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TheOrbiting Astronomical Observatory (OAO)satellites were a series of four Americanspace observatories launched byNASA between 1966 and 1972,[1] managed by NASA Chief of AstronomyNancy Grace Roman. These observatories, including the first successful space telescope, provided the first high-quality observations of many objects inultraviolet light. Although two OAO missions were failures, the success of the other two increased awareness within the astronomical community of the benefits of space-based observations, and led to the instigation of theHubble Space Telescope.
The firstOrbiting Astronomical Observatory was launched successfully on 8 April 1966, carrying instruments to detectultraviolet,X-ray andgamma ray emission.[2] Before the instruments could be activated, a power failure resulted in the termination of the mission after three days. The spacecraft was out of control, so that the solar panels could not be deployed to recharge the batteries that would supply power to the electrical and electronic equipment on board.
Orbiting Astronomical Observatory 2 (OAO-2, nicknamedStargazer) was launched on 7 December 1968, and carried 11 ultraviolettelescopes.[3] It observed successfully until January 1973, and contributed to many significant astronomical discoveries. Among these were the discovery thatcomets are surrounded by enormous haloes ofhydrogen, several hundred thousand kilometres across, and observations ofnovae which found that their UV brightness often increased during the decline in their optical brightness.
OAO-B carried a 38 in (97 cm) ultraviolet telescope, and should have provided spectra of fainter objects than had previously been observable.[4] The satellite was launched on 30 November 1970 with "the largest space telescope ever launched",[5] but never made it into orbit. The payload fairing did not separate properly during ascent and the excess weight of it prevented the Centaur stage from achieving orbital velocity. The Centaur and OAO reentered the atmosphere and broke up, destroying a $98,500,000 project. The disaster was later traced to a flaw in a $100 explosive bolt that failed to fire.[6]
OAO-3 was launched on 21 August 1972,[7] and proved to be the most successful of the OAO missions. It was a collaborative effort between NASA and theUK's Science Research Council (currently known as theScience and Engineering Research Council).[8] After its launch, it was namedCopernicus to mark the 500th anniversary of the birth ofNicolaus Copernicus in 1473.
Copernicus operated until February 1981,[7] and returned high resolution spectra of hundreds of stars along with extensive X-ray observations.[9] Among the significant discoveries made byCopernicus were the discovery of several long-periodpulsars such asX Persei that had rotation times of many minutes instead of the more typicalsecond or less, and confirmation that most of the hydrogen in interstellar gas clouds existed in molecular form.[10]
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