This month, the SpaceX CRS-14 resupply mission to the International Space Station will carry a satellite the size of a small fridge, dubbed RemoveDebris, with the goal of tackling the problem.
And the problem isn’t a small one. About 7,500 tonnes, or more than 100 million pieces, of human-made debris larger than a millimetre are zooming around the Earth – a clear and present danger to working satellites and astronauts.
Parts of defunct satellites, used rocket stages, and fragments from disintegration and collisions are spinning at up to 28,000km/h. “Impact by debris over 1cm can cause catastrophic break-up, and each collision creates more debris,” said Luisa Innocenti, head of the Clean Space Office at the European Space Agency.
Radar and telescopes help researchers keep track of the larger junk and try to avoid collisions, but there is no technology in orbit actively capturing it.
RemoveDebris is aimed at changing that. Built by Surrey Satellite Technology with funding from the European Commission, the satellite will be unpacked at the space station. Astronauts will then use the station’s robotic hand, the Japanese Experiment Module Robotic Manipulator System, to send it into orbit.
Once there, RemoveDebris will launch two CubeSats to imitate space junk. One will inflate a bigger balloon-like structure for the mothership to capture with a net and drag like a fish. RemoveDebris will also use a lidar and cameras to create a 3D image of the second CubeSat – so that future ‘cleaners’ can know what they are working with. It will also extend a 1.5m arm holding a 10cm2 target, and fire a harpoon to haul it in. When finished, RemoveDebris will deploy a plastic membrane, creating a ‘dragsail,’ to pull itself down towards death by fire in the atmosphere.
Zapping junk
That’s not the only effort to deal with space debris. A Chinese team at the Air Force Engineering University in Xi’an has proposed using an infrared laser from a satellite in orbit to blast the junk into smaller, less harmful pieces.
Another team, at Stanford University in California, is working with NASA’s Jet Propulsion Laboratory on a tool that mimics the gecko’s grip to grasp larger junk. Vacuum, radiation, extreme temperatures and microgravity mean that many adhesion technologies don’t work in space, said Elliot Hawkes, one of the Stanford researchers – but gecko-like adhesion would.
The researchers developed a material with ‘controllable adhesion’, meaning that it sticks to surfaces only when forces are applied in a particular direction.
“If you have a gecko run over your hand, it won’t feel sticky, but if you pull from the palm to the tip of the toe it suddenly grabs,” said Hawkes’ colleague Mark Cutkosky. “We wanted the same property for a robot, providing adhesion only when you need it.”
The scientists used a silicon material with microscopic sharp wedges that adheres to surfaces when applying a tangential force. “If you just make a big area of the adhesive, there will be some level of defect, causing a localised failure that will propagate across the whole surface,” said Cutkosky. “So instead we divided the large areas into many small islands, with a mechanism that ensures that the total force is very evenly and uniformly divided among them.”
While the tool would grasp larger objects, it would be “of little use” when two satellites have crashed into each other, with hundreds or thousands of tiny particles flying about, said Cutkosky. “In that case, you would probably need something more like a net” – similar to the RemoveDebris solution.
The researchers tested the gecko-like material in a low-temperature and high-radiation environment, and in a vacuum. On the NASA Robodome air-bearing floor and in the zero-gravity aeroplane, the gripper successfully grasped and manipulated a 370kg
floating robot.
But to get it to operate in space would “require technological advancement in robotics, advanced image processing, and complex guidance and navigation software,” said Innocenti.
The adhesive could have other applications, too. NASA is already using it on Astrobee, a small cube-like flying robot that will soon jet around the International Space Station to help astronauts with research, monitoring and housekeeping. And it could be used for manufacturing operations on Earth, to handle items that are particularly difficult to grasp.
Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.