CAPE CANAVERAL, Florida--America's space program suffered another setback yesterday when a computer reported a valve problem and aborted the test-firing of space shuttle Discovery's engines a fraction of a second before ignition.
There was no word on how long it would take to ready Discovery again for the test, but launch control center commentator Hugh Harris said "tentatively we're going for a 48-hour recycle." That would mean an attempt tomorrow.
It was the fifth postponement of the test in two weeks. The test is considered crucial for qualifying Discovery for the first shuttle flight since the Challenger explosion 2 years ago.
"It's another problem," said NASA administrator James Fletcher. "It's a good thing it happened on an FRF and not on a launch," FRF stands for Flight Readiness Firing, the official name of yesterday's test.
The engines were to have begun firing six seconds before the zero mark in an otherwise perfect countdown. The shutdown came "just after the `go' for main engine start was issued" but before ignition actually began, Harris said. The shuttle's master computer system had taken control of the countdown 31 seconds before ignition. When it detected a problem in the computer that controls the engine firing sequence, it automatically sent a shutdown signal, NASA said.
"We had just got up to the point of main engine start," Harris said.
Harris said the computer "did not see that the engine bleed valve had fully closed." He said engineers were trying to determine if there was a faulty valve or if the sensor had given an incorrect reading.
The bleed valve vents off excess gases.
Harris said that immediately after the shutdown, the launch team remotely began to make the vehicle safe as it sat on the pad, its tank loaded with 385,000 gallons of liquid hydrogen and 143,000 gallons of liquid oxygen.
He said the propellants would be drained from the fuel tank, and the igniters in each engine would have to be replaced before another attempt.
Program managers have been grooming Discovery for the first shuttle flight since the loss of Challenger and its crew of seven in an explosion 73 seconds after liftoff on January 28, 1986.
The mission is scheduled for late September, but even before yesterday many officials believed the launch would slip into October because of earlier delays in the engine test and an unresolved gas leak in a steering engine system that is separate from the main engines.
Launch director Bob Sieck said Wednesday that a one-day delay in the firing test would move back the launch one day.
Soon after the test firing, shuttle managers expect to give the go-ahead to a plan for engineers to cut a hole through the rear wall of Discovery's cargo bay in an effort to reach and repair a nitrogen tetroxide leak.
The shuttle program also must pass another key propulsion test before Discovery can be certified for flight: a fullscale firing, the fifth in a series, of the redesigned solid fuel booster rocket at the Morton Thiokol plant in Utah. It is scheduled about August 20.