Endeavour will remain on Earth for another week. Photo: NASA

Launch of the shuttle Endeavour on a space station assembly mission is off at least a week - and possibly longer - because of troubleshooting to fix a leak in one of two systems that feed oxygen to the ship's crew cabin. But the delay to the evening of Monday, Nov. 18, is a best-case scenario and launch could slip even more depending on what is actually needed to fix the problem.

NASA had hoped to launch Endeavour at 12:59 a.m. today on a flight to ferry a fresh three-man crew to the space station and to deliver a 14.5-ton solar array truss segment. But Sunday afternoon, when valves were opened to begin allowing oxygen to flow into the shuttle's crew cabin from tanks mounted below the ship's cargo bay, engineers noticed higher-than-expected concentrations of gaseous oxygen in the midbody area.

Additional testing showed a one-pound-per-hour leak of oxygen in supply system No. 2. The leak is believed to be in an area just below the orbiter-station docking system in the forward part of the shuttle's cargo bay. In any case, mission managers decided to scrub the launch shortly after 9:30 p.m. Sunday, just as Endeavour's crew was beginning to strap in.

"I'd like to welcome you aboard, but tonight's not our night," NASA test director Steven Altemus radioed commander James Wetherbee. "The MMT has declared a scrub for a potential leak in the O2 system. We're going to continue to troubleshoot that tonight and try to understand where we're at with that before we declare the length of the scrub necessary here. I know you guys are going to be disappointed, but I think we want to give you a healthy vehicle before we cut you loose from the Cape here."

"Absolutely, you guys are doing great. Thank you," Wetherbee replied from the cockpit.

The astronauts pose for a pre-launch photo in the dining room of their quarters before heading to pad 39A Sunday evening. Photo: NASA

Engineers, meanwhile, met to discuss possible repair options and told mission managers that if all goes well, Endeavour could be ready for another launch attempt next Monday night, between 7 p.m. and 11 p.m. An updated flight plan, targeted on the opening of the four-hour launch period, is posted on the Current Mission page.

"It sure is disappointing to come and talk with you tonight and tell you we're not in a position to launch," shuttle program manager Ronald Dittemore told reporters at an 11:30 p.m. news conference. "And it sure was a good evening to go have a launch and a good start to a fantastic space mission that we all anticipate."

The leak showed up as soon as valves were opened in the shuttle's midbody. Those valves and associated plumbing are below the floor of the payload bay just forward of the aft end of the orbiter docking system. Engineers believe they can gain access to the area in a small gap between the forward end of the shuttle's payload, a 45-foot-long solar array truss segment, and the aft end of the docking system.

Shuttle launch director Michael Leinbach said engineers hope to gain access to the area Wednesday, after the shuttle's external tank is drained, after the ship's internal tanks of hydrogen and oxygen are emptied and after payload bay liner blankets are removed. Five shifts of work - about two days - have been allocated to find and fix the leak, pressurizing the system with helium to pinpoint the problem area.

"It could be as simple as a seal on the flex lines, or it could be a dynatube fitting on another portion of the line, either one of which is accessible with the plan we have to get underneath the payload bay liner to get to these lines. So once we get access, the repair itself will probably be fairly simple. It's the problem of getting detanked, getting access and then getting back into launch countdown that takes us all the way out to next Monday. The repair itself will probably go very quick."

Said Dittemore: "With the size of this leak, it should be pretty easy to spot."

If all of that goes well - and that's still a fairly big if regardless of Dittemore's current optimism - Endeavour could be ready for launch by Nov. 18. But that assumes the leak is where engineers currently suspect and that repairs are relatively straight forward.

"The primary reason for us delaying today was the fact that we had done a pressure integrity check on this line already in the OPF (orbiter processing facility)," Dittemore said. "And both lines had passed successfully. The last time we flew this vehicle, they worked fine, there were no leaks. And we had done no work in these areas that would cause us to have any suspicions of an area that might have had some re-work. So it's like this leak just appeared out of the blue.

"For that alone, and knowing we still have the shake, rattle and roll to go through to get to orbit, caused us to pause and want to understand it better. Granted, these are redundant systems, we could probably support this leak and not have any issue either for ascent or for landing. (But) it's the unknown, why this happened after it passed its checks, did we have some collateral damage, is it trying to tell us something, is it really worse than the data are indicating? We just couldn't go and launch in the blind."

And so the launching was delayed.

Endeavour's seven-man crew will remain in medical quarantine, but the astronauts will fly back to Houston to await word on when they'll get a second launch attempt. The crew of the international space station, when informed of the launch delay, offered a noncommital "copy that" in response. If anything, a one-week launch delay will give the crew more time to prepare for the shuttle's arrival and to adjust their sleep cycles to synch up with Endeavour's crew.

One wild card in all of this is Boeing's new heavy lift Delta 4 rocket, scheduled to blast off Saturday on the program's maiden flight. All rockets launched from the East Coast, including the space shuttle, use radar tracking systems provided by the Air Force Eastern Range. Rockets making their first flights typically get three days of range support in case of technical glitches or bad weather. Depending on how the Delta 4 campaign actually plays out, Endeavour's flight could slip beyond next Monday regardless of the oxygen line repair work.

Assuming a launch next Monday, however, Endeavour would land the day after Thanksgiving. Asked if ground crews might have to sacrifice holiday time off, Dittemore joked "no, I would expect they will be well fed for landing."

Video coverage for subscribers only:
   VIDEO: NEWS CONFERENCE GIVES DETAILS ABOUT LEAK QT or RV
   VIDEO: NASA ANNOUNCES THE LAUNCH IS POSTPONED QT or RV
   VIDEO: COMMANDER INFORMED OF LAUNCH SCRUB QT or RV
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