Active Debris Removal (ADR)

Active debris removal (ADR) is the class of missions that go up and take debris down: a servicer spacecraft rendezvouses with an uncontrolled object, captures it, and either deorbits both together or tows the target to a disposal orbit. It answers the gap mitigation cannot close — even perfect compliance from today's launches leaves thousands of legacy derelicts whose random collisions and break-ups would keep feeding the cascade; long-term environment models consistently find that removing on the order of five large objects per year from the worst bands stabilises the population. The engineering is unforgiving: the target is dead, often tumbling, never designed to be grabbed. Capture concepts span robotic arms gripping launch-adapter rings, nets, harpoons, and magnetic capture of ferromagnetic plates fitted to newer satellites; ESA's ClearSpace-1 and Astroscale's demonstrator series have taken the first commercial and agency steps from studies to flight. ADR overlaps with on-orbit servicing — the same rendezvous and capture stack — and raises legal questions, since touching another state's object requires consent under the Outer Space Treaty framework.