The Orbital Test Satellite (OTS) programme was an experimental satellite system inherited by the European Space Agency (ESA) in 1975 from its predecessor, the European Space Research Organisation (ESRO).

It 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 865 kg (1,907 lb), the OTS satellite bus was hexagonal with overall dimensions of 2.4 by 2.1 x 1.7 m. Two solar panels with a span of 9.3 m provided 600 watts of electrical power.

[1] British Aerospace was the prime contractor from the European MESH consortium which developed the satellite.

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.