CAPE CANAVERAL, Fla. — A potentially dangerous hydrogen gas leak during fueling Friday caused yet another delay for space shuttle Discovery's final voyage — possibly until the end of the month.
It was the latest and most serious problem to hit NASA's oldest and most traveled shuttle over the past week.
Another launch attempt will not be made before Monday.
Midway through the fueling process Friday morning, hydrogen gas began leaking from where a vent line attaches to the external fuel tank. It's the same type of problem that forced delays for two shuttle missions last year and had not reoccurred since then.
Discovery's final mission already had been running four days late because of technical and weather problems. The six astronauts had yet to board the shuttle when launch director Mike Leinbach halted the countdown two hours after fueling began.
Monday represents the last opportunity until the end of the month for NASA to send the shuttle to the International Space Station with a load of supplies and the first humanoid robot bound for orbit. Otherwise, the flight will be off until Nov. 30 because of unacceptable solar angles.
When it does launch, it will be the 39th and final flight of Discovery. The shuttle first flew in 1984.
Leinbach said it will be a challenge to fix the problem by Monday, in just three days, but he hopes the repair can be made quickly and the shuttle launched.
"That's my hope," he said. "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."
Last year, a minimum of four days was needed to replace the leaky parts. The leak was considered serious because hydrogen gas is flammable. Friday's leak was the biggest one yet.
Friday was the closest NASA had come to launching Discovery on this mission and the veteran crew of astronauts led by commander Steven Lindsey. News of the leak came as a huge disappointment.
All morning, until the leak erupted, the words "Go Discovery" echoed from the firing room, as well as up at the space station, where six astronauts eagerly awaited the shuttle's arrival.
"The Space Shuttle Discovery awaits release on her final voyage. We'll be watching closely," station commander Douglas Wheelock wrote in a Twitter update.
Thursday's launch attempt was thwarted by stormy weather. Three previous delays were caused by helium and nitrogen gas leaks and a sluggish circuit breaker. Monday was the original launch date.
The space agency will close out its 30-year-old shuttle program next year. Endeavour is set to lift off at the end of February. Atlantis may make one extra flight next summer, but Washington has yet to provide the money for it.
The White House has instructed NASA to shift its focus from launching astronauts into orbit, to sending them to asteroids and Mars. Given the budget limitations, the space agency can achieve that only by giving up the costly shuttle program.