Shuttle Discovery's Launch Enters Extended Delay

A diagram of the engine cutoff (ECO) sensors inside the external tanks used by NASA's space shuttle. CREDIT: NASA.

CAPE CANAVERAL, Fla. - NASA's planned launch of the space shuttle Discovery is suffering an extended delay, with engineers still puzzled over a fuel sensor glitch that scrubbed an attempted space shot two days ago.

"Right now we are on a day-by-day basis until we find and fix the problem," said Wayne Hale, NASA's deputy shuttle program manager, adding that once a fix is made, Discovery could launch four days later. "What is that date going to be? I don't know."

NASA had hoped to launch Discovery and its STS-114 astronaut crew on July 13 after a two and a half year hiatus from shuttle flight that followed the 2003 Columbia disaster that destroyed one orbiter and killed seven astronauts. The mission, designed to test new tools and techniques for shuttle flight safety, could launch by late next week, but only if engineers are able to not only isolate the anomaly, but fix it fast.

"That would require a very near-term, lucky find," Hale said during a press briefing here at NASA's Kennedy Space Center (KSC). "But we are not in any sense of the word pessimistic about making the July [launch] window. We are here for the duration."

NASA has until July 31 to launch Discovery if it is to make the current launch window under shuttle flight restrictions. Clear, daylight views of Discovery's launch, external tank separation and docking at the International Space Station (ISS) are required to track any debris or damage to the orbiter's thermal protection system. To get those views, NASA must launch the orbiter by the end of the month or wait until the next launch window for those conditions, which opens on Sept. 9.

Flight controllers scrubbed Discovery's July 13 launch after a fuel level sensor inside the orbiter's external tank failed a standard countdown test. The sensor, one of four used to measure liquid hydrogen fuel levels inside the external tank, tracks propellant during launch to make sure Discovery's main engines shut down before the tank runs dry. If the sensors don't perform properly during launch - reporting a full status when the tank is dry, or an empty status when fuel still remains - it could spell disaster for the shuttle and its crew.

Engineers aren't sure whether the faulty sensor readings detected during the July 13 countdown are the result of a bad sensor, wiring problems or the complicated electronics box inside Discovery that processes the sensor readings. If the problem is with the box, NASA does have a spare, but that unit has voltage issues and it could take anywhere between 10 days and three weeks to build a new one, shuttle officials said earlier this week.

Twelve teams of engineers are working through the weekend to try and pin down the fuel sensor anomaly.

"We need to know that the problem doesn't have implications for more sensors," said John Muratore, manager of space shuttle systems and engineering at KSC, adding that engineers must tread softly inside Discovery. "Every time we go into the ship to do something, there's...the risk of damaging something we can't repair."

The sensor problem has come up before, on a different external tank, which shuttle engineers mated to Discovery and later filled with fuel during an April tanking test. But after wiring and electronics box adjustments, and a second tanking test that showed no sensor glitches, the matter was deemed an "unexplained anomaly."

Now, Hale said, shuttle engineers will do as much as possible to understand the current problem before they consider flying with it unresolved.

"We're off to try to find this problem and solve it, not fly with some unexplained situation," he added.

• Fixing NASA: Complete Coverage of Space Shuttle Return to Flight