Compton Gamma Ray Observatory
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Compton Gamma Ray Observatory(Compton Observatory; CGRO) The second in NASA's series of Great Observatories, launched by the space shuttle Atlantis into a low Earth orbit Apr. 1991. It took its name from the 20th-century US physicist Arthur Holly Compton. Providing nearly six orders of magnitude in spectral coverage, from 15 keV to 30 GeV, it studied a broad range of topics over its nine years of operational life. The 16-tonne observatory contained four gamma-ray telescopes on a stabilized platform.
BATSE, the burst and transient source experiment, measured gamma-ray brightness variations on time scales down to milliseconds; sources included gamma-ray bursts, gamma-ray transients, and solar flares. The instrument consisted of eight identical scintillator-crystal (NaI) detector modules that covered the entire sky, detecting photons in the energy band 0.03–1.9 MeV, plus a smaller spectroscopy detector optimized for broad energy coverage (0.015–110 MeV) and fine energy resolution.
OSSE, the oriented scintillation spectrometer experiment, observed gamma-ray sources in the 0.1–10 MeV range, with a limited capability above 10 MeV. The telescope consisted of four identical detector systems, each articulated to provide a 192° rotation. Normally, two detectors viewed the source, and two a nearby off-source region; the combination was reversed at regular intervals and the difference represented the net source flux.
COMPTEL, the imaging Compton Telescope, carried out a sensitive survey of the entire sky in the range 1–30 MeV. Discrete and extended sky images were reconstructed over a wide field of view with a resolution of the order of 1°.
EGRET, the energetic gamma-ray experiment telescope, covered the range 0.02–20 GeV (approx.). The instrument had an imaging capability at the degree level over a wide field of view. The basic imaging portion consisted of a spark chamber arrangement within a plastic scintillator veto system; imaging was achieved by following the trajectories of the electron-positron pair through the spark chamber to a large NaI scintillation crystal where the photon energy was estimated.
The CGRO was one of the most efficient and successful space telescopes ever launched. It fulfilled its mission almost flawlessly, proving that gamma-ray bursts come from very distant regions of space and are the most powerful explosions in the Universe. In June 2000, NASA scientists deorbited the CGRO, which broke up during a controlled re-entry into the Earth's atmosphere. NASA plans to launch a successor to the CGRO, the Gamma-ray Large Area Space Telescope (GLAST), in 2006.