NASA engineers are loading shuttle Endeavour's external tank without problems so far and managers say storm-stalled work can be completed in time for a planned 5:40 a.m. launch from Kennedy Space Center.
An extra astronaut is being added to the close-out crew that will help the Endeavour space fliers board the orbiter and strap into their seats. And the astronauts will head out to the launch pad about an hour later than originally planned.
NASA Shuttle Launch Director Mike Leinbach said it appears all prelaunch work will be done in time to launch during a 10-minute window that opens at 5:35 a.m. But he added that the agency will call it a day if the launch cannot be carried out in a safe manner.
"We're not going to short-cut anything. If we get to a situation where we just can't make it tonight, we'll just call it and say we can't make it," Leinbach said. "Right now we're thinking we can get there fine."
NASA started external tank fuel-loading operations almost three hours later than planned, so the catch-up the agency is attempting is unprecedented.
"It would be a record for us. The previous record was tanking an hour and 45 minutes late. This adds about an hour to that, so it would be another record for the launch team, but we enjoy challenges and the team really is performing in an outstanding manner," Leinbach said.
"We're going to give it our shot, and again, if don't get there, we just don't get there."
Endeavour's seven astronauts will be heading out to launch pad 39A at 2:50 a.m. The astronauts should be donning partial-pressure launch-and-entry suits just after 2 a.m. -- or about the time that NASA expected to finish external tank fuel-loading operations.
NASA at about 1:15 a.m. will be keeping a close eye on a vent line that routes gaseous hydrogen from the external tank to a flare stack about 1,000 feet away from the shuttle, where it can be burned off harmlessly.
The propellant-loading operation will be about 98 percent complete, and that's the same point that gaseous hydrogen leaks prompted delays to both Endeavour last Saturday and Discovery in mid-March.
NASA swapped out the seven-inch quick disconnect valve thought to be the culprit in both cases, as well as seals within it.
Endeavour and its crew aim to deliver the third and final segment of the $1 billion Japanese Kibo science research facility to the International Space Station.
Five spacewalks and highly choreographed construction crane work will have to be carried out simultaneously to get the job done.
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