Orbital debris

NASA defines orbital debris as any human-made object orbiting Earth that no longer serves a useful purpose. Examples include derelict spacecraft, spent launch-vehicle stages, fragments from explosions or collisions, material released during operations, and small flecks such as paint. It is distinct from naturally occurring meteoroids, although both can pose impact hazards to spacecraft.

Objects in orbit travel rapidly relative to one another. Even a small fragment can carry enough kinetic energy to damage spacecraft components; the risk depends on the object's size, orbit, relative velocity, and the spacecraft's design. Larger objects can be tracked more readily, while many smaller particles are difficult or impossible to monitor individually. NASA therefore combines tracking of larger objects with measurements and models to estimate smaller debris populations.

Spacecraft and rocket stages can become debris when they reach the end of their useful lives. Break-ups caused by stored energy, explosions, or collisions add fragments to the orbital environment. Further collisions can produce still more debris, creating a feedback process sometimes called the Kessler syndrome. Its effects vary by orbit; it describes a possible growing collision cascade, not an inevitable sudden event.

The United Nations Committee on the Peaceful Uses of Outer Space adopted voluntary space-debris mitigation guidelines in 2007. They call for measures such as limiting debris released during normal operations, reducing accidental break-ups and collisions, avoiding intentional destruction that creates harmful debris, and limiting the long-term presence of spacecraft and launch stages in low-Earth and geosynchronous orbits after missions. These guidelines are not legally binding international law; states are invited to implement them through national mechanisms. End-of-life disposal and prevention reduce future accumulation, while removing existing objects is technically and economically challenging and is being developed as a complementary approach.