Tim Furniss/LONDON
The $670 million Compton gamma ray observatory re-entered the Earth's atmosphere over the Pacific Ocean on 4 June, ending a mission which began with its deployment from the Space Shuttle Atlantis STS37 in April 1991.
One of NASA's Great Observatory series of spacecraft - others include the Hubble Space Telescope and the Chandra X-ray observatory, both still in orbit - Compton returned unprecedented images and data of violent gamma ray bursts, anti-matter fountains and streams of particles from black holes. The observatory detected more than 2,600 gamma ray bursts during its mission.
The 14,970kg (33,000lb) spacecraft made a controlled re-entry with four carefully-timed firings of its thrusters, breaking up over a 4,100km 2,550 miles)-long corridor stretching from south east of Hawaii to the northern coast of South America.
Larger pieces of debris from the telescope which were expected to survive the re-entry were seen falling into the ocean at a location predicted by NASA engineers.
NASA's decision to end the mission has been claimed as unnecessary and premature by many astronomers and scientists. It was prompted by the failure of one of the satellite's three attitude control gyros. The failure of another gyro would have made it difficult to control the spacecraft, possibly resulting in an uncontrolled re-entry over inhabited areas.
NASA decided to preclude this possibility, after its experience with the uncontrolled re-entry of the Skylab space station in 1979 which showered parts of sparsely populated areas of Western Australia with debris, without causing casualties.
The safe and controlled de-orbiting of Compton may also have been a demonstration by NASA and the White House to put pressure on Russia to consider seriously its plans for safely deorbiting the Mir space station.
In addition to claiming that the continuation of operations on Mir is a diversion of Russian resources away from the International Space Station, NASA believes the longer the station remains aloft, the greater the chances of being unable to safely deorbit it if there is a major malfunction.
The station, however, is operating well and is being manned by two cosmonauts. There are also plans for further refurbishment conducted by commercially supported crews.
A NASA briefing to the White House claims that the impact point of debris from an uncontrolled Mir re-entry could not be predicted and the re-entry poses a significant hazard to populated regions.
Source: Flight International
