satellite applications

A satellite image of Shanghai, the leading port and industrial centre of China. Nearby iron mines supply major manufacturing plants, and cotton, both imported and local, supplies textile mills. The port deals with a large amount of international shipping, but also serves the interior, using the Chang Jiang and Huangpu river systems.

A photo of the central and eastern Mediterranean region, taken by an orbiting satellite. The first vehicle in the Landsat series took over 300,000 pictures of the Earth's surface between 1972 and 1978; subsequent Landsats have contributed greatly to accurate mapping of the world's remoter regions.

Spartan 201 before deployment during shuttle mission STS-87. The solar observation satellite is held by Columbia's Canadarm. When released, Spartan did not perform as expected, owing to a problem with its altitude control system, and it was unable to collect science data. Spartan was recaptured and returned to Earth.

The sophisticated Terra satellite, which began a 15-year Earth-observation mission in December 1999, is pictured here ready to be encased in the Atlas II rocket fairing beyond.

The European Space Agency's Environment Satellite (Envisat). The data it gathers will allow earth scientists to monitor the evolution of environmental and climatic changes. Commercial applications of the satellite are also being considered.

The Television Infrared Observation Satellite (Tiros). Tiros 1 was 107 cm/42 in in diameter, 48 cm/19 in high, and weighed 123 kg/270 lb. It was made of aluminium alloy and stainless steel covered with 9,200 solar cells. The solar cells charged the nickel-cadmium (nicad) batteries. Three pairs of solid-propellant spin rockets were mounted on the base plate.

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, the US Skylab, and the largest of all satellites, the International Space Station.

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 dozens of Navstar satellites that enable users (including walkers and motorists) to find their position, typically to about 15 m/50 ft. ‘Selective availability’, which denied the highest precision to civilians and the armed forces of countries other than the US and its allies, was ended in 2000. However, the military can still achieve greater accuracy than civilian users.

Communications A complete worldwide communications network is now provided by satellites such as those of the US-run Intelsat system and the Molniya satellites of the Russian Orbita system.