Orbital Test Satellite

The Orbital Test Satellite, or OTS, was an experimental European communications satellite programme that the European Space Agency inherited in 1975 from its predecessor, the European Space Research Organisation. It was the first three-axis-stabilised Ku-band satellite, and its design inspired later European satellites, including the Maritime European Communications Satellite and European Communications Satellite series. OTS 1 was lost when its Delta launcher exploded on 13 September 1977, but OTS 2 reached geostationary orbit after launch on 11 May 1978, carrying six Ku-band transponders able to handle 7,200 telephone circuits. British Aerospace was prime contractor for the European consortium that built it. OTS 2 completed its primary mission in 1984, was used for experiments for six more years, and was moved to a graveyard orbit in January 1991.