Source: Xinhua

03-12-2009 09:01

Special Report:   Tech Max

WASHINGTON, March 11 (Xinhua) -- U.S. space shuttle Discovery’s launch to the International Space Station is now targeted for no earlier than March 15, NASA said in a statement on Wednesday.

Space shuttle Discovery stands ready at pad39a in  the early morning hours before a scheduled evening launch at Kennedy Space Center in Cape Canaveral,  Fla., Wednesday, March 11, 2009.(AP Photo/John Raoux)

Liftoff on March 15 would be at 7:43 p.m. EDT (2343 GMT). The exact launch date is dependent on the work necessary to fix the hydrogen leak problem, according to the statement. Managers will meet on Thursday at 4 p.m. (2000 GMT) to further assess the troubleshooting plan.

NASA postponed Discovery's launch again on Wednesday due to a hydrogen leak in a liquid hydrogen vent line between the shuttle and the external tank. The vent line is at the intertank region of the external tank and is the overboard vent to the pad and the flare stack where the vented hydrogen is burned off.

The leak was discovered at 2:15 p.m. EDT (1815 GMT), about two hours after ground crews began filling the shuttle's massive orange external fuel tank. The problem forced them to halt fueling immediately.

Discovery had been scheduled to blast off on Wednesday night from Cape Canaveral, Florida, on a mission to finish installing the International Space Station's power system. Its 14-day mission will deliver the International Space Station's fourth and final set of solar arrays, completing the orbiting laboratory's truss, or backbone. The shuttle will also carry a replace distillation assembly for the station's new water recycling system.

Wednesday's launch delay is the latest in a series of setbacks that have postponed Discovery's STS-119 mission for a month. The shuttle was initially slated to launch on Feb. 12, but concerns with suspect fuel control valves in the spacecraft's main engines prompted additional delays so engineers could replace them.

Like the leaky gas hydrogen line that thwarted Discovery's Wednesday launch, the shuttle's three fuel control valves are also designed to maintain the proper pressure inside the liquid hydrogen fuel reservoir of the orbiter's attached external tank. Asimilar valve on the shuttle Endeavor cracked during a November 2008 launch and NASA wanted to be sure a similar problem did not pose a risk to Discovery and its crew.

Discovery's valves were replaced twice, with mission managers deciding earlier this month that the shuttle was fit to fly.

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