Mechanics Replace Valve, Sensor That Delayed Shuttle Engine Test

Mechanics reconnected pipes and electrical lines on the space shuttle Discovery on Sunday after replacing a part that caused a computer to scrub a crucial test-firing of the shuttle’s main engines.

The 1-inch hydrogen bleed valve and the sensor that reports its open or closed position were replaced Saturday inside the shuttle’s cramped engine compartment.

“Everything is going perfectly so far,” said Lisa Mallone, spokeswoman for the space center.

But a decision on whether to attempt the delayed but crucial test Wednesday or Thursday was not expected until today.

To fire the engines Wednesday, shuttle engineers said they would have to resume an oft-delayed countdown around 6 p.m. Tuesday at the T-minus 11-hour mark to set the stage for fuel loading later that night--and that may be too optimistic.

Engineers still faced a series of tests, including checking the reconnected lines for leaks as well as electrical checks on the engine system, and it was not known Sunday if the work could be completed in time for a Wednesday engine ignition. National Aeronautics and Space Administration managers last week deliberately avoided naming a target date, although most officials thought Thursday was a likely candidate.

The valve, which must be closed during engine firing, was reported by the faulty sensor to be partially open Thursday, and computers stopped the test.

A successful test is required before the shuttle can be launched on America’s first manned mission since the Challenger disaster in January, 1986. No launch date has been set but a launch appears to be impossible until at least early October.