NASA Saying Goodbye to Universe Eye


Updated 12:15 PM ET May 27, 2000
By PAUL RECER, AP Science Writer
WASHINGTON (AP) - The Compton Gamma Ray Observatory is poised for a suicide
plunge to Earth, ending a successful nine-year $670 million space mission
that opened a new window on the universe.

Starting Tuesday, NASA engineers will send signals to the satellite to
perform a series of rocket firings that will drop the Compton from its
317-mile orbit and send it into a final, fiery dive to the Pacific Ocean
early on June 4.

"It will be like losing a member of the family," said Donald A. Kniffen, a
NASA scientist who has worked with the Compton since 1979, when the
astronomical observatory was little more than engineering sketches and
scientific dreams.

Even though the Compton still was capable of collecting science for the
world's astronomers, the craft is ailing. After a gyroscope failed, engineers
from the National Aeronautics and Space Administration decided to
deliberately crash the 17-ton spacecraft while they still could control it.

An analysis showed that if NASA did nothing, the craft would eventually fall
on its own, with one-in-1,000 chance of killing someone on Earth. The craft's
orbit carries it over some of the most populated areas of the world,
including Mexico City, Miami and Bangkok, Thailand.

Using the remaining guidance and control equipment on Compton reduces that
risk of fatality to about one in 29 million. NASA chief scientist Ed Weiler
said he chose safety over science.

"How much science is worth the risk of even one human life?" Weiler asked
when announced his decision.

NASA was not eager to repeat the nail-biting experience of Skylab, the 78-ton
space station that crashed in 1979. Engineers had no control over the station
when it dropped from space and spread hundreds of pounds of hot metal across
the Indian Ocean and into a remote section of western Australia. No one was
hurt.

The Compton will be the largest spacecraft brought down in a deliberate,
controlled crash.

NASA engineers plan to dump the Compton in a remote part of the Pacific
Ocean, 2,500 miles southeast of Hawaii. The impact target is a corridor 16
miles wide and some 1,426 miles long. It angles across the equator, northwest
to southeast, and ends about 680 miles south of the Galapagos Islands.

A rocket firing to lower the orbit is scheduled for Tuesday night from the
space agency's Goddard Space Flight Center in Greenbelt, Md. A second firing
is set for Wednesday. That will set the craft up for two final firings June
4.

The rocket thrust will slow the Compton enough to drop it into the
atmosphere, where friction heat will burn up most of the craft. The main
concern is for six 1,800-pound aluminum I-beams that may survive the re-entry
and splash into the ocean.

Kniffen said he is approaching the end of Compton with a mixture of sadness
and pride.

Since the craft was launched April 5, 1991, he said, the instruments on the
Compton have completely changed the way astronomers view the universe.

The instruments were designed to detect gamma rays, an energetic form of
light invisible to the eye and hardly detectable on Earth.

But in space, the Compton found that the whole universe was bathed in gamma
rays, with explosions occurring in distant galaxies almost daily.

Before Compton, Kniffen said, astronomers thought gamma ray bursts, the most
energetic events in the universe, could be detected only in the Milky Way,
the home galaxy of the Earth and Sun.

"Within months of its launch, we had proof that gamma ray bursts were coming
from all directions in the universe," he said. "We realized that some of them
were coming from very early in the history of the universe," which means they
were far beyond the Milky Way and were very, very powerful.

During its mission, the Compton recorded more 2,500 gamma ray bursts, while
only about 300 had been detected previously, NASA said. Some of its
detections came quickly enough to alert other observatories which then
collected observations in visible light and X-rays.

The cause of the gamma ray bursts is still a puzzle, but Kniffen said the
libraries of data from Compton may help astronomers find answers.

Compton also detected gamma rays streaming from black holes, from exploding
stars and from the sun.

An analysis of the data has helped astronomers, for the first time, begin to
understand how black holes can trigger jets of X-rays and gamma rays that
streak outward at velocities approaching the speed of light.

The Compton was originally expected to last only two years. But when that
time was up, the mission was extended repeatedly. It took its last bit of
data - a gamma ray snap shot of the sun - on Friday.

"It performed far beyond our expectations," Kniffen said. "Dollar for dollar,
it was one of the most successful missions NASA has ever had."

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