Although some malfunctioning satellites can be repaired by the crew of an orbiting shuttle, and in future may be repaired on the proposed space stations, repairs are at present usually impossible. Each material and component part must undergo extensive testing before launch, with a carefully considered degree of redundancy in electronic components and circuitry. The problems arising from the near vacuum environment of space, from the bombardment of cosmic rays, micrometeorites, etc., and from magnetic fields and radiation belts must also be considered.
Artificial satellites have a great range of functions. Some astronomical Earth satellites study the radiations from space that cannot penetrate the atmosphere: X-ray, gamma-ray, ultraviolet, and infrared astronomy have been revolutionized by the recent launching of satellites specializing in these fields. Astronomical satellites can also make measurements at optical, radio, and infrared wavelengths that can penetrate, but may be severely affected by, the atmosphere. Other scientifically orientated satellites study the resources, atmosphere, and physical features of the Earth.
Satellites are also used for communications (usually in geostationary orbit and allowing global long-distance live television broadcasting and telephony), for weather forecasting, and as navigational aids. In addition, the military potential of satellites has been exploited.