Hubble shuttle flight faces higher space junk risk

CAPE CANAVERAL, Fla. -- Next month's shuttle flight to the Hubble Space Telescope faces an increased risk of a destructive impact by space junk because it will be in a higher, more littered orbit than usual, NASA said Monday.

Managers at NASA's highest levels will need to sign off on the mission because of the increased risk.

New number-crunching puts the odds of a catastrophic strike by orbital debris including bits of space junk at about 1-in-185 during Atlantis' upcoming mission to Hubble. That compares to 1-in-300 odds for a shuttle flight to the international space station, shuttle program director John Shannon said Monday.

Hubble is at a considerably higher and dirtier, so to speak, orbit than the space station -- 350 miles versus just over 200 miles. That extra altitude will expose Atlantis to more pieces of space junk, any of which could slam into the shuttle.

Space debris, though, has not caused significant damage to Hubble since its launch in 1990, said Preston Burch, NASA's Hubble program manager.

NASA's usual limit is a 1-in-200 chance of a catastrophic hit by space junk. While that's an arbitrary baseline, anything greater than that must be considered at the highest levels of NASA, Shannon said at a news conference.

Flight reviews will be held later this week and again, with top-level executives, later this month.

Seven astronauts will be aboard the spaceship, which is scheduled to launch Oct. 10.

Orbital debris is the biggest threat to an orbiting space shuttle, surpassing even the liftoff dangers of the main engines and booster rockets, and the always-dangerous re-entry, Shannon said.

In part, that's because of the breakup of several orbiting craft in the past few years, Shannon said. China deliberately destroyed an old satellite last year, the U.S. military shot down a damaged spy satellite in February and a Russian satellite broke apart this past spring. All that generated a considerable amount of junk in orbit.

NASA also understands more about the hazards of micrometeoroid and orbital debris, and how to process the numbers, Shannon said. Some steps will be taken during the Atlantis flight -- like reorienting the shuttle in orbit -- to reduce the danger as much as possible.

After a shuttle flight, Shannon said there are small dings on the wings and holes in the radiators, and the space station looks like it has bullet holes from space debris hits.

"It's not theoretical," he said of the debris risk. "We just don't get it in critical places, typically."

Overall, NASA puts the odds of a catastrophic loss of a space shuttle during a mission at about 1-in-80. Shannon noted that history has shown the odds to be about 1-in-60.

Challenger was destroyed during liftoff in 1986; it was the 25th shuttle flight. Columbia shattered during re-entry in 2003; it was the 113th shuttle flight.

The upcoming mission will be No. 124.

Another shuttle, Endeavour, will be at the other launch pad ready to rush to the Atlantis astronauts' aid in case of damage that might endanger them during descent. The rescue mission was put in place two years ago.

As it turns out, the risk of launch debris has lessened because of improvements made in the wake of the Columbia accident, while the threat of orbital debris has intensified, Shannon said.

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