Satellite Telecommunications Systems - Link architectures

A satellite is a self-contained communications system capable of receiving signals from Earth or another source, and retransmitting these signals either to Earth or to another satellite. To this end, each satellite is equipped with a radio signal receiver and transmitter, together known as a "transponder".

Satellites are designed to provide long-distance links where cable investment would be difficult.

The concept of satellite communication has been proposed by various authors. In 1929, in "The Problem of Space Travel", the Hungarian Herman Erman Potočnik was the first to describe how space conditions could be used for scientific, peaceful and military applications. Later, the Russian Konstantin Tsiolkovsky, before the American Clarke in "Wireless World" magazine in 1945, why a satellite placed at an altitude of 35,786 km above the Earth's surface and in the equatorial plane, moved at the same speed relative to the Earth. This orbit, known as the "geostationary orbit" (or "Clarke's Belt"), is ideal, since it enables equipment with a ground antenna to communicate with a satellite 24 hours a day without having to change its position.

Other satellite positions are also possible, but with their own constraints, depending on the objectives being pursued. Satellites can carry communications equipment, sensors or imagers, or even telescopes, in order to relay the desired information, for example scientific information, to dedicated ground stations.

A satellite has to withstand severe mechanical and thermal stresses during launch, and for the entire duration of its operation, estimated at between 5 and 25 years. It must operate with a high degree of reliability (over 99.9%) in the vacuum of space, with little prospect of maintenance or repair.

The first artificial satellite, Sputnik 1, was launched by the Soviet Union on October 4, 1957 for demonstration purposes. The first satellite to relay voice signals was the US government's SCORE (Signal Communication by Orbit Relay Equipment) project, on December 19, 1958. On April 6, 1965, the first Intelsat satellite, Early Bird (also known as Intelsat 1), was built by Hughes Aircraft Company. Early Bird was the first operational commercial satellite to provide regular communications and multimedia broadcasting services...