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The Compton Gamma Ray Observatory (CGRO) was a space observatory detecting light from 20 keV 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.[1] 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).
Costing $617 million,[2] 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.[3] 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.
CGRO carried a complement of four instruments that covered an unprecedented six decades of the electromagnetic spectrum, from 20 keV to 30 GeV (from 0.02 MeV to 30000 MeV). In order of increasing spectral energy coverage:
Gamma ray burst 990123 (23 January 1999) was one of the brightest bursts recorded at the time, and was the first GRB with an optical afterglow observed during the prompt gamma ray emission (a reverse shock flash). This allowed astronomers to measure a redshift of 1.6 and a distance of 3.2 Gpc. Combining the measured energy of the burst in gamma-rays and the distance, the total emitted energy assuming an isotropic explosion could be deduced and resulted in the direct conversion of approximately two solar masses into energy. This finally convinced the community that GRB afterglows resulted from highly collimated explosions, which strongly reduced the needed energy budget.
By Oct 1993 the 450 km orbit had decayed to 340 km and a reboost rocket firing took it back up to 450 km.[5] A second reboost from 440 km to 515 km was done between April and June 1997.[6] After this it was hoped CGRO would operate until 2007.
After one of its 3 gyroscopes failed in December 1999, the observatory was deliberately de-orbited. At the time, the observatory was still operational; however the failure of another gyroscope would have made de-orbiting much more difficult and dangerous. With some controversy, NASA decided in the interest of public safety that a controlled crash was preferable to letting the craft come down on its own at random.[2] Unlike the Hubble Space Telescope, it was not designed for on-orbit repair and refurbishment. It entered the Earth's atmosphere on 4 June 2000, with the debris that did not burn up ("six 1,800-pound aluminum I-beams and parts made of titanium, including more than 5,000 bolts") falling harmlessly into the Pacific Ocean.[7]
This de-orbit was NASA's first intentional controlled de-orbit of a satellite. [8]
Apollo program, International Space Station, Soviet Union, Mars, Space Shuttle
Space Shuttle, European Space Agency, Nasa, James Webb Space Telescope, International Space Station
Northrop Grumman, Project Mercury, Project Gemini, Simon Ramo, Dean Wooldridge
Hubble Space Telescope, James Webb Space Telescope, Nasa, Spitzer Space Telescope, Space Shuttle
Nasa, Milky Way, Great Observatories program, Compton Gamma Ray Observatory, X-Ray
Star, Variable star, Hubble Space Telescope, Infrared, Galaxies
Nucleosynthesis, Iowa, Osse, Texas, Nickel
Nasa, Physics, Infn, United States Department of Energy, General Dynamics