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).
The Sun, Moon and Earth's oblateness lead to long-periodic perturbations of the inclination of geostationary satellites. The period is 54 years and the maximum inclination is 15º. Thus, uncontrolled satellites will steadily gain an inclination of 15º after 27 years. They will then cross the geostationary orbit twice a day with a velocity of 3,000 kms/hour with respect to other, controlled geostationary satellites.
