Between the launch of Sputnik on 4 October 1957 and 1 January 2008, approximately 4600 launches have placed some 6000 satellites into orbit, of which about 400 are travelling beyond geostationary orbit or on interplanetary trajectories.
Today, it is estimated that only 800 satellites are operational - roughly 45 percent of these are both in LEO and GEO. Space debris comprise the ever-increasing amount of inactive space hardware in orbit around the Earth as well as fragments of spacecraft that have broken up, exploded or otherwise become abandoned. About 50 percent of all trackable objects are due to in-orbit explosion events (about 200) or collision events (less than 10).
What happens after an explosion in space? A geostationary satellite has a velocity of about 3 kms/second (11,000 kms/hour). The fragments are ejected with a much lower velocity and thus stay close to the initial orbit. However, some will travel a bit faster and others a bit slower. Within a few days the debris cloud will form a diffuse ring at 36,000 km altitude around the Earth.
