Early British involvement with space satellites consisted mainly of tracking those launched by other countries, but in October 1971 Britain successfully launched its own satellite when the Black Arrow rocket took to the skies over Woomera, South Australia and placed Prospero in low Earth orbit. Far from marking the start of extensive British involvement in space launch vehicles, Black Arrow, which built on the earlier Blue Steel missile and Black Knight rocket, was the end point of independent British efforts and the programme was cancelled. From then on British involvement in space concentrated mainly on satellite design and collaborative ventures, particularly as part of the European Space Agency. An exception to this was the HOTOL (Horizontal Take-Off and Landing) project carried out by Rolls-Royce and British Aerospace during the 1980s,but this did not get beyond the design phase. British scientists and engineers have also been active in designing instruments that have been carried by satellites to observe the earth or explore the solar system.