John Raoux  /  AP
Space shuttle Discovery, shown here on Jan. 14, 2009, is scheduled for liftoff on Wednesday, March 11.
updated 3/6/2009 7:57:45 PM ET 2009-03-07T00:57:45

NASA has finally settled on a Wednesday night launch for space shuttle Discovery.

The flight to the international space station was originally set for mid-February, but was delayed four times because of concern over critical shuttle valves. On Friday, senior NASA managers meeting at Kennedy Space Center put the valve issue to rest for Discovery and cleared the shuttle for flight.

Seven astronauts will ride Discovery into orbit, taking with them one final set of solar wings for the space station.

Launch director Mike Leinbach said spirits are much higher now than they were when the flight kept being put off.

"The mood is very, very upbeat," he said. With a firm launch date now, "everybody feels really good."

Managers had ordered extensive testing of the hydrogen gas valves after one broke during the last shuttle launch. The valves control the flow of hydrogen gas feeding into the external fuel tank during the 8 1/2-minute climb to orbit.

The broken valve didn't cause any problems, but NASA wanted to make certain that there was little chance of rupturing Discovery's downstream lines by a valve fragment and, if that did happen, it would not be catastrophic.

A new technique for finding cracks in the steel valves helped convince engineers, over the past two weeks, that the three now in Discovery's engine are free of defects. Valves were replaced when the new method found tiny cracks.

Space shuttles have likely flown many times before with bigger cracks in the valves, believed to be the result of wear-and-tear, and the valves remained intact, said shuttle program manager John Shannon.

Slideshow: Month in Space: January 2014

Bill Gerstenmaier, head of NASA's space operations, said he cautioned the shuttle team that "it's time to step back from the issue of the day and think about all the other things we need for flight readiness."

There is a slightly increased risk of danger, for instance, because of last month's two-satellite wreck in orbit. The odds of a catastrophic hit by a piece of space junk is an estimated 1-in-318 for Discovery's two-week mission because of all the extra satellite scrap now circling Earth. Before the satellite collision, the odds were 1-in-336, said Gerstenmaier.

NASA has until March 16 to launch Discovery before having to wait until April. A Russian Soyuz rocket is scheduled to blast off March 26 with a fresh space station crew, and the shuttle needs to be gone by then.

Copyright 2009 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.


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