This story has been updated at 2:45 p.m. EDT.
CAPE CANAVERAL, Fla. ? A fuel leak and crack on the space shuttle Discovery's huge external tank has forced NASA to call off any attempts to launch before Nov. 30 ? the latest in a series of delays for the spacecraft's final voyage.
NASA discovered the crack during an inspection after finding a potentially dangerous liquid hydrogen fuel leak on the 15-story external tank that thwarted the shuttle's launch plans for today (Nov. 5). The crack is located in the inner foam on a different part of the tank than the fuel leak.
"There's about a seven-inch long crack with what we call an offset, which means it's cracked and moved a little bit," Mike Moses, NASA's shuttle integration manager, said in a news briefing. "That gives a place for ice to form, and that's not something we like to see. I don't know if that would have passed our criteria to be 'go' for launch, but it certainly would have been something that would have generated a whole lot of discussion."
NASA must repair the fuel leak and foam crack before Discovery can blast off toward the International Space Station. That means the next possible time the shuttle can try to launch is Nov. 30 at 4:05 a.m. EST (0905 GMT).
Details about the extent of the crack, and what it will take to repair it, remain unknown at the moment. In the meantime, NASA officials are pressing ahead with the Nov. 30 timeline ? though the date of the next official launch attempt will be contingent on the necessary repair work. [GRAPHIC: NASA's Space Shuttle ? From Top to Bottom]
"We have a lot to do before we actually settle in on a new launch date," Moses said. "We're going to make sure we fix the problems and then worry about the launch date later. So, November 30 is the first time the window opens, and I can't commit to saying that's exactly when we're going to launch, but that's what we're going to start setting schedules for."
Discovery was slated to launch at 3:04 p.m. EDT (1904 GMT) today from a seaside pad here at the Kennedy Space Center before the fuel leak was discovered. The leak posed an explosion risk at the launch pad.
The mission had already been delayed four days due to minor gas leaks, an electrical glitch and, most recently, uncooperative weather. NASA had until Nov. 8 to launch Discovery on its mission to the International Space Station before the sun angles at the station would become unfavorable.
Discovery's STS-133 crewmembers will head back to the Johnson Space Center in Houston today.
The hydrogen gas leak was detected at around 7:30 a.m. EDT (1130 GMT) in a location known as the Ground Umbilical Carrier Plate, which is an attachment point between the external tank and a 17-inch pipe that carries gaseous hydrogen safely away from the shuttle to the flare stack, where it is burned off. [Photo of the shuttle fuel leak location]
Similar leaks have occurred during launch preparations for two previous shuttle missions, both in 2009. Both of these were caused by misalignment of seals within the Ground Umbilical Carrier Plate. This new leak, however, cropped up earlier in the tanking process, and leaked significantly greater amounts of hydrogen, than those previous events, said NASA's shuttle launch director Mike Leinbach.
"The last two that we experienced were pretty much the same," Leinbach told SPACE.com. "Because it started sooner and had a higher magnitude, it says to a lot of us that it's a different type of leak."
The external tank is now being drained of the propellant, but it will take an additional 22 hours or so to allow excess hydrogen in that area to be purged away before technicians can return to the pad to investigate the cause of the leak.
"Right now it's a lot of speculation, but the hardware was obviously talking to us ? it was leaking significantly," Leinbach said. "We elected to scrub, and that was the best course of action."
Technicians discovered the leak while filling Discovery's distinct, orange external tank with liquid oxygen and liquid hydrogen. This procedure, known as tanking, fills the external tank with the 520,000 gallons of cryogenic propellant that will be used to fuel the shuttle during liftoff and ascent into space.
Discovery was set to fly an 11-day supply mission to the International Space Station to deliver a humanoid robot helper for the station crew and a new storage room for the orbiting lab.
The STS-133 mission will be Discovery's grand finale in space before being retired along with the rest of NASA's shuttle fleet in 2011.
"It's disappointing for the team today, for sure," Leinbach said. "But, as we always say - and it's the truth - we're going to fly when we're ready, and clearly we're not ready to fly today."
- GRAPHIC: NASA's Space Shuttle ? From Top to Bottom
- Gallery: Building Space Shuttle Discovery
- Video ? Space Shuttle Discovery: A Retrospective, Part 2, Part 3
Follow SPACE.com Staff Writer Denise Chow on Twitter @denisechow as she covers Discovery's final space voyage from Cape Canaveral, Fla. Click here for mission updates, new stories and a link to NASA's live webcast coverage.