NASA Will Crash CGRO into the Pacific Ocean in June

By Keith Cowing
March 24, 2000
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NASA has decided to deorbit the Compton Gamma Ray Observatory (CGRO) due to safety concerns that it could reenter on its own and pose a threat to people on Earth. NASA plans to maneuver the spacecraft and alter its orbit such that it will impact on Earth on 3 June 2000.

Compton was launched by Space Shuttle mission STS-37 in 1991 for a 5 year mission. It has operated for more than 9 years and has met all of its primary science objectives. CGRO has made many scientific discoveries, some of them “fundamental” according to NASA Associate Administrator for Space Science Ed Weiler.

Weiler noted that the Level 1 specs” i.e. the main requirements for the mission state that if only 2 gyroscopes remain operational that plans be made to deorbit the spacecraft. “Everyone knew this and signed up to it” said Weiler.

CGRO is one of the heaviest spacecraft ever launched by NASA. It currently weighs around 33,000 pounds. When it reenters the atmosphere its is expected that large pieces will survive and hit the earth. Some pieces could be as large as 1 ton and hit at 200 miles per hour. The debris field or footprint is expected to be rather large. For this reason the plan is to bring it back to Earth in a remote region of the Pacific Ocean.

Should the spacecraft reenter the atmosphere on its own, there is a probability of 1/1000 that a human life could be lost according to Weiler. Current estimates of when the spacecraft would come in if not done so in a controlled fashion range between 3 and 11 years. The 3 year estimate would be the case if solar maximum activity is at its highest possible level while the 11 year end of the range would be the case if solar activity is low.

Weiler closed by saying “my job is to do as much science as I can” and that making such as decision was “not easy”. He justified his decision by saying that he cannot sanction a trade off between science and an increased risk of loss of human life.

CGRO is a NASA cooperative program with participation from Germany, the Netherlands, the European Space Agency, and the United Kingdom. According to the STS-37 press kit: “the instruments onboard GRO, with sensitivities 10 times greater than that of earlier instruments, will scan active galaxies for new information on celestial objects. GRO also can detect the very high temperature emissions from the vicinity of stellar black holes, thereby providing evidence for the existence of these exotic objects. GRO observations of diffuse radiation will not only help resolve questions relating to the large scale distribution of matter in the universe, but also about the processes that may have taken place shortly after the universe began in the theoretical energetic explosion or “Big Bang”.


° NASA’s Successful Compton Gamma Ray Telescope Mission Comes to an End, NASA press release

° NASA News Briefing Announcement, NASA PAO

° NASA Briefing Chart describing progress in deorbiting CGRO

° Reboosting the Compton Gamma-Ray Observatory, NASA GSFC

° Compton Gamma Ray Observatory (CGRO), NASA GSFC

° STS-37 Mission, Deployed CGRO in April 1991, NASA KSC

° NASA Preparing Plans for Destructive Reentry to End Compton Gamma Ray Observatory’s Mission, 14 Jan 2000, SpaceRef

° CGRO Users’ Committee Meeting Portsmouth, New Hampshire, 14 September 1999, NASA GSFC

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