Planners call off Discovery launch

Setback is blamed on faulty fuel gauge

Sat. earliest it could fly

July 14, 2005|By Jeremy Manier | Jeremy Manier,CHICAGO TRIBUNE

CAPE CANAVERAL, Fla. - In a disappointing setback for NASA's effort to return the space shuttle to flight, mission planners called off the launch of Discovery just hours before its scheduled liftoff yesterday, blaming a faulty fuel gauge in the vehicle's external tank.

Engineers could not immediately pinpoint the source of the glitch, which affected a sensor intended to shut down the spacecraft's engines if the fuel level gets too low. Mission planners said the earliest Discovery could fly would be Saturday afternoon, though the problem could set the flight back weeks or even months.

Shuttle engineers have struggled since April with the kind of sensor that caused trouble yesterday. Two of the sensors malfunctioned during testing at that time - a failure technicians never fully understood, though the glitch seemed to resolve itself after engineers replaced some circuitry on the orbiter.

The latest problem raised a new mystery. When flight controllers sent a signal that should have switched the four fuel sensors to a reading of "empty," one failed to respond.

"All I can say is shucks," said shuttle program deputy manager Wayne Hale.

Launch director Mike Leinbach informed a disappointed crew that the launch would be scrubbed.

"I appreciate all we have been through together, but this one is not going to result in a launch attempt today," Leinbach told shuttle commander Eileen Collins, who was strapped into the cockpit.

This is the second time NASA has had to cancel a Discovery launch. In May, managers scrubbed a launch because of a separate issue with the external tank that required installation of a modified tank.

Shuttle engineers said that if the spacecraft were to fly without working fuel gauges, the engines might not shut off in the event that the tank ran out of hydrogen propellant sooner than expected. That would result in the engines' running dry - something they were not designed to do.

The sensors "are there to protect us in case we run out of gas," Hale said. He said it took the shuttle managers about five minutes to decide that the faulty sensors meant the mission could not go forward.

Mission planners have not given up on the possibility that the problem could be resolved soon. They said that the astronauts will remain in Florida for the time being and that engineers will conserve energy in the shuttle's fuel cells so the spacecraft could launch in the next few days.

The current launch window runs through July 31. If the shuttle does not launch by then, the next opportunity would not arise until September.

At several safety meetings including a final one Tuesday, some NASA technicians had questioned whether the shuttle should fly at all until engineers understood what had caused the earlier fuel sensor problems.

But Hale said that at the last meeting the team decided unanimously that it would be safe to fly the shuttle even without understanding the problem, because pre-launch tests would detect any malfunction.

That is exactly what came to pass, he said.

"You would really like to be able to say, `This was it and I can prove it conclusively,'" Hale said. "But gosh, life's not like that all the time."

The Chicago Tribune is a Tribune Publishing newspaper.

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