Orbiting Astronomical Observatories
- Series of four US astronomy satellites launched between 1966 and 1972. OAO1 lasted only three days in orbit. OAO2 was a two-tonne satellite which made observations for just over four years from 1968 to 1973, with an array of seven ultraviolet and four optical telescopes. OAO-B, the third of the series, never reached orbit. The fourth of the series, OAO3, also called Copernicus, carried a large ultraviolet telescope, an X-ray telescope and optical telescopes.