Space shuttle Discovery's final voyage is off until at least the end of the month because of a large hydrogen gas leak that forced yet another launch delay.

It's the fourth postponement in a week for Discovery's mission to the International Space Station with six veteran astronauts and the first humanoid robot bound for orbit.

NASA tried to launch Discovery on Friday, but a potentially dangerous hydrogen gas leak cropped up midway through the fueling process and the countdown was halted.

The launch was initially put off until at least Monday. But by early afternoon, it was clear that more time was needed to fix the problem on the fuel tank.

"It's a machine and, every now and then, machines break," said launch director Mike Leinbach. "We're not jinxed at all. We're just dealing with one problem after another. Does it get frustrating? It gets frustrating because we'd rather be launching."

NASA is now targeting Nov. 30 — at the earliest — for Discovery's final liftoff. The space agency has to wait until then because of unacceptable solar angles for most of November. Those sun angles would cause the shuttle to overheat while docked to the station.

But the launch window in December lasts just one week and will jeopardize the amount of science that can be conducted. Only three astronauts will be aboard the space station then, rather than the usual six.

When it does launch, it will be the 39th and final flight of Discovery, NASA's oldest and most traveled shuttle. The shuttle first flew in 1984. NASA is retiring the fleet and closing out its shuttle program next year after three decades.

Friday's fuel leak occurred 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.

Last year, a minimum of four days was needed to replace the leaky parts. Escaping hydrogen gas is considered serious because of its flammability. Friday's fuel leak was the biggest one yet.

"We thought we had it licked, so we're going to take our time to make sure we do have it licked," said Mike Moses, head of the prelaunch mission management team.

Another potentially big problem was discovered after the countdown was halted: a 7-inch crack in the insulating foam on Discovery's fuel tank. Moses said the damage itself could have resulted in a postponement. NASA has been extra cautious with the foam ever since the 2003 Columbia disaster.

"We have a lot to do before we actually settle in on a new launch date," he told reporters.

Friday was the closest NASA had come to launching Discovery on this mission, and news of the leak came as a huge disappointment. All morning, until the leak, the words "Go Discovery" echoed from the firing room, as well as up at the space station, where the crew eagerly awaited the shuttle's arrival.

A launch attempt Thursday 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.

Shuttle commander Steven Lindsey and his crew headed back home to Houston on Friday afternoon. As for Robonaut, the humanoid robot, he'll remain packed up aboard Discovery.

"We'll wait awhile, get everything ship-shape and try again. I can stand being Earth-bound a little longer, I guess," read an update on Robonaut's Twitter account.

After Discovery, space shuttle Endeavour is set to lift off at the end of February. But if Discovery's flight ends up slipping into early next year, Endeavour's flight almost certainly would be bumped. Shuttle Atlantis may make one extra flight next summer, but Washington has yet to provide the money.

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.



NASA: http://www.nasa.gov/mission_pages/shuttle/main/index.html