Source: Xinhua
03-12-2009 09:07
Special Report: Tech MaxWASHINGTON, March 11 (Xinhua) -- The launch of U.S. space shuttle Discovery was postponed again on Wednesday due to a hydrogen gas leak found several hours before its scheduled liftoff, NASA said.
"The STS-119 launch was scrubbed at 2:37 p.m. EDT (1837 GMT) due to a hydrogen leak in a liquid hydrogen vent line between the shuttle and the external tank," NASA said in a statement.
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 launch team is resetting to preserve the option of attempting a Thursday night liftoff at 8:54 p.m. EDT (0054 GMT March 13) depending on what repairs are needed and what managers decide. The Mission Management Team is meeting at 5 p.m. Wednesday to discuss the issue, according to the statement posted on NASA's website.
Ground crews have begun to unload the liquid hydrogen fuel from the tank to lower the pressure so they can study the situation more. NASA space shuttles uses super-chilled liquid hydrogen propellant and liquid oxygen oxidizer to feed their three main engines during launch.
"Teams are going to get together and assess the repair options," said NASA spokesman Allard Beutel.
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.
The mission, NASA's first shuttle flight of the year, will also ferry Japanese astronaut Koichi Wakata to the station, where he will replace NASA astronaut Sandra Magnus as a member of the orbiting lab's three-person crew. Wakata is Japan's first long-duration astronaut and is due to return to Earth later this summer.
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.
NASA 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 to fly to the station at the end of the month.
If Discovery's tentative launch date holds, there will be no effect on the next two shuttle launches: STS-125 to NASA's Hubble Space Telescope and STS-127 to the International Space Station. 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.
Editor:Liu Fang
