NASA moves with care. Despite media glare, shuttle will be grounded until it passes muster

Caught in increasingly close news media glare, NASA is proceeding cautiously in readying the space shuttle Discovery for launch. The test firing of the space shuttle's main engines was aborted yesterday morning when the shuttle's master computer system detected problems related to an engine valve.

Despite the delay, John Talone, Discovery's flow director, said that everyone involved with the process feels the challenge ``when you see launch staring you in the eye.''

During the past few weeks, the launch itself is not all that has been staring National Aeronautics and Space Administration in the eye. The media have followed the process step by step.

``It's a no-win situation for NASA,'' says John Logsdon, director of the Space Policy Institute at George Washington University. ``They recognize what they are doing is of immense interest - that there is no way to avoid micro-scrutiny.''

NASA managers stress that the system is designed to catch such failures and that is why these tests are needed. They said everything up until seconds before the scheduled firing had gone very smoothly.

``It's not surprising that there are these relatively minor problems,'' Dr. Logsdon says. Because of the intense interest, ``everything gets magnified. You've made almost 600 changes in hardware, totally modified procedures, and you've got essentially a different organization controlling the thing. All of those have to be brought up to speed. What they are doing is requalifying a whole new system.''

The main engine firing is a major step toward ensuring that the shuttle is ready to fly after 2 years. The engines are ignited while the shuttle is bolted to the launch pad.

NASA officials say the problem detected yesterday could involve either the sensor that monitors the valve or the mechanics of the valve itself. The shuttle could be readied for another test within three to seven days, they said.

Shuttle managers and engineers are examining the test data to determine whether or not the sensor that monitors the valve was malfunctioning. If so, the computer software could be adjusted and the testing could resume within three days, says Mr. Talone.

The shuttle's master computer system controls the launch countdown during the last 31 seconds before the engines ignite. The computer system is designed to prevent ignition if a low-pressure valve in the engine is not 20 percent closed seconds before firing. The valve should close completely before actual ignition. Yesterday the system gave a shutdown signal just as the go-ahead was given to fire the main engines.

The valve is designed to let small amounts of the hydrogen fuel into the engine to prepare it for a rush of the supercold fuel coming into the engine from a different direction later. If the low-pressure valve is not completely closed before the rush, hydrogen fuel could push into and rupture lines and seals that are designed only for low pressures. According to Talone, such a scenario could lead to an explosion.

If there is a mechanical problem, the subassembly where the valve is located will have to be removed and repaired. This could take a week, Talone says.

According to a NASA spokesman, the intricate launch timing is such that no reading of the valve can be taken to see if it has closed 100 percent before the engines are fired. Based on previous tests, the launch criteria allowed for the valve to be 20 percent open split seconds before firing.

Managers and engineers will also review the rationale for setting that 20 percent limit. Joseph Lombardo, the shuttle's main engine project manager, said he ``recalled a tighter number'' earlier in the program, but he wasn't sure of the conditions under which that number was decided upon. He also said he thinks the ``test philosophy is still sound.''

The recent setback comes after several other delays because of leaks in hydrogen fueling lines that supply the external tank.

Before the test, the shuttle had been scheduled for launch in mid-September. At press time no new official launch date had been set. NASA managers seem to be sticking by an earlier decision to wait until the engine test-firing had been completed before looking further down the road.

Scheduling for the shuttle's cargo is even more uncertain than the Discovery's launch date. The cargo manifest ``is pure fiction right now,'' Logsdon says.