Voyager 2 Approaching Uranus
This artist's conception shows the final approach of the unmanned spacecraft Voyager 2 toward the planet Uranus on January 24, 1986. Voyager 2 discovered four new rings and ten new moons around Uranus.
Manned and unmanned space probes have provided a great new source of scientific data on the nature and origin of the solar system and the universe; earth-orbiting satellites have improved global communications, weather forecasting, navigational aids, and reconnaissance of the earth's surface for the location of mineral resources and for military purposes.
 The space age and practical astronautics commenced with the launching of Sputnik 1 by the Union of Soviet Socialist Republics (USSR) in October 1957 and of Explorer 1 by the United States in January 1958. In October 1958 the National Aeronautics and Space Administration (NASA) was created in the United States. During the next three decades, thousands of spacecraft of all varieties were launched, mostly in earth orbit. Twelve men walked on the moon's surface and returned to earth. By 1995 about 8000 artificial objects-mostly spent, upper stages of space-launch vehicles and inert spacecraft-larger than 10 cm (4 in) in diameter were circling the earth.