Space debris is the collection of objects in orbit around Earth that were created by humans but no longer serve any useful purpose. These objects consist of everything from spent rocket stages and defunctsatellites to explosion and collision fragments. The debris can include slag and dust from solid rocket motors, surface degradation products such as paint flakes, coolant released by RORSAT nuclear powered satellites, clusters of small needles, and objects released due to the impact of micrometeoroids or fairly small debris onto spacecraft.
The current equipment used to gather such information is only capable of tracking objects down to about 5 centimetres (2.0 in) diameter in low Earth orbit, and about 50 centimetres (20 in) in geosynchronous orbit. Out of the estimated 600,000 objects above 1 centimetre (0.39 in) diameter, only 19,000 can be tracked as of today. This leads to wide uncertainties in the estimated quantities of debris, and the predicted path of their orbits.
If a collision with larger debris does occur, many of the resulting fragments from the damaged spacecraft will also be in the 1 kilogram (2.2 lb) mass range, and these objects become an additional collision risk. As the chance of collision is a function of the number of objects in space, there is a critical density where the creation of new debris occurs faster than the various natural forces that remove these objects from orbit. Beyond this point a runaway chain reaction can occur that quickly reduces all objects in orbit to debris in a period of years or months. This possibility is known as the “Kessler Syndrome”, and there is debate as to whether or not this critical density has already been reached in certain orbital bands.
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