Saundra Bullock’s character nearly got killed by space debris in the movie “Gravity” — but had she been equipped with the gecko-like robot built by researchers from Stanford University and NASA’s Jet Propulsion Laboratory, there would have been a lot less drama.
Stanford’s Hao Jiang and his colleagues created a space gripper equipped with patches of sticky material that look superficially like refrigerator magnets. Those looks can be deceiving, though: Magnets don’t work on glass or aluminum, and other grappling methods such as suction or chemical adhesion don’t work in a vacuum. To create “magnets” suitable for grabbing space debris, the team stole a trick from the geckos instead.
The technology is described this week in a paper published by Science Robotics.
Aaron Parness from JPL’s Extreme Environments Robotics Group is part of the research team, and explained how the robotic grippers work last year during a NASA briefing. “Geckos stick using something called Van der Waals forces,” he said. “They have tiny hairs on their feet that allow them to take advantage of these forces.”
The tiny hairs are structured to produce an attractive force that makes them adhere to a surface without glue. While current manufacturing methods can’t create microscopic spindles as fine-scaled as the hairs on a gecko’s feet, the sticky patches on the mechanical gripper are close enough to the general shape to take advantage of Van der Waals forces.
Parness said geckos can change the directionality of the hairs on their feet to stick onto a surface, and then let go at will. “If the gecko pulls down on its foot, it’s very sticky, but if the gecko doesn’t pull down or pushes up or to the side, it’s not sticky at all,” he said.
The researchers’ gecko gripper is built the same way. Parness explained that the on-off ability is important, because if something is just generally sticky, you’d have to give it a hard pull to get it unstuck. This can be a problem in space, where a sharp pull can send space junk hurtling off in the wrong direction.
The team tested the gripper at JPL in Pasadena, Calif., where it successfully grappled test objects weighing as much as 800 pounds. They also tried it out during brief periods of zero-G on NASA’s reduced-gravity airplane, known as the “Weightless Wonder” or the “Vomit Comet.” Those tests showed that that the gripper could grab onto flat and round objects with just a gentle tap, and release the objects with the push of a button.
Follow-up tests on the International Space Station confirmed that the technology worked during prolonged weightlessness as well. If the astronauts left the gripper engaged, it could maintain stickiness for weeks at a time.
A round object, such as a low-mass inflatable beach ball, presents a challenge because the gripper could push the object out of reach. “Although it doesn’t require much adhesion, it does require a very tiny engagement force because it is easy to knock the ball away,” Jiang said.
When the experiments took advantage of that engagement force, the gripper’s success rate was 100 percent for a test sphere, compared to 75 percent for a cube and 81 percent for a cylinder. “The failures were due to excessive misalignment between the gripper and the objects, caused by inaccurate positioning by the human operator or by the object bumping into obstacles that caused substantial disturbance,” the researchers said in their study.
The gecko adhesive was also tested on NASA’s Limbed Excursion Mechanical Utility Robot 3, better known as LEMUR 3. The robot can use tiny hooks to grab onto rocky surfaces, and use gecko grippers to walk across smooth surfaces like solar panels or the exterior surface of a spacecraft. Such a robot could be used for inspections and repairs that astronauts would normally have to do themselves.
Experts say space is cluttered with more than 20,000 pieces of orbiting junk that are bigger than a softball, plus millions of smaller pieces that have gone unrecorded. A wide range of strategies have been proposed to clean up the mess — for example, pulling in pieces of debris with a robotic arm, or harpooning them, or pushing them into a net.
Such procedures can pose a risk of breaking the debris into bunches of smaller pieces, however. Gecko grippers may offer a gentler way for space robots to clean up the mess, thanks in part to the lessons we’ve learned from the reptiles.
In addition to Jiang and Parness, the co-authors of the Science Robotics study, titled “A Robotic Device Using Gecko-Inspired Adhesives Can Grasp and Manipulate Large Objects in Microgravity,” include Elliot Hawkes, Christine Fuller, Matthew Estrada, Srinivasan Suresh, Neil Abcouwer, Amy Han, Shiquan Wang, Christopher Ploch and Mark Cutkosky.