NASA Aims for Tuesday Shuttle Launch

NASA Aims for Tuesday Shuttle Launch

NASA Aims for Tuesday Shuttle Launch By MARCIA DUNN, AP Aerospace Writer
2 minutes ago



NASA will try to launch Discovery on the first space shuttle mission in more than two years next Tuesday, and may press ahead with liftoff even if there´s a repeat of the fuel gauge problem that halted last week´s countdown.

Mission managers decided Wednesday night to bypass another fueling test of Discovery and go straight for the real thing in an effort to understand and either fix or work around the fuel gauge failure. The most probable cause is an electrical grounding problem lurking inside the spacecraft.

"We believe the best way to go through this is to do a countdown," said shuttle program manager Bill Parsons. "If the sensors (gauges) work exactly like we think they will, then we´ll launch on that day. If anything goes not per the plan that we´ve laid out in front of us, then we´ll have a scrub and we´ll have to talk about it."

Multiple safety nets are in place "to ensure we don´t proceed unless we feel we´re safe to go fly," he added.

But in what would be an almost certainly controversial move in the wake of the 2003 Columbia tragedy, NASA might also proceed with the liftoff if the fuel gauge problem recurs but is considered well understood. That would mean revoking a launch rule requiring all four hydrogen fuel gauges at the bottom of Discovery´s external tank to be working properly, and instead relying on just three out of four.

That looser three-out-of-four rule was thrown out after the 1986 Challenger launch explosion.

The fuel gauges are intended to keep a shuttle´s main engines from shutting down too early or too late after liftoff, both potentially disastrous situations. Only two of the four are needed to ensure safety, but ever since the Challenger accident, NASA has required all four to be operating.

"Right now, we think we have eliminated all the common causes that we believe could do this and we´ve done everything we possibly could on the vehicle," Parsons said.

The countdown — the first since Columbia´s final flight — was halted shortly before the scheduled liftoff July 13 when one of the fuel gauges malfunctioned. The same type of problem marred a fueling test of Discovery back in April with a different external tank; it was written off as an "unexplained anomaly."

Despite a week of exhaustive scrutiny by hundreds of engineers, NASA has been unable to pinpoint the precise cause or location of the fuel gauge failure. An electrical grounding problem is considered the most likely cause, and the space agency is holding out hope that it can trace the problem to interference from shuttle equipment in the next few days.

Among the many shuttle parts suspected of possibly causing electromagnetic interference are newly installed heaters on the external fuel tank. The heaters are meant to prevent the kind of lethal damage suffered by Columbia at liftoff.

"We have a great amount of work in front of us to get us through this and get us ready," Parsons said. "But we´ve all agreed that this work is doable."

The countdown will begin Saturday for a Tuesday morning launch attempt.

If Discovery and its crew of seven aren´t flying by the beginning of August, their trip to the international space station will be bumped to September to ensure a daylight launch and good surveillance photography throughout the shuttle´s ascent. NASA wants to see any Columbia-type damage that might occur.

A chunk of fuel-tank foam insulation tore a hole in Columbia´s left wing at liftoff and led to its catastrophic re-entry on Feb. 1, 2003. All seven astronauts were killed.