Since the launch of Sputnik on 4 October 1957, more than 4,200 launches have placed some 5500 satellites into orbit. Currently about 700 satellites are used operationally for science and other applications. 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.
The Sun and Moon also pull on satellites. The Earth's equator and hence also the orbits of geostationary satellites are inclined by 23 deg in respect to the orbital plane of the Earth. Therefore the gravity of the Sun changes the orbital plane of geostationary satellites.
Together with the attraction of the Moon this causes the inclination to oscillate between 0 and 15 deg once every 54 years. During this time the inclination vector, which is perpendicular on the orbit plane and shown in green here, draws a complete circle.
