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Saturday, June 3, 2000

Gamma ray
observatory falls
into ocean tonight

The satellite should hit Earth
2,300 miles southeast of Hawaii

By Helen Altonn


A bus-size NASA observatory launched in 1991 to look for gamma rays in space from nuclear explosions is expected to plunge back to Earth tonight in pieces.

It will fall about 2,300 miles southeast of Hawaii if it hits in the center of the predicted impact area, NASA said. Debris could be scattered along an area of the Pacific Ocean about 16 miles wide by 962 miles long, from southeast of Hawaii toward the northern coast of South America.

The space agency started a controlled descent of its Compton Gamma Ray Observatory satellite Tuesday after one of its three stabilizing gyroscopes failed.

An Air Force intelligence plane from Hickam Air Force Base and the Maui Space Surveillance Complex on Haleakala will track the satellite's descent in the eastern Pacific at about 8:22 p.m.

Capt. Sam McNiel, commander of the Haleakala station, said it has a narrow field of view, so it hopes to lock onto a large piece of the satellite and follow it. "We want to see where it goes and see what we learn about how it breaks up."

McNiel said it might be possible for people in Hawaii to see the satellite as it streaks through the southern half of the sky, going west to east. It could look like a meteorite or falling star, he speculated.

Maj. Mike Birmingham, with the Air Force Space Command at Peterson Air Force Base, said it is assisting to make sure the observatory does not collide with any other object in space.

A piece of debris or satellite passing through the atmosphere is "like a stone skipping off a lake," he said. "It can skip 3,000 miles either way."

He said it may be possible to see the observatory coming in from orbit, depending on where it is and the conditions. "It will be re-entering the earth's atmosphere screaming in at 17,000 mph."

Spacecraft generally begin breaking up about 48 miles above the surface when they fall into the atmosphere. Pieces will range from pebble size to big chunks.

University of Hawaii astronomer J. Patrick Henry, who works with NASA's Chandra X-ray Observatory, doubts people will be able to see the disintegrating satellite. "It's like, could you see Los Angeles from Mauna Kea?"

The Compton observatory studied the universe through gamma rays, which are "very high-energy X-rays, even higher than what you do when you get your teeth or bones X-rayed," Henry explained.

It was designed to test for nuclear explosions in space, and began to see bursts of gamma rays, Henry said. There are gamma ray bursts coming from very distant galaxies, "probably some sort of exploding star in galaxies far away," Henry added.

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