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How can humans clean up our space junk?

Humans filled waterways, landfills, and streets with trash, so it’s no surprise the same thing happened in Earth’s orbital neighborhood. Now our species will finally take a crack at cleaning up.

Some missions focus on dead satellites, aiming to catch them with robotic arms, spear them with harpoons, or slow them with sails or tethers. Others aim for smaller pieces with lasers or stick to them with adhesive. It’s all an effort to keeping low-Earth orbit, the region up to 1,200 miles from the surface, usable. “Keeping all this litter in space, it’s like litter on the floor,” said Jason Forshaw a research fellow at the University of Surrey. “It’s becoming more of a risk.”

The next few missions are RemoveDebris from Britain, on which Forshaw is one of the lead scientists; Japan’s just-launched Kounoutori 6 satellite, carrying the Kounotori Integrated Tether Experiment; and e.Deorbit from the ESA. Even the private sector is getting into the act: Japanese startup Astroscale is designing a debris-removal satellite. RemoveDebris is planned for 2017, while Astroscale plans to launch in 2018. e.Deorbit’s flight is scheduled for 2023 or 2024.

Low-Earth orbit is certainly crowded. There are currently about 780 satellites in the region as of mid-2016, with more planned all the time, according to the Union of Concerned Scientists. The satellites share the area with about 500,000 pieces of junk a half inch across and larger, according to NASA estimates. Paint chips, pieces of blown-up satellites, spent rocket stages — it’s all there. Since everything moves at thousands of miles an hour, a paperclip can smack into a satellite with more energy than a heavy machine gun round. In April, a micrometer-sized piece of debris put a half-inch pit in an ISS window, even though the station orbits well below the majority of the junk.

The ISS shielding is limited to objects less than about a half an inch across. NASA, working with the Department of Defense’s Space Surveillance Network, can track anything larger than about two inches, which covers about 21,000 objects. “There’s a gap between what they are shielding for and what they can track,” says Gene Stansberry, program director of NASA’s orbital debris office.

While the new missions are testing ways to pick up junk, technology isn’t the main reason we haven’t already got a United Galaxy Sanitation Patrol. Salvage rules don’t apply in space, says Brian Weeden, technical advisor at the Secure World Foundation and author of several studies of space debris. “[The launching state] has jurisdiction and control,” he said. “And yes, that means you have to get their permission to interact with a piece of space junk.”

Liability is another complication; officially the launching state is responsible for anything that happens. “Up to now it’s just been between the U.S. and Russia, saying ‘I’m good if you’re good,’” Weeden said. The liability provisions of various international agreements simply haven’t been invoked, largely because proving fault in space is time consuming and costly. Other countries facing a private party may feel differently. “Imagine I’m company X and I touch a satellite and it explodes, and six months later it hits someone else’s satellites,” Weeden said. That could involve any of a dozen spacefaring nations.

These legal wrinkles are one reason governments would rather have an institution like the University of Surrey back a mission, which at 15 million euros is cheap, Forshaw said. RemoveDebris will go after whole satellites, because tracking small objects and targeting them (to say nothing of determining a fragment’s owner) is harder. Using cubesats, small satellites that can be fit together like Lego bricks, it will test three technologies for bringing satellites down: a net, a harpoon, and a sail — two of which would work in tandem.

For the net, a cubesat will launch from the ISS and inflate a balloon. A second cubesat will follow and fire a net to grab the inflated satellite. The inflated satellite should fall back to Earth as the slight atmospheric drag causes it to slow down. In a real deployment, the net would likely have a tether line attached to the firing satellite, which would tug on the target spacecraft to create even more drag. The harpoon will test one satellites ability to target and hit another — an important point if the aforementioned net is going to scale. In this case a cubesat will extend a target on an arm, and another will fire the harpoon. Last is the dragsail, in which a cubesat deploys a huge sail like a parachute. The increased drag will, again, bring down the satellite.

e.Deorbit is after bigger fish. The target is the ENVISAT, a 8-ton remote monitoring satellite launched in 2002. The ESA hasn’t settled on a design yet; it is considering either a robotic arm which would grab the satellite, or a net. In the meantime the agency wants to demonstrate tracking, guidance, and capture technologies to see what will work best.

Some technologies will use the magnetic field of the Earth itself to get the satellites down; that’s the aim of JAXA’s Kounotori Integrated Tether Experiment. The craft will trail a long conductive cable, and run current through it. As satellites and cables pass through the Earth’s magnetic field, the interaction of the field and current generates a small force on the tether. (This is the same way electric motors work). The tests will occur in January, as the KITE ship is currently docked with the ISS doing double duty as a supply run.

All three missions are geared toward sending satellites plummeting to a watery graveyard in the South Pacific, east of New Zealand.

For hunting smaller pieces, Astroscale plans is to launch a satellite called ELSA-1, that will track debris and stick to it with glue. Other more out-there proposals include using ISS- or satellite-mounted lasers to vaporize the surfaces of small pieces and force them down, but that will take more technical development of the lasers so they could maximize the amount of energy delivered to the debris.

One reason there are so many methods is there’s little or no data on what might work — it’s largely uncharted territory. Forshaw says there’s still a possibility that it’s “back to the drawing board” if they fail. Satellite rendezvouses, for example are not trivial, and aiming what amounts to a gun at another satellite at close range adds more complexity. It’s not unlike the early days of aviation or automobiles, when engineers tried all kinds of designs before settling on a few that worked best.

No matter which technology proves itself, space junk isn’t going away. Even if launches ceased tomorrow, the problem could persist for a couple of centuries and even get worse, according to a 2008 NASA study. In 2009 a Russian military communications satellite and an Iridium collided and scattered debris, threatening some Chinese satellites; two years later the ISS also had to dodge the shrapnel. New launches — at least those licensed in the US, Japan, and Europe — are required to have a plan for getting a satellite down when it’s at the end of its life. Forshaw, however, calls the mitigation a welcome step. “People have been taking about debris since the 1960s,” he said. “But until now nobody has actually funded missions to study and deal with it.”

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