NASA scrubs Saturday morning space shuttle launch

CAPE CANAVERAL, Fla. — NASA delayed the launch of space shuttle Endeavour on Saturday by at least four days because of a potentially dangerous hydrogen gas leak similar to one that cropped up three months ago.

The countdown was halted shortly after midnight, about 2 hours into the fueling of the external tank and less than seven hours before Endeavour was due to blast off on the space station construction mission. The astronauts had yet to suit up.

Launch director Mike Leinbach said it was a significant leak. Hydrogen gas is extremely volatile and can burn in large enough quantities, he noted.

"There's no way we could have continued," Leinbach said at a hastily called news conference. "It's a commodity you just don't mess with."

The hydrogen gas leak is similar to one that NASA faced in March during the launch countdown of Discovery. That flight ended up being delayed by four days because of the problem and forced NASA to shorten Discovery's flight by a day and eliminate a space walk.

NASA's launch team immediately began draining Endeavour's external fuel tank while trying to figure out what went wrong. In March, the leak occurred where a vent line hooks up to the tank. The hookup was replaced along with a couple of seals and the seepage stopped, but engineers never did determine the exact source of the trouble.

Mission managers are up against a tight deadline. A four-day delay would make the next launch attempt Wednesday. But that's the day the space agency is supposed to launch a moon-bound spacecraft aboard an unmanned rocket.

Mike Moses, chairman of the mission management team, said it was too soon to say which mission would take priority.

"We haven't even begun to work that yet," Moses said.

In any event, if Endeavour isn't flying by about June 20, it will have to wait until July 11 for the next launch attempt because of unfavorable sun angles that would make the shuttle too hot while docked at the international space station.

During the 16-day mission, Endeavour and its crew of seven are supposed to deliver the final segment of Japan's huge space station lab, along with some spare parts for the orbiting outpost and more than 600 pounds of food for the six men living there.

When Endeavour pulls up, there will be 13 people together in orbit for the first time.