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Faulty sensor stymies shuttle

There was a problem with a sensor in the external fuel tank, and NASA will try again today. If unsuccessful, the launch will be put off for weeks.

Published September 9, 2006

CAPE CANAVERAL - NASA has called space shuttle Atlantis' mission to restart construction of the international space station one of the most difficult in the agency's history.

Getting off the ground is proving hard enough.

Friday's launch was the latest to be scrubbed, and this time the culprit was an old nemesis: a faulty sensor in the external fuel tank. The same problem delayed two earlier shuttle launches, the first since Columbia broke up over Texas in 2003.

Inside NASA they have another name for the troublesome sensors - but it's not printable.

"We affectionately refer to them in ways that are probably not very flattering," said LeRoy Cain, the launch integration manager.

Today's 11:15 a.m. launch window is the last for weeks. The next would be later this month or October, to avoid conflict with a Russian mission to the space station.

The delay further squeezes NASA's tight construction schedule for the space station: 14 more shuttle missions by 2010. After that the shuttle would be replaced by the new Orion vehicle, which would take astronauts to the space station, then the moon and eventually Mars.

Originally set to lift off Aug. 27, Atlantis has been grounded by thundershowers, a lightning strike at the launch pad, Tropical Storm Ernesto and a faulty power-generating fuel cell.

Friday's call was made by Cain, chairman of the mission management team. But he had an influential backer on the committee: veteran astronaut Ken Bowersox, head of the astronaut office. Senior managers said Bowersox didn't want to override NASA's safety rules: The shuttle can fly with only three working sensors, but the reason for the fourth's failure must be known. Engineers were still working on that.

Launch director Mike Leinbach announced the decision at 11:15 a.m., 26 minutes before scheduled liftoff. He said the launch team should "feel good" about the decision.

"We understand," said Navy Capt. Brent Jett, Atlantis' commander, from the orbiter. "We concur 100 percent."

The problematic fuel sensor was discovered Friday while supercold liquid hydrogen fuel was pumped into the launch vehicle. When they refuel Atlantis for today's rescheduled launch, engineers hope to figure out why the sensor indicated the tank was "dry" when it should have indicated "wet."

Speed and power are supposed to determine when the shuttle's three main engines shut down as the spacecraft reaches orbit. If that fails, the sensors are a critical backup. If fuel is low, the sensors cut off the flow to the engines.

But a faulty sensor could lead to two potentially disastrous results:

It could cut off engine power in mid launch, before the spacecraft reaches orbit, forcing the shuttle to execute a dangerous emergency landing at runways at the cape or in France or Spain.

Or it could let the engines suck up all the fuel. The engines could rupture in mid launch. The result would be catastrophic.

Humor can help crew cope

CAPE CANAVERAL - For go-go astronauts, the way to cope with the no-go of a launch delay is with a joke. Even at their own expense.

NASA's king of launch delays, former astronaut Steve Hawley, had some advice for Atlantis' six astronauts awaiting a fifth liftoff attempt today: Have a little pessimism and a lot of humor.

Hawley has sat through 12 launch delays for five liftoffs. When his 1986 Columbia mission set a record with six scrubs, Hawley decided he was the problem. So for the seventh attempt he put on a disguise: Groucho Marx glasses, eyebrows and nose and duct tape over his nametag "so the orbiter didn't know it was me."

Columbia launched after Hawley donned his disguise.

Information from the Associated Press was used in this report.

[Last modified September 9, 2006, 01:35:37]

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