Robotic pincers inspired by geckos could help collect garbage in space, a new study finds.
In experiments, the device was able to glom on to objects in the lab and even floating items within the International Space Station. Someday, such grippers could be used in maintenance robots in space or factory robots on Earth, according to the researchers, who reported the results of their study in the June 28 issue of the journal Science Robotics.
More than 500,000 pieces of debris currently orbit Earth, according to NASA. This space junk can travel at speeds of up to about 17,500 mph (28,100 km/h), posing a major hazard to astronauts, satellites and spacecraft. [Worst Space Debris Events of All Time]
Collisions with orbiting debris have already led to millions of dollars in losses. Moreover, such disasters can generate more debris that could go on to destroy more objects in space — a catastrophic chain-reaction scenario known as the "Kessler syndrome."
Despite the hazards that space junk poses, space debris is not collected today, in part because technologies used to grab on to items on Earth often do not perform well in space, the researchers said in their study. For instance:
* Conventional robotic hands are not suited for large, smooth pieces of space debris.
* Magnets do not stick to glass or aluminum.
* Suction cups require an atmosphere to work.
* Traditional sticky materials, such as tape, are largely useless because the chemicals they rely on cannot withstand the extreme temperature swings they would experience in space.
* Harpoons and nets could push objects in unintended directions.
Now, scientists have developed robotic pincers inspired by geckos to help grab space trash. The device was able to successfully snag floating objects in microgravity flights on both Earth and the International Space Station.
"We are really amazed at how much the gripper could achieve in floating environments," study lead author Hao Jiang, a mechanical engineer at Stanford University in California, told Space.com.
Geckos are reptiles that can scale vertical walls and even hang upside down by just their toes. The animals' plump toes are covered in hundreds of microscopic bristles that generate a kind of electric force strong enough to keep the lizards stuck onto surfaces. Scientists have developed many synthetic adhesives with gecko-like properties, enabling researchers to climb walls and seal wounds.
The new gripper is not as complex as a gecko's foot. Its adhesive uses flaps that are about 40 micrometers (millionths of a meter) wide, whereas geckos rely on structures that are about 200 nanometers (billionths of a meter) wide.
Still, the artificial adhesive works much in the same way as that on gecko feet. Making each flap stick only requires a light push in the right direction, and the flaps remain sticky if pushed in that specific direction. The pads unlock in a similarly gentle manner. The minimal forces that the new grippers need to stick onto and unstick from objects are key in the microgravity found in space, where any tiny push or pull can send an item drifting away, the researchers said.
The scientists created grippers of various sizes. The front of each gripper is covered with a grid of adhesive squares, and on either side of this grid is an arm whose inner surface is covered with thin adhesive strips. The grid can stick onto flat objects, such as solar panels, that might be abandoned as part of space debris, while the arms can grab curved items, such as rocket bodies. [Meet the Space Custodians: Debris Cleanup Plans Emerge]
The researchers tested how their grippers performed in microgravity on the space station and flights aboard NASA's C-9B aircraft, the Weightless Wonder, which dived 80 times to generate moments of weightlessness. In these experiments, the grippers could successfully grasp and let go of cubes, cylinders and beach balls with a gentle enough touch that the objects barely moved when released.
"The objects were really easy to knock away, so we are really happy that our adhesive gripper could grasp them with very little pressing force," Jiang said.
The grippers could handle items up to 880 lbs. (400 kilograms) in mass and 100 times larger than the grippers in volume. Sensors on the grippers could detect when the devices made contact and were aligned correctly.
One challenge the researchers faced was devising a system of pulleys to make sure the load on the adhesive strips was distributed evenly. Without this system, uneven stresses on the adhesives would cause the strips to fail one by one in a chain reaction, they said.
The scientists also equipped robots on Earth with these grippers. Future research could lead to robots that could pick up space junk, as well as maintenance robots that could conduct inspections and repairs while climbing on the outside of telecommunications satellites, space telescopes, the space station and future deep-space human missions, the researchers said. Other possible applications include construction robots in space or factory robots on Earth, they added.
Jiang cautioned that any potential future missions to rendezvous with space debris would likely be very complex. However, the researchers are "building step-by-step progress towards this goal," Jiang said.
Next steps for this new device include adding tactile sensors to the grippers to help them monitor adhesion in real time, Jiang said. In addition, the scientists are preparing for tests outside the space station with adhesives that can withstand the extreme temperatures and high levels of radiation found in space.
"We are confident that this technology will be used in outer space soon," Jiang said.