<Tr> <Th_colspan="2"> Instruments </Th> </Tr> <Tr> <Td_colspan="2"> BATSE, OSSE, COMPTEL, EGRET </Td> </Tr> <P> The Compton Gamma Ray Observatory (CGRO) was a space observatory detecting photons with energies from 20 k eV to 30 GeV, in Earth orbit from 1991 to 2000 . It featured four main telescopes in one spacecraft, covering X-rays and gamma rays, including various specialized sub-instruments and detectors . Following 14 years of effort, the observatory was launched from Space Shuttle Atlantis during STS - 37 on April 5, 1991, and operated until its deorbit on June 4, 2000 . It was deployed in low earth orbit at 450 km (280 mi) to avoid the Van Allen radiation belt . It was the heaviest astrophysical payload ever flown at that time at 17,000 kilograms (37,000 lb). </P> <P> Costing $617 million, the CGRO was part of NASA's "Great Observatories" series, along with the Hubble Space Telescope, the Chandra X-ray Observatory, and the Spitzer Space Telescope . It was the second of the series to be launched into space, following the Hubble Space Telescope . CGRO was named after Arthur Holly Compton (Washington University in St. Louis), Nobel prize winner, for work involved with gamma ray physics . CGRO was built by TRW (now Northrop Grumman Aerospace Systems) in Redondo Beach, California . CGRO was an international collaboration and additional contributions came from the European Space Agency and various universities, as well as the U.S. Naval Research Laboratory . </P>

When was the compton gamma ray observatory launched