http://news.yahoo.com/s/afp/20080908...eastronomynasa

WASHINGTON (AFP) - The US shuttle Atlantis faces nearly twice the
risk of being struck by debris on a mission next month to the Hubble
telescope, due to the high levels of space litter floating at the
altitude of Hubble's orbit, NASA said Monday.
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"It's a very challenging mission. We have hazards we don't typically
have for an ISS (International Space Station) mission," NASA space
shuttle program manager John Shannon told a news conference.

"We have a one-in-180 chance of getting some type of catastrophic
damage from micro-meteorites/orbiting debris (MMOD) compared to an ISS
mission, which is typically a one-in-300 chance," he said.

Hubble is orbiting some 563 kilometers (350 miles) above earth,
compared with 354 kilometers (220 miles) for the ISS.

When the risk faced by a shuttle mission is greater than one-in-200,
the decision to go ahead with the flight has to come from the highest
authorities in NASA, said Shannon.

But he expected they would give the green light for the Atlantis
mission to lift off on what will be its final mission to conduct
maintenance work on Hubble.

"Our risk has increased, but our ability to mitigate the risk has
increased. So it makes us feel pretty good about it," said Shannon.

"MMOD is the biggest risk for all shuttle flights" and the risk grows
the higher above the earth's surface the shuttle flies, he said.

Space has become more littered and dangerous in the past year due to
mishaps, tests and aborted missions involving American, Chinese and
Russian satellites and rockets, he said.

NASA developed new methods to inspect and repair damage to the space
shuttle after heat tiles on the Columbia shuttle were damaged on
lift-off in 2003, causing the vehicle to disintegrate as it re-entered
the earth's atmosphere, killing everyone on board.

The US space agency has plans to replace the aging shuttle fleet with
a new space vehicle Orion, set to launch in 2014.

The new spacecraft will pick up where the shuttle leaves off,
re-supplying the International Space Station, as well as undertaking
other space missions, including moon landings.

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