Originally created 03/24/01

Stuff falls from the sky all the time



The Russian space station Mir's plunge to Earth became a highly watched international phenomenon, but the orbiter is just one of hundreds of manmade objects that fall to Earth every year.

"People talk about the Mir coming down like it's the only satellite to fall," University of Colorado professor Robert Culp said. "I kind of hate to tell them something fell down last night."

Some 8,300 satellites, rocket pieces and other fragments, currently orbit the Earth and are tracked by the U.S. Space Command, said a spokesman, Master Sgt. Larry Lincoln.

That number is only one-third of the 26,000 items the center has tracked since 1957. "The rest have re-entered," he said.

On average, one satellite a day has fallen to Earth in the last 40 years, said Nicholas Johnson, chief scientist and program manager for orbital debris at NASA's Johnson Space Center.

Mir's descent was different, however, because of its size: at 143 tons it was not only the largest manmade object to fall to Earth, but its mass equaled the total of all manmade objects that drop to Earth in an average year.

"It's all year's worth in one night," Johnson said.

Four fragments from the disintegrating Mir flashed above the beaches of Fiji like white balls of fire Friday, leaving a swarm of smaller debris in their wake and illuminating the evening sky.

Such streaking images are not unusual for manmade objects falling to Earth. Most people hardly notice them plunging, however, and if they do, they sometimes mistake them for meteors, said Culp, who specializes in space debris.

"All of these (items) are visible," to the naked eye, Culp said. "You can find a dozen or so satellites, but it must be a dark sky."

Some Websites even show what manmade items will be cruising through the sky -- and when -- around the world.

Falling space debris does not pose a threat because most land in isolated areas, the water or burn up in the atmosphere, Johnson said.

But some materials that have high melting temperatures -- such as titanium and stainless steel -- help old satellites and rocket pieces survive the fiery re-entry to the Earth's atmosphere, making for some dramatic plunges.

In January 1997, for example, a 1,500-pound fuel tank fell from space and onto a Texas couple's rural homestead. A 150-pound ball tumbled from the sky over Saudi Arabia in January of 2001.

Debris floating in space poses more of a problem in the heavens because it can collide with functioning space craft -- and at 17,000 miles an hour.

Although Mir was the largest manmade craft to fall from space, other notable ones have made fiery plunges to the Earth. The Russian satellite Cosmos 954 scattered debris over a wide area of northwest Canada when it descended on Jan. 24, 1978, and the 75-ton U.S. space station Skylab, fell in a shower of red-hot fragments across western Australia July 1979.

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