Grabbing an object in space—like a piece of debris from a disabled satellite—is harder than you might think.
Suction cups are useless in a vacuum, tapes and glues don’t hold up in extreme temperatures, and hand-like devices can’t always grasp large or smooth surfaces. But geckos might be able to help.
Researchers from Stanford University and NASA’s Jet Propulsion Laboratory have developed a robotic device that mimics the sticking power of gecko feet to grab onto objects with only the lightest contact.
When tested in zero-gravity airplane flight, the device was able to grasp and release floating cubes, cylinders, and spheres without affecting their motion. On Earth, the gripper was able to attach to, push, and release 800-pound robots meant to simulate drifting space debris.
The trick? Van der Waals forces. Geckos are able to run up walls not because their feet are sticky, but because they are covered with microscopic hair-like structures that lie flat when a sideways force is applied. This increases the contact area between the hairs and the surface, allowing the gecko to make use of a weak molecular attraction—the van der Waals force—that occurs when molecules are extremely close together.
The researchers recreated this effect with their shoebox-sized device, which has small adhesive tiles lining the bottom. To attach to curved objects, a pair of adhesive film-lined moveable arms extend from either end.
Each tile is about the size of a postage stamp and is covered with hundreds of thousands of tiny silicone wedges. In their neutral “off” position, the tips of those wedges are barely making any contact with the surface they touch, said Mark Cutkosky, co-author of the group’s study . But, by moving the adhesives a microscopic distance to one side, the wedges bend over and the contact area goes way up, allowing van der Waals forces to create adhesion. To release the object, the tiles shift back, and the wedges spring back up so only their tips are in contact.
Leah Crane, reporting for New Scientist:
“It’s hard to get all those little gecko pads in contact with the surface and evenly distribute the load, especially if it’s going to work with both flat and curved objects,” said Matthew Spenko of the Illinois Institute of Technology. “What’s really impressive in this work is that they scale it up and show that it works in a larger size.”
The tiles are placed in pairs so that they act against one another and impart no outside force on the object. This is crucial when trying to capture space debris, Cutkosky says, because “the last thing you want to do is accidentally send it into some other orbit.”
Even tiny pieces of debris can cause serious damage to satellites and space vehicles. NASA and the Department of Defense track over half a million pieces of debris as they orbit the Earth, including both natural and man-made objects, which can range from nonfunctional spacecraft to fragments of exploded rockets. Some 20,000 of these objects are larger than a softball and if you bump them, you risk sending them into a more hazardous orbit or causing them to tumble or spin, making it even more difficult to capture them, said Aaron Parness, co-author of the paper.
“You can imagine if an object is moving 17,500 miles per hour, you really are better off trying to match its speed very exactly and grabbing lightly as opposed to reaching out and trying to catch it at mach 22,” Parness said.
Grabbing onto space debris isn’t the only application for the adhesives. Researchers also hope to use them to allow repair and maintenance robots to scramble over the exterior of spacecraft—sort of like a gecko.
Image credit:Jiang et al., Sci. Robot. 2, eaan4545 (2017)