The catalogued population
As of 2024, the US Space Surveillance Network tracks roughly 35,000 objects larger than 10 cm. Estimates suggest 1 million objects between 1–10 cm, and 130 million smaller than 1 cm. Only the large ones are tracked. The rest are statistical threats — and they can still destroy a satellite.
Space Fence (AN/FPS-85 follow-on)
The US Space Fence, operational since 2020, is a massive S-band phased array in the Marshall Islands. It can detect objects as small as a marble in low Earth orbit, updating the catalogue automatically. Previous systems relied on mechanical dishes; the new fence is all solid-state, tracking thousands of objects simultaneously.
TIRA and European assets
Germany's TIRA (Tracking and Imaging Radar) is a 34 m dish operating at 1.3 GHz. It can image objects in orbit at metre resolution, distinguishing a tumbling rocket body from an intact satellite. France's GRAVES is a bistatic radar system that fills gaps in southern coverage. Together with optical telescopes, these systems form a global debris surveillance network.
Collision avoidance
When a tracked object is predicted to pass within a few kilometres of an active satellite, operators are warned. The satellite can fire thrusters to dodge. This happens dozens of times per year for the ISS alone. Without radar tracking, every satellite would be flying blind through a shooting gallery.