CAPE CANAVERAL, Fla. - Space shuttle Discovery's final voyage is off until at least the end of the month because of a large fuel 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.