NASA will attempt Endeavour launch on Wednesday

CAPE CANAVERAL, Florida -- NASA will try to launch space shuttle Endeavour again Wednesday, after repairing a hydrogen gas leak that thwarted the first attempt.

Top officials decided Monday to bump an unmanned moon mission so Endeavour could have another shot at flying to the international space station. The delayed moon mission is NASA's first in a decade and is critical to the space agency's long-term effort to return humans to the lunar surface.

The Atlas V rocket had been scheduled to blast off Wednesday with a pair of lunar probes — a moon-mapping orbiter and a craft meant to crash into a shadowed crater at the moon's south pole. That launch is now scheduled for no earlier than Thursday.

"If you've spent any time on the Space Coast and monitoring launches, you notice that they tend to attract each other, and we've got that very situation here," said Chuck Dovale, launch director for the moon mission.

NASA ended up having to choose between the two missions because Endeavour could not launch this past Saturday. The potentially dangerous hydrogen gas leak in the vent line leading to the shuttle's external fuel tank halted the countdown.

It was the same kind of leak that stalled a shuttle flight back in March. Technicians finished the repairs Monday, replacing the vent line hookup and a pair of seals.

Launch time on Wednesday is 5:40 a.m.

Each mission faces a tight launch schedule.

Endeavour and its crew of seven must be flying by this weekend, otherwise it will have to wait until mid-July. That's because of unfavorable sun angles that would heat the shuttle too much while it is docked to the space station.

Delaying Endeavour's 16-day trip until July would end up postponing the next few shuttle missions and, as a result, make it harder for NASA to complete its eight remaining missions by the end of next year. That's the deadline imposed by the White House so NASA can focus on its next spaceship, intended to carry astronauts to the moon by 2020.

NASA's newest moon probes, on the other hand, need to be launched by Saturday. Otherwise, the space agency will have to wait until the end of June before trying again. Waiting that long would complicate the moon-impacting craft's flight and use more fuel.