First space telescope

The first space telescope was Orbiting Astronomical Observatory 2 (OAO-2, or "Stargazer"), which launched on 7 December 1968. This orbital observatory made important observations of comets and cataloged 5,068 UV stars, before finally being shut down in February 1973.

Stargazer had two sets of instruments, arranged so that they looked out of opposite ends of the satellite body. At one end was a cluster of photometers and spectrometers called the Wisconsin Experiment Package (WEP), while at the other was a set of ultraviolet detectors called the Smithsonian Astrophysical Observatory (SAO), or "Celescope".

The design was an updated version of OAO-1, which had failed shortly after its launch in April 1966. In addition to its scientific discoveries, Stargazer was important as a technological proof-of-concept, demonstrating the viability of a steerable, ground-controllable orbital telescope.

There were some earlier satellites – such as the Soviet Proton and American SOLRAD series – that gathered data on high-energy particles and other aspects of the radiation environment in Earth orbit. These satellites were simple spin-stabilized detectors with omnidirectional antennas, however, and can't really be described as telescopes.