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Orbiting Astronomical Observatory

Phase: Past

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The Orbiting Astronomical Observatory (OAO) was a series of four satellites launched by NASA between 1966 and 1972. Two of the missions were successful and two were failures. However, the program’s overall success increased awareness in the astronomical community of the benefits of orbiting telescopes. The Orbiting Astronomical Observatory program eventually set the stage for the development of the Hubble Space Telescope (HST) and other orbiting observatories.

OAO-1, the first OAO observatory, was launched April 8, 1966 and experienced a power failure shortly after achieving orbit. The mission was terminated after three days and its science payload was never used.

OAO-2 was a success. Launched on December 7, 1968, the satellite operated successfully until January 1973 and made significant contributions to ultraviolet astronomy by studying high energy environments such as nova and supernovae, and it discovered that comet’s have a huge hydrogen haloes.  OAO-2 carried 11 ultraviolet telescopes aloft and for the first time, scientists were able to observe in the ultraviolet region of the spectrum with no intervening atmosphere to block the light.

OAO-B was launched November 3, 1970 carrying a 38 inch ultraviolet telescope. The satellite failed to separate from its rocket and never achieved earth orbit, eventually tumbling back into the atmosphere and burning up. 

OAO-3, Copernicus, was a joint effort between NASA and the United Kingdom (SERC). It was launched August 21, 1972 and orbited successfully until February 1981. Copernicus carried the Princeton University UV Telescope and an X-ray experiment developed by the University College London Mullard Space Science Laboratory which consisted of four co-aligned X-ray detectors and a proportional counter. At the time, the ultraviolet telescope was the heaviest scientific payload launched by NASA, having a launch mass of 2220 kg.  Copernicus returned high resolution spectra of hundreds of stars along with numerous X-ray observations. Significant discoveries made by Copernicus include the discovery of several pulsars.

Last updated: April 24, 2015

Related Links
  • OAO-1 1966 -
  • OAO-2 1968 -
  • More about OAO-2 -
  • OAO-B 1970 -
  • OAO-3/Copernicus 1972 -
  • More about Copernicus -