Geckos, some of nature’s most skilled climbers, may hold the key to cleaning up the enormous amount of debris clogging up the space around Earth. Scientists at NASA and Stanford have developed a prototype robot that can grip objects in space, the same way a gecko sticks to walls. Such a robot could be a critical tool for grabbing and relocating space trash, helping to clean up Earth orbit and make it much safer for space travel.
The robot capitalizes on the same concept that geckos use to climb. The animal’s feet aren’t actually sticky; they’re covered in thousands of microscopic hairs that, together, act like a flexible adhesive. To imitate gecko feet, the robot has special pads outfitted with thousands of tiny silicone rubber hairs, which are 10 times smaller than the hairs on your head. This allows the robot to use the same forces to “grab” simply by placing its pads on an object’s surface.
And just like a gecko, the grip can easily be turned on and off. The hairs on a gecko’s feet are tilted so that the lizard must place its foot at a certain angle in order to stick. It can then simply remove its foot by pulling in a different direction. The “hairs” on the robot also have a tilt, so the gripper can easily remove itself from an attached object by pulling away in a different direction.
This kind of sticking technique could be crucial for getting ahold of unruly space trash. Much of this junk includes out-of-commission satellites or rocket parts that have run out of fuel, all moving at thousands of miles per hour in orbit. These objects are often spinning or moving erratically, and their surfaces can be relatively smooth and hard to grasp. But the gecko gripper, described today in Science Robotics, doesn’t need a handle to grab — any surface will do. “It’s a new way to handle these non cooperative pieces of garbage,” Aaron Parness, a robotics engineer at NASA’s Jet Propulsion Laboratory who helped create the technology, tells The Verge.
A trashy orbit
Space debris threatens future space travel. Hundreds of thousands of pieces of abandoned space hardware zoom around the planet. That makes Earth orbit very crowded, and it clogs up valuable real estate. For instance, areas over major cities are prime places to put communications satellites. “But if there’s a piece of garbage in that position, it’s a very expensive piece of garbage there,” says Parness.
Space trash is dangerous, too. Every now and then, the International Space Station has to change its position in orbit to avoid collisions with debris. But as the amount of junk grows, the probability of in-space collisions increases, and that leads to even more debris. That happened in 2009, when a Soviet-era satellite collided with one owned by the US company Iridium, creating thousands of pieces of debris. If enough of these collisions occur, eventually Earth orbit will be filled with so much junk that we won’t be able to safely go into space anymore.
There are regulations in place to make sure that the stuff we put up must come down. Satellite operators have to dispose of out-of-service vehicles, either by burning these objects in Earth’s atmosphere or by putting them in a higher orbit — called a graveyard orbit — where they won’t get in the way of functioning satellites. But these regulations weren’t in place when satellites were being launched throughout the ‘60s, ‘70s, and ‘80s, so there’s a lot of old trash to watch out for.
People have come up with innovative ways to take out the trash, such as burning hardware up with lasers. But grabbing this junk hasn’t been an option. Space is a vacuum, so suction cups don’t work; most trash isn’t magnetic, so magnets won’t help; and the extreme temperatures mean most glues won’t work either, says Mark Cutkosky, an engineering professor at Stanford and one of the authors on the study, tells The Verge. “If you want to grab something in space, almost nothing else works” besides the gecko grip, says Cutkosky.
Geckos’ grips are unusual: the tiny hairs on their feet can get incredibly close to an object’s surface — nanoscale distances apart. “And that’s the key,” says Cutkosky. “You need to have really intimate proximity.” This allows the atoms in the hairs to mingle with the atoms on a surface. The electrons of these atoms actually sync up in such a way that they cause an attraction between molecules. The force of each hair adds up, creating a strong overall attraction over the entire foot.
The “feet” or pads of the robotic gripper work the exact same way. The silicone rubber hairs are a fifth of the diameter of a human hair at 20 microns; they’re shorter than the width of a human hair, too, at just 60 microns tall. (A human hair is roughly 100 microns in diameter.) The robot is also designed to turn off its stickiness, just like the lizard. Motors inside pull the pads in the direction needed to get a grip. When the gripper approaches a surface, the motors make tendons inside the robot tighten, causing the hairy pads to move together in the right direction to stick. Then, when the robot needs to let go, the motors loosen the tendons, moving the pads in the opposite direction for an easy release.
This gripping technique has already been tested in space. Little strips of the hairs, called Gecko Grippers, were sent to the ISS in 2016 to see how well they worked in microgravity. But the team wanted to see how a robot, with the special motorized movement, fared in zero-g as well. So they took a gripping robot on a plane that simulates zero gravity — nicknamed the Vomit Comet. The plane does parabolas in the sky to create short periods of weightlessness. Aboard the Vomit Comet, Parness used the robot to grip different types of shapes you might find in space, such as a sphere, a cube, and a cylinder.
Jiang et al., Sci. Robot. 2, eaan4545 (2017)
The motorized gripper worked just fine in zero-g — sometimes even better than when gravity was in play. And when it came time to release the objects it had grabbed, the robot did so effortlessly. “Nothing happens when he lets go,” says Cutkosky. “It doesn’t jerk the object, and that was the key requirement. It’s an absolutely smooth, effortless detachment.”
Gripping in space
Building on their success, the team is now hoping to test out the robot’s abilities in space. Earth orbit gets incredibly cold, and the researchers will need to build a new robot that can withstand such an unwelcoming environment. Plus, they need to prove that the adhesive technique can work just as well at much colder temperatures.
But if the robot does hold up, the team envisions two types of vehicles that could be used to clear up space debris in the future. One design is a large 2,000-pound satellite, equipped with a gripper that moves through space grabbing and relocating debris — either to the graveyard orbit or so that it eventually burns up in the atmosphere. Such a vehicle wouldn’t be able to clean up all the trash, but it could target either the most dangerous junk or the pieces lurking in valuable places in orbit. The other option is to create a tiny satellite, no more than a couple of pounds, that travels to one piece of debris and removes it from orbit. The vehicle wouldn’t last for very long — since it wouldn’t have much fuel — but the style is much cheaper to build and fly.
There even other applications beyond clearing up space debris. A gripping robot could be a valuable asset on board the ISS, and it could help on the outside of the ship for repairs and inspection. That could potentially cut down the number of dangerous and time-consuming spacewalks astronauts have to do.
No matter what the robot is used for, Parness says most of the design credit goes to the gecko. “If the gecko didn’t exist, humans would never have come up with this idea,” says Parness. “It’s not an intuitive thing, we would never have invented it if it weren’t for the biological example.”