This year is the 60th anniversary of the Space Age, which has already seen many giant leaps for humanity. We've gone from Sputnik to space stations to Pluto probes in one human lifetime, unleashing a galaxy of science and technology in the process.
Unfortunately, we've also unleashed a galaxy of garbage. Our trash already accumulates in remote earthly locations from Midway Atoll to Mount Everest, but like many frontiers before it, Earth's exosphere is increasingly cluttered, too. Hopefully the same ingenuity that helped us reach space can still help us clean it up, too.
Waste in space
Earth's orbital environment contains about 20,000 pieces of human-made debris larger than a softball, 500,000 pieces larger than a marble and millions of others that are too small to be tracked. (Image: ESA)
Commonly known as space junk, this orbital trash mainly consists of old satellites, rockets and their broken parts. Millions of pieces of human-made debris are currently hurtling through space overhead, moving at speeds of up to 17,500 mph. Because they're whizzing by so quickly, even a tiny piece of space junk could cause catastrophic damage if it collides with a satellite or spacecraft.
But the space around Earth is too important for us to let ourselves ruin it with garbage. Satellites alone are key to services like GPS, weather forecasting and communication, plus we need to safely pass through this region for bigger-picture missions into deeper space. It's obvious we need to remove space junk, but for a place that's already a vacuum, space can be surprisingly hard to clean up.
Even just figuring out how to grab a piece of space junk is tricky. The first rule is to avoid making more space junk, which can easily happen when pieces collide, so it's helpful for any junk-collecting spacecraft to keep a safe distance from its target. That may mean using some kind of tether, net or robotic arm to do the actual corralling.
Suction cups don't work in a vacuum, and the extreme temperatures in space can render many adhesive chemicals useless. Harpoons rely on high-speed impact, which could chip off new debris or push an object in the wrong direction. Yet the situation isn't hopeless, as some recently proposed ideas suggest.
A magnetic, tugboat-esque chaser satellite would corral derelict satellites by targeting electromagnetic components known as 'magnetorquers,' which use Earth's magnetic field to adjust satellites' orientation. (Image: Emilien Fabacher/ISAE-Supaero)
The European Space Agency (ESA), which actively tracks space debris, supports an array of debris-fighting projects under its Clean Space program. The ESA also announced funding for an idea developed by researcher Emilien Fabacher of the Institut Supérieur de l'Aéronautique et de l’Espace (ISAE-SUPAERO), at the University of Toulouse in France.
Fabacher's idea is to collect space junk from a distance, but not with a net, harpoon or robotic arm. Instead, he hopes to reel it in without even touching it.
"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," Fabacher explains in a statement from the ESA. "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."
Target satellites wouldn't need to be specially equipped in advance, he adds, since these magnetic tugboats could take advantage of electromagnetic components, known as "magnetorquers," that help many satellites adjust their orientation. "These are standard issue aboard many low-orbiting satellites," Fabacher says.
This isn't the first concept to involve magnetism. Japan's space agency (JAXA) tested a different magnet-based idea, a 2,300-foot electrodynamic tether extended from a cargo spacecraft. That test failed, but it failed because the tether didn't release, not necessarily due to a flaw in the idea itself.
Still, magnets can only do so much about space junk. Fabacher's idea is mainly focused on removing entire derelict satellites from orbit, since many smaller pieces are too tiny or non-metallic to be reined in with magnets. That's still valuable, though, since one large piece of space junk can quickly become many pieces if it collides with something. Plus, the ESA adds, this principle could also have other applications, like using magnetism to help clusters of small satellites fly in precise formation.
Grabby gecko bots
Another clever idea for collecting space junk comes from Stanford University, where researchers worked with NASA's Jet Propulsion Laboratory (JPL) to design a new kind of robotic gripper that can grab and dispose of debris. Published in the journal Science Robotics, their idea takes its inspiration from sticky-fingered lizards.
"What we've developed is a gripper that uses gecko-inspired adhesives," says senior author Mark Cutkosky, a professor of mechanical engineering at Stanford, in a statement. "It's an outgrowth of work we started about 10 years ago on climbing robots that used adhesives inspired by how geckos stick to walls."
Geckos can climb walls because their toes have microscopic flaps that create something called "van der Waals forces" when in full contact with a surface. These are weak intermolecular forces, created by subtle differences among electrons on the outsides of molecules, and thus work differently from traditional "sticky" adhesives.
The gecko-based gripper isn't as intricate as a real gecko's foot, the researchers acknowledge; its flaps are about 40 micrometers across, compared with just 200 nanometers on an actual gecko. It uses the same principle, though, adhering to a surface only if the flaps are aligned in a specific direction — yet also needing only a light push in the right direction to make it stick.
"If I came in and tried to push a pressure-sensitive adhesive onto a floating object, it would drift away," says co-author Elliot Hawkes, an assistant professor from the University of California, Santa Barbara. "Instead, I can touch the adhesive pads very gently to a floating object, squeeze the pads toward each other so that they’re locked and then I'm able to move the object around."
The new gripper can also tailor its collection method to the object at hand. It has a grid of adhesive squares on the front, plus adhesive strips on moveable arms that let it grab debris "as though it's offering a hug." The grid can stick to flat objects like solar panels, while the arms can help with more curved targets like the body of a rocket.
The team has already tested its gripper in zero gravity, both on a parabolic airplane flight and on the International Space Station. Since those tests went well, the next step is to see how the gripper fares outside the space station.
These are just two of many proposals for cleaning up low-Earth orbit, joined by other tactics like lasers, harpoons and sails. That's good, because the threat of space junk is big and diverse enough that we may need several different approaches.
And, as we should have already learned here on Earth, no giant leap forward is really complete without a few small steps back to clean up after ourselves.