Stanford University engineers recently designed a robotic gripper featuring a gecko-inspired adhesive to be used for collecting space debris. Researchers successfully completed preliminary trials in several zero gravity environments, including on board the International Space Station.

In recent years, Gecko’s have been headlining major news stories for their remarkable biotechnological capabilities. Researchers have been mimicking geckos’ unparalleled grippy feet that enable them to scale almost any surface at almost any angle. Now, Stanford engineers are using gecko tech to solve another human problem, space trash.

Over 500,000 Pieces of Human-made Debris Remain in Space

Ever since Sputnik I, the first artificial satellite launched into orbit in 1957, there has been a steady influx of orbital satellites – many of which have since been abandoned. Currently, more than 500,000 pieces of man-made space debris remain in orbit around Earth.

In the harsh conditions of space, every satellite’s lifespan is limited. Satellites only remain functional for so long before their parts grow old and wear out. Eventually, all artificial satellites will die and will become part of the ever increasing number of space debris encircling Earth. Currently, more than 95% of the satellites remaining in orbit are no longer functional.

Space debris poses a threat to other satellites and instrumentation in orbit around Earth. Traveling at thousands of kilometers an hour, a strike from a piece of rogue space debris could destroy another satellite or potentially kill an astronaut aboard a space station. Each year, many more satellites are sent up into space, cluttering passageways. Stanford engineers want to alleviate the situation before it cascades into a major problem. Their proposed solution is to use gecko-grippers to extract space debris.

A Gecko-inspired Robotic Gripper

Tidying up space debris poses a unique problem, one that traditional technologies cannot accomplish. In space, the conditions are harsh. There is no air, and it is insanely cold.

Typical adhesives like tape cannot withstand the extreme temperature changes. The heat causes the chemicals to physically change, and the cold makes everything brittle.

For obvious reasons, suction cups are not a viable solution either. With no atmosphere to create a vacuum, suction is impossible.Therefore, as researchers from Stanford University and NASA’s Jet Propulsion Laboratory (JPL) see it, there is only one clear solution: gecko grippers.

A Sticky Situation

Geckos get their grip from microscopic hairs that split off into even smaller segments at the tip. The ends split off into billions of contact points. As they near a surface, the tips get a grip from what is known as Van der Waals forces.

Electrons largely determine the polarity of a molecule. However, they are also moving around incredibly fast which can momentarily change the polarity of an atom or molecule. The momentary shift gives a molecule just enough time to bind to another. 

As science describes: “This force comes from fluctuations in charge distributions between neighboring molecules, which need not be polar; their charge fluctuations naturally fall into sync, creating an attractive force.”

The force is incredibly weak. However, using billions of contact points exponentially increases the grip. Typically, a greater load on the contact points increases the grip. Therefore, by reducing the load, the grip is easily released since there is no physical bond.

Stanford researchers make use of this effect by implementing millions of microscopic flaps along a flexible sheet. When in contact and under a load, the flaps bend, creating the contact points and allowing the material to latch onto an object.

“There are many missions that would benefit from this, like rendezvous and docking and orbital debris mitigation,” says Aaron Parness, MS ’06, PhD ’10, group leader of the Extreme Environment Robotics Group at JPL. “We could also eventually develop a climbing robot assistant that could crawl around on the spacecraft, doing repairs, filming and checking for defects.”

Getting a Grip with Geckos

The micro-flaps used to comprise the contact points are many times larger than the hairs on a gecko’s foot.

“The flaps of the adhesive are about 40 micrometers across while a gecko’s are about 200 nanometers – but the gecko-inspired adhesive works in much the same way,” reports Stanford University.

The adhesive’s flexible properties enable it to conform to an uneven object without impeding on the force of its grip. The flexibility is imperative for a robot destined to collect many satellites made of many materials with many shapes.

“Imagining that you are trying to grasp a floating object, you want to conform to that object while being as flexible as possible, so that you don’t push that object away,” explains Hao Jiang, a graduate student in the Cutkosky lab and lead author of the paper. “After grasping, you want your manipulation to be very stiff, very precise, so that you don’t feel delays or slack between your arm and your object.”

The Results

On Earth, the conditions are incredibly different in comparison to the extreme conditions of space. Nevertheless, the Stanford researchers behind the project devised ingenuitive experiments to test out their robot on Earth.

The robotic grippers were tested in a vacuum chamber to prove its grippy capabilities in near vacuum conditions. The results were largely a great success, leading the researchers to take the next steps into testing the robot’s capabilities in zero gravity situations.

The team took the robot inside a specially modified plane that flew to a high altitude. Then, by controlling the rate of descent and matching its acceleration to gravity, everything inside the plane became “weightless”.

“[In the plane] we had one robot chase the other, catch it and then pull it back toward where we wanted it to go,” says Hawkes. “I think that was definitely an eye-opener, to see how a relatively small patch of our adhesive could pull around a 300 kilogram robot.”

Lastly, Parness’s lab developed a small gripper that went up in the International Space Station (ISS), where they tested how well the grippers worked inside the station.

Next steps for the gripper involve readying it for testing outside the space station, including creating a version made of longer lasting materials able to hold up to high levels of radiation and extreme temperatures. The current prototype is made of laser-cut plywood and includes rubber bands, which would become brittle in space. The researchers will have to make something sturdier for testing outside the ISS, likely designed to attach to the end of a robot arm.

Perhaps sometimes soon, NASA and other agencies may begin to clean up the remains of the satellite cemetery encircling Earth that continues to grows a little larger each year.

Source: Stanford University, NASA