This story has been updated at 9:39 a.m. EDT.
CAPE CANAVERAL, Fla. ? A fuel leak on the space shuttle Discovery thwarted NASA efforts to launch the spacecraft today, delaying the shuttle's final liftoff to no earlier than Monday, Nov. 8.
Discovery was slated to launch at 3:04 p.m. EDT (1904 GMT) today (Nov. 5) but a leak of flammable liquid hydrogen discovered during fueling forced NASA to stand down.
The next attempted launch of Discovery and its six-astronaut crew remains to be determined, but will come no earlier than Monday at 12:53 p.m. EST (1653 GMT). Top mission managers will meet at 11 a.m. EDT (1500 GMT) today to determine the next course of action.
NASA originally had until Sunday, Nov. 7 for Discovery to launch within the current window, but mission management teams were able to squeak out an extra day (Monday) as a cushion. It was also determined that extending the window to Tuesday is not possible, meaning if NASA is unable to launch Discovery on Monday, the agency will now have to wait until at least Nov. 30 for the next window to open, according to NASA spokesman Mike Curie.
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.
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," said Mike Leinbach, NASA's shuttle launch director. "We elected to scrub, and that was the best course of action."
Similar issues have affected launch attempts for two previous shuttle missions, both in 2009. [GRAPHIC: NASA's Space Shuttle ? From Top to Bottom]
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 will 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 orbiter has already faced down a series of setbacks, including a pair of gas leaks, an electrical glitch and, most recently, uncooperative weather.
The current weather forecasts show a 90 percent chance of favorable launch conditions for Monday.
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.
- 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.