Engineers at Stanford University have combined adhesives inspired by the gecko with a custom robotic gripper to create a device that can grab space debris.
Currently, there are around 500,000 pieces of human-made debris whizzing around space, orbiting Earth at speeds up to 28,000km/hr. This space rubbish poses a threat to satellite, space vehicles and any astronauts aboard these vehicles.
The location of this debris makes it very challenging to clean up. Suction cups do not work in the vacuum of space. Traditional sticky substances, like sticky tape, rely on chemicals that lose their effectiveness or break apart from the extreme temperature swings. Magnets only work on magnetic objects.
Proposed solutions, like debris harpoons, require or cause forceful interaction with the debris, which could cause the objects to break up into smaller fragments, or push them in unintended, unpredictable directions.
To tackle this issue, researchers from Stanford University collaborated with NASA's Jet Propulsion Laboratory (JPL) to design a new kind of robotic gripper which can grab and dispose of the debris.
According to Mark Cutkosky, professor of mechanical engineering and senior author of the paper, the gripper uses gecko-inspired adhesives.
“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.”
The group tested their gripper, and smaller versions, in their lab and in multiple zero gravity experimental spaces, including the International Space Station. These tests have yielded promising results, and the next step would be to try them outside the space station.
The technology could be useful not just for cleaning up debris, but also other missions, such as rendezvous and docking operations. It could also be the basis of a climbing robot that could crawl around on spacecraft, doing repairs, recording and checking for defects.
In fact, the adhesives have previously been used in climbing robots, and a system that allowed humans to climb up certain surfaces. They took their inspiration from geckos, which can climb walls due to the microscopic flaps on their feet that, when in full contact with a surface, create a Van der Waals force between the feet and the surface.
While the gecko's foot utilises 200nm flaps, the gripper's adhesive flaps are only about 40 micrometres across. However, it works in much the same way: the adhesive is only sticky when the flaps are pushed in a specific direction, and just a light push in the right direction is sufficient to make it stick.
Because the adhesive is not strictly pressure-sensitive, there is no need to use a lot of force on a piece of drifting debris, and risk pushing them away. Instead, users can touch the adhesive pads very gently to a floating object, squeeze the pads toward each other so that they’re locked and thus be able to move the object around.
The pads unlock with the same gentle movement, and thus there is very little force applied against the object.
The gripper the researchers created has a grid of adhesive squares on the front and arms with thin adhesive strips that can fold out and move toward the middle of the robot from either side. The grid can stick to flat objects, like a solar panel, and the arms can grab curved objects, like a rocket body.
One of the biggest challenges of the work was to make sure the load on the adhesives was evenly distributed, which the researchers achieved by connecting the small squares through a pulley system that also serves to lock and unlock the pads. Without this system, uneven stress would cause the squares to unstick one by one, until the entire gripper let go. This load-sharing system also allows the gripper to work on surfaces with defects that prevent some of the squares from sticking.
The group first tested the gripper in the lab, measuring the amount of load the gripper could handle, and what happened when different forces and torques were applied and how many times it could be stuck and unstuck. Through their partnership with JPL, the researchers also tested the gripper in zero gravity environments, including on board a parabolic plane flight. A small version of the gripper was also flown to the International Space Station for testing.
[Caption: Close up of the robotic gripper made by the Cutkosky lab at Stanford University. The gripper is designed to grab objects in zero gravity using their gecko-inspired adhesive. Image credit: Kurt Hickman.]