ABSTRACT

In nearly 35 years of space activities more than 3,400 missions ave reached Earth orbit or beyond. The consequences of this activity have left in excess of 7,000 satellites in near-Earth space which are trackable by terrestrial sensors. From this population only approximately 5% represent spacecraft which continue to provide useful services. A small fraction (<1%) of cataloged satellites possess radioactive materials which raise special long-term issues. The actual number of man-made objects orbiting the Earth, including debris as small as 1 cm in diameter, is estimated to be several times the official count. The spatial density of the near-Earth environment is highly non-uniform with distinct regions of elevated satellite concentrations in both low Earth orbit and in the geostationary ring. The greatest influences on the growth of the Earth satellite population are launch and space operations, unplanned satellite fragmentations, and solar activity.

Historical Launch Activity

As of 1 April 1992, a total of 3,415 space missions to Earth orbit or beyond had been registered since the flight of Sputnik 1 on 4 October 1957. This figure does not include the numerous launch attempts which succumbed prior to reaching orbital velocity. However, contrary to popular opinion, no significant increase in space launch activity has occurred since the mid-1960's. By 1965 the world launch rate exceeded 100 missions per year, a level maintained (between 101 and 129) until 1991 when only 88 space missions successfully attained Earth orbit (Figure 1).