CAPE CANAVERAL For the second time in a week, NASA officials scrubbed the launch of the space shuttle Endeavour early Wednesday because of a potentially explosive hydrogen fuel leak. 'We were just not comfortable pressing on. As much as we tried to fix the leak we just couldn't do it,' said launch director Mike Leinbach. The shuttle was supposed to lift off Saturday morning, but a leak forced the switch to Wednesday at 5:40 a.m. Thunderstorms delayed filling of the fuel tank for three hours until around 11 p.m. Tuesday. The liftoff was abandoned around 2 a.m., just before the seven astronauts set to travel to the International Space Station started making their way to the launch pad. The mission isn't likely to be rescheduled until July. 'We'll put together a more detailed troubleshooting plan this time,' Leinbach said. The leak occurred in the same place as one that cropped up Saturday, in the hydrogen gas vent line that hooks up to the external fuel tank. A similar problem stalled a shuttle flight three months ago. Mission managers had ordered repairs following Saturday's delay. The hookup itself and two seals were replaced. The same repair worked back in March, but engineers never found the cause of the problem. Endeavour was set to deliver the third and last segment of Japan's massive space station lab along with hundreds of pounds of food for the six space station occupants. A new space station resident also was supposed to go up and swap places with a Japanese astronaut who's been up there since March. Moving Endeavour's launch date on Wednesday bumped the liftoff of an unmanned lunar mission to today at 5:12 p.m. That mission marks NASA's first trip to the moon since 1998. It's intended to find potential landing sites for future missions that would take astronauts to the moon. Those plans, though, face an uncertain future. President Barack Obama in May ordered a panel to review NASA's efforts to return astronauts to the moon by 2020. It's expected to make recommendations by the end of August. Information from the Associated Press was used in this report. Janet Zink can be reached at jzinksptimes.com or (813) 226-3401. 