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- WASHINGTON -- You can hum
the tune: "Raindrops keep falling on my head, they keep falling."
But if it were a chunk of flaming space debris, a knock on the noggin would
likely be deadly.
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- Earlier this year, it was the 17-ton Compton Gamma Ray
Observatory. It had to be purposely deorbited, with hunks of the spacecraft
harmlessly splashing into a pre-selected zone in the eastern Pacific.
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- This month, the first Iridium telecommunications satellite
may be dropped out of orbit. With no apparent taker to operate the multibillion
dollar constellation of 88 "flopsats," the entire network may
be brought down one after another. Some Iridium components will likely
reach Earth's surface.
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- Then, of course, there's the Russian Mir space station
that continues to loop Earth.
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- If new monies can't be found to keep Mir aloft, it too
is destined for a destructive slam dunk into the atmosphere. Space-debris
experts have their fingers crossed that if the huge Russian station comes
down, it can be controlled to avoid leftovers from falling into populated
areas.
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- So add to the old adage: What goes up, must come down...but
head's up!
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- Junkyard
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- Since the first satellite was hurled spaceward in 1957
-- the former Soviet Union's Sputnik 1 -- all manner of spacecraft from
numbers of nations have plowed their way into the heavens.
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- Today, some 9,000 objects are being tracked. In addition,
there are more than 100,000 bits of debris too small to follow. Then there
are even tinnier particles slipping through space, and they number in the
tens of millions.
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- From paint chips and lens covers to discarded space reactors
and spent rocket stages, after four decades of heaving satellites into
Earth orbit, space has become a polluted junkyard.
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- New data compiled by the Aerospace Corporation's Center
for Orbital and Reentry Debris Studies (CORDS) in El Segundo, California
found that over 425,000 pounds (193,000 kilograms) of material reentered
Earth's atmosphere in 1999.
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- "We believe that 84,000 pounds (38,000 kilograms)
of that total survived reentry," said William Ailor, director of CORDS.
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- Since 25 percent of Earth's surface is land, CORDS estimates
that 21,000 pounds (9,500 kilograms) actually struck land.
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- "There were no reports of individuals or property
struck or damaged. Given all that stuff that came down in 1999, I saw no
report of any recovered debris from any of that," Ailor told <http://SPACE.comSPACE.com.
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- Space survivor
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- When space hardware nosedives to Earth, there is a possibility
of space debris surviving reentry.
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- Hunks of burning flotsam typically do not survive the
severe heating that takes place during their fall from grace. Clutter that
does pierce through the atmosphere is likely to careen into the oceans
or other bodies of water. Remote stretches of unpopulated terra firma,
like the Canadian tundra, the Australian outback or Siberia may also be
on the receiving end of plummeting space debris.
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- "Actually, there is less debris coming down annually
than there was 10 years ago," said Nicholas Johnson, chief scientist
in NASA's orbital debris program office at the Johnson Space Center in
Houston, Texas.
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- "The satellite launch rate is substantially reduced.
If you look at total amount of mass entering the Earth's atmosphere from
orbit every year, we are definitely much better off than we were a decade
ago," Johnson said.
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- "Debris falling to the Earth is not a significant
problem, simply because the Earth is a large, uninhabited sphere,"
said Robert Culp, a space-debris expert at the University of Colorado's
Center for Astrodynamics Research in Boulder.
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- "Debris falling to the Earth will continue to provide
us with amusing anecdotes of people awakening to find a large chunk of
metal in the back pasture. It also provides brilliant streaks across the
night sky," Culp said.
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- Picking up the pieces
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- Still, the potential threat from falling space clutter
is real. A little space history shores up the need to keep a watchful eye
on the sky.
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- For example, on January 24, 1978 a Soviet Cosmos 954
deorbited and slammed into Canada's Great Slave Lake area of the Northwest
Territories. Making matters worse, that radar snooping spacecraft was powered
by a nuclear reactor.
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- A shower of radioactive debris spread itself over a large
area in Canada. After weeks of picking up the pieces, the Canadian government
issued the Soviets a cleanup bill for several million dollars. Moscow eventually
paid less than half the bill.
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- In July of the following year, the U.S. Skylab space
station bowed out of Earth orbit. It weighed a massive 77 tons (70,000
kilograms). Huge pieces of Skylab fell through Australian skies, creating
visual effects, even sonic booms, as debris passed overhead. Several charred
remains from Skylab were recovered on the ground.
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- The Australian government chided America by issuing NASA
a littering ticket.
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- Then in February 1991, Russia's Salyut 7 complex tumbled
out of orbit, crash landing on the east coast of South America. Luckily,
no one was hurt as tons of station came down in one fell swoop.
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- Splat attack
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- And there has been a recent spate of spectacular space
debris splats.
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- Last April, mysterious glowing objects had been falling
out of the sky over Cape Town, South Africa. Three separate pieces of space
garbage fell to the ground, with witnesses to all three falls stunned by
what they saw.
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- The objects were later identified. They were remnants
of the second stage of a Delta 2 rocket that had hurled into orbit a Global
Positioning Satellite over four years earlier. The biggest chunk was a
large propellant tank. The other pieces were a pressurization sphere and
a rocket-exhaust nozzle.
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- Interestingly, after nine months in space, an identical
Delta 2 upper stage reentered over the southern U.S. in January 1997.
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- As in South Africa, large pieces of debris were also
picked up, this time in Texas and Oklahoma. The 563-pound (256-kilogram)
stainless steel fuel tank landed just 50 yards (45 meters) from a farmer's
home. A woman in Tulsa, Oklahoma was hit by a small piece of charred metal
mesh. It did not injure her.
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- Duck and cover?
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- According to studies by CORDS, there are approximately
100 to 200 reentries of large objects each year.
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- But the risk that an individual will be hit and injured
is estimated to be less than one in 1 trillion. By comparison, the risk
that an individual in the U.S. will be struck by lightning is about one
in 1.4 million.
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- "After 43 years, there hasn't been anybody identified
as being hurt by falling debris," NASA's Johnson said.
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- The Aerospace Corporation's Ailor said that space hardware
is reentering all the time. "It's a fact that I don't think the public
has a feel as yet," he said, yet the prospect of somebody getting
hit by falling space junk is very small.
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- To better help satellite and rocket builders, Ailor said
that CORDS welcomes any space debris that are found. Understanding how
and why space hardware can survive the fiery fall from space is challenging,
he said.
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- By recovering and studying space debris, knowledge can
be gained about how and why satellites and rocket parts beat the heat.
That, in turn, can help manufacturers design in ways that lessen the chance
of future space hardware making it to Earth's surface, Ailor said.
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- "There are things that can be done. It's just getting
people aware of the potential risks," Ailor said.
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