A fuel-line leak and the finding of a crack on the Space Shuttle Discovery’s foam-covered external tank forced NASA to call off any attempts to launch before Nov. 30, the opening of this year’s final launch window.

NASA discovered the crack Nov. 5 after scrubbing that day’s launch attempt due to a potentially dangerous liquid-hydrogen fuel leak.

“The hydrogen leak may have been a lucky break,” wrote NASA astronaut Alvin Drew, one of the six astronauts set to launch on Discovery, in a Twitter post. “Found a crack in the [external tank] outer foam with ice underneath. Don’t know that we’d have caught it.”

Discovery had been slated to launch Nov. 1 but two different minor gas leaks, an electrical glitch and stormy weather prompted NASA to scrub liftoff four days in a row before the hydrogen leak prompted the fifth and final scrub of the shuttle’s eight-day launch window.

NASA had until Nov. 8 to launch Discovery. After then, the angle of sunlight Discovery would encounter while docked at the station could cause some parts of the orbiter to overheat.

The hydrogen gas leak detected Nov. 5 was in a location known as the Ground Umbilical Carrier Plate, which is an attachment point between the external tank and a 43-centimeter pipe that carries gaseous hydrogen safely away from the shuttle to the flare stack, where it is burned off.

“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.”

Technicians discovered the leak while filling Discovery’s orange external tank with liquid oxygen and liquid hydrogen. This procedure, known as tanking, fills the external tank with 200,000 liters of cryogenic propellant the shuttle burns during liftoff and ascent into space.

When it finally launches, Discovery will fly an 11-day supply mission to the station to deliver a new storage room for the orbiting lab and Robonaut 2 — a humanoid robotic helper for the crew.

The STS-133 mission will be Discovery’s final flight before being retired along with the rest of NASA’s shuttle fleet in 2011.