Orbital Test Satellite
The Orbital Test Satellite programme was an experimental satellite system inherited by ESA in 1975 from its predecessor, the European Space Research Organization (ESRO).
The first of the pair of OTS satellites (OTS-1) were lost at launch in the failure of its US Delta launcher in September 1977. OTS-2 was successfully launched in 1978, again using the Delta rocket and became one of the first geostationary communications satellites to carry six Ku-band transponders and was capable of handling 7,200 telephone circuits. With a mass of approximately 445 kg on station, the OTS 2 bus was hexagonal with overall dimensions of 2.4 m by 2.1 m. Two solar panels with a span of 9.3 m provided 0.6 kW of electrical power. British Aerospace was the prime contractor from the European MESH consortium which developed the OTS vehicle. It completed its primary mission in 1984 after which the spacecraft was involved in a 6-year program of experiments, including the testing of a new attitude control technique taking advantage of solar radiation pressure forces. In January 1991, OTS 2 was moved out of the geostationary ring and into a graveyard orbit.