Shuttle Faces More Delays as Valve Problem Halts Test

A computer spotted a valve problem and scrubbed NASA’s test-firing of space shuttle Discovery’s engines in the final second Thursday, dealing another setback to America’s 2 1/2-year effort to return to space.

Engineers said it will be three to seven days before they can try the test again. The postponement was the fifth in two weeks and made it almost certain that Discovery’s flight will be delayed from late September into October.

“That’s why we have flight readiness firings, to work the bugs out of equipment before we launch,” said James C. Fletcher, administrator of the National Aeronautics and Space Administration.

Last Flight Was in 1986

No American has been launched into space since the shuttle Challenger exploded 73 seconds after liftoff on Jan. 28, 1986, killing seven crew members.

The problem Thursday either was a valve that didn’t close as fast as it was supposed to or a sensor that gave a wrong reading of the valve’s open-closed position.

“We don’t know whether it was a faulty indication or really a malfunction in the valve,” said Joseph A. Lombardo, engine program director at NASA’s propulsion facility in Mississippi.

Engineers were looking at the possibility that the sensor might have been affected by long exposure to the extreme cold of the liquid hydrogen fuel. The tanks were loaded for 10 hours, four hours longer than normal, so that special tests could be run on the fuel system.

To remain liquid, hydrogen must be kept at 423 degrees below zero.

Computer Reacted

The computer, which controls all operations in the final 31 seconds of a launching countdown, received an indication that a valve still was partly open, which would allow high-pressure gases to enter areas unable to accommodate them, possibly causing a rupture and explosion. The computer reacted appropriately.

“The actual start commands to the engine were never given,” Lombardo said. “The incident that occurred was not that we had a start failure of the main engines but that we had a failure to start.”

If the sensor is at fault, Lombardo said, a change in computer commands might be a way around the problem.