NASA aims for March 12 launch of space shuttle

The space shuttle Discovery lands ending Mission STS-124 to the International Space Station at the Kennedy Space Center in Cape Canaveral, Florida June 14, 2008.

CAPE CANAVERAL, Florida (Reuters) - After four delays, NASA on Wednesday set March 12 as the target date for the next launch of the space shuttle Discovery.

The flight, the first of five planned for this year, has been on hold due to concerns that a fuel valve could crack and critically damage the spaceship. Three valves keep the pressure in the shuttle's fuel tank controlled during the ship's 8.5-minute climb into orbit.

Discovery will carry the final set of solar wing panels to the space station, a $100 billion project of 16 nations that has been under construction for more than a decade.

Under a plan laid out by the Bush administration, NASA has eight missions remaining to complete assembly of the station and a final servicing call to the Hubble Space Telescope before retiring the space shuttles in 2010. Those plans, however, are under review.

Managers decided to replace Discovery's valves with spares that haven't been flown as often and which should be less susceptible to cracking.

During NASA's last shuttle flight in November, a sliver of one valve broke off, raising questions about what could happen if a bigger piece dislodged, or if a break were to occur at a more critical time during the ascent.

The valves operate like pop-up lawn sprinklers to regulate the flow of liquid hydrogen back into the fuel tank to maintain proper pressure.

NASA spokesman Kyle Herring said managers planned to meet again on March 4 to gauge progress. They then would hold a formal review on March 6 to set an official launch date.

The agency has just a few days in March to get Discovery off the launch pad in time to avoid a schedule conflict with a Russian Soyuz capsule that is scheduled to fly to the station at the end of the month. The shuttle needs to complete its planned 10-day stay at the outpost before the Soyuz arrives.

If weather or technical problems prevent a liftoff on March 12 or 13, NASA could decide to launch on March 14 or 15, but may have to cut off a day or two from the mission.

If Discovery is not ready to fly in March, the next opportunity for launch would be April 7, after the Soyuz departs the station. Postponing until April would bump NASA's high-profile Hubble repair mission from May to June.