Computers Halt Shuttle Liftoff : Faulty Valve Scrubs Trip 3 Seconds Before Blastoff

The launching of the space shuttle Challenger was aborted Friday when computers aboard the space vehicle shut down the rocket engines even as they began to fire.

The shutdown occurred only three seconds before the planned liftoff, but the seven crew members were not injured. The danger, however, was apparent. Huge water cannons immediately poured water on the lower parts of the spacecraft to prevent fire or explosion.

The crewmen left the shuttle cabin 40 minutes later and were driven back to their Kennedy Space Center quarters. Gordon Fullerton, commander of the flight, said that they were “disappointed” but added: “We were thankful the system worked as it should. The seven of us had a keener interest in everything being up to snuff than anybody.”

It will be at least seven to 10 days before the flight can be rescheduled.

Officials of the National Aeronautics and Space Administration said that the abort was caused by the failure of a valve system feeding liquid hydrogen into one of the shuttle’s main engines.

During a launching, the shuttle’s liquid-fueled engines begin firing 6.5 seconds prior to liftoff. The much larger booster engines that provide most of the thrust for the ascent do not fire until the last second of countdown and did not ignite.

Last summer, another valve failure on the shuttle caused an abort with four seconds remaining in the countdown. But NASA officials said that Friday’s shutdown with three seconds remaining was produced by a different valve or control system. None of the crew members on Friday’s aborted flight were on the earlier scrubbed shuttle mission.

Redundancy Lost

Robert Lindstrom, one of the flight’s managers, said that the valve feeding hydrogen refused to obey a computer command to close down to 70% of capacity. A second command produced the desired response, but the mission was aborted because the system had lost its “redundancy,” or dual controls.

Tom Utsman, shuttle manager at Kennedy Space Center, said that the vehicle could be repaired within seven to 10 days but added that his prediction depended on the damage’s being limited to the single valve system.

Last summer, the flight of the orbiter Discovery was delayed for more than a month by its valve failure. That repair required a rollback of the shuttle to the huge maintenance facility here at the space center.

Repairs on Launching Pad

This time, Utsman said, NASA hopes to complete the repairs on the launching pad, which would speed the pace significantly.

NASA officials are under some pressure to launch the Challenger flight as soon as possible. On Aug. 24, the space agency is scheduled to launch another shuttle flight involving the deployment of three satellites.

And, on Sept. 19, still another flight is planned, this one a secret mission for the Department of Defense.

Although the shuttle managers were obviously disappointed by the aborted flight, they praised the shutdown procedure.

At an afternoon press conference, Lindstrom said that the entire sequence leading to the abort decision took about 70 milliseconds.

Got Quick Response

The procedure, which is controlled by computers, is “a very sensitive system, and we got a very quick response,” Lindstrom said.

If the flight had not been aborted, it would most likely have been completed without incident, Lindstrom said. The decision to abort was made because a margin of safety had been lost in the failure of the valve control system.

“We could have gone ahead and risked lifting off,” Lindstrom said. “But we have a very valuable cargo and we determined it’s best to have an abort on the ground rather than take the risk of a problem in the air.”