Encyclopedia Astronautica

GRO Deployment
Credit: NASA
Credit: NASA
American gamma ray astronomy satellite. One launch, 1991.04.05, Compton Observatory. The Compton Gamma Ray Observatory (CGRO) was the gamma-ray element of NASA's Great Observatories program .

The spacecraft carried seven tons of instruments to detect, image and analyze gamma rays emitted by cataclysmic cosmic events. CGRO was to have addressed fundamental questions about the process of energy transfer in the universe and lead to a better understanding of the nature of astronomical objects that produce this very high-energy radiation.

The specific objectives of the Compton Gamma Ray Observatory included (1) studying gamma-ray sources emitting in the Milky Way Galaxy and beyond, (2) investigating evolutionary forces in neutron stars and black holes, (3) performing detailed studies of nucleosynthesis, and (4) searching for primordial black hole emissions. The program included participation from Germany, the Netherlands, the United Kingdom, and ESA. The other Great Observatories were the HST (visible), AXAF (X-ray), and SIRTF (infrared).

The spacecraft was 3-Axis stabilized by a zero momentum biased control system using reaction wheels. Two solar array generated 4500 W (BOL) power and fed three 50 Ahr NiCd batteries. The hydrazine propulsion system (with 1900 kg fuel) had four 100-lbf thrusters and eight 5-lbf ACS thrusters. The S-band telecom system used a 1.52 m diameter high gain antenna on a 4.4 m boom. This provided uplink at 1 kbps and downlink (via the TDRSS relay satellite) at 256-512 kbps. GRO was the first spacecraft designed for on-orbit refueling, servicing and maintenance.

Four instruments were carried. The OSSE (Oriented Scintillation Spectrometer Experiment) by the Naval Research Laboratory detected gamma rays entering the field of view of any of four detectors in the 100 kev to 10 Mev range. The Imaging Compton Telescope by the Max Planck Institute was tuned to the 1-30 Mev energy range and determined the angle of arrival within a degree and the energy of photons to within five percent at higher energies. The Energetic Gamma Ray Experiment Telescope (EGRET) measured high energy (20 Mev to 30 gev) gamma ray source positions to a fraction of a degree and photon energy to within 15 percent. EGRET was developed by NASA GSFC, the Max Planck Institute, and Stanford University. The Burst and Transient Source Experiment (BATSE) by NASA MSFC scoured the sky for short duration gamma ray bursts (20 to 600 kev) and conducted full sky surveys for long lived sources.

AKA: Compton Gamma Ray Observatory.
Gross mass: 15,620 kg (34,430 lb).
Height: 9.10 m (29.80 ft).
Span: 21.30 m (69.80 ft).
First Launch: 1991.04.05.
Number: 1 .

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Associated Countries
See also
  • Shuttle The manned reusable space system which was designed to slash the cost of space transport and replace all expendable launch vehicles. It did neither, but did keep NASA in the manned space flight business for 30 years. More...

Associated Launch Vehicles
  • Shuttle American winged orbital launch vehicle. The manned reusable space system which was designed to slash the cost of space transport and replace all expendable launch vehicles. It did neither, but did keep NASA in the manned space flight business for 30 years. Redesign of the shuttle with reliability in mind after the Challenger disaster reduced maximum payload to low earth orbit from 27,850 kg to 24,400 kg. More...

Associated Manufacturers and Agencies
  • NASA American agency overseeing development of rockets and spacecraft. National Aeronautics and Space Administration, USA, USA. More...
  • TRW American manufacturer of rockets, spacecraft, and rocket engines. TRW Corporation, Redondo Beach, CA, USA. More...

  • McDowell, Jonathan, Jonathan's Space Home Page (launch records), Harvard University, 1997-present. Web Address when accessed: here.
  • JPL Mission and Spacecraft Library, Jet Propulsion Laboratory, 1997. Web Address when accessed: here.
  • McDowell, Jonathan, Launch Log, October 1998. Web Address when accessed: here.
  • NASA Report, Messengers of creation: The NASA Gamma-Ray Observatory mission, Web Address when accessed: here.

Associated Launch Sites
  • Cape Canaveral America's largest launch center, used for all manned launches. Today only six of the 40 launch complexes built here remain in use. Located at or near Cape Canaveral are the Kennedy Space Center on Merritt Island, used by NASA for Saturn V and Space Shuttle launches; Patrick AFB on Cape Canaveral itself, operated the US Department of Defense and handling most other launches; the commercial Spaceport Florida; the air-launched launch vehicle and missile Drop Zone off Mayport, Florida, located at 29.00 N 79.00 W, and an offshore submarine-launched ballistic missile launch area. All of these take advantage of the extensive down-range tracking facilities that once extended from the Cape, through the Caribbean, South Atlantic, and to South Africa and the Indian Ocean. More...
  • Cape Canaveral LC39B Shuttle, Saturn V, Saturn I launch complex. LC39A and LC39B, part of the Kennedy Space Center, were built on Merritt Island (north/northwest of the Cape) to support the Saturn V/Apollo lunar landing program in 1963-1966. The sites were modified in the last half of the 1970s to support the manned Space Shuttle program. More...

GRO Chronology

1991 April 5 - . 14:22 GMT - . Launch Site: Cape Canaveral. Launch Complex: Cape Canaveral LC39B. LV Family: Shuttle. Launch Vehicle: Shuttle. LV Configuration: Space Shuttle STS-37R.
  • Compton Observatory - . Payload: Gamma Ray Observatory. Mass: 15,620 kg (34,430 lb). Nation: USA. Agency: NASA Greenbelt. Class: Astronomy. Type: X-ray astronomy satellite. Spacecraft: GRO. Decay Date: 2000-06-04 . USAF Sat Cat: 21225 . COSPAR: 1991-027B. Apogee: 453 km (281 mi). Perigee: 448 km (278 mi). Inclination: 28.5000 deg. Period: 93.60 min. Astrophysical laboratory for gamma ray observations; deployed from STS-37 4/7/91; renamed Compton Gamma Ray Observatory. The Compton Gamma Ray Observatory was intentionally deorbited on by NASA over the objections of the scientific community on June 3, 2000. NASA decided to end the mission after several orientation gyroscope failures. They felt that if another gyroscope was lost, the heavy spacecraft might eventually reenter out of control.

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