NASA satellite falls to earth
The US space agency, NASA, says its six-tonne Upper
Atmosphere Research Satellite has plunged to earth, showering debris over a
still unknown part of the planet.
Re-entry of the defunct satellite - about the size of a bus
- was expected between 03:45 and 04:45 GMT on Saturday, NASA said.
NASA was attempting to confirm the re-entry location and
time.
Public risk 'remote'
The UARS, stretching 10.6 metres long and 4.5 metres in
diameter, is the largest American space agency satellite to plummet
uncontrolled into the atmosphere in about 30 years.
It is slimmer in comparison to NASA's 75-tonne Skylab
station, which crashed to earth in 1979.
Russia's last space station, the 135-tonne Mir, crashed into
the Pacific Ocean in 2001, but it was a guided descent.
NASA now plans for the controlled re-entry of large
spacecraft, but it did not when UARS was designed.
The 5,897kg satellite was dispatched into orbit by a space
shuttle crew in 1991 to study ozone and other chemicals in earth's atmosphere.
It completed its mission in 2005 and slowly lost altitude
ever since, pulled by the planet's gravity.Most of the spacecraft is likely to
have burnt up during its descent through the atmosphere, but about 26
individual pieces, weighing a total of about 500kg, are expected to have
survived the incineration and landed somewhere on earth.
The debris field spans about 805km, but exactly where is
still being confirmed.
North America is within the probable impact zone, although
an extremely unlikely one.
With most of the planet covered in water and vast uninhabited
deserts, the chance that someone could have been hit by falling debris is
1-in-3,200, NASA said.
"The risk to public safety is very remote," it
said.
Approximately 20,000 pieces of space debris are loitering in
orbit around earth. Something the size of UARS falls back into the atmosphere
about once a year.
Source: aljazeera.net/
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