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      CAPE CANAVERAL, Fla. — A 6-ton NASA satellite on a
collision course with Earth clung to space Friday, apparently
flipping position in its ever-lower orbit and stalling its death
plunge.


      The old research spacecraft was targeted to crash through the
atmosphere sometime Friday night or early Saturday morning, putting
the U.S. back in the potential crosshairs, although most of the
satellite should burn up during re-entry.


      "It just doesn't want to come down," said Jonathan McDowell of
the Harvard-Smithsonian Center for Astrophysics.


      McDowell said the satellite's delayed demise demonstrates how
unreliable predictions can be. That said, "the best guess is that
it will still splash in the ocean, just because there's more ocean
out there."


      Until Friday, increased solar activity was causing the
atmosphere to expand and the 35-foot satellite to free fall more
quickly. But late Friday morning, NASA said the sun was no longer
the major factor in the rate of descent and that the satellite's
position, shape or both had changed by the time it slipped down to
a 100-mile orbit.


      "In the last 24 hours, something has happened to the
spacecraft," said NASA orbital debris scientist Mark Matney.


      NASA cautioned there was now a slim chance any surviving debris
would land in the United States. Earlier this week, NASA said North
America would be in the clear.


      "It is still too early to predict the time and location of
re-entry with any certainty," NASA said in a statement.


      The Aerospace Corp., which tracks space debris, estimates the
strike will happen sometime between about 6 p.m. and 4 a.m. EDT,
which would make a huge difference in where the debris might wind
up. Those late-night, early morning passes show the satellite
flying over parts of the United States.


      Any surviving wreckage is expected to be limited to a 500-mile
swath.


      The Upper Atmosphere Research Satellite, or UARS, will be the
biggest NASA spacecraft to crash back to Earth, uncontrolled, since
the post-Apollo 75-ton Skylab space station and the more than
10-ton Pegasus 2 satellite, both in 1979.


      Russia's 135-ton Mir space station slammed through the
atmosphere in 2001, but it was a controlled dive into the Pacific.
      Some 26 pieces of the UARS satellite - representing 1,200 pounds
of heavy metal - are expected to rain down somewhere. The biggest
surviving chunk should be no more than 300 pounds.


      Earthlings can take comfort in the fact that no one has ever
been hurt by falling space junk - to anyone's knowledge - and there
has been no serious property damage. NASA put the chances that
somebody somewhere on Earth would get hurt at 1-in-3,200. But any
one person's odds of being struck were estimated at 1-in-22
trillion, given there are 7 billion people on the planet.


      "Keep in mind that we have bits of debris re-entering the
atmosphere every single day," Matney said in brief remarks
broadcast on NASA TV.


      In any case, finders definitely aren't keepers.


      Any surviving wreckage belongs to NASA, and it is against the
law to keep or sell even the smallest piece. There are no toxic
chemicals on board, but sharp edges could be dangerous, so the
space agency is warning the public to keep hands off and call
police.


      The $740 million UARS was launched in 1991 from space shuttle
Discovery to study the atmosphere and the ozone layer. At the time,
the rules weren't as firm for safe satellite disposal; now a
spacecraft must be built to burn up upon re-entry or have a motor
to propel it into a much higher, long-term orbit.


      NASA shut UARS down in 2005 after lowering its orbit to hurry
its end. A potential satellite-retrieval mission was ruled out
following the 2003 shuttle Columbia disaster, and NASA did not want
the satellite hanging around orbit posing a debris hazard.


      Space junk is a growing problem in low-Earth orbit. More than
20,000 pieces of debris, at least 4 inches in diameter, are being
tracked on a daily basis. These objects pose a serious threat to
the International Space Station.

Gallery

A 6-ton NASA satellite on a collision course with Earth clung to space Friday, apparently flipping position in its ever-lower orbit and stalling its death plunge.

Falling satellite slows down, Earth strike delayed

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