A "significant" hydrogen leak in a vent arm attached to the shuttle Discovery's external tank will delay another launch attempt until at least Monday, the final day of the current launch window, NASA officials said Friday. If Discovery is not off the ground by then, launch will be delayed to Nov. 30, the opening of the year's final shuttle launch opportunity.

Credit: NASA TV

Engineers are draining the shuttle's external tank in preparation for gaining access to the hydrogen vent line over the weekend. Launch Director Michael Leinbach said the magnitude of the leak was so high engineers suspect they will find an obvious defect when the mechanism is disassembled for an inspection.

"The signature of the leak is similar to what we've seen in the past when we've had leaks there, although the magnitude was higher this time and it occurred earlier in our tanking process," said Leinbach. "It actually occurred during fast-fill where in the past we'd gotten into a topping regime before the leak occurred."

Engineers cycled the vent valve in the mechanism in hopes of clearing whatever might be preventing a tight seal, but the leak persisted and Leinbach ordered a launch scrub at 8:11 a.m. EDT.

"The leak followed the vent valve cycling very closely, every time we cycled the vent we saw the leak, so that's indicative of something going wrong down inside of that quick-disconnect," Leinbach said.

It will take almost a full 24 hours to drain and "inert" the huge external tank, preventing inspections and troubleshooting until Saturday.

"It's my hope that given the magnitude of the leak that once we get the GUCP (gaseous umbilical carrier plate) taken apart, we'll see something wrong that's obvious to us, go fix it, put it back together and get a launch attempt before the end of this window," Leinbach said. "That's my hope. I'm not sure that's how it's going to turn out, but that's the challenge that we've put out to the team."

In the meantime, he said, launch was off until at least Monday.

"We've gone officially into a 72-hour scrub turnaround, knowing that's our last launch attempt in this window," Leinbach said. "There's certain tricks that we might be able to do when we pull the GUCP apart that says you get to the work quicker. A lot of the engineering contingent are going to want to take very, very detailed measurements as we're taking this thing apart, and that may end up being what we do. If we do all that detailed work, that probably extends the timeline because that's what we did in the past to get to that 72 hours.

"So we're not going to push the team, but we have asked them if 'is there anything you can do in a 72 to get to that launch attempt on Monday' because a lot of us believe that given the magnitude of the leak we're going to see something obvious when we get it apart. If that's the case, then we'll change out whatever has gone wrong and put it back together and hopefully that supports Monday."

NASA's Mission Management Team will meet Saturday to discuss repair options and whether to press ahead for a Monday launch attempt.

"We're going to get together later this morning with the OPS and engineering teams, review that kind of top-level assessment, top-level plan that we've asked (the team to carry out)," Leinbach said. "Then the detailed engineering reviews and troubleshooting plans will kick in later this afternoon. We'll present that to the program tomorrow sometime, what the actual options are. We won't know what's gone wrong with the GUCP until we get our hands on it, which will be tomorrow afternoon.

"So right now it's a lot of speculation, but obviously the hardware was talking to us, it leaked significantly and it was a case where we were violating not only launch commit criteria but also some of our ground safety requirements -- limits on hydrogen in free air. So we elected to scrub, obviously, and that was the best course of action."

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