Editing Great Observatories program (section)

=== Chandra X-ray Observatory ===
[[File:Chandra_artist_illustration.jpg|thumb|Chandra X-ray Observatory]]

{{Main|Chandra X-ray Observatory}}

In 1976 the [[Chandra X-ray Observatory]] (called AXAF at the time) was proposed to NASA by [[Riccardo Giacconi]] and [[Harvey Tananbaum]]. Preliminary work began the following year at [[Marshall Space Flight Center]] (MSFC) and the [[Smithsonian Astrophysical Observatory]] (SAO). In the meantime, in 1978, NASA launched the first imaging X-ray telescope, [[Einstein Observatory]] (HEAO-2), into orbit. Work continued on the Chandra project through the 1980s and 1990s. In 1992, to reduce costs, the spacecraft was redesigned. Four of the twelve planned mirrors were eliminated, as were two of the six scientific instruments.  Chandra's planned orbit was changed to an elliptical one, reaching one third of the way to the Moon's at its farthest point. This eliminated the possibility of improvement or repair by the [[Space Shuttle program|Space Shuttle]] but put the observatory above the Earth's [[Van Allen radiation belt|radiation belts]] for most of its orbit.