The uses to which artificial satellites are put. These include:

scientific experiments and observation

Many astronomical observations are best taken above the disturbing effect of the atmosphere. Satellite observations have been carried out by the Infrared Astronomy Satellite (1983) which made a complete infrared survey of the skies, and Solar Max (1980), which observed solar flares. The Hipparcos satellite, launched in 1989, measured the positions of many stars. The Röntgen Satellite, launched in 1990, examined ultraviolet and X-ray radiation. In 1992, the Cosmic Background Explorer satellite detected details of the Big Bang that mark the first stage in the formation of galaxies. Medical experiments have been carried out aboard crewed satellites, such as the Russian space station Mir and the US Skylab.

reconnaissance, land resource, and mapping applications

Apart from military use and routine mapmaking, the US Landsat, the French Satellite Pour l'Observation de la Terre, and equivalent Russian satellites have provided much useful information about water sources and drainage, vegetation, land use, geological structures, oil and mineral locations, and snow and ice.

weather monitoring

The US National Oceanic and Atmospheric Administration series of satellites, and others launched by the European Space Agency, Japan, and India, provide continuous worldwide observation of the atmosphere.

navigation

The US Global Positioning System uses 24 Navstar satellites that enable users (including walkers and motorists) to find their position to within 100 m. The US military can make full use of the system, obtaining accuracy to within 1.5 m. The Transit system, launched in the 1960s, with 12 satellites in orbit, locates users to within 100 m.

communications

A complete worldwide communications network is now provided by satellites such as the US-run Intelsat system.