What is orbital debris?
Orbital debris (space debris or space junk) comprises all human-made objects in Earth orbit that no longer serve any useful purpose. The catalogue includes: defunct satellites (satellites that have failed or been retired without deorbit), spent rocket upper stages, hardware released during missions (lens caps, separation bolts, cables), and fragmentation debris generated by collisions, explosions, and anti-satellite tests. As of 2025, ESA tracks approximately 35,000 objects larger than 10 cm, estimates 1 million objects between 1–10 cm, and models approximately 130 million fragments between 1 mm and 1 cm.
Why size matters
At orbital velocities of 7–10 km/s, even a 1 cm aluminium sphere carries the kinetic energy of a hand grenade. A 10 cm fragment can disable a satellite. A 1 mm particle can penetrate a pressure vessel. The Whipple shield (aluminium bumper plates) used on the International Space Station protects against particles up to ~1 cm but is ineffective against larger fragments. The challenge: only objects larger than 10 cm are tracked with sufficient precision for collision avoidance manoeuvres.
Major debris-generating events
Three events dominate the orbital debris catalogue: China's 2007 Fengyun-1C ASAT test (3,500+ fragments, mostly at 800–900 km), the 2009 Iridium-Cosmos collision (2,300+ fragments at ~789 km), and a Soviet anti-satellite test series in the 1970s–80s. In 2021, Russia's ASAT test destroyed its own Kosmos-1408 satellite, generating 1,500+ trackable fragments and forcing ISS crew to shelter in the Soyuz escape vehicle.