Space debris: how much junk is in orbit, and why it matters
Dead satellites, spent rocket stages and millions of fragments circle Earth. How much there is, where it came from, how it is tracked, and what the Kessler syndrome is.
How much is up there
Tens of thousands of objects larger than about 10 cm are tracked and cataloged, and only a minority of them are working satellites. The rest are dead satellites, old rocket stages and fragments. ESA estimates there are also around a million pieces between 1 and 10 cm and well over a hundred million smaller than that, too small to track but moving at about 8 km/s, fast enough for a paint fleck to chip a window.
Where it came from
- Explosions of old rocket stages and batteries left with fuel or charge on board.
- The 2007 Chinese anti-satellite test, which destroyed the Fengyun-1C weather satellite and created thousands of tracked fragments.
- The 2009 collision between the working Iridium 33 and the dead Kosmos 2251, the first accidental collision of two satellites.
- Everyday releases: lens covers, bolts and tools lost during spacewalks.
The Kessler syndrome
In 1978 NASA scientist Donald Kessler pointed out that if objects in an orbit become dense enough, collisions create fragments that cause further collisions, a chain reaction that could make some orbits unusable for generations. This is why operators now plan to remove satellites at the end of their lives, and why deliberate debris-making tests draw international criticism.
Living with it
Tracking networks warn operators of close approaches, and satellites (including the ISS) move out of the way several times a year. The ISS also carries shielding against small particles. Low debris eventually falls back and burns up; above about 800 km it can stay for centuries, which is why the most crowded high orbits matter most.