Robotic rescue of NASA telescope highlights challenge of capturing space junk

Growing debris population drives push for satellites built for service

For most of the space age, satellites have been disposable — moved aside or replaced when they ran low on fuel or failed, Kanjumba wrote in an article published by The Conversation and republished by United Press International. That was manageable decades ago, when orbit was far less crowded, she said.

Now, space surveillance networks track tens of thousands of human-made objects, and the European Space Agency estimates more than 1.2 million pieces of satellite and spacecraft debris larger than half an inch are in orbit, Kanjumba said. Even chunks that small can cause severe damage in a collision, she wrote.

The hardest part of removing a dead satellite before it breaks apart into new debris is not reaching it — it is understanding how it moves, how to approach without hitting it, and controlling the instant when two free-flying objects touch, Kanjumba wrote.

Kanjumba, who studies how to approach defunct satellites in a controlled way for her doctoral research, described the challenge of catching a noncooperative satellite — one that was never designed to be serviced.

Some satellites, called prepared satellites, carry a built-in feature that works like a tow hook, Kanjumba said. The servicer knows where to attach, what loads the hook can bear, and what its cameras can use as landmarks. Northrop Grumman’s Mission Extension Vehicles have docked onto communications satellites this way and taken over their propulsion and pointing, she wrote.

Swift is an example of an unprepared satellite, Kanjumba said. It was not built with any standardized fixture that a repair craft can latch onto. Without one, there is no obvious place to grab and no guarantee it survives capture, she wrote.

LINK’s mission is what engineers call noncooperative capture: catching a spacecraft that cannot help the servicer, may be tumbling unpredictably, and was never built to be caught, Kanjumba said.

When the servicer’s robotic arm touches a tumbling satellite, the force from that contact pushes the servicer back, she said. The arm acts like a long lever, so even a gentle nudge at its tip can throw it off course, Kanjumba wrote.

Designing a satellite with a standardized fixture to grab onto and navigation markers to help the servicer line up can reduce uncertainty, Kanjumba said. But those features cannot fully replace precise navigation, she wrote.

Two upcoming missions show different approaches, she said. Astroscale’s ELSA-M will capture commercial satellites fitted with a magnetic docking plate before launch — targets built to be serviced. The European Space Agency’s ClearSpace-1, planned for 2029, will tackle the harder case by capturing the unprepared, noncooperative Proba-1 satellite and dragging it down to burn up, Kanjumba wrote.

“The next few years will show whether the space industry really leaves disposable satellites behind and starts building them to be caught and repaired, or simply gets neater about throwing them away, designing them to burn up on the way down,” Kanjumba wrote.