Sharp-eyed mini robots that will protect the ISS and repair defunct satellites have been flight-tested aboard the space station

Testing, testing… (Image: NASA)

IN SPACE, junk can make you scream. The International Space Station (ISS)regularly changes orbit to avoid colliding with derelict satellites, rocket stages and other objects whizzing around Earth at thousands of kilometres per hour. Soon robots may fly out to assess the danger presented by the vast array of objects not already tracked by radar.

Alvar Saenz-Otero and his colleagues at the Massachusetts Institute of Technology have built several self-guided robots. Each is a little smaller than a soccer ball and designed to investigate potentially damaging objects from a safe distance with a 3D stereo camera. The images are relayed to the crew aboard the ISS, who can decide how to proceed.

The risks a space object poses need to be assessed without putting people in danger, but even robots must give unknown objects a wide berth. “Inspection is not a low-risk activity,” says Saenz-Otero. “An autonomous inspector could collide with the object and make problems worse. So very good sensors must be used to allow the vehicle to move safely around the object it is inspecting.”


In a test aboard the ISS, the robots successfully manoeuvred around an “unknown” object floating in microgravity. Using their cameras and internal gyroscopes to navigate, they maintained a safe distance from the object as they filmed it. The robots streamed the 3D footage to a crew elsewhere on the ISS, who could evaluate what they were seeing. The work is due to appear in the Journal of Spacecraft and Rockets (doi.org/vfm).

The experiments proved the robots could avoid an object without any prior knowledge of its shape or size – a crucial safety measure when approaching an object that could vary from a few centimetres in diameter to the size of a truck.

The robots could avoid an object without knowing its shape or size beforehand – a crucial safety measure

“Aboard the ISS we are now working on cooperative debris inspection, where more than one of the robots has cameras,” says Saenz-Otero. The work is also feeding into the Phoenix programme, funded by the US Defense Advanced Research Projects Agency. The plan is to build robots that will travel to geosynchronous Earth orbit – much further away than most satellites. Once there they will repair and maintain old or broken satellites – tasks that would be not be feasible for a human crew.

It’s all vital research, says Hugh Lewis, who studies space debris at the University of Southampton, UK. “Space radiation and thermal cycling effects cause the materials used on spacecraft and rocket stages to age or degrade, and it is important we can inspect them to understand the risks.”

This article appeared in print under the headline “Space balls hunt for junk”