Systèmes de communications par satellite

A satellite is essentially an autonomous communications system capable of receiving signals from Earth and retransmitting them using an integrated receiver and a radio signal transmitter, together known as a "transponder". Satellites are designed to provide long-distance links where investment in cables would be difficult.

The concept of satellite communication was proposed by Arthur C. Clarke in an article published in Wireless World magazine in 1945. A satellite placed at an altitude of 35,786 km above the Earth's surface moves at the same speed, and therefore remains in a fixed position relative to the Earth. This orbit, known as the "geostationary orbit", or "Clarke's Belt", is ideal, since it enables a ground antenna to communicate with a satellite 24 hours a day without having to change its position. .

A satellite has to withstand high acceleration during launch, reaching an orbital speed of 28,100 km/h, in a hostile space environment where it may be subjected to radiation and extreme temperatures, for an estimated lifespan of 20 years. In addition, the satellite must be as light as possible, as the high cost of launching it is based on weight. To meet these challenges, a satellite must be made from lightweight, durable materials. It must operate with a very high reliability of over 99.9% in the vacuum of space, with no prospect of maintenance or repair.

The first artificial satellite, Sputnik 1, was launched by the Soviet Union on October 4, 1957. 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 broadcasting services between North America and Europe.