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space debris

Objects in low Earth orbit travel at roughly seven to eight kilometres per second, meaning even a debris fragment a few centimetres across carries kinetic energy comparable to a small explosive on impact. Objects below about ten centimetres are generally too small for current ground-based tracking systems to catalogue individually, which means operators of satellites and crewed spacecraft cannot manoeuvre to avoid them in the way they can for larger tracked objects. This untrackable population, estimated to number in the hundreds of thousands to millions of fragments, is in some ways the more concerning part of the problem precisely because it cannot be avoided, only shielded against or statistically tolerated.

• Roughly 30,000-plus objects are large enough (generally above about ten centimetres) to be individually tracked and catalogued.
• Untrackable fragments below that threshold are estimated to number from the hundreds of thousands into the millions.
• A 2007 Chinese anti-satellite weapons test and a 2009 collision between an active and a defunct satellite each generated large, long-lived debris fields still being tracked today.
• Large satellite constellations have substantially increased the number of active objects sharing low Earth orbit and, correspondingly, the number of collision-avoidance manoeuvres operators must perform.