Observers: Shuttle Can't Launch That Early

Even invested optimists like NASA shuttle program manager Wayne Hale have their doubts.

"It is theoretically possible that we could still launch on Sunday," Hale said, quoted by the Palm Beach Post. "But I've got to tell you that this represents a really optimistic good-luck scenario, which I think is not very credible."

This, after NASA engineers remained stumped Thursday over the failure of a fuel depletion sensor within the shuttle's huge external fuel tank. That failure forced NASA to scrub Wednesday's launch about two hours before lift-off. Hale has formed a dozen teams to troubleshoot the problem. The faulty sensor is one of four inside the tank and is absolutely necessary to prevent the shuttle's main engine from trying to run without fuel.

The sensors control fuel pumps that typically spin at 40,000 rpm. If those pumps continued to spin without fuel, they'd tear themselves -- and the shuttle -- apart.

Engineers were able to duplicate the problem Thursday. While the sensor correctly read "dry" as the huge fuel tank was drained, it refused to do so when sent a specific test signal. That, Hale said, "means that we now have an intermittent, transient failure, which is the worst kind of thing to troubleshoot."

Hale suggested there might be three reasons for the transient: a bad sensor, bad wiring to the sensor and a computer that acts on data from the sensor. Sunday suddenly looks like it's not that far away.

"I think the repair that might get us to Sunday is we go in and wiggle some of the wires and find a loose connection," Hale said. "If we found a loose connection, OK, we might be back in business." But the deputy program directly didn't think that solution likely.

If the problem is the sensor itself, that could mean a much more lengthy delay, Hale said. That would mean sending workers into the tank, a move that would require the shuttle be moved once again back to the Vehicle Assembly Building.

"We would like to not go into the liquid hydrogen tank," Hale said. "That tank has hydrogen vapors in there. We have to inert that tank. To put people in there, it's a confined space, they have to have breathing apparatus. It becomes an operation you'd just as soon not do."

If that's the case, then Discovery probably won't be launched until September -- if then.

FMI: www.nasa.gov