The shuttle was scheduled to deliver a fourth and final set of solar arrays to the International Space Station.
NASA has delayed the launch of its shuttle until Sunday at the earliest, so inspectors can check and fix a gas leak.
The STS-119 was scheduled to launch Wednesday but a hydrogen gas vent line began to leak during countdown, prompting the postponement. Shuttle Launch Director Mike Leinbach said Wednesday that the leak developed on a pipe that runs from the launch tower to a valve outside the shuttle's external tank.
The pipe carries hydrogen gas from the shuttle to a flare stack, where the hydrogen gas burns off at a safe distance from the shuttle and launch pad. Leinbach said that the leak did not pose a danger to the shuttle during fueling but it allowed too much gaseous hydrogen to escape the vent line.
The shuttle will deliver a fourth and final set of solar arrays to the International Space Station. The arrays will power science experiments and support the station's crew. It also will carry new equipment that converts urine to potable water. That water purification system will replace a unit that failed.
The shuttle will carry Commander Lee Archambault, Pilot Tony Antonelli, and mission specialists Joseph Acaba, Steve Swanson, Richard Arnold, John Phillips, and Japan Aerospace Exploration Agency astronaut Koichi Wakata. It will mark the 26th launch for NASA's discovery program.
Astronauts will embark on four spacewalks to install and deploy the solar arrays on the right side of the station.
NASA's space shuttle program is expected to receive a $2 billion funding increase for the next fiscal year but the current shuttle is scheduled to end in 2010. The Orion is scheduled to begin in 2015, leaving a five-year gap in space shuttle programs.
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