Uars Satellite Will Fall to Earth, NASA Doesn't Know Where

Sep 22, 2011, 07:39 by R.E. Christian

A large satellite as big as a bus will fall to Earth this week but NASA scientists say they aren't sure which day or where it will hit.

NASA says the 12-500-pound Upper Atmosphere Research Satellite will probably fall to Earth Friday but it could be Thursday or Saturday. The exact time and location of any dead satellite's return through the Earth's atmosphere is difficult to predict with precision, The Washington Post reported.

The UARS -- launched in 1991 to conduct climate studies of Earth's atmosphere -- will partially burn up during re-entry, NASA said, and break into about 100 pieces, creating a light show that should be visible even in daytime.

An estimated 20 larger pieces will survive and land in a debris field about 500 miles long, but just where is still unknown.

"There are too many variations on solar activity which affect the atmosphere, the drag on the vehicle," Nicholas Johnson, chief scientist for orbital debris at NASA, said.

Even within as close to 2 hours of re-entry, the margin of error for estimating the exact time could be off by 25 minutes.

"That equated to plus or minus 5,000 miles," Johnson said. "That's a lot of real estate"

Dead satellites, rocket bodies and spent fuel tanks fall to Earth often, Johnson said, "and in over 50 years of these things coming back around the world, no one has ever been hurt. There has never been any significant property damage."

Source: UPI