications between the Earth and space.

It's an exciting development that will help to safeguard the wide range of vital applications of space technology in the 21st century.
The research was funded by the Australian Government's Cooperative Research Centre Program, EOS, ANU, RMIT University and partners in Japan and the USA.

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New Laser to Help Clear the Sky of Space Debris

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Researchers at The Australian National University (ANU) have harnessed a technique that helps telescopes see objects in the night sky more clearly to fight against dangerous and costly space debris. "Adaptive optics is like removing the twinkle from the stars." The researchers' work on adaptiv

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Space junk is becoming a real problem.

It's a serious issue. There's a common misconception that things in space are just kindof floating out there, moving slowly-and given videos of spacewalks and what we see in movies, that's understandable.

But it's wrong. There are thousands of satellites orbiting the Earth, moving at incredibly high speeds. Note the plural, "speeds"; not everything is traveling at the same speed or in the same direction. Two objects moving at 25,000 kph in different orbits can have a relative speed of several kilometers per second. At that velocity, a fleck of paint can have a catastrophic impact.

If two entire satellites collide, the problem is hugely worse; they create a shower of debris that expands and can hit more satellites, creating a cascade of debris. This was the basis of the movie "Gravity", you may recall. That flick grossly exaggerated the problem for dramatic effect, but the overall idea was based on reality. In fact, in 2009 just such a situation occurred when a defunct Russian communication satellite slammed into Motorola Iridium satellite; the energy of the impact utterly destroyed the two and created two clouds of debris moving in different directions.

Space debris is a very real threat. What can be done about it? NASA and the Department of Defense have been cooperating on this for a long time, but the European Space Agency is looking into taking the next step: a satellite called e.Deorbit. It's in the proposal stage, awaiting ESA approval to actually get started. But if approved, the hope is that it will be tag, snag, and bag large pieces of orbital debris, then perform a de-orbit burn to drop them both into Earth's atmosphere where they will burn up.

It's ambitious, I'll say that, but the basic idea makes sense. It will use advanced imaging techniques to identify debris, approach it carefully, securely capture the debris (either by deploying a net or harpoon that will hook it, or a grapple that will grab it), then drop down to a fiery disposal during re-entry.

ESA put together a nice video explaining the concept:

I think this is a good step in reducing the problem. Bear in mind it's one step; the problem of small (centimeter-sized) debris is still a huge one. There are quite a few ideas floating around (so to speak) on how to mitigate that, including using lasers to heat up the debris and change their orbit, dropping them down into the atmosphere to burn up, and a Japanese idea to use a space tether to create an electromagnetic field that alters the orbits of debris. It would also help to create satellites that shed less debris in the first place, and ESA is looking into that as well.

I'm all for that. If we go about business as usual, the space around Earth will get clogged with material, making routine access to space more dangerous. Something must be done, and it's nice to see government agencies taking it seriously.

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What Do You Do With a Problem Like Space Debris?

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Space junk is becoming a real problem. It's a serious issue. There's a common misconception that things in space are just kindof floating out there, moving slowly-and given videos of spacewalks and what we see in movies, that's understandable. But it's wrong. There are thousands of satellites orbiting the Earth, moving at incredibly high speeds.

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Researchers at The Australian National University (ANU) have harnessed a technique that helps telescopes see objects in the night sky more clearly to fight against dangerous and costly space debris.

"Adaptive optics is like removing the twinkle from the stars."

The researchers' work on adaptive optics - which removes the haziness caused by turbulence in the atmosphere - has been applied to a new 'guide star' laser for better identifying, tracking and safely moving space debris.

Space debris is a major threat to the $US700 billion of space infrastructure delivering vital services around the globe each day. With laser guide star adaptive optics, this infrastructure now has a new line of defense.

The optics that focus and direct the guide star laser have been developed by the ANU researchers with colleagues from Electro Optic Systems (EOS), RMIT University, Japan, and the USA as part of the Space Environment Research Centre (SERC).

EOS will now commercialize the new guide star laser technology, which could also be incorporated in tool kits to enable high-bandwidth ground to space satellite communications.

The laser beams used for tracking space junk use infrared light and aren't visible. In contrast, the new guide star laser, which is mounted on a telescope, propagates a visible orange beam into the night sky to create an artificial star that can be used to accurately measure light distortion between Earth and space.

This guiding orange light enables adaptive optics to sharpen images of space debris. It can also guide a second, more powerful infra-red laser beam through the atmosphere to precisely track space debris or even safely move them out of orbit to avoid collisions with other debris and eventually burn up in the atmosphere.

Lead researcher, Professor Celine D'Orgeville from ANU, says adaptive optics is like "removing the twinkle from the stars."

"But that's a good thing," Professor D'Orgeville said.

"Without adaptive optics, a telescope sees an object in space like a blob of light. This is because our atmosphere distorts the light traveling between the Earth and those objects.

"But with adaptive optics, these objects become easier to see and their images become a lot sharper. Essentially, adaptive optics cuts through the distortion in our atmosphere, making sure we can clearly see the incredible images our powerful telescopes capture.

"This includes small, human-made objects - like weather and communication satellites, or space junk.

"That's why this development is such an important breakthrough when it comes to our efforts to clear our night skies of the ever-increasing clutter of space debris."

The EOS guide star laser and the ANU adaptive optics systems are located at the ANU Mount Stromlo Observatory in Canberra, Australia.

The ANU researchers will now work with EOS to test the new technology and apply it to a range of other applications including laser communications between the Earth and space.

It's an exciting development that will help to safeguard the wide range of vital applications of space technology in the 21st century.
The research was funded by the Australian Government's Cooperative Research Centre Program, EOS, ANU, RMIT University and partners in Japan and the USA.

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New Laser to Help Clear the Sky of Space Debris

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Researchers at The Australian National University (ANU) have harnessed a technique that helps telescopes see objects in the night sky more clearly to fight against dangerous and costly space debris. "Adaptive optics is like removing the twinkle from the stars." The researchers' work on adaptiv

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www.machinedesign.com is using a security service for protection against online attacks. This process is automatic. You will be redirected once the validation is complete.

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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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Research Paper - ElectroDynamic Debris Eliminator (EDDE):Design, Operation, and Ground Support 

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Research Paper - ElectroDynamic Debris Eliminator (EDDE):Design, Operation, and Ground Support 

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www.machinedesign.com is using a security service for protection against online attacks. This process is automatic. You will be redirected once the validation is complete.

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Shen Shuangyan is a Ph.D. student at the Equipment Academy. His main research interest is laser propulsion and application.

Jin Xing is a professor at the Equipment Academy. His main research interest is advanced propulsion technologies.

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Cleaning space debris with a space-based laser system

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Shen Shuangyan is a Ph.D. student at the Equipment Academy. His main research interest is laser propulsion and application. Jin Xing is a professor at the Equipment Academy. His main research interest is advanced propulsion technologies.

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How do solar sails work? Bill Nye explains.

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The major advantage of a solar-sail spacecraft is its ability to travel between the planets and to the stars without carrying fuel. Solar-sail spacecraft need only a conventional launch vehicle to get into Earth orbit, where the solar sails can be deployed and the spacecraft sent on its way. These spacecraft accelerate gradually, unlike conventional chemical rockets, which offer extremely quick acceleration. So for a fast trip to Mars, a solar-sail spacecraft offers no advantage over a conventional chemical rocket. However, if you need to carry a large payload to Mars and you're not in a hurry, a solar-sail spacecraft is ideal. As for traveling the greater distances necessary to reach the stars, solar-sail spacecraft, which have gradual but constant acceleration, can achieve greater velocities than conventional chemical rockets and so can span the distance in less time. Ultimately, solar-sail technology will make interstellar flights and shuttling between planets less expensive and therefore more practical than conventional chemical rockets.

Related HowStuffWorks Links

Other Great Links
The Planetary Society Solar Sail information

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The major advantage of a solar-sail spacecraft is its ability to travel between the planets and to the stars without carrying fuel. Solar-sail spacecraft need only a conventional launch vehicle to get into Earth orbit, where the solar sails can be deployed and the spacecraft sent on its way.

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Thousands of small-sized pieces of Space debris orbit around the Earth, posing a threat to satellites. Using Earth-based lasers, an EU-funded project expects to do a proper clean-up.

Industrial Technologies

Current Space debris monitoring systems rely on catalogues that mainly contain data from radars and passive optical technology. Removal of debris in the low Earth orbit by laser illumination requires precise knowledge of the object position and trajectory during and after orbit modification. High-precision tracking of centimetre-based debris can be provided by active optical systems. Development of this technology paves the way for laser-based debris removal. The EU-funded project CLEANSPACE (Small debris removal by laser illumination and complementary technologie) looked into the role laser technology plays in removing small debris. The project defined a global architecture for surveillance, identification and tracking to be used with a ground-based laser protection system. Scientists defined a technology roadmap of the laser system for taking debris out of orbit - a main part of the debris removal concept. In essence, a laser pulse creates a small thrust on space debris by surface ablation. This should change its course, avoiding collision while simultaneously starting the process of atmospheric re-entry (desorbitation). CLEANSPACE introduced innovative concepts at the technical level. Researchers studied laser-matter interaction in a vacuum and demonstrated coherent coupling of laser beams of moderate energy. Furthermore, they demonstrated the suitability of ceramic technology to develop large-size samples with a complex shape and luminescent dopant repartition. An international organisation was proposed to ensure lasting international support and a smooth debris removal process. Simulation tools were developed to predict the change in trajectory for single-pass operation. The project performed four experiments. One was named debris tracking mock-up, one showed the laser ablation propulsion, one was a thin-disk laser and finally one demonstrated the coherent coupling of nine lasers. The CLEANSPACE roadmap for developing a laser-based Space debris removal system should help protect EU Space assets from collisions. In the long term, it just might enable continued Space missions that would otherwise have become impossible because of increasing debris.

Keywords

Laser, Space debris, tracking, surface ablation, laser-matter interaction, simulation

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Laser technology to remove orbital debris | CLEANSPACE Project | Results in brief | FP7 | CORDIS | European Commission

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Thousands of small-sized pieces of Space debris orbit around the Earth, posing a threat to satellites. Using Earth-based lasers, an EU-funded project expects to do a proper clean-up. Industrial Technologies Current Space debris monitoring systems rely on catalogues that mainly contain data from radars and passive optical technology.

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The easiest (and probably best) way to deal with the space junk problem is to stop producing space junk in the first place. We're trying to do that, which is great. But even if space agencies and commercial launch companies all commit, tomorrow, to rockets and satellites that will deorbit themselves after no more than 25 years, there's still all kinds of debris flying around up there, threatening our orbital infrastructure.

Many ways of dealing with orbital debris have been proposed, and some are even being tried out. Researchers working at RIKEN, a research institution in Japan, are leading an international team that wants to put a laser cannon on the International Space Station to try to shoot down small pieces of junk on the fly.

One of the most difficult parts of dealing with space junk is finding it in the first place. To then shoot it with a laser at a distance of 100 kilometers or more, you have to be able to track it very precisely, which necessitates a very sensitive wide-angle optical telescope. Fortunately, the ISS is about to get one. EUSO, the Extreme Universe Space Observatory, will be installed on the ISS in 2017, and the researchers at RIKEN must have said to themselves, "hey, we could slap a laser on that thing and blast space junk." So they're going to give it a try.

RIKEN plans to use a fiber laser originally developed to drive particle accelerators and mount it along side of EUSO. During twilight, EUSO will look for the telltale twinkle of small bits of debris reflecting sunlight, and send targeting information to the laser, which zaps them. If a 20% scale proof of concept laser system is successful in space, a version 100 times stronger will be installed next.
Illustration: RIKEN
"Our proposal is radically different from the more conventional approach that is ground based," says RIKEN lead researcher Toshikazu Ebisuzaki. "We believe it is a more manageable approach that will be accurate, fast, and cheap."

The laser wouldn't have to utterly annihilate pieces of space junk to be effective. Instead, it performs "high-velocity plasma ablation" on junk, meaning that the laser vaporizes just a little bit off of the surface of the junk with each shot. The vaporization results in a tiny puff that acts like an itty bitty (and very short lived) rocket engine in microgravity. As long as the ISS is in a higher orbit than the space junk, or orbiting ahead of it, a few puffs is enough to cause the junk to begin to deorbit itself.

Without a bigger laser, the ISS system will only be able to handle debris up to a maximum size of about a centimeter. Centimeter-scale orbital debris is particularly dangerous, because it's small enough to be hard to keep track of but large enough to punch holes in just about anything it hits. It's the sort of stuff that gets created when things accidentally smash into other things and explode. This has only happened a few times, but considering how much space is in space (a lot), the fact that it's happened at all is testament to the amount of junk that's flying around up there. Beyond a certain point, there will have been enough collisions generating enough debris that there will be no way to stop a runaway chain reaction. The technical term for this is the Kessler effect, and the less technical term for this is spacejunkpocalypse. And once we hit this point, it could render much of Earth orbit impassable.

One small space-based laser is certainly not going to solve the orbital debris problem. Ultimately, it may not even be the best way to go about dealing with orbital debris at all. What's important is that we're starting to experimentally determine how to tackle this problem, and if the full scale tests on the ISS go well, a free-flying satellite could eventually be placed into an 800km polar orbit. A dedicated system like this, according to Ebisuzaki, "could remove most of the centimeter-sized debris within five years of operation."

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Proposal Would Put Laser Cannon on ISS to Blast Space Junk

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The easiest (and probably best) way to deal with the space junk problem is to stop producing space junk in the first place. We're trying to do that, which is great.

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Bill Nye Explains the Science Behind Solar Sails | WIRED

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Video - Building CubeSats to test electrodynamic tethering in space with MiTEE

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Video - Building CubeSats to test electrodynamic tethering in space with MiTEE

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Building CubeSats to test electrodynamic tethering in space with MiTEE

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Demonstration designs for the remediation of space debris from the International Space Station

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We present here designs for a staged implementation of an orbiting debris remediation system comprised of a super-wide field-of-view telescope (EUSO) and a novel high efficiency fibre-based laser system (CAN). Initial proof of concept stages will operate from the International Space Station (ISS) wh…

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How Solar Sails Are Remaking Space Exploration

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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."

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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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Solar-Propelled Invention Designed to Clean Up Space Trash

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Solar-Propelled Invention Designed to Clean Up Space Trash

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A sail that unfurls itself to propel a cube satellite using the sun's power - developed by Embry-Riddle Aeronautical University researchers - suggests a sustainable way to remove dangerous debris from space for years at a time.

More than 27,000 pieces of orbital debris currently litter space, NASA has reported. In low Earth orbit, space junk can travel up to 15,700 miles per hour, creating serious hazards for spacecraft and astronauts.

To clean up some of that junk, Embry-Riddle student researchers Ankit Rukhaiyar and Jonathon G. Nadeau created a prototype technology that would use nearly infinite solar energy to autonomously sail around low Earth orbit aboard a cube satellite (CubeSat), nabbing garbage.
Graduate student Ankit Rukhaiyar serves as co-lead on the project to develop the solar-powered CubeSat prototype. (Photo: Embry-Riddle/David Massey)
The "deployable solar sail" concept was suggested by Michael Dupuis of NASA's Kennedy Space Center during discussions with students at Embry-Riddle's Engineering Physics Propulsion Lab (EPPL).

"There is a big problem with space debris," said EPPL Director Dr. Sergey Drakunov, professor of Engineering Physics. "We want to get a spacecraft into the space debris field, capture an object using robotics and leverage solar pressure radiation to bring that junk to a lower altitude, so that it can de-orbit by itself."

A fleet of CubeSats with deployable solar sails could cruise around in space, autonomously conducting long-term missions, Rukhaiyar said. "Because they are propelled by solar radiation, the cleanup technology would not require fuel and it's only limited by the survivability of the hardware components," he explained. "At the end of its mission life cycle, with the sail deployed, the CubeSat could re-enter the atmosphere and burn up, thus preventing it from becoming space junk itself."

Radiation pressure from the sun would speed up or slow down the CubeSat's orbit, depending on whether the sail faces toward or away from the sun. "You would keep switching modes to bring debris down to about 300 kilometers above the Earth, where atmospheric drag would burn it up," said Rukhaiyar, who recently earned his master's degree and will soon become a Ph.D. student at Embry-Riddle. "Radiation pressure is pretty much constant on Earth, so we should have enough radiation pressure to complete long-term cleanup missions."

Solar power "makes it possible to increase the spacecraft's orbit for free, without using the fuel," Drakunov noted. Heavy spacecraft must otherwise be launched into orbit using large amounts of expensive fuel.

Embry-Riddle's prototype version, intended for technology demonstrations, uses a small (6U) CubeSat and a 32-meter sail. In tests, the prototype solar sail unfurled efficiently and as expected. Rukhaiyar and Nadeau worked with other students to painstakingly test their designs, which were informed by NASA concepts.

Now, researchers have a goal to increase the speed of the technology and standardize the manufacturing of ding-proof sails.
A solar-powered sail that deploys during its orbit around the Earth in order to catch space debris is pictured here. (Photo: Embry-Riddle)
While solar power is at the heart of the invention, Drakunov said that student power was the real key to success. "Students like Ankit and Jonathon come to Embry-Riddle with all their enthusiasm and they do great things," he said. "They took an idea from NASA and they tested and tested it. During the pandemic, they had to work in masks and separated from others. Their hard work will advance space technology, and they are also helping to inspire another generation of student researchers."

With Ankit Rukhaiyar and Jonathan Nadeau, M. Catherine Yopp, Adam Duke, Kyle Fox, Dylan Ballback and Michael Tomaso co-authored the pre-print article that describes this research, along with Drakunov and Dr. Patrick Currier, associate professor and associate chair of Mechanical Engineering at Embry-Riddle.

Other contributors to the research have included Embry-Riddle Ph.D. student and Firefly Aerospace Director of Design and Analysis Brigette Oakes, alumna Michelle Nadeau and graduate student Kayla Ormiston.

To date, the solar sail research has been internally funded by Embry-Riddle's College of Arts and Sciences, College of Engineering, and Council of Philanthropy.
Engineering Physics Propulsion Lab
Since 2015, Embry-Riddle's Engineering Physics Propulsion Lab (EPPL) has been advancing innovative space-propulsion methods and related feedback control to support space exploration and aeronautics. EPPL research has included advanced control systems for spacecraft, space-based autonomous systems, prototype space robots for asteroid mining and spacecraft in-orbit repair systems. The lab uses Virtual Reality and Augmented Reality tools to mimic space and planetary environments and enhance human-machine interactions for space missions.

Posted In: Engineering | Space

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Solar-Propelled Invention Designed to Clean Up Space Trash

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A sail that unfurls itself to propel a cube satellite using the sun's power - developed by Embry-Riddle Aeronautical University researchers - suggests a sustainable way to remove dangerous debris from space for years at a time. More than 27,000 pieces of orbital debris currently litter space, NASA has reported.

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Enhancement on spacecraft propulsion technology "solar sails" will likely lead to novel interstellar missions. UCLA Engineering professor Artur Davoyan led a team of scientists offering insights on how to improve solar sails to propel future spacecraft across the solar system with great velocity.

Optica recently published the overview. Davoyan and his co-authors focused on the need for a new generation of photonic materials, which carry and manipulate light, to advance next generation solar sails.

"With proper investments in research and development of optical materials and nanotechnology, solar sail-enabled spacecraft for fast-transit solar-system exploration and interstellar-probe missions could be launched in the next five to 10 years," said lead author Davoyan, an assistant professor of mechanical and aerospace engineering at the UCLA Samueli School of Engineering. "In this paper, we've presented a roadmap that can transform these concepts into reality."

Solar sails are similar to the sails found on oceangoing ships. Rather than being pushed by wind, however, solar sails are propelled by sunlight reflected off their giant mirrored surfaces. There are distinct advantages for solar sail-propelled spacecraft. The method eliminates the need to carry onboard fuel and power, as is the case for both chemical and electrical rockets. Several spacecraft using solar sails have been launched, with LightSail 2 being the most recent demonstration. However, future solar sail missions would require new materials and methods for control and navigation.

Spacecraft driven by solar sails could potentially go fast enough to reach more than 20 astronomical units - approximately 1.86 billion miles - in one year. At that speed, spacecraft could get to the outer planets of the solar system in several months, instead of taking many years as it does today. For comparison, Voyager 1 took more than 30 years to reach the interstellar medium beyond the edge of the solar system.

Up to now, interstellar objects have been beyond reach. According to Davoyan, solar sail-propelled spacecraft, with its unprecedentedly high velocity, could intercept interstellar asteroids, such as 'Oumuamua, that travel at 5-6 astronomical units - approximately 500 million miles - per year.

In order to advance current solar sail technology, enhancement is needed on multipurpose materials used to manage a spacecraft's movements and temperature. For example, sails built out of thin film materials with nanoscale adjustable elements could help control a spacecraft's speed and direction. At the same time, those materials could help keep the sails cool as the spacecraft approaches the sun for a slingshot maneuver to get beyond the solar system.

The authors also noted that concurrent advancements for solar sail-powered spacecraft would need to be considered for sail-deployment mechanisms, deep-space communications, and power and navigation systems.

NASA recently announced its support for this line of research through the agency's highly competitive Innovative Advanced Concepts program. Specifically, a solar sail-mission study led by Davoyan has been selected for phase II.

Davoyan's team, which includes scientists and a number of UCLA mechanical and aerospace engineering undergraduate students, will examine solar-sail requirements for fast transit missions across the solar system and will perform early-stage materials development and testing.

Co-authors of the paper published in Optica include Jeremy Munday of UC Davis; Nelson Tabiryan of BEAM Co. in Orlando, Florida; Grover Swartzlander, Jr. of the Rochester Institute of Technology in New York; and Les Johnson of NASA's Marshall Space Flight Center in Huntsville, Alabama.

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Reinventing Solar Sail Technology to Push Space Exploration Boundaries

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Enhancement on spacecraft propulsion technology "solar sails" will likely lead to novel interstellar missions. UCLA Engineering professor Artur Davoyan led a team of scientists offering insights on how to improve solar sails to propel future spacecraft across the solar system with great velocity. Optica recently published the overview.

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Research paper - Strategy for Active Debris Removal Using Electrodynamic Tether

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Research paper - Strategy for Active Debris Removal Using Electrodynamic Tether

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The physics behind solar sails

Introduction | Solar Sail Physics

Solar sails harness light photons on a large surface called a sail. When light hits the reflective layer of a solar sail there is a force applied to the solar sail due to the lights enormous speed. Lasers can also be used to propel a solar sailed powered spacecraft. When the photon hits the reflective layer, most of the photons bounce off the perpendicular to the sail surface. The photons that are not reflected are absorbed, then emitted though the emissivity layer in the form of thermal energy which has a negative effect on the spacecraft's speed as it produces a negative effect. It is important to note that solar sails are extremely dependent on light as a source of fuel, the further you get away from the light source the less efficient the sails become because less photons hit the sail. If there is very little light intensity, the sails will accelerate at a slower rate than before. When there are no photons hitting the sail, the spacecraft will still travel through space, but without acceleration, it will decrease in speed, becoming extremely slow because space is not 100% vacuum. For instance, Jupiter has about 1/24 the amount of light intensity of Earth, so a spacecraft by Jupiter would have to be 24x larger to produce a similar force of a solar sail close to Earth. Solar sails have a maximum speed which is 10% the speed of light, which equates to 18,600 miles per second or, 67,100,000 mph. Solar powered spacecrafts are able to travel faster than conventional rocket fueled spacecrafts due to constant light pressure being applied to the sail propelling it forward.

Diagrams | Light reflecting off Solar Sail

Forces and Momentum | How it works

Initial Momentum

The initial momentum is the momentum of protons from a light source. This momentum applies a force into the solar sail.

Reaction Momentum

Reaction momentum is the reaction from the initial momentum from the light source. The reaction momentum is always perpendicular to the solar sail's surface, as seen in case 2 diagram.

Reaction Force

The reaction force is thermal energy which is due to the solar sail being heated up. The emissivity layer emits thermal heat, which creates a reaction force which is a negative force on the spacecraft trajectory.

Solar Sail

The solar sail is the spacecraft's propulsion that holds the reflection and emissivity layers.

Reflection Layer

The reflection layer is the material that faces the sun or incoming light, this surface reflects incoming photons and also takes in heat due to a reflective value less than 1.0 which is a perfect reflection.

Emissivity Layer

Emissivity layer faces away from the light source powering the solar sail. This layer emits thermal energy.

Physics | Calculations

Force of a Solar Sail | Calculating

Calculations to find the force of a solar sail.

Perfect Sail:

Nothing is perfect in our universe, a more realistic sail would have an equation similar to:

Realistic Sail:

Momentum | Light Particles

Reflectivity Scale

Light has an extremely small mass, basically zero, but it has an incredible high velocity. With such high, velocity light partials or photons have momentum.

Momentum of 0.0 reflectivity surface

Solar sails have a reflective layer which reflects the light particle, which produces even more momentum as it pushes off the reflective layer.

Momentum of 1.0 reflectivity surface

Force | Solar Sail

As momentum hits the solar sail it gives off a force, this force value is based on the reflectivity value of the reflective material and solar energy that hits the solar sail

The problem here does not take into account for gravitational forces, non perfect reflective surface, emissivity layer, and estimated atmospheric drag.

Velocity | Calculating the Velocity

Initial equation used to find velocity

Moving dv to the right side of the equation

Substituting mdv into the equation and mulitple the momentum by a factor of 2. This is due to the reaction momentum

Substituting

dV = LA

L = ct c = speed of light

t = time in seconds

substituting the speed of light into the equation and canceling one c in numerator

Let's assume the following for a spacecraft who just left earth, m = 70 lbs, using one large solar sail with a surface area of 124x124 feet and the sails are perfectly reflective.

Now we will plug in the numbers.

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The physics behind solar sails Introduction | Solar Sail Physics Solar sails harness light photons on a large surface called a sail. When light hits the reflective layer of a solar sail there is a force applied to the solar sail due to the lights enormous speed.

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In more than 50 years of spaceflight, over 30,000 t of satellites and rockets have been sent to space. It is estimated that near 3000 t [1] of non-functioning space debris remain in Low Earth Orbit (LEO) in varied forms ranging from fragments to spent rocket bodies and fully intact multi-ton satellites. Since their orbital velocities are very high, collisions can involve relative impact velocities of the order of 10 km/s as shown in Fig. 1(a), even the fragments with greater than MJ kinetic energies may cause a severe or catastrophic damage on functioning satellites such as the International Space Station (ISS). In fact, in 1993, the Inter-Agency Space Debris Coordination Committee was established and the discussions concerning control of space debris among space agencies have started.

From a combination of techniques including ground-based radar, surface-impact measurements and statistical modelling the number of debris above 1 cm in size is estimated as >. For most spacecraft, including the ISS, debris smaller than 1 cm can be tolerated with adequate shielding. Objects larger than 10 cm can be mitigated using collision avoidance manoeuvres if such debris are first identified and tracked. However, the great majority are not known or catalogued, especially debris with sizes <10 cm, and hence these hyper-velocity projectiles pose an increasing risk to spacecraft as their population builds. This problem is mounting, since the triggered destruction of a number of satellites in LEO over the last decade including Iridium 33, Cosmos 2251 and Fengyun-1 C. Such large objects are the main source of new debris when hit by numerous smaller fragments in LEO. The small cm-size debris are thus the main threat for impacting the functioning and derelict payloads. The evolution of this population is shown in Fig. 1(b). Much of the increase after 2000 is attributed to the breakup of the aforementioned satellites with significant increases seen for the sun-synchronous polar orbit near 800 km altitude.

Due to their small size and high relative velocity (up to 10 times that of a bullet) there are few viable solutions to remove these projectiles before they collide with larger satellites. The laser impulse control is perhaps such a candidate for remediation of their orbits. Here pulsed ablation of the debris surface leads to a momentum transfer via the rocket effect. If the orbital velocity is sufficiently reduced, reduction in the altitude of the debris׳s perigee will enable atmospheric re-entry. With laser pulse thrust of ⪡1 N, a rapid train of pulses is required to deliver a total Δ v≈10 2 m/s.

Since the late 1980s a number of designs for delivering laser pulses to debris have been proposed operating either from ground-based or space-based. For the latter case, this began with Metzger et al. [3] who proposed a nuclear-powered debris-sweeper with a 10 kJ, 1 Hz krypton fluoride laser ( of 248 nm). Recently, Phipps [4] proposed a solar-powered space-based system L׳ADROIT to be launched consisting of a super-wide-field debris detector with a powerful Nd-Yag laser system with pulse energy of ~38 J or more. Schall [5] was the first to propose to use the ISS as a platform for testing debris sweeping technology.

Here in this present paper, we propose to implement a staged approach for evaluating such space based concepts utilising a large wide-field of view detector in tandem with a short pulsed laser beginning with prototypes on-board the ISS as depicted in Fig. 2. At the ISS altitude near 400 km the combined remediation technology can be tested and improved prior to a future design and deployment of freely orbiting systems at higher altitudes such as near 800 km where the debris population in LEO peaks.

Precision determination of debris position and trajectories is a necessity both in the case of avoidance manoeuvres and for attempts at remediation. Here we propose to apply the technology developed for the JEM-EUSO (Extreme Universe Space Observatory on-board Japanese Experiment Module, hereafter EUSO telescope) and designed for the ISS. The JEM-EUSO mission is to detect UV light emitted from the extensive air-showers produced by the ultra-high energy cosmic rays entering the atmosphere at night [7], [8]. This detector has a super wide-field of view (FoV) as large as ±30° with three double-side Fresnel lenses and a short time resolution down to a few with highly pixelized photo-multipliers. During daylight operation, this same detector can provide a unique technology for the detection and position determination of the non-catalogued debris from orbit. Pulsed laser technology has rapidly advanced in the last two decades and it allows us now to consider a space-borne pulsed-laser system. In fact, Soulard et al. [9] proposed to use a space-based laser system applying their Coherent Amplifying Network (CAN) fibre-based technology. A CAN laser is comprised of an array of fibres, each producing a laser beam of ~1 mJ, which is phase combined into a beam of total energy of a 1-100 J. Excellent electrical efficiency approaching 30% and a repetition rate higher than 10 kHz are possible which is an ideal solution method for tracking, and impulse delivery to the high velocity debris. Both of these instruments, EUSO and CAN, have been designed for applications in independent physics experiments which are on-going in their development.

This paper is organised as follows. In Section 2, we describe the method of the detection, tracking, and laser impulse control of small debris. In Section 3, a proof-of-principle prototype is described utilising the mini-EUSO telescope which will be installed on the ISS together with a scaled down CAN laser. In Section 4, we present a full scale system designed to test impulse delivery to small space debris from the ISS. In Section 5, we mention a free-flyer mission, dedicated to debris remediation in a polar orbit with the altitude of near 800 km and evaluation of its performance.

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Demonstration designs for the remediation of space debris from the International Space Station

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In more than 50 years of spaceflight, over 30,000 t of satellites and rockets have been sent to space. It is estimated that near 3000 t [1] of non-functioning space debris remain in Low Earth Orbit (LEO) in varied forms ranging from fragments to spent rocket bodies and fully intact multi-ton satellites.

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Research Paper - Use of Electrodynamic Tethers for Satellite End of LifeDeorbit Maneuvers

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Research Paper - Use of Electrodynamic Tethers for Satellite End of LifeDeorbit Maneuvers

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An international team of scientists have put forward a blueprint for a purely space-based system to solve the growing problem of space debris. The proposal, published in Acta Astronautica, combines a super-wide field-of-view telescope, developed by RIKEN's EUSO team, which will be used to detect objects, and a recently developed high-efficiency laser system, the CAN laser that was presented in Nature Photonics in 2013, that will be used to track space debris and remove it from orbit.
Space debris, which is continuously accumulating as a result of human space activities, consists of artificial objects orbiting the earth. The number of objects nearly doubled from 2000 to 2014 and they have become a major obstacle to space development. The total mass of space debris is calculated to be about 3,000 tons. It consists of derelict satellites, rocket bodies and parts, and small fragments produced by collisions between debris.

Because the debris exists in different orbits, it is difficult to capture. The objects can collide with space infrastructure such as the International Space Station (ISS) and active satellites. As a result, developing remediation technology has become a major challenge. The EUSO telescope, which will be used to find debris, was originally planned to detect ultraviolet light emitted from air showers produced by ultra-high energy cosmic rays entering the atmosphere at night. "We realized," says Toshikazu Ebisuzaki, who led the effort, "that we could put it to another use. During twilight, thanks to EUSO's wide field of view and powerful optics, we could adapt it to the new mission of detecting high-velocity debris in orbit near the ISS."

The second part of the experiment, the CAN laser, was originally developed to power particle accelerators. It consists of bundles of optical fibers that act in concert to efficiently produce powerful laser pulses. It achieves both high power and a high repetition rate.

The new method combining these two instruments will be capable of tracking down and deorbiting the most dangerous space debris, around the size of one centimeter. The intense laser beam focused on the debris will produce high-velocity plasma ablation, and the reaction force will reduce its orbital velocity, leading to its reentry into the earth's atmosphere.

The group plans to deploy a small proof-of-concept experiment on the ISS, with a small, 20-centimeter version of the EUSO telescope and a laser with 100 fibers. "If that goes well," says Ebisuzaki, "we plan to install a full-scale version on the ISS, incorporating a three-meter telescope and a laser with 10,000 fibers, giving it the ability to deorbit debris with a range of approximately 100 kilometers. Looking further to the future, we could create a free-flyer mission and put it into a polar orbit at an altitude near 800 kilometers, where the greatest concentration of debris is found."

According to Ebisuzaki, "Our proposal is radically different from the more conventional approach that is ground based, and we believe it is a more manageable approach that will be accurate, fast, and cheap. We may finally have a way to stop the headache of rapidly growing space debris that endangers space activities. We believe that this dedicated system could remove most of the centimeter-sized debris within five years of operation."

The research was done by Toshikazu Ebisuzaki, Satoshi Wada, Lech Wiktor Piotrowski, Yoshiyuki Takizawa, and Marco Casolino of RIKEN, Toshiki Tajima of the University of California at Irvine, Mark N. Quinn, Remi Soulard and Gerard Mourou of IZEST EcolePolytechnique, Philippe Gorodetzky and Etienne Parizot of The AstroParticle and Cosmology laboratory/University of Paris 7, and Mario Bertaina of the University of Torino.

Reference

Toshikazu Ebisuzaki, Mark N. Quinn, Satoshi Wada, Lech Wiktor Piotrowski, Yoshiyuki Takizawa, Marco Casolino, Mario E. Bertaina, Philippe Gorodetzky, Etienne Parizot, Toshiki Tajima, Rémi Soulard, and Gérard Mourou, Demonstration designs for the remediation of space debris from the International Space Station, Acta Astronautica, doi:10.1016/j.actaastro.2015.03.004

Contact

Chief Scientist
Toshikazu Ebisuzaki
Computational Astrophysics Laboratory
Chief Scientist Laboratories

Jens Wilkinson
RIKEN Global Relations and Research Coordination Office
Tel: +81-(0)48-462-1225 / Fax: +81-(0)48-463-3687
Email: pr@riken.jp
Graph showing how space debris is growing year by year Schematic of the proposed system based on the EUSO telescope and a CAN laser system The EUSO telescope

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A blueprint for clearing the skies of space debris

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An international team of scientists have put forward a blueprint for a purely space-based system to solve the growing problem of space debris. The proposal, published in Acta Astronautica, combines a super-wide field-of-view telescope, developed by RIKEN's EUSO team, which will be used to detect objects, and a recently developed high-efficiency laser system, the CAN laser that was presented in Nature Photonics in 2013, that will be used to track space debris and remove it from orbit.

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Kilometer-Long Space Tether Tests Fuel-Free Propulsion

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Kilometer-Long Space Tether Tests Fuel-Free Propulsion

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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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Design and development today - Space Tether Could Prevent Dead Satellites from Hitting Earth

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Design and development today - Space Tether Could Prevent Dead Satellites from Hitting Earth

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The E.T.PACK-Fly consortium, coordinated by the Universidad Carlos III de Madrid (UC3M) and made up of the University of Padova, the Technical University of Dresden (TU Dresden), the Spanish company SENER Aeroespacial and the German start-up Rocket Factory Augsburg (RFA), has received €2.5 million from the European Innovation Council (EIC) to develop a device based on a space tether to deorbit space debris.

Due to the high cost involved, most satellites are not removed after their mission is completed. This fact, together with spontaneous explosions in orbits as a result of the harsh space environment, has caused the accumulation of a high number of space debris in Low Earth Orbit. They represent a threat since, when a collision occurs between two objects in orbit, a cloud of dangerous shrapnels for operational satellites is generated.

E.T. PACK-Fly aims to solve this problem by developing a device capable of deorbiting, that is, decreasing the altitude of the orbit of the space debris until it is eliminated during the reentry in the Earth's atmosphere. Unlike conventional propulsion systems, the E.T. PACK-Fly equipment uses a disruptive technology, known as an electrodynamic space tether, that does not require propellant. This electrodynamic tether is a very thin aluminium tape (about two centimetres wide and a couple of kilometres long), which works by using the plasma around the Earth and the geomagnetic field to generate an electric current. This electrodynamic effect results in a force known as the Lorentz drag. This force deorbits the satellite up to the reentry into the Earth's atmosphere, where it is eliminated by the heat generated by this process. The tether is the fundamental part of the deorbiting device which, since it does not require fuel, is small and light. It is also designed to stabilise the attitude of the satellite, and to control the deorbiting manoeuvre in order to avoid possible collisions with other objects.

The European Innovation Council (EIC) has funded the E.T. PACK-Fly project through its EIC Transition programme. With a duration of two and a half years, the project will start in September 2022 and it aims to prepare the flight model of a deorbit device to be launched into orbit in 2025. RFA and SENER Aeroespacial have already signed the launch service agreement. The E.T. PACK-Fly project is the continuation of the E.T. PACK project, also funded by the EIC. A first prototype of the deorbit device was developed and built in the framework of E.T.PACK. "We are very grateful to the EIC for the trust it has placed in us and its commitment to the development of technologies that allow a sustainable use of the space environment", says Gonzalo Sánchez Arriaga, Associate Professor at UC3M and coordinator of the E.T. PACK and E.T. PACK-Fly projects. "It is important to invest in disruptive technologies that can mitigate the proliferation of space debris while generating wealth and new business opportunities," he concludes.

Furthermore, Lorenzo Tarabini, director of the E.T.PACK-Fly project at SENER Aeroespacial, points out: "This project gives us the opportunity to build and qualify for space, through a complete series of tests, a light, compact and completely autonomous platform for deorbiting the final stages of launchers. The E.T.PACK-Fly platform is expected to be launched in 2025 with RFA to demonstrate its proficiency and pave the way for commercial exploitation of deorbiting technology." In the same vein, the CCO at RFA Jörn Spurmann adds that "we are very pleased that this innovative initiative will continue to receive funding to take it to the next level. Space debris removal is one of the most pressing challenges in space and it is part of RFA's philosophy and vision to enable sustainable solutions like E.T-PACK".

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Space Tether Could Prevent Dead Satellites from Hitting Earth

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The E.T.PACK-Fly consortium, coordinated by the Universidad Carlos III de Madrid (UC3M) and made up of the University of Padova, the Technical University of Dresden (TU Dresden), the Spanish company SENER Aeroespacial and the German start-up Rocket Factory Augsburg (RFA), has received €2.5 million from the European Innovation Council (EIC) to develop a device based on a space tether to deorbit space debris.

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Don't let the name fool you; despite their small size, dwarf planets are worlds that are just as compelling as their larger siblings. Dwarf planets are defined by astronomers as bodies massive enough to be shaped by gravity into a round or nearly round shape, but they don't have enough of their own gravitational muscle to clear their path of other objects as they orbit the Sun. In our solar system, dwarf planets are mostly found in the Kuiper Belt beyond Neptune; Pluto is the best-known example. But the largest object in the asteroid belt is the dwarf planet Ceres. Like Pluto, Ceres shows signs of active geology, including ice volcanoes.

Besides Pluto, some of the mysterious worlds of the Kuiper Belt include dwarf planets Makemake, Haumea, and Eris. Like asteroids and comets, Kuiper Belt objects are time capsules, perhaps kept even more pristine in their icy realm.

OSIRIS-REx - Now heading home to Earth from asteroid Bennu where it retrieved a sample.

New Horizons - On Jan. 1, 2019, the spacecraft flew by the small Kuiper Belt object officially known as Arrokoth - or by its original designation (486958) 2014 MU69 - the most distant and most primitive object ever explored by a spacecraft. Images showed a double-lobed object that looked like a partially flattened snowman.

Psyche - The spacecraft will explore a metallic asteroid of the same name, which may be the ejected core of a baby planet that was destroyed long ago.

Lucy - Lucy was launched on Oct 16, 2021, on the first space mission to explore a population of small bodies known as the Trojans. The Trojans are outer solar system asteroids that orbit the Sun "in front of" and "behind" the gas giant Jupiter, at the same distance from the Sun as Jupiter.

Dawn - Dawn launched in 2007 and visited two-time capsules of the solar system - asteroid Vesta and dwarf planet Ceres, the largest bodies of the main asteroid belt.

The Japan Aerospace Exploration Agency (JAXA)'s Hayabusa2 - The spacecraft studied asteroid Ryugu, collected samples, and brought them to Earth for analysis. The spacecraft is on an extended mission to asteroid 1998 KY26.

The European Space Agency (ESA)'s Rosetta - Orbited the comet 67P/Churyumov-Gerasimenko and dispatched a lander to its surface.

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10 Things: What's That Space Rock? - NASA Science

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The path through the solar system is a rocky road. Asteroids, comets, Kuiper Belt Objects-all kinds of small bodies of rock, metal and ice are in constant motion as they orbit the Sun. But what's the difference between them? Why do these miniature worlds fascinate space explorers so much?

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The latest LightSail mission gave us a glimpse into the future of solar sailing.

After three years in space, the Planetary Society's LightSail 2 mission burned up in the atmosphere on Thursday, November 17th. During its mission, the crowdfunded spacecraft made 18,000 orbits of the planet using its giant reflective sail and demonstrated that controlled solar sailing is possible.

LightSail may now be over, but it has opened the door to the use of solar sailing in space exploration. "It doesn't fit every situation, but now it gives another arrow in the quiver of options for types of propulsion you can use," said Bruce Betts, Chief Scientist and LightSail program manager.

LightSail 2 operated in Earth orbit, while future solar sailing missions would likely be in deep space. That makes the requirements somewhat different. "We had the challenge that's analogous to sailing a sailboat in the harbor versus out in the ocean," Betts said. LightSail had an easier time with issues like communications than deep space missions would but had to constantly turn to keep in orbit.

The biggest drawback in using solar sailing for space exploration is that the forces involved are so small that craft start out traveling very slowly. "The disadvantage is that you're using a push from the sun that is really, really tiny," Betts explained. "The push on our entire sail if it were reflecting perfectly, from the sun at Earth's distance, is about the same force that a housefly has when it's sitting on your hand, pushing down." But the advantage of the method is that this force just keeps building up over time, allowing acceleration up to high speeds without using up fuel.

Upcoming programs like NASA's NEA Scout and Advanced Composite Solar Sail System (ACS3) will also use solar sailing. The ideal targets for these kinds of missions are within the inner solar system, as the craft stays close enough to the sun to get enough force from the sunlight to keep moving and to change an orbit.

Another type of exploration solar sailing enables is entering orbits that would otherwise be impossible using conventional propulsion systems. Missions that orbit around the sun, for example, currently have to sit in very particular regions called Lagrange points to be in a stable orbit. Trying to get closer to the sun would use up too much fuel. But with a solar sail, a spacecraft can orbit closer to the sun and use its sail to maintain its orbit by making constant adjustments.

There's also plenty of room for improvement in solar sailing technologies. Researchers are eager to explore ideas such as the use of lasers to push at sails and the development of more sophisticated steering systems. Betts compared the LightSail program to learning to crawl, with the next wave of new technologies enabling the equivalent of walking.

In the extremely long term, one use for solar sailing is the potential to visit other star systems. Interstellar travel is still generations and generations away from being anything like a real possibility, with major technical challenges standing in the way of exploring beyond our solar system. Chemical propulsion systems like those used on the Voyager probes, the most distant man-made objects, would take tens of thousands of years to visit the nearest star systems. But spacecraft with solar sails could potentially reduce that timescale as they can continue to accelerate as they travel. "It's the only technology we've got so far that shows anything resembling practical ability to do that someday," Betts said.

As for more immediate uses, the most likely use of solar sailing isn't that it will replace chemical propulsion systems but that it'll be a viable option for use in certain specific missions.

"In 10 or 20 years, when people are planning a mission, they'll think about, 'Hey, would solar sailing work for that?' And for some of them, it will," Betts said. "It'll be part of the real choices for a science mission. And that's what we've contributed to with one step in the pioneering of this."

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LightSail 2 just met its fiery end, but solar sailing is just getting started

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After three years in space, the Planetary Society's LightSail 2 mission burned up in the atmosphere on Thursday, November 17th. During its mission, the crowdfunded spacecraft made 18,000 orbits of the planet using its giant reflective sail and demonstrated that controlled solar sailing is possible.

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Surrey Nanosats SSC Mission Delivery Team

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Space Lasers Is A Probable Solution For Space Junk

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Space junk is a real problem now. With millions of pieces of debris floating in Earth’s orbit, chances are they may hit something on their way up. The

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China just boosted a high-tech, mysterious new satellite into orbit. It might be a weapon. It might not be a weapon. There's no way to be certain, either way-and that's a problem for all spacefaring countries.

Especially the United States and China. Washington and Beijing are lofting more and more of these ambiguous satellites into orbit without agreements governing their use. In failing to agree to the proverbial rules of the orbital road, the two governments risk ongoing suspicion, or worse-a misunderstanding possibly leading to war.

The Roaming Dragon satellite rode into space atop a Long March 7 rocket that blasted off from Hainan in southern China on June 25. Officially, Roaming Dragon is a space-junk collector. Its job, according to Beijing, is to pluck old spacecraft and other debris from Earth's orbit and safely plunge them back to the planet's surface.

For sure, orbital debris poses a real hazard to the world's spacecraft. In the summer of 2015, astronauts aboard the International Space Station-including two Russians and an American- sought shelter inside an escape craft when a chunk of an old Russian satellite appeared to be on a collision course with the station.

Luckily, the debris missed the space station. All the same, NASA and other space agencies have voiced their concern over the accumulation of manmade junk in space-and have taken initial steps to remove the most dangerous chunks.

Hence Roaming Dragon's official mission. "China, as a responsible big country, has committed to the control and reduction of space debris," Tang Yagang, a scientist with the China Aerospace Science and Technology Corporation, wrote on the Chinese space agency's website.

But the Roaming Dragon's design-specifically, its maneuverability and its nimble, extendable robotic arm-mean it could also function as a weapon, zooming close to and dismantling satellites belonging to rival countries.

Stephen Chen, a reporter for the Hong Kong-based South China Morning Post-which has historically has been critical of the Chinese central government in Beijing- quoted an unnamed "researcher with the National Astronomical Observatories in Beijing" calling into question the satellite's purported peaceful mission.

"It is unrealistic to remove all space debris with robots," the anonymous researcher allegedly stated, implying that Roaming Dragon would, in reality, be doing something else up there in orbit.

But there's no way to prove that Roaming Dragon is a weapon until it actually attacks another satellite. And at that point, the world would surely have much bigger problems than mere spacecraft taxonomy, as an orbital ambush would almost certainly be a prelude to a much more destructive conflict on the surface.

"Space robotic arms, like many other space technologies, have both military and non-military applications, and classifying them as a space weapon depends on the intent of the user, not on the inherent capabilities of the technology," Kevin Pollpeter, deputy director of the Study of Innovation and Technology in China Project at the University of California, San Diego, wrote in a widely cited 2013 research paper.

"China's space robotic arm technology is thus a case study in the challenges of defining 'space weapon' and the difficulty in achieving space arms control," Pollpeter added.

It's an old problem, by space standards. Jeffrey Lewis, a strategic-weapons expert who blogs at Arms Control Wonk, pointed out in an email to The Daily Beast that NASA's space shuttle, which first launched into orbit in a dramatic test in 1981, inspired the same worry in Moscow that Roaming Dragon could inspire in Washington.

Specifically, Russian analysts questioned the purpose of the shuttle's famous "Canadarm"-the Canadian-made "Shuttle Remote Manipulator System" that prominently appears in many photos of the now-retired shuttle's cargo bay. American analysts are not wrong to point out the potential military applications of Roaming Dragon's robotic arm. But "the Russians said the same thing about the Canadian arm on the space shuttle," Lewis told The Daily Beast.

As far as we know, the space shuttle, which last flew in 2011, never attacked another spacecraft. Nor, apparently, have any of the many other spacecraft that possess arms and maneuverability similar to Roaming Dragon-the majority of which, it's worth noting, are American.

The proliferation of these spacecraft underscores a failure on the part of the world's governments to agree to orbital codes of conduct. "All the spacefaring countries are developing small satellites capable of conducting so-called autonomous proximity operations-and there are absolutely no rules about this," Lewis explained.

"If China wants to build an inspector satellite to shadow one of our warning satellites, that's just ducky as far as space law is concerned. In such an environment, even innocent programs will engender suspicion and initiate the basic arms race dynamics that threaten the use of space for everyone."

That suspicion is already having a very real effect on the U.S. defense establishment. Growing ever more fearful of a possible ambush in space, in early 2015 Deputy Defense Secretary Bob Work instructed John Hyten, the four-star general in charge of U.S. Air Force Space Command, to prepare his space operators and their satellites for a possible war in orbit.

But to a great extent, the paranoia is unjustified, according to Brian Weeden, a former Air Force space operator who is now a technical adviser to the Secure World Foundation in Colorado. "A lot of the so-called space weapons technologies that have been hyped by pundits or the media for decades are not actually very good weapons," Weeden told The Daily Beast in an email.

For starters, it's hard for a killer satellite to sneak up on one of America's own spacecraft, what with NASA and the Air Force constantly monitoring Earth's orbit via radar and telescope. "We would notice it maneuvering to match orbits with the target hours [or] days in advance," Weeden said.

For that reason, "there are better, faster, or cheaper ways to accomplish the same goal" of knocking out a satellite, Weeden added.

Ground-based rockets, for example. The same boosters that propel satellites into orbit can, if aimed carefully, strike and destroy spacecraft in certain orbits. China famously tested a so-called direct-ascent satellite-killing rocket in 2007, striking an old weather sat and scattering thousands of pieces of debris-ironically, the same kind of debris Roaming Dragon ostensibly was designed to help clean up.

"I still worry a lot more about China's direct-ascent ASAT," Lewis said, using a popular acronym for an anti-satellite weapon.

Contrary to the South China Morning Post's reporting, it's entirely possible that Roaming Dragon is what Beijing claims it is-an orbital trash-collector. "It's not crazy to think about trying to pull large pieces of junk out of high-traffic orbits, since those are potential sources of thousands of pieces of deadly smaller debris if the piece breaks up," Gregory Kulacki, a space expert with the Massachusetts-based Union of Concerned Scientists, told The Daily Beast in an email.

And to China's credit, it apparently has been fairly transparent about Roaming Dragon-more transparent, in fact, than the United States is with many of its own spacecraft. Weeden said Chinese officials could go a step further in reassuring the world about Roaming Dragon's mission. "They could release details of its orbit and provide advance notification of any maneuvers. That would set a very good example for other countries testing similar capabilities to follow, including the United States."

As long as there's such a fine line between war and peace in space, bold acts of transparency are the only way to prevent suspicion and conflict. That applies to Roaming Dragon and any other satellite-be it Chinese, American, Russian, or other-that can transform from an instrument of science to a weapon of war with the flip of a few switches.

"We should probably try talking to each other about it," Lewis advised.

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Is China's Mysterious New Satellite Really a Junk Collector-or a Weapon?

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China just boosted a high-tech, mysterious new satellite into orbit. It might be a weapon. It might not be a weapon. There's no way to be certain, either way-and that's a problem for all spacefaring countries. Especially the United States and China.

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Credit: NASA

While rocket fuel has provided the energy for most space travel so far, solar energy may provide the boost for spaceships in the future. Just like cloth sails harness the wind, giant reflective sheets called solar sails can harness the sun's energy . These sheets could save fuel and provide maneuverability, but cannot function deep in space.

Solar sails work by capturing the energy from light particles as they bounce off a reflective surface, according to the Department of Energy. Each light particle has momentum, and when it strikes a reflective surface, it imparts that momentum to the reflective sheet, just like a collision of two billiard balls.

As billions of light particles hit the sheet, they push the sail strongly enough to move a spacecraft. Over time, the solar particles could keep pushing a spaceship faster and faster, allowing it to attain very high speeds, according to scientists at Argonne National Laboratory.

The sails can be as large as football fields, but are 40 to 100 times thinner than a sheet of paper, according to NASA's Marshal Space Flight Center. Inflatable booms provide the sheets with rigidity, and tether the solar sail to the spacecraft.

Unlike rocket propulsion, which relies on a finite quantity of fuel, solar sails harness the virtually infinite propulsive power of the sun's light, according to NASA. This limitless energy source could allow spaceships equipped with solar sails to hover and maneuver in fashions too costly for ships reliant on fuel-based propulsion systems.

However, solar sails do have their limitations. In our solar system, at distances beyond the orbit of Mars, the sun becomes too faint to push a solar sail, which limits their use deep in space, according to NASA.

The solar panels on some satellites have been used as rudimentary solar sails, but no country has yet launched a spacecraft that relies primarily solar sails for propulsion. That will change this year, when both the Japanese Aerospace Exploration Agency (JAXA) and the American Planetary Society launch solar sail probes.

The Japanese probe, called IKAROS, will travel to Venus with scientific equipment, according to JAXA. And LightSail-1 will circle the Earth, testing solar sail technology, according to the American Planetary Society.

The concept of a solar sail dates back almost 400 years. Johannes Kepler, the astronomer best known for calculating the elliptical orbits of the planets, observed solar radiation creating a comet's tail. Even then, he grasped that a sail could harvest that force just as terrestrial sails trap wind power to propel ships, according to NASA.

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While rocket fuel has provided the energy for most space travel so far, solar energy may provide the boost for spaceships in the future. Just like cloth sails harness the wind, giant reflective sheets called solar sails can harness the sun's energy . These sheets could save fuel and provide maneuverability, but cannot function deep in space.

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Research paper - Test of Tethered Deorbiting of Space Debris

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Research paper - Test of Tethered Deorbiting of Space Debris

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Introduction

Since the introduction of the space tether concept [ 1], a wide number of applications from orbital momentum exchange devices to electrodynamic systems have been proposed; a complete review can be found in [ 2, 3, 4, 5]. More recently, ground tests and numerical models focused on innovative uses of space tethers, among them formation flight [ 6, 7], rendezvous and docking maneuvers [ 8], space tugging operations [ 9], and asteroids [ 10, 11] and non-cooperative objects [ 12] capture.

To date, many investigations of space tethers are for applications in debris removal. The growing problem of space debris and their influence on the access to orbit became commonly recognized by the scientific community after the definition of the so-called "Kessler Syndrome" [ 13], introducing the risk of losing access to Earth orbit regions due to the constant growth of debris and the consequent catastrophic impacts cascade effect. Despite efforts to reduce new spacecraft influence on the debris environment (e.g., [ 14, 15]), the recent plans for large constellations [ 16, 17] are constantly scrutinized and their short and long term influence on the space debris environment stability is under evaluation [ 18, 19, 20]. In this context the scientific community is evaluating further mitigation strategies, considering both the utilization of enhanced protections [ 21] and the implementation of post mission disposal (PMD) [ 22] and active debris removal (ADR) [ 23] operations. Among the different strategies for PMD and ADR [ 24], Electrodynamic Tethers (EDTs) have been investigated as a reliable and convenient solution in low-Earth orbit (LEO) [ 25, 26]. For further information on EDTs and the most recent evolution, the low-working-function tethers (LWTs), see [ 27, 28, 29, 30].

The advantages of tether systems are not limited to the disposal manoeuvre, as flexible connections between two modules reduce the loads transmitted between them with respect to solid joints. Furthermore, with such connections the vehicles involved can remain at a safe distance while maintaining a physical connection. For this reason, tethers have been also proposed for space tug configurations and both experimental investigation [ 31, 32] and simulation activities [ 9, 33, 34] have been carried out.

In this context, the H2020 Future Emerging Technologies FET OPEN Project E.T.PACK-Electrodynamic Tether Technology for Passive Consumable-less Deorbit Kit [ 35] is currently investigating a number of technologies for PMD with EDTs [ 36, 37], including safe tether deployment [ 38]. In this paper, some preliminary tests on tether technologies for deorbiting are presented. In particular, a tether deployment and retrieval mechanism developed in the framework of ETPACK project is introduced. A breadboard prototype of the deployer was manufactured and the deployment and rewind of a thin aluminium tape tether were tested. Test results include the determination of the tether visco-elastic characteristics, the direct measurement of spikes and oscillations and the estimation of the proposed system damping capabilities. The prototype, while designed principally for the ETPACK kit tether deployment, can be employed also for tethered systems formation flight and space tugging, thanks to the capability to control both the tether deployment and retrieval.

Tether Deployment Background

One of the most challenging operations with tethers is the deployment phase, as several issues have to be taken into consideration, such as the libration stability during the process [ 39, 40, 41]. The most investigated approach, employed also on the TSS-1 demonstration [ 42], starts with releasing a tethered tip mass from the host spacecraft (i.e. the ETPACK deployer kit from the main spacecraft, or the tagging unit from a tugged satellite). Due to the negligible authority of gravity gradient forces acting on the system after separation, the tip mass is provided with an initial momentum to reel the tether out; once few hundreds of meters are deployed, the gravity gradient can become the leading driver in the deployment process. A continuous control of the tip mass is requested during the deployment, as uncontrolled oscillations can lead to system instability (see [ 43] for a more detailed description of stability conditions and range). To provide the requested stability, reference deployment trajectories can be defined and optimal values for the tip mass initial attitude and velocity can be computed; the values adopted for ETPACK are reported in [ 38].

The deployer shall therefore be able to follow the predefined deployment profiles by providing the requested initial momentum and by controlling the tape reel-out by passive or active control systems. Mechanical (springs [ 8, 44, 45]), electro-mechanical (deployed masts [ 46]) or propulsive (cold gas actuators [ 38, 47]) systems have been proposed to provide the initial momentum, with the latter one selected for ETPACK. With regards to deployment mechanisms, they can be classified in three main categories: stationary spools, rotating reels, and folded "origami", depending on the tether stowing strategy; again, for this work a rotating reel configuration was selected.

Among the several in-space (e.g.: TSS-1 [ 42, 48], ProSEDS [ 49]-cancelled after Shuttle Columbia accident, YES II [ 50, 51], SEDS [ 52], SEDS II [ 53]) and ground verifications on deployment mechanisms ([ 44, 45, 54]), only the TSS-1 [ 48] and the STAR prototype [ 45] demonstrated the ability to reel in. More recently, the TEPCE CubeSat technology demonstrator was conceived and flown to deploy a 1-km-long tether; to date, confirmation of 500-m deployment is available [ 55]. The low success rate of tethered systems can be related to the complexity of deployment operations, in which minimal disturbances such as internal components friction can greatly influence the reel-out process up to stop completely the tether deployment. For this reason, the proposed deployer employs a system of motorized pulleys to control the tether motion and to decouple the internal mechanism dynamics from the external motion subjected to orbital dynamics.

An important constraint for E.T.PACK deployer mechanism is the utilization of a tape tether instead of a round wire. This was first introduced by BETs project [ 28] due to tapes higher survivability to space debris impacts [ 56], their increased performance in collecting electrons and the faster deorbiting they provide. The utilization of a tape greatly affects the design of the deployer mechanism, as the bulk and shape of a tape coil is different from a wire one, as well as the extraction technology to deploy it.

Paper Contents

The remainder of this paper is organized as follows. Section 2 presents the deployer concept, while Sect. 3 introduces the experimental setup employed for tests reported and discussed in Sect. 4.

Tether deployment module

The deployer mechanism described in this work in the framework of the E.T.PACK project is sketched in Fig. 1. It consists of a Cold Gas Actuator (CGA) propulsive unit, employing two nozzles, a tank, and the relative fluidic system, and a deployment/reel-in subsystem, composed by a rotating reel, a system of pulleys to control the tape deployment, and a motor coupled to the reel to brake it during deployment and actuate it during reel-in operations. Thanks to the pulleys system, the proposed layout is able to decouple the tether dynamics outside of the deployment module from one of the internal mechanisms, leading to a safer deployment. With this configuration, the whole module can act as tip mass during the deployment, as well as perform the reel-in operations by switching the motor function.

In more details, a tether deployment procedure (see [ 38] for E.T.PACK reference profiles) starts with the release of the module. In a first acceleration phase, the CGA provides enough momentum to the tip mass and keeps the tape in tension, while the pulleys system controls the tether deployment. In this phase, the brake is not active (i.e., the brake torque is negligible) letting the module to accelerate. After this stage the deployment motion is controlled only by the pulleys, the tip mass momentum, and, after a sufficient length of tape is deployed, by the gravity gradient. In this second phase, the tape velocity is not constant and while the pulleys can control the deployment profile, the reel rotation is controlled by the brake to avoid tape unwinding inside the module. On the contrary, rewind procedure requires the actuation of the reel; in this case the brake is switched to the motor and controls the reel-in procedure, while the pulleys system is not actuated.

The capability of the proposed module to deploy and retrieve a tether was assessed with a campaign of tests on a low-friction table, as described in the following sections. It is important to assess the early separation phase of deployment because the thrust direction depends on the attitude of the deployer module and this coupling effect must be analysed. Similarly, the tether retrieval requires further investigation because, due to the conservation of angular momentum, any attitude motion of the tip mass is amplified by the rewind process.

Experimental Setup

The experimental setup consists of a scaled deployment module (S-DM) mounted on board an air carriage system including three air bearings on its bottom part for a low-friction motion on a low-friction test table.

The S-DM is shown in Fig. 2, with its main subsystems highlighted: the CGA, the deploy and reel-in subsystem, and the control and communication electronics. The whole module is painted in black to reduce the interference by multiple reflexions with the laboratory motion capture system.

The air carriage system and the test table are part of the SPARTANS facility [ 57, 58, 59, 60], that can be seen in Fig. 3. The facility consists in a 3 × 2 m test table and a spacecraft test mock-up (composed by a translational module and an attitude module); a Motion Capture (MC) system with 6 infrared cameras tracks the motion of the mock-up.

In the investigated configuration the S-DM is directly mounted on SPARTANS mock-up translational module replacing the original attitude module; the total mass of the free-floating system is about 25 kg, comparable to the E.T.PACK mass. With this configuration, the S-DM acquires three degrees of freedom (DoF), the two translations on the test table and the rotation around the local vertical axis. The free end of the tether is constrained to a dedicated structure on one edge of the test table. The constraint on the tether end is an adequate approximation of a larger mother-satellite (i.e., with a mass ratio > 10) that is unaffected by the transient loads transmitted by the tether during the operations simulated in the laboratory experiments. A load cell is placed on the interface between the tether and the fixed structure to assess the magnitude of the transmitted loads.

The S-DM is equipped with a Wi-Fi communication link; an external control station is employed to start experiments, log data and monitor the whole system.

This experimental setup allows the investigation of tether proximity operations (i.e., the early phase of deployment and the final stage of reel-in). Specifically, the coupling between translation and attitude dynamics was evaluated, as well as the effect of the CGA thrust on the deployment profile.

Experimental Campaign

The experimental campaign reported in this section consisted in four different activities: the verification of (1) the CGA thrusters force authority and (2) the tape mechanical characteristics and the tests of (3) deployment and (4) retrieval manoeuvers.

Thrusters Authority

The CGA thrusters are designed as simple convergent nozzles and a linear relation between inlet pressure and thrust force is expected. The inlet pressure is directly measured with an on-board sensor placed in the low-pressure section of the fluidic subsystem; the data live stream is transmitted through the Wi-Fi link to the control station. To evaluate the thrust, the S-DM is connected with a thin line of about 1.5 m to a load cell constrained to one vertex of the test table; independently from the mechanical characteristics of the line, once the system is in steady-state configuration (i.e. the S-DM does not present rotational and translational motions) the load cell measures the force actuated by the two thrusters on board the S-DM. Experimental results (red dots) are reported in Fig. 4 with a first-order fit (blue dashed line), indicating a linear relation between the inlet static pressure and trust authority, with a coefficient of determination R 2  = 0.9997.

The thrust levels are comparable to those required by the E.T.PACK reference deployment profile [ 38].

Tape Mechanical Characteristics Verification

The stiffness and damping of a flexible line can be verified by applying a constant tensile load in slack conditions and then measuring the line dynamic response in terms of tension spikes, oscillations, and damping. With the proposed experimental setup, the verification can be performed by constraining a section of the line with known length to a fixed structure and to the S-DM, and then actuating the S-DM thrusters with the line in the initial slack condition.

Due to the high stiffness of the employed aluminium tape (about 30 kN/m for a sample 1.5 m long), the verification is performed in two steps. First, the setup employed for thrusters authority verification is used to test the proposed method with a 1.5 m long polyamide line with a diameter of 0.3 mm (theoretical stiffness of 129 N/m); the S-DM motion detected with the MC system is reconstructed and compared to simulations, as well as loads measured with the load cell mounted on the constrained end. In a second phase, the line is substituted with the aluminium tape and the test is repeated with the same parameters but without the load cell, whose stiffness is comparable to that of the tape and might therefore invalidate the experiment. This approach allows a first validation of the proposed method with the elastic polyamide line and then the verification of the tape characteristics.

Results for the polyamide line are reported in Fig. 5, for two different thrust conditions (0.38 and 0.62 N). It can be seen that experimental data match simulations results; small discrepancies can be related to residual friction effects between the module and the test table.

Aluminium tape verification results can be seen in Fig. 6. As previously mentioned, due to the higher stiffness of the tape with respect to the polyamide line the load cell is removed from the setup to avoid undesired effects. To match simulations with experimental data a high damping coefficient (480 N s/m) is employed; the consequent damping ratio of 0.22 is higher than expected for aluminium alloys and can be related to memory effects of the tape sample undergoing testing.

Deployment Manoeuvre

The objective of this test is the verification of the deployer capability to follow a predefined reference deployment trajectory, in terms of tether length and length rate. While in operative configurations the deployment would last tens of minutes (up to 1 h in [ 38]), the test table available area limits it to less than 1 min. Despite such constraint, the test allows to determine the behaviour of the deployment system and to verify the capability to follow a reference reel-out profile. Furthermore, the test aims to verify the capability of the deployment motor to follow a profile with a high initial acceleration as well as to monitor the effect of such acceleration on the S-DM dynamics. The reference profile, therefore, presents an initial acceleration of 7 mm/s 2 (about one-third of the in-orbit case value, as reported in [ 38]), and then a constant-velocity phase at 0.1 m/s. The other parameters (CGA thrust, S-DM mass) are comparable to the E.T.PACK reference ones [ 38].

Figure 7 reports the results of a deployment test, with the reconstructed trajectory from the MC system, the comparison of the deployment profiles with the reference ones, and some frames from the deployment video. It can be noted that the S-DM is capable to follow the pre-imposed deployment profile, with minimal discrepancies related to the dynamical response of the tape (small oscillations and spikes).

It can be noted that the S-DM is subjected to a small rotation on its centre of mass around the vertical axis, which is aligned to the tape coil axis: due to angular momentum conservation, the initial coil angular acceleration causes a small counter-rotation on the module. This issue will be addressed in future upgrades of the deployment hardware with a dedicated attitude control strategy modulating the module thrusters firing. It shall be underlined that the tape tension creates a restoring torque on the S-DM opposing the coil-induced torque, limiting the rotation to less than 45 deg.

Reel-In Operations Example

The capability to reel-in the tape is an important feature of the proposed system. Figure 8 reports an example of a reel-in manoeuvre at a constant retrieval velocity of 0.02 m/s, with the reconstructed trajectory from the MC system, the reel-in and reel-in rate profiles, and some frames from the corresponding video. In this test after the initial acceleration, the coil rotation is constant; the thrusters are firing during the whole manoeuvre to maintain the tape in tension. Again, it can be noted an initial rotation of the S-DM due to the initial angular acceleration of the tape coil; as expected, the tape creates a small restoring torque opposing the module rotation.

This test demonstrates the proposed system general capability to reel-in at a constant velocity; further investigation will be performed to verify the capability to follow a reference retrieval profile and the possibility to perform it without the assistance of the propulsion system.

Conclusions

This paper presented the low-friction tests of a tether deployer and reel-in system developed in the framework of the H2020 ETPACK project. The system is based on a rotating coil concept, with a system of pulleys to control the deployment and a motor coupled to the coil to brake it during the reel-out and actuate it for the reel-in. The proposed system is integrated on a small module equipped with a cold gas system for propulsion purposes, and it is tested on the low-friction test table of the SPARTANS facility.

The first tests verified the cold gas system trust authority and the employed aluminium tape mechanical characteristics; it was found that a linear relation exists between the inlet static pressure and the thrust and that the aluminium tape presents a larger damping ratio than expected, due most likely to memory effects present in the tested tape sample.

A controlled deployment test demonstrated the system capability to reel-out the tape following a reference trajectory; it has been found that the angular acceleration of the tape coil affects the attitude of the deployment module but does not influence the deployment profile. Similarly, a reel-in test demonstrated the capability of the proposed system to retrieve the tape.

It can be concluded that the proposed system demonstrated its desired features. Future works will focus on two main topics: the attitude control of the module during the manoeuvres will be implemented by modulating the thrusters firing and more complex deployment and retrieval operations will be tested.

Acknowledgements

The authors wish to thank Mr Francesco Babolin, Mr. Mirco Bartolomei, and Mr Alex Caon for the support in the development of the experimental setup. This work was supported by the European Union's H2020 Research and Innovation Programme under Grant Agreement no. 828902 (E.T.PACK Project).

Funding

Open access funding provided by Università degli Studi di Padova within the CRUI-CARE Agreement.

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Authors and Affiliations

CISAS "G. Colombo", University of Padova, Via Venezia 13, 35131, Padua, Italy

Lorenzo Olivieri, Giulia Sarego & Enrico C. Lorenzini

DII, University of Padova, Via Venezia 1, 35131, Padua, Italy

Andrea Valmorbida & Enrico C. Lorenzini

University of Padova, Padua, Italy

Enrico Lungavia & Davide Vertuani

Corresponding author

Correspondence to Lorenzo Olivieri.

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Olivieri, L., Valmorbida, A., Sarego, G. et al. Test of Tethered Deorbiting of Space Debris. Adv. Astronaut. Sci. Technol. 3, 115-124 (2020). https://doi.org/10.1007/s42423-020-00068-9
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Keywords

Space tethers

Deployment

Active debris removal

Low friction test

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Test of Tethered Deorbiting of Space Debris - Advances in Astronautics Science and Technology

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Current investigations on space tethers include their application to space debris deorbiting, specifically on the set of manoeuvres performed by a chaser tug to change the orbital parameters of a target body. Targets can be cooperative spacecraft at the end of their life or uncontrolled objects such as defunct satellites without clearly available capturing interfaces.

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Think you've got a tough job? How would you like to have to measure the weight of all the trees on the planet? That's what Barry Coyle '86 is doing as a NASA physicist at the Goddard Space Flight Center in Greenbelt, Maryland.

But he's doing it with brains not brawn.

Over the last 20 years, Coyle has built the laser systems for an aircraft-based laser altimeter developed by his NASA colleague (and good friend) Brian Blair, along with a University of Maryland geographical scientist, Ralph Dubayah. After several starts and stops, proposals, aircraft campaigns and instrument evolutions, the Global Ecosystem Dynamics Investigation, or GEDI, was launched in early December and is now scanning the forests of the world from the International Space Station (ISS).

Why would anyone want to do that? For a number of reasons, but primarily to calculate the carbon load of the planet's vegetation.

"It's the last big data point in the global climate model and will significantly help quantify the global effects of climate change," says Coyle, who majored in physics at the College. "We know winds, sea temperature, ground coverage, clouds and everything else that's in the mix, but we don't know carbon volume and density as well as we need to. That's why this is a unique measurement: we're going to literally weigh the trees."

Carbon makes up about half of vegetation biomass, so the $100 million mission to quantify it will allow NASA scientists - and scientists around the world - to calculate the carbon sequestration potential of forests under future climate and land use situations.
RELATED: Learn more about Barry Coyle's work as a NASA laser physicist.
The GEDI laser works like a radar but instead of radio waves, it uses pulses from an infrared laser, dangerous up close, but harmless from orbit. The four beams leave the ISS 254 miles above earth at a diameter of about an inch-and-a-half, but produce a 600-meter footprint (about 200 feet). GEDI is expected to produce about 10 billion cloud-free observations during its two-year mission. (The name GEDI is an homage to Star Wars since JEDI fighters use laser swords.)

"It's like a push broom that will go on continuously for two years because trees are always changing," says Coyle, who often hires CofC students for the summer. "We turned on GEDI and finished full commissioning exercises in February. The science team has taken over now, and they say it's like drinking from a fire hose with the 3.5 million laser shots an hour. It's a lot of data."

Coyle can trace his interest in lasers back to when he first started working with with them in the 1980s while in physics professor Fred Watts' laser lab at CofC. It was a seminal moment that set him on a life-changing trajectory.

"I have Dr. [Bob] Dukes and Dr. Watts to thank as two of the most influential professors in my life, as was the whole physics department in the mid-80s" he says. "The day in early December when GEDI launched into space was easily the proudest day of my career to date, and it made me super proud to be a CofC physics alumnus."

And the fruits of his labor now pouring in from the heavens look a lot like an echo cardiogram as the "lidar" systematically and consistently samples the vertical structure of the world's forests - a first in and of itself since no one has ever measured how tall trees are globally.

"All the trees and vegetation breathe in the CO2 and make oxygen," says Coyle. "As we're pumping more and more carbon out of the ground, we need to know how much we can absorb per year. Are we past the tipping point? How bad is it? That's where this can help."

Coyle says the effort, and the data it will produce, is the result of unparalleled teamwork.

"Ultimately, I may have designed and evolved the laser design, but I had a team of unmatched engineers and technicians - all great friends - that made it all possible to build these to flight quality units ready for the ISS," he says. "This is what working at NASA is all about."
Featured image: Barry Coyle works on the GEDI laser ahead of its launch in December to the International Space Station.

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Physics Alum is Laser-Focused on His Work at NASA

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Think you've got a tough job? How would you like to have to measure the weight of all the trees on the planet? That's what Barry Coyle '86 is doing as a NASA physicist at the Goddard Space Flight Center in Greenbelt, Maryland. But he's doing it with brains not brawn.

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Japan Eyes Laser to Get Rid of Dangerous Space Junk

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Space debris is a growing problem as humanity launches more and more satellites into Earth orbit, making space increasingly crowded.

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How do Solar Sails Impact the Environment?

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How do Solar Sails Impact the Environment?

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Solar sailing is done in space, not at sea. It involves using solar radiation rather than rocket fuel or nuclear energy to propel spacecraft. Its energy source is nearly unlimited (at least for the next few billion years), its benefits can be substantial, and it demonstrates the innovative use of solar energy to propel modern civilization.

How Solar Sailing Works

A solar sail works the same way that photovoltaic (PV) cells work in a solar panel-by converting light into another form of energy. Photons (light particles) don't have mass, but anyone who knows Einstein's most famous equation knows that mass is merely a form of energy.

Photons are packets of energy moving by definition at the speed of light, and because they are moving, they have momentum proportional to the energy they carry. When that energy hits a solar PV cell, the photons disturb the cell's electrons, creating a current, measured in volts (thus the term photovoltaic). When a photon's energy hits a reflective object like a solar sail, however, some of that energy is transferred to the object as kinetic energy, just as happens when a moving billiard ball hits a stationary one. Solar sailing may be the only form of propulsion whose source is massless.

Just as a solar panel produces more electricity the stronger the sunlight hitting it, so too a solar sail moves faster. In outer space, unprotected by Earth's atmosphere, a solar sail is bombarded with portions of the electromagnetic spectrum with more energy (such as gamma rays) than are objects on the surface of Earth, which is protected by Earth's atmosphere from such high-energy waves of solar radiation. And since outer space is a vacuum, there is no opposition to the billions of photons striking a solar sail and moving it forward. As long as the solar sail remains close enough to the Sun, it can use the Sun's energy to sail through space.

A solar sail operates just like the sails on a sailboat. By changing the angle of the sail relative to the Sun, a spacecraft can sail with the light behind them or tack against the direction of light. The speed of a spacecraft depends on the relationship between the size of the sail, the distance from the light source, and the mass of the craft. Acceleration can also be enhanced by the use of Earth-based lasers, which carry higher levels of energy than ordinary light. Because the bombardment of the Sun's photons never ends and there is no resistance, the acceleration of the satellite increases over time, making solar sailing an effective means of propulsion over long distances.

Environmental Benefits of Solar Sailing

Getting a solar sail into space still takes rocket fuel, since the force of gravity in Earth's lower atmosphere is stronger than the energy that a solar sail can capture. For example, the rocket that launched LightSail 2 into space on June 25, 2019-SpaceX's Falcon Heavy rocket-used kerosene and liquid oxygen as rocket fuel. Kerosene is the same fossil fuel used in jet fuel, with roughly the same carbon dioxide emissions as home heating oil and slightly more than gasoline.

While the infrequency of rocket launches makes their greenhouse gases negligible, the other chemicals that rocket fuel releases into the upper layers of Earth's atmosphere can cause damage to the all-important ozone layer. Replacing rocket fuel in outer orbits with solar sails reduces the cost and atmospheric damage caused by burning fossil fuels for propulsion. Rocket fuel is also expensive and finite, limiting the speed and distance that spacecraft can travel.

Solar sailing is impractical in low-Earth orbits (LEOs), due to environmental forces like drag and magnetic forces. And while interplanetary travel beyond Mars becomes more difficult, due to the decreasing energy in sunlight in the outer solar system, spacecraft solar sailing can help reduce costs and limit damage to Earth's atmosphere.

Solar sails can also be paired with solar PV panels, which convert sunlight into electricity just as they do on Earth, allowing the satellite's electronic functions to continue working without other external fuel sources. This has the added benefit of allowing satellites to remain in a stationary position over the poles of the Earth, thus increasing the ability to constantly monitor by satellite the effects of climate change on the polar regions. (A "stationary satellite" normally stays in the same place relative to the Earth by moving at the same speed as the Earth's spin-an impossibility at the poles.)

A Timeline of Solar Sailing

1610

Astronomer Johannes Kepler suggests to his friend Galileo Galilei that some day ships could sail by catching solar wind.

1873

Physicist James Clerk Maxwell demonstrates that light exerts pressure on objects when it reflects off of them.

1960

Echo 1 (a metallic balloon satellite) records pressure from sunlight.

1974

NASA angles the solar arrays of Mariner 10 to work as solar sails on its way to Mercury.

1975

NASA creates a prototype of a solar sail spacecraft to visit Haley's Comet.

1992

India launches INSAT-2A, a satellite with a solar sail meant to balance the pressure on its solar PV array.

1993

The Russian Space Agency launches Znamya 2 with a reflector that unfurls like a solar sail, though this is not its function.

2004

Japan successfully deploys a non-functioning solar sail from a spacecraft.

2005

The Planetary Society's Cosmos 1 mission, containing a functional solar sail, is destroyed on launch.

2010

Japan's IKAROS (Interplanetary Kite-craft Accelerated by Radiation Of the Sun) satellite successfully deploys a solar sail as its main propulsion.

2019

The Planetary Society, whose CEO is famed science educator Bill Nye, launches the LightSail 2 satellite in June 2019. LightSail 2 is named one of TIME magazine's 100 Best Inventions of 2019.

2019

NASA selects the Solar Cruiser as a solar sail mission for deep space research.

2021

NASA continues development of the NEA Scout, a solar sail spacecraft meant to explore near-Earth asteroids (NEA). Planned launch is November 2021, delayed from May 2020.

Key Takeaway

Solar sailing still requires fossil fuels to launch spacecraft into orbit or beyond, but it nonetheless has its environmental benefits, and-perhaps more importantly-demonstrates the potential of solar energy to solve Earth's most pressing environmental problems.

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What Is Solar Sailing, and How Does It Impact the Environment?

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Solar sailing is done in space, not at sea. It involves using solar radiation rather than rocket fuel or nuclear energy to propel spacecraft. Its energy source is nearly unlimited (at least for the next few billion years), its benefits can be substantial, and it demonstrates the innovative use of solar energy to propel modern civilization.

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Research paper - Space debris removal with bare electrodynamic tethers 

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Research paper - Space debris removal with bare electrodynamic tethers 

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Several hundred thousand pieces of waste, commonly known as space junk, litter low-Earth orbit, potentially causing hazardous conditions for rockets and satellites. A group of scientists would like to shoot this junk from the ground with high-powered laser pulses.

The heat from the laser blasts would vaporize a minuscule part of a piece of space junk, resulting in a plasma jet that could slow the object down enough to bring it out of Earth orbit.

"You're essentially creating a laser-powered rocket, using the object to be its own fuel," said engineer Claude Phipps of the company Photonic Associates, LLC, who co-authored the laser-removal paper, published Oct. 17 on arxiv.

Space junk, which ranges from tiny paint flecks to bulky decommissioned satellites and spent rocket stages, is reaching a tipping point. After decades of assuming that low-Earth orbit could handle almost unlimited waste, space agencies have recently realized that the current density of space junk is high enough for collisions to start becoming inevitable, with each crash potentially creating hundreds of new objects to worry about.

This scenario, originally posited by astrophysicist Donald Kessler back in 1978, means that spacecraft entering low-Earth orbit would have to fear running into space junk that could puncture their hulls. Two years ago, a communications satellite crashed into a defunct Russian spacecraft in the first major sat-on-sat collision. And earlier this year, the crew aboard the International Space Station was forced to take shelter in the Soyuz escape craft when a bit of space junk wandered precariously close.

NASA has considered many proposals for cleaning up space, including mesh nets strung between inflatable booms or unmanned collecting barges that would fly around picking up trash. They have even previously contemplated a ground-based laser removal system: a medium-powered laser that would use the small momentum imparted by photons to nudge an object out of orbit. But such an approach would be mostly limited to lighter objects, leaving behind the most hazardous material, said Kessler, who is NASA's former Senior Scientist for Orbital Debris Research.

More powerful lasers, with roughly 150 kilowatts of power, should be capable of adjusting the orbit of almost any size object. The smallest debris (less than 3 feet in size) would burn up in the Earth's atmosphere after being slowed down and falling out of orbit, while larger pieces might need to be aimed properly to land in the Pacific Ocean.

Using ground-based lasers eliminates the need to launch a vehicle into space, which could cost hundreds of millions of dollars. Phipps' team estimates that removing a small object would cost a few thousand dollars and large objects would be about $1 million.

Still, the technique requires caution, said Kessler.

"If you're not careful, you might hit the wrong part of a satellite or could vaporize enough to cause it to explode," he said.

Phipps is confident that a dedicated 10-meter telescope could be built with the necessary capabilities to track space junk and properly calculate where and how to hit it. All of the technology needed for such a facility, including a large enough mirror and powerful enough laser, currently exists or is under development.

Perhaps the main criticism of such a project would come from the international community, which might fear that a powerful enough laser could be used for military purposes such as hitting enemy satellites. Because of such political complications, NASA's official line is that "any laser proposal is dead on arrival," said Kessler.

But Phipps, who has advocated for the ground-based laser solution since 1996, thinks that the junk-tracking facility would have to be part of an international effort. Roughly half of space debris comes from either Russia or the U.S., so they should be natural partners in addressing this issue, he said. Other countries interested in space launches could also get involved.

"If we get the right international cooperation, no one would believe the laser to be a weapon in sheep's clothing," he said.
Image: E. Victor George, Centech Corporation, Carlsbad CA
See Also: - Lost in Space: 8 Weird Pieces of Space Junk

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Space Junk Crisis: Time to Bring in the Lasers

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Several hundred thousand pieces of waste, commonly known as space junk, litter low-Earth orbit, potentially causing hazardous conditions for rockets and satellites. A group of scientists would like to shoot this junk from the ground with high-powered laser pulses.

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To address the dangers posed by orbiting space junk, researchers have found a way to manipulate the debris with spinning magnets that may allow robots to one day remove the speeding trash.

There are more than 27,000 pieces of space debris bigger than the size of a softball currently orbiting Earth, according to NASA. Hurtling at speeds of up to 17,500 mph, even small pieces of junk left behind by years of space missions threaten to damage or destroy satellites and spacecraft.

A team led by University of Utah mechanical engineering professor Jake J. Abbott published a paper in the j ournal Nature that describes using spinning magnets to manipulate orbiting debris. The method could eventually be used to robotically repair or maneuver space junk into deep space or into a death spiral headed toward Earth without touching any pieces.

Jake J. Abbott, a University of Utah professor of mechanical engineering, led a team of researchers that discovered how to manipulate objects in space with spinning magnets. (Dan Hixson, University of Utah)

"NASA is tracking thousands of space debris the same way that air traffic controllers track aircraft. You have to know where they are because you could accidentally crash into them," Abbott said, noting that the United States and other countries recognize the problem of accumulating space junk.

"What we wanted to do was to manipulate the thing, not just shove it, but actually manipulate it like you do on Earth," Abbot said. "That form of dexterous manipulation has never been done before."

This process involves manipulating non-magnetized, metallic objects with spinning magnets, which subject the objects to a changing magnetic field. That causes electrons within the metal to circulate in loops, like swirling coffee in a cup.

The method turns a piece of space junk into an electromagnet that produces torque and force, which allows manipulation of the junk without touching it. The researchers built on previous understanding of magnetic currents to discover that using multiple magnetic-field sources in a coordinated fashion allowed the objects six degrees of movement, including rotation. In the past, researchers only knew how to move objects by just one degree, like a single push.

The above image depicts some of the thousands of objects currently circling the Earth, as seen from about 15,534 miles in space. (NASA Orbital Debris Program)

The new method would give scientists the ability to stop a damaged satellite's wild spinning to repair it. "You have to take this crazy object floating in space, and you have to get it into a position where it can be manipulated by a robot arm," Abbott said. "But if it's spinning out of control, you could break the robot arm doing that, which would just create more debris."

The new method also allows scientists to manipulate with gentle magnetic force especially fragile objects that could be damaged by the claw of a robotic arm.

During their tests, the researchers used magnets to move a copper ball on a plastic raft in a tank of water to simulate slow-moving objects in microgravity. The ball moved not only in a square but also rotated. This method can use either a spinning magnet on a robotic arm, a stationary magnet that creates spinning magnetic fields or a spinning super-conductive electromagnet resembling magnetic resonance imaging (MRI) scanners.

"I'm starting to open my mind to what potential applications there are," Abbot said. "We have a new way to apply a force to an object for precise alignment without touching it."
Edited by Richard Pretorius and Kristen Butler

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Spinning Magnets Could Help Clean Up Space Junk

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To address the dangers posed by orbiting space junk, researchers have found a way to manipulate the debris with spinning magnets that may allow robots to one day remove the speeding trash. There are more than 27,000 pieces of space debris bigger than the size of a softball currently orbiting Earth, according to NASA.

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Anyone who has seen the 2013 film Gravity has a grasp of the hazards of "space junk," the literally millions of bits of relict debris from past space missions that still orbit Earth. Could high-energy lasers help clean up this orbital wreckage? New modeling from a team of German scientists suggests that the answer might be yes-but only if society can live with an increase in risk attributable to some individual pieces of the stuff (Opt. Eng., doi: 10.1117/1.OE.56.1.011007).

Not science fiction

Gravity notwithstanding, space debris isn't science fiction, but a growing problem for near-Earth missions, particularly as an increasing number of countries put new probes into space. The U.S. National Aeronautics and Space Administration (NASA) currently tracks more than half a million items of such orbital debris, the size of a marble or larger, and says that there are "many millions of pieces" of additional debris too small to be tracked.

The debris consists largely of the relics of old, abandoned space missions-decaying satellites or rockets that have slowly broken apart or collided in orbit. Traveling at speeds of 8 to 15 kilometers per second, this orbital flotsam can indeed, if not avoided, rip through vehicles such as the International Space Station and other manned and unmanned probes. And avoiding the proliferating debris has become an increasing problem. Indeed, there's a real worry that, if the mess isn't cleaned up, new low-Earth-orbital missions, ranging from weather satellites to orbiting telescopes, could become impossible to launch.

A laser solution?

For years, high-energy lasers have been floated as one possible way to sweep out Earth's orbital neighborhood. The idea is that laser-induced ablation of material on the orbiting junk leads to a recoil and momentum transfer that can nudge the debris to a lower orbit and, eventually, cause it to burn up in Earth's atmosphere. Analytical modeling has suggested that such laser nudging, coupled with extremely high-resolution optical detection to pick out orbiting objects, might well constitute part of the solution to space junk.

The problem with this earlier modeling, according to researchers Stefan Scharring, Jascha Wilken and Hans-Albert Eckel of the German Aerospace Center in Stuttgart, is that these studies have largely been premised on analog models using simple hypothetical debris shapes, such as spheres, cubes, or flat plates, that are optimally oriented with respect to the laser beam. Real space junk is much more irregular, heterogeneous and randomly oriented, putting its real-world behavior completely out of the range of analog modeling.

It's complicated

To get a more rigorous answer to how space debris might respond to a high-energy laser push, the German team developed a sophisticated numerical model to the simulate momentum coupling in detail. The model and accompanying experiments, including a Monte Carlo simulation on the predictability of outcomes from zapping space debris with lasers, was designed to take into account irregular shapes as well as variations in orientation and in laser fluence across the target surface.

The results suggest that the effects of lasers on space debris are, to say the least, highly unpredictable. In particular, the orientation of the object with respect to the laser made a big difference in the change in the object's trajectory, introducing lateral momentum components that were very difficult to call in advance. And there were substantial variations in the actual amount of momentum coupling-and, thus, potential debris-removal efficiency-depending on object shape and orientation relative to the beam.

Still a place for a "laser broom"

Notwithstanding these complications, the work did suggest, according to the researchers, that laser-based removal of space debris has "great potential." The Monte Carlo simulations, involving half a million different conditions, did show a tendency for laser nudging to be broadly effective in a range of object shapes and orientations, albeit with a healthy dose of uncertainty.

What that means, the study concludes, is that high-energy laser ablation can still represent an important part of eliminating the space-junk problem-but only if the laser solution isn't viewed as a deterministic one, and if society is prepared to accept the idea that, for some pieces of space junk, zapping with lasers could make things worse. "A probabilistic assessment of the concept is necessary," they write, "taking into account ... the risk to transiently push space debris into an orbit that is even more dangerous than before."

Yet in the long haul, they think that's a risk worth taking. Drawing a homely analogy, the scientists write that "even if the trajectory of dust particles is unpredictable when sweeping the floor, the space is promised to be cleaned in the long run."
Publish Date:

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Could High-Energy Lasers Sweep Away Space Debris?

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Anyone who has seen the 2013 film Gravity has a grasp of the hazards of "space junk," the literally millions of bits of relict debris from past space missions that still orbit Earth. Could high-energy lasers help clean up this orbital wreckage?

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Institution of mechanical engineers - Space tether could de-orbit space junk without using propellant

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Institution of mechanical engineers - Space tether could de-orbit space junk without using propellant

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Engineering news

As more and more satellites are launched into space each year, the threat of collisions and space debris grows. A new project aims to tackle the issue to enable sustainable use of the space environment - all without propellant.

The consortium behind the project received funding of €2.5m from the EU's European Innovation Council (EIC) today (17 May). The money will be used to develop the device, known as the electrodynamic space tether.

Due to the high cost involved, most satellites are not removed after their mission is completed. Combined with the threat of spontaneous explosions because of the harsh space environment, the issue has caused the accumulation of space debris in low Earth orbit, threatening future launches.

Co-ordinated by the University Carlos III of Madrid (UC3M) and involving the University of Padua in Italy, the Technical University of Dresden, the Spanish company Sener Aeroespacial and the German start-up Rocket Factory Augsburg, the E.T.Pack-Fly consortium aims to tackle the problem by developing a device capable of deorbiting space debris - decreasing its altitude until it is destroyed by re-entry into the atmosphere.

Unlike conventional systems, the electrodynamic space tether does not require propellant. Instead, the very thin and very long aluminium tape (about 2cm wide and 2km long) is designed to work by using the plasma and the geomagnetic field around Earth to generate an electric current. This electrodynamic effect results in a force known as the Lorentz drag, which deorbits the satellite. The tether is also designed to stabilise the orientation of the satellite, and to control the deorbiting to avoid possible collisions with other objects.

The project will start in September, aiming to launch a device into orbit in 2025. A first prototype was developed and built during the previous E.T.Pack project, also funded by the EIC.

"We are very grateful to the EIC for the trust it has placed in us and its commitment to the development of technologies that allow a sustainable use of the space environment," said project co-ordinator Gonzalo Sánchez Arriaga from UC3M. "It is important to invest in disruptive technologies that can mitigate the proliferation of space debris while generating wealth and new business opportunities."

Lorenzo Tarabini, director of the project at Sener Aeroespacial, said: "This project gives us the opportunity to build and qualify for space, through a complete series of tests, a light, compact and completely autonomous platform for deorbiting the final stages of launchers."
Want the best engineering stories delivered straight to your inbox? The Professional Engineering newsletter gives you vital updates on the most cutting-edge engineering and exciting new job opportunities. To sign up, click here. Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.

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'Space tether' could de-orbit space junk without using propellant

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Engineering news As more and more satellites are launched into space each year, the threat of collisions and space debris grows. A new project aims to tackle the issue to enable sustainable use of the space environment - all without propellant.

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Lucas Martin | Published: Monday, April 11, 2022

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How drag sails could help our space junk problem

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The technology to deorbit satellites could lower the risk of catastrophic collisions in low Earth orbit.

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Wherever we humans go, we leave behind a mess. That goes for space, too.

Today, our species is responsible for more than 500,000 pieces of junk hurtling around Earth at phenomenal speeds, and if we don't start actively removing the largest pieces, the risk of collisions will only grow worse.

"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," says Jan Wörner, European Space Agency (ESA) director general.

"That is the current situation in orbit, and it cannot be allowed to continue."

It's almost as if we need a tow truck to remove all the thousands of failed satellites from our orbit; incidentally, that's exactly what the ESA is working on.

By 2025, the agency plans on launching the world's first orbiting junk collector, a four-armed robot that tracks down space waste like Pac-Man in a maze.

The first-of-its-kind mission, known as ClearSpace-1, will start out small, collecting only a single piece of space junk to prove the concept works. The target in this case is called Vespa, a leftover remnant from ESA's Vega rocket launch in 2013.

This piece of junk weighs roughly the same as a small satellite and has a simple shape that should make it easy to grab with four robotic arms. Once it's safely in the arms of the garbage collector, it will then be dragged out of orbit and allowed to burn up in the atmosphere.

Unfortunately, this will also destroy the collector, but in the future, the agency hopes to create a way for the robot to safely eject the rubbish and continue capturing and de-orbiting other pieces.

The ultimate goal is to create a spacecraft that can propel and direct itself in low orbit with a " high level of autonomy", according to the Swiss startup, ClearSpace, which is in charge of designing the machine.

"The space debris issue is more pressing than ever before. Today we have nearly 2,000 live satellites in space and more than 3,000 failed ones," says ClearSpace CEO Luc Piguet.

"And in the coming years the number of satellites will increase by an order of magnitude, with multiple mega-constellations made up of hundreds or even thousands of satellites planned for low Earth orbit."

Creating a network of garbage collectors for these satellites comes with its challenges. Powering a spacecraft, after all, costs a lot of money, and while scientists have been exploring cheaper options for years - like using the garbage it collects as fuel - nothing has so far come to fruition.

The ClearSpace mission is set to cost 117 million euro (US$129 million), but another company based in Tokyo called Astroscale may beat it to the punch. It plans on launching its first demonstrations within the year, but whether or not it can prove cost-efficient is another matter. Watch this space.

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The First Mission to Remove Space Junk From Orbit Has Just Been Commissioned

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Wherever we humans go, we leave behind a mess. That goes for space, too. Today, our species is responsible for more than 500,000 pieces of junk hurtling around Earth at phenomenal speeds, and if we don't start actively removing the largest pieces, the risk of collisions will only grow worse.

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Laser-based removal of irregularly shaped space debris

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While the feasibility of laser space debris removal by high energy lasers has been shown in concept studies and laboratory proofs of principle, we address the question of the effectiveness and responsibility associated with this technique. The large variety of debris shapes poses a challenge for pre…

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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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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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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.
You may also be interested in:

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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.

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

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

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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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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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New Method for Cleaning up Space Debris Using Magnets | Digital Trends

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Researchers have found a way to maneuver metallic, non-magnetic pieces of debris by using spinning magnets.

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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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Australians lead efforts to move space junk with lasers

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Hundreds of thousands of objects are orbiting in high-velocity swarms around the Earth. Many of these, in the event of a collision, could ignite catastrophic accidents junking the world's orbital telecommunications networks. Australian company Electro Optic Systems (EOS) is leading efforts to track this potentially killer debris 38,000km (24,000 miles) above our heads, and is at the forefront of a boom in Australian space research.

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Several hundred thousand pieces of waste, commonly known as space junk, litter low-Earth orbit, potentially causing hazardous conditions for rockets and satellites. A group of scientists would like to shoot this junk from the ground with high-powered laser pulses.

The heat from the laser blasts would vaporize a minuscule part of a piece of space junk, resulting in a plasma jet that could slow the object down enough to bring it out of Earth orbit.

"You're essentially creating a laser-powered rocket, using the object to be its own fuel," said engineer Claude Phipps of the company Photonic Associates, LLC, who co-authored the laser-removal paper, published Oct. 17 on arxiv.

Space junk, which ranges from tiny paint flecks to bulky decommissioned satellites and spent rocket stages, is reaching a tipping point. After decades of assuming that low-Earth orbit could handle almost unlimited waste, space agencies have recently realized that the current density of space junk is high enough for collisions to start becoming inevitable, with each crash potentially creating hundreds of new objects to worry about.

This scenario, originally posited by astrophysicist Donald Kessler back in 1978, means that spacecraft entering low-Earth orbit would have to fear running into space junk that could puncture their hulls. Two years ago, a communications satellite crashed into a defunct Russian spacecraft in the first major sat-on-sat collision. And earlier this year, the crew aboard the International Space Station was forced to take shelter in the Soyuz escape craft when a bit of space junk wandered precariously close.

NASA has considered many proposals for cleaning up space, including mesh nets strung between inflatable booms or unmanned collecting barges that would fly around picking up trash. They have even previously contemplated a ground-based laser removal system: a medium-powered laser that would use the small momentum imparted by photons to nudge an object out of orbit. But such an approach would be mostly limited to lighter objects, leaving behind the most hazardous material, said Kessler, who is NASA's former Senior Scientist for Orbital Debris Research.

More powerful lasers, with roughly 150 kilowatts of power, should be capable of adjusting the orbit of almost any size object. The smallest debris (less than 3 feet in size) would burn up in the Earth's atmosphere after being slowed down and falling out of orbit, while larger pieces might need to be aimed properly to land in the Pacific Ocean.

Using ground-based lasers eliminates the need to launch a vehicle into space, which could cost hundreds of millions of dollars. Phipps' team estimates that removing a small object would cost a few thousand dollars and large objects would be about $1 million.

Still, the technique requires caution, said Kessler.

"If you're not careful, you might hit the wrong part of a satellite or could vaporize enough to cause it to explode," he said.

Phipps is confident that a dedicated 10-meter telescope could be built with the necessary capabilities to track space junk and properly calculate where and how to hit it. All of the technology needed for such a facility, including a large enough mirror and powerful enough laser, currently exists or is under development.

Perhaps the main criticism of such a project would come from the international community, which might fear that a powerful enough laser could be used for military purposes such as hitting enemy satellites. Because of such political complications, NASA's official line is that "any laser proposal is dead on arrival," said Kessler.

But Phipps, who has advocated for the ground-based laser solution since 1996, thinks that the junk-tracking facility would have to be part of an international effort. Roughly half of space debris comes from either Russia or the U.S., so they should be natural partners in addressing this issue, he said. Other countries interested in space launches could also get involved.

"If we get the right international cooperation, no one would believe the laser to be a weapon in sheep's clothing," he said.
Image: E. Victor George, Centech Corporation, Carlsbad CA
See Also: - Lost in Space: 8 Weird Pieces of Space Junk

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Space Junk Crisis: Time to Bring in the Lasers

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Several hundred thousand pieces of waste, commonly known as space junk, litter low-Earth orbit, potentially causing hazardous conditions for rockets and satellites. A group of scientists would like to shoot this junk from the ground with high-powered laser pulses.

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Knock Knock!

Who's there?

I got a whole lotta.

I got a whole lotta who?

I got a whole lotta of satellites in my collection, wanna see it?

Introducing the new Satellite Collection object!

The Satellite Collection - which was a preview feature in STK 12.2 - is all grown up and is now a standard feature in STK 12.4! You might be asking yourself: What is a collection object and what do I use if for? The Satellite Collection object is a container of satellite orbit definitions that simplifies the analysis and visualization of problems involving large numbers of satellites. Perhaps a little simulated Q&A (we do produce simulation software after all) will provide some additional insight into the utility of the Satellite Collection object.
Visualizing the full space catalog is easy
So, what does the Satellite Collection object do?

The Satellite Collection object provides an efficient mechanism for defining and managing large numbers of satellites without cluttering up your scenario with tons of individual satellite objects. You can define the entries in the collection in three ways:

As a multi-shelled Walker constellation

As a subset of the public space catalog (or the entire space catalog)

Using your own custom orbit elements or ephemerides

While the Satellite Collection object has limited reporting and visualization capabilities, it is integrated with traditional STK analysis tools and capabilities such as Deck Access, Coverage, Communications, and Conjunction Analysis. In general terms, the Satellite Collection object enables you to perform the types of analyses that STK is famous for on large numbers of satellites in an efficient manner.
Coverage analysis of a ridiculous constellation design
What are the benefits of using a Satellite Collection over individual satellites?

You can use the Satellite Collection object when you do not need custom configurations (beyond the trajectory) for each of the satellites in your scenario. Grouping satellite definitions together inside a collection enables you to:

Reduce the number of entities in the object browser

Save and load your scenario in a fraction of the time required when using individual satellites

Efficiently set graphical properties for all (or many) of your satellites at once

Maintain multiple configurations of a proposed large constellation design in a single scenario

On the other hand, using individual satellite objects enables you to completely customize configurations on a per satellite basis, exposes more detailed orbit propagation options, and provides access to more extensive reporting, graphing, and visualization options.

What is a "large number" of satellites?

We have performed tests involving over 600,000 orbiting objects! How many orbiting objects do you have?
Dual shell Walker Constellation containing upwards of 600,000 satellites
Why a "Collection" instead of a "Constellation"?

While large (dare we say mega?) constellations are certainly of interest to the community, we designed the Satellite Collection to be more versatile. You can put any combination of satellites you want into it. For example, you can create a collection of all the Starlink satellites in the public catalog, or you can create a collection of all objects in Low Earth Orbit.
All Starlink Satellites, can you spot the satellites from a recent launch?
What about all the other settings and behaviors that normal satellites have? Can I control those as well?

The Satellite Collection object provides the option to associate one or more reference satellite(s) with all or part(s) of the collection. When Satellite Collection entries have an associated reference satellite, they inherit all non-trajectory settings of the reference when they are used in analyses.

For example, if you wanted to determine which elements of the collection were lit during visibility periods to a ground station, you could set a lighting condition constraint on a reference satellite associated with the collection and then run a Deck Access operation. Or, your collection may consist of groups of satellites of different build configurations. In this case, you can use multiple reference satellites to represent the variety of builds and associate collection entries accordingly.
Reference satellite assignment by Shell in dual-shell Walker Constellation
What if I want to take a closer look at one of my satellites?

Sounds like you need a promotion! Or more appropriately, you need to promote that collection entry to be a full-fledged satellite object. Luckily, you can do just that through the right-click menu in the 3D window.
Promote to a full satellite from 3D window
So, what's next?

Well, we have a few more ideas up our sleeves to further round out the Satellite Collection capability in STK 12.5 and beyond, but we would also love to hear from you. Your feedback can help shape the future of the Satellite Collection and other future collection objects!

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STK 12.4: The One with the Satellite Collection

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Knock Knock! Who's there? I got a whole lotta. I got a whole lotta who? I got a whole lotta of satellites in my collection, wanna see it? The Satellite Collection - which was a preview feature in STK 12.2 - is all grown up and is now a standard feature in STK 12.4!

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Solar sails are the only method of spacecraft propulsion in which no fuel is needed. Until recently spacecraft powered by solar sails were the stuff of science fiction. However, following the success of the Japanese spacecraft IKAROS which flew close to Venus in 2010, and in 2019 the crowd-funded Light Sail 2 spacecraft it is likely that spacecraft powered by solar sails will play an increasing role in future space exploration.
The Sunjammer a 1964 short story by Arthur C Clarke. IKAROS on its way to Venus in 2010 - image credit Wikimedia Commons It features the racing of space-yachts powered by solar sails.
How do solar sails work?

Solar sails work by using radiation pressure from sunlight to produce thrust. Effectively a solar sail is a mirror, reflecting sunlight that hits it.

Light consists of a stream of photons, whenever a photon hits the surface of a mirror it is reflected back at the same angle it strikes the mirror, shown as the Greek letter theta (θ) above. Some of the photon's momentum is transferred to the mirror -pushing it away in a direction at right angles to its surface. The the net effect of the vast numbers of photons in sunlight is to generate a force or thrust accelerating the mirror away from the Sun in the direction shown by the red arrow.

Because the direction of the thrust is at right angles to the mirror's surface it is possible to change it by orientating the mirror at different angles to the Sun, making it possible to steer a solar powered spacecraft.
The diagrams show how the direction of the thrust changes with the solar sail's orientation to the Sun.

The table above shows thrust on a scale where the value when the mirror is perpendicular to the Sun is 100%. It assumes that all sunlight is reflected from the sail. Light absorbed by the mirror
The magnitude of the thrust also varies with the sail's orientation. It is at its greatest when the sail is perpendicular to the Sun's direction and falls off as the angle to the Sun decreases. When the sail is edge on, i.e. at an angle of 0 o to the Sun, the thrust is zero.
Variation with distance from the Sun
In reality, no mirror is 100% efficient, reflecting all light that hits it. Some light is always absorbed. The direction of the thrust caused by photons which are absorbed rather than reflected is always where the light is coming from regardless of the orientation of the mirror. This is illustrated below. In addition, the maximum thrust caused by absorbed light is only 50% of that caused by reflected light.

The intensity of sunlight, and therefore the thrust on a solar sail falls as the inverse square of the distance from the Sun.

Using solar sails as a method of propulsion

Force is measured in newtons (for those of you in the UK and the US who prefer imperial units 1 newton equals 0.225 pounds force). At the Earth's distance from the Sun, the intensity of sunlight a number known as the solar constant is 1.361 kilowatts per square metre. Assuming that:

all sunlight is reflected, (i.e none is absorbed by the sail) and

the sail is perpendicular to the Sun,

this value of the solar constant provides a thrust of 0.000 009 08 newtons per square metre of sail. So, a sail having an area of 100 square metres would have a maximum thrust of 0.000 908 newtons (0.0002 pounds in imperial units).

This is a very weak thrust compared to traditional rockets. For example, the first stage of the SpaceX Falcon 9, which lifts the spacecraft off the launchpad, generates a massive 7.6 million newtons (1.7 million pounds) of thrust and burns for only 162 seconds before all its fuel is exhausted. The second stage, which produces 930 000 newtons of thrust, then kicks in and burns for a further 400 seconds to take the payload into orbit. Even the small thrusters on the SpaceX Dragon 2 space capsule, which fire for a short time to adjust its position each develop 400 newtons of thrust.

From Isaac Newton's second law of motion.

Force (i.e. thrust on the spacecraft) = mass x acceleration ( i.e. rate of change of velocity)
A simple illustration
So, the acceleration provided by a solar sail is its thrust divided by the mass of the spacecraft. To maximise acceleration the thrust must be as large as possible and the mass of the spacecraft as small as possible.

If we have a solar sail measuring 30 by 30 metres, giving a total area of 900 square metres and we assume that it is 90% efficient then its thrust is

900 x 0.000 009 08 x 0.9 = 0.0074 newtons

If we make the sail out of a material 0.01 mm thick having a density of 1 grammes per cubic centimetre (1000 kg per cubic metre) then the total mass of the sail (area x thickness x density) is

900 x 0.00001 x 1000 = 9 kg

However, in addition to the mass of the sail the spacecraft has its own mass. If we assume that the total mass of the spacecraft and sail is 40 kg then the acceleration (thrust divided by mass) provided by the sail is a meagre

0.0074 newtons/ 40kg = 0.000185 metres/second 2

However, the great beauty of solar sails is that they require no fuel. They provide a small continual acceleration in contrast to rockets which provide a powerful thrust for a short time (which is usually measured in minutes)

So, assuming there were no other forces acting on the spacecraft, over a period of one day (86 400 seconds) the spacecraft could change its velocity by:

86 400 x 0.000185 ≈ 16 metres per seconds ( which is roughly 58 km/h).

Although this is still a small change in velocity, over six months the spacecraft could increase its velocity by 10 600 km/h - without any fuel being used.

This illustrates the key feature of solar sails- they cannot produce the large thrusts needed to lift rockets off the ground, but the small acceleration mounts up over a period of time to produce large changes in velocity. This could make them suitable for powering unmanned spacecraft travelling between planets.

Some more concrete examples

The illustration above is an oversimplification, because it assumes that the only force acting on the spacecraft is the solar sail thrust.

In reality, things are a little more complicated.
Here are some example trajectories Example 1

The spacecraft will be in orbit around the Sun, and the force of the Sun's gravity will pull it toward the Sun. The Sun's gravity and the spacecraft's initial orbital parameters (distance and starting velocity) must be taken into account when calculating its trajectory.

If the spacecraft passes another massive object, e.g. a planet, then the effect of the gravitational force due to the object will need to be taken into account.

The thrust provided by the solar sail and the gravitational force due to the Sun are continually changing as the distance to the Sun varies.

If the orientation of the solar sail to the Sun changes, both the magnitude and direction of the thrust will change.

In this case, the spacecraft has a mass of 10 kg and starts off in a circular orbit at a distance of one astronomical unit (AU), which is 150 million km, from the Sun. It has a very large solar sail, inclined at an angle of 45 degrees to the direction of the Sun, which produces a thrust of 0.003 newtons.

Note that at the initial distance of 150 million km from the Sun the force of the Sun's gravity on a 10 kg mass is 0.0593 newtons, roughly 20 times the thrust provided by the solar sail. Interestingly, because the force of the Sun's gravity and the intensity of sunlight both fall as the inverse square of the spacecraft's distance from the Sun, provided the sail maintains an orientation of 45 degrees to the Sun's direction, then the Sun's gravity will always be twenty times larger than the thrust on the sail regardless of the spacecraft's distance from the Sun.
The numbers show the distance from the Sun in astronomical units. After 18 months the spacecraft will be approximately 1.6 AU from the Sun. Example 2
Assuming the orientation remains at 45 degrees to the direction of the Sun, the spacecraft will gradually spiral away from the Sun. Over an 18-month period it will follow the trajectory shown below.

This is the same as the previous example with the exception that the sail is orientation in such a way as to decelerate the spacecraft in its orbit, i.e the thrust is directed to cause the spacecraft to lose energy.
After 12 months the spacecraft will be only 0.56 AU from the Sun Example 3
In this case assuming the orientation remains at 45 degrees to the direction of the Sun, the thrust provided by the sail will cause the spacecraft to steadily lose energy and it will spiral inwards towards the Sun. Over a 12-month period it will follow the trajectory shown below.

In this case, once again the spacecraft has a mass of 10 kg and starts off in a circular orbit at a distance of 1 AU from the Sun. This time the sail is orientated at an angle of 90 degrees to the direction of the Sun and produces a thrust of 0.006 newtons.
Example 4
In this case the spacecraft's orbit changes shape from circular to elliptical. Its closest distance from the Sun is 1 AU and its furthest is 1.25 AU. It takes 460 days to complete its new orbit.

This is a modified version of example 1; as in all the previous examples, the spacecraft has a mass of 10 kg and starts off in a circular orbit at a distance of 1 AU from the Sun. However, this time, it has an extremely large solar sail, orientated at an angle of 45 degrees to the direction of the Sun. This produces a thrust of 0.03 newtons, - roughly half the strength of the Sun's gravity.

In this case the thrust is strong enough for the spacecraft to rapidly escape the Sun's gravity. Rather than gradually spiralling outwards, the spacecraft escapes from the solar system on a hyperbolic trajectory into interstellar space. After nine months the spacecraft will be 4.4 AU from the Sun.

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Solar sails are the only method of spacecraft propulsion in which no fuel is needed. Until recently spacecraft powered by solar sails were the stuff of science fiction. However, following the success of the Japanese spacecraft IKAROS which flew close to Venus in 2010, and in 2019 the crowd-funded Light Sail 2 spacecraft it is...

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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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Could We Use Magnets To Clear Up Our Space Junk?

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Could We Use Magnets To Clear Up Our Space Junk?

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Hello! I have no formal knowledge with the technological space industry nor physics for that matter. However, lately I have been researching space debris, and I love how it is a problem the whole world is trying to solve. My question is this; why can't we consolidate the debris before moving onto a series of steps, ending with eliminating it. I do know that electromagnetism doesn't lose its ability in space due to natural physics. Has anyone ever implemented the idea of bringing the debris together to a central point, maybe a controllable magnetic source, with the end goal of maneuvering that magnetic source into a position in which it is no longer a threat; or a position that can act as a destruction point? Thank you!

The great thing about solutions to space debris is that pretty much every off-the-wall idea has been suggested with some degree of seriousness. (This is also the only great thing about space debris.) Many of these suggestions never make it off the ground, but the suggestions are there. Space debris is a problem with no clear solution - the nature of the debris itself is so varied that no single approach is likely to solve it. However, any solution is better than no solution, and we're still in a phase of learning what methods are likely to best help clean up after ourselves.

Any solution to space debris has a number of significant hoops to jump through to be considered useful, but the number one rule for debris-hunting missions is "do not generate more debris." The last thing you want to do is send up a new satellite, crash it into a dead satellite, and then lose control of both the new one, the old one, and have bits break off of both. When two satellites collide, you can generate thousands of new and dangerous pieces of shrapnel, the very definition of not helping the problem. Space debris is moving at an astonishing speed around our planet, and so any collisions between objects up there are extremely energetic. It is very easy to break a rigid object in space by hitting it with another object coming at it from the other direction - even a stray bolt can do a huge amount of damage if it's moving at more than 10,000 miles per hour.

If you want to catch a satellite, with a magnet or with any other method, you need to do so very, very carefully in order to avoid disaster. This usually means you can't use the main body of the satellite to do the catching, which in turn means you need some kind of maneuverable grabbing arm, or you need a deployable net. These methods work best with large objects, like satellites which are still intact, and you still have to approach them carefully, because most satellites aren't designed to withstand sudden changes in velocity. A high velocity whiplash to a satellite could easily snap off solar panels, antennas, or other protruding objects.

A satellite which is defunct but intact (a best-case space junk scenario) has the additional complication of not being particularly regular in shape. Because there's very little atmospheric drag at these altitudes, the satellites have no obligation to be aerodynamic like airplanes do, and so often have instruments poking out in all directions. A partially destroyed satellite will have the same set of protrusions, but will also have a sharp edge where it broke. On the one hand, these irregularities mean it might be easier to snag the satellite somehow. On the other hand, catching it comes with a much higher risk of damaging whatever's doing the catching. (This is another reason nets seem appealing; it's relatively hard to puncture something that's mostly empty space.)

But there's a more significant problem with using a magnet on a tether to collect space debris, even if it is maneuverable. A huge chunk of our space debris isn't magnetic.

Satellites are very finely-tuned computers, designed to make a series of measurements extremely accurately and precisely, but they're also designed to be light; the lighter the satellite, the less fuel required to push it into orbit, and the less expensive that satellite's launch becomes. Metal is heavy! And even the metals that are used aren't necessarily magnetic - aluminum isn't. So a magnet as a collecting device might collect stray bolts, or some of the internal supports to a broken-apart satellite, but it would totally miss the rocket debris imaged above, or a plastic circuitboard. And that's just the big pieces; trying to catch a tiny fleck of paint with a magnet is an exercise in futility.

The debris that's most likely to be collected together before being pulled out of orbit are those tiny ones. If you could catch a sufficient number of them, you might be able to gradually clear our skies of some of the tinier pieces of debris which otherwise go pinging at high speeds into our still functional satellites (and sometimes our crewed missions). Plucking tiny flecks of paint out of the sky is impractical in the extreme, but we may be able to take a lazier approach. Something more like very durable flypaper has been suggested for this purpose - anything that a piece of grit could impact, get stuck to, but not break or bounce off of. Aerogel is often the material of choice here; it's very light, so cheap to launch, and very good at catching tiny pieces of stuff. We used it to catch pieces of a comet and bring them back to earth with the Stardust mission, and we had some up on the Mir space station for a time to help identify what the tiny pieces of space junk were in the first place. Once the aerogel fills, you could send it down Earthwards to burn up in our atmosphere.

We are still working on how to catch space debris. Rather than using a magnet to collect a number of satellites at one time, most of the are focusing on capturing individual, large, dead satellites. Again, it's not a cure-all, but removing any of these hazards is better than removing none of them. The European Space Agency is working on e.Deorbit, which is taking a fishing net on a tether approach. The irregular shape of the satellites will help trap the net on its surface, and then the net-launching satellite can drag its cargo back into the atmosphere, where it will either burn up or crash safely in the ocean.

Japan's space agency JAXA has a prototype for a new system of dealing with space junk, which, if it works, will deal with both magnetic tiny objects and one large object per mission. Currently tightly coiled and attached to the ISS resupply capsule Kounotori 6 is a 700 meter long tether made out of conducting metal, called the Kounotori Integrated Tether Experiment (KITE). When the resupply capsule leaves the ISS, loaded up with the ISS' old batteries and other unneeded goods, but before it re-enters the atmosphere, the tether will unspool, and a charge will be run through it. The motion of the long charged cable through the Earth's magnetic field will create a force pushing other objects down towards the Earth - hopefully tossing some small pieces of metal down towards the atmosphere. In its final form, the tether will have a grappling hook attached to its other end, which can be attached to a dead satellite and then used to tug the defunct satellite down to Earth. This current test, however, will end with the tether being released, in an orbit where it will fall back to Earth after a few weeks. Hopefully it will have cleared at least a little bit of our mess away with it.

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Could We Use Magnets To Clear Up Our Space Junk?

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Hello! I have no formal knowledge with the technological space industry nor physics for that matter. However, lately I have been researching space debris, and I love how it is a problem the whole world is trying to solve. My question is this; why can't we consolidate the debris before moving onto a series of steps, ending with eliminating it.

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Perched on the slopes of Tenerife's Mount Teide, ESA's latest tracking station is focused on the challenge of space debris. Instead of radio waves, the IZN Laser Ranging Station relies on laser light. Its laser pulses probe hundreds of kilometres into space, making contact with items of debris as well as intact satellites, fixing their position down to a matter of centimetres.

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Abstract

As a for suppressing space debris growth (P. Eighler, A. Bade, Chain Reaction of Debris Generation by Collisions in Space-A Final Threat to ? in: 40th Congress of the International Astronautical Federation, IAA-89-628, October 1989), the National Aerospace Laboratory of Japan is investigating a satellite capture, repair and removal system for non-cooperative satellites, part of which involves assessing the viability of electrodynamic tether (EDT) technology as an countermeasure Spaceflight orbital transfer system. In this paper, some results concerning the time required to remove existing satellites, the behavior of flexible tethers during the debris separation phase, and orbital transfer strategies of EDT systems during space debris removal operations are described. From numerical simulations, it is found that EDT systems can transfer satellites from LEO to orbits with a short lifetime within a realistic timeframe. It is also found that the stability of EDT systems is compromised when debris separation occurs both while a tether current is running and when the ratio of the end mass to that of the service satellite is high. To ensure stability, the end mass should be selected from the target debris group with due regard for the maximum possible mass that can be maneuvered safely. Moreover, it is also found that orbital elements (a, e, i) can be changed independently with an adequate current control strategy.

Introduction

After about 45 years of space exploration, there are growing concerns that the accumulation of space debris is leading to environmental degradation in near-Earth space [2]. In order to conserve the environment, it is very important to deorbit large artificial objects such as post-mission satellites and rocket upper-stages, since they pose a collision risk with other objects, and with it the possible generation of countless smaller debris. Densely populated regions already exist (e.g. altitude 1000 km, inclination ; altitude 1500 km, inclination 74/). Investigations by our group have shown that the re-orbiting of large space debris objects to lower orbits with a short lifetime (NASA [1]/NASDA/ESA proposes a 25-year limit as a safety standard.) would be a very effective countermeasure against debris growth.

The National Aerospace Laboratory of Japan is now investigating a capture, repair and removal system for satellites which have ended their missions, or have malfunctioned. Electrodynamic tether (EDT) technology is under study for its possible use as an orbital transfer system. An EDT system has a pair of plasma contactors at either end of the tether which enable electric current to flow through it by closing the circuit via the ambient plasma. The tether then generates a Lorentz force via interaction between the current and the geomagnetic field. Therefore, EDT systems can provide acceleration or deceleration without the need for propellant, and show promise as a next-generation non-chemical thruster. However, the generated thrust is low, and its direction depends on the local geomagnetic field vector and the tether orientation. Thus, current has to be tightly controlled during orbital transfer to achieve the desired effect. Since tether tension decreases discontinuously during debris separation, there is possibility that EDT systems could become unstable. Stability during this phase must therefore be confirmed by numerical simulations of the dynamics, taking into account tether mass and flexibility.

The goal of this study is to investigate the viability of EDT systems for space debris removal by addressing the following points:

Hereafter, we will call the non-cooperative satellite to be captured and disposed of the "target", and the spacecraft that captures and propels it the "service satellite".

Section snippets

Outline of space debris removal mission

The space debris mission considered in this study involves one spacecraft removing a number of space debris objects from their orbits, consecutively. Fig. 1 illustrates each phase of the mission. First of all, the service satellite transfers its orbit, by means of an electrodynamic tether, to approach a target debris object (phase I). Once close enough, it retrieves the tether and uses a conventional propulsion system for rendezvous-electrodynamic tethers cannot provide sufficient thrust for

EDT system

In this paper, the EDT system contains plasma contactors (hollow cathodes) at both ends of the tether, to enable current to flow in both directions [3]. The tether is multi-stranded to improve its survivability against impacts by small space debris during long missions [4], [5], and it is insulated from the ambient space plasma over its entire length.

Neither the performance of the plasma contactors nor the structure of the multi-stranded tether is considered; the tether material is assumed to

Required time for space debris removal

In this section, the time required for satellite removal using an EDT system is determined analytically. The calculation makes the following assumptions:
The required time is the turn-around trip time considering only orbital transfer time. The time required by both the capture and separation phases of the mission

The system behavior in separation phase

In this section, the behavior of the system during debris separation phase is discussed using the results of simulations which take into account tether mass and flexibility. The tether model applied here is the lumped mass model described above.

Case A: separation from a stable tether oriented along the local vertical.

Case B: separation while a continuous tether current is running.

Case C: separation with no current

Orbital change of EDT system

As mentioned in the introduction, the direction and magnitude of the Lorentz force depend on the local geomagnetic field vector; this complicates orbital transfer, since the direction of Lorentz force changes periodically during orbit. Thus, appropriate tether current control is required in order to achieve successful orbital transfer.

As examples, some simulation results using a simple tether model are shown in Fig. 11, which plots the time histories of the orbital elements (semi-major axis,

Orbital plane change utilizing the earth's rotation

The direction of the Lorentz force and the thrust of the EDT system cannot, in general, be controlled independently, since they both depend on the local geomagnetic field vector. The exception to this rule is the orbit of zero inclination. It is difficult to control these parameters separately, and so appropriate current application is required to achieve the desired orbital transfer. In this section, some strategies are investigated which enable separate control of the orbital elements

Summary

The on-orbit environment is deteriorating year by year owing to the build-up of space debris, and there is already widespread acknowledgment worldwide that a space debris problem exists. A service satellite dedicated to the repair and removal of non-cooperative satellites is under investigation at the National Aerospace Laboratory of Japan as a means to conserve the near-Earth space environment. An electrodynamic tether (EDT) system is studied as the main propulsion system from the point of

NASA Safety Standard, Guidelines and Assessment Procedures for Limiting Orbital Debris, NASA NSS 1740, 14, August,...

Chain Reaction of Debris Generation by Collisions in Space-A Final Threat to Spaceflight?

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Study on electrodynamic tether system for space debris removal

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As a for suppressing space debris growth (P. Eighler, A. Bade, Chain Reaction of Debris Generation by Collisions in Space-A Final Threat to ? in: 40th Congress of the International Astronautical Federation, IAA-89-628, October 1989), the National Aerospace Laboratory of Japan is investigating a satellite capture, repair and removal system for non-cooperative satellites, part of which involves assessing the viability of electrodynamic tether (EDT) technology as an countermeasure Spaceflight orbital transfer system.

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Magnet Technology Used To Clean Up Space Junk

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The World Economic Forum is an independent international organization committed to improving the state of the world by engaging business, political, academic and other leaders of society to shape global, regional and industry agendas. Incorporated as a not-for-profit foundation in 1971, and headquartered in Geneva, Switzerland, the Forum is tied to no political, partisan or national interests.