Spaceflight Now: CGRO deorbit

A fiery goodbye to Compton Gamma Ray Observatory
BY JUSTIN RAY
SPACEFLIGHT NOW

Posted: June 4, 2000

  Heating
Animation shows CGRO feeling heat of reentry. Photo: NASA TV/Spaceflight Now
 
NASA officials and scientists around the world bid a fond farewell to the prized Compton Gamma Ray Observatory early Sunday as the 9-year old craft made a controlled crash back to Earth.

The 17-ton telescope plummeted into the atmosphere just after 2 a.m. EDT (0600 GMT) after a week-long process of lowering its orbit through a course of lengthy thruster firings. Contact was lost at 2:10 a.m. EDT (0610 GMT) as controllers saw temperatures skyrocketing and indications the craft was tumbling.

"At this point, the spacecraft is probably breaking up," said Thomas Quinn, the reentry coordinator.

"We did expect to lose the solar arrays fairly early, they're going to pop off, some of the loose elements of the spacecraft are going to start to fall apart. As things heat up, the primary structure's going to start to melt and larger components are going to start to break off the spacecraft."

"This is a painful time for the scientists who have used the Compton Observatory for the last nine years as the spacecraft plunges into the atmosphere and flies apart," said project scientist Neil Gehrels.

Read our Mission Status Center for reports filed throughout the final hours of CGRO's life and the reentry.

Break up
Animation shows CGRO beginning to break apart, with the solar arrays first. Photo: NASA TV/Spaceflight Now
 
 
About six tons of debris was expected survive the searing plunge, splashing down in a predetermined stretch of the Pacific Ocean southeast of Hawaii at about 2:19 a.m. EDT (0619 GMT). Lighter pieces could take another 20 minutes to fall to the water surface.

Experts said six 1,800 pound aluminum I-beams, titanium parts and more than 5,000 bolts from CGRO would survive the reentry.

Observers aboard an Air Force surveillance aircraft in the area confirmed seeing the satellite breaking up and landing in the planned safety zone.

Officials said it would take a couple of days to determine the exact location and dimensions of the debris field.

CGRO's demise ends one of NASA's most successful science missions, which began when the observatory was launched into space aboard shuttle Atlantis on April 5, 1991.

Compton made 51,658 orbits around Earth.

Built by TRW, the $671 million craft was the second of NASA's Great Observatory family, along with sisters Hubble Space Telescope, Chandra X-ray Observatory and the future Space Infared Telescope Facility.

  Destruction
Animation shows CGRO completely destroyed. Photo: NASA TV/Spaceflight Now
 
"The end of an era, a discovery era, for gamma ray astronomy," Gehrels said. "This is the Compton Gamma Ray Observatory Mission Operations Room at the Goddard Space Flight Center in Greenbelt, Maryland, signing off."

NASA ordered the controlled reentry in March after one of CGRO's three stabilizing gyroscopes failed. The space agency decided to deorbit the craft to protect public safety because an additional failure could have meant a dangerous crash like Skylab in 1979.

Officials calculated there was a 1-in-1,000 chance a person could be killed by CGRO if it reentered uncontrollably. The craft's orbital track ranged from 28.5 degrees to either side of the Equator.

"Our goal for the science community was a five-year mission to open the gamma ray universe to observation for the first time," Ed Weiler, NASA's associate administrator for space science, told reporters Sunday morning. "We certainly have met our commitment to the science community. Compton has greatly exceeded its expectations with a 9-year mission."

Footprint
A map shows the reentry zone. Photo: NASA
 
 
"And a few hours ago, NASA met its commitment to the billions of humans who live under the Compton orbital path by safely reentering Compton into the Pacific."

During its tenure in space, CGRO studied violent and invisible gamma ray bursts, antimatter fountains and particle jets streaming millions of miles per hour away from black holes. The telescope detected more than 400 gamma ray sources, 10 times more than were previously known, and recorded over 2500 gamma ray bursts when only 300 had been detected before.

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