Gas Leak Delays Space Shuttle Launch
A nearly full Moon sets as the space shuttle Discovery sits atop Launch pad 39A at the Kennedy Space Center in Cape Canaveral, Florida, in the early morning hours of Wednesday, March 11, 2009.
Credit: NASA/Bill Ingalls

This article was updated at 7:05 p.m. EDT.

CAPE CANAVERAL, Fla. - NASA's shuttle Discovery and its seven-astronaut crew will have to wait at least a few more days to rocket into orbit after a last minute gas leak prevented a Wednesday launch attempt.

Mission managers called off Discovery?s launch attempt after detecting a leak of gaseous hydrogen in a line that runs into the shuttle?s attached external fuel tank. NASA is now targeting a launch for no earlier than March 15 at 7:43 p.m. EDT (2343 GMT). The extra time will allow engineers to take a look at the leak and make necessary repairs, mission managers said in a briefing after the launch attempt.

The leak occurred in a gaseous hydrogen vent line that runs into Discovery?s 15-story fuel tank to keep its supply of liquid hydrogen propellant adequately pressurized. NASA space shuttles use super-chilled liquid hydrogen propellant and liquid oxygen oxidizer to feed their three main engines during launch.

NASA officially scrubbed the launch plan at 2:37 p.m. EDT (1837 GMT). Discovery was scheduled to lift off from the seaside Pad 39A here at NASA's Kennedy Space Center at 9:20 p.m. EDT (0120 March 12 GMT).

"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. Weather forecasts had predicted a pristine 95 percent chance of favorable flight conditions for tonight?s launch attempt.

A new delay

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. A similar valve on the shuttle Endeavour 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.

Commanded by veteran shuttle flyer Lee Archambault, Discovery's seven-astronaut crew will launch toward the International Space Station carrying the outpost's final pair of U.S.-built solar wings and the last segment of its backbone-like main truss. The 14-day mission 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.

Set to launch spaceward aboard Discovery with Archambault and Wakata are STS-119 pilot Tony Antonelli and mission specialists Joseph Acaba, Steven Swanson, Richard Arnold II and John Phillips.

Discovery?s two-week mission will mark NASA's first shuttle flight of the year.

If Discovery is unable to launch Thursday, a third attempt is possible on Friday. NASA has until March 17 to launch the shuttle before standing down due to a previously scheduled Soyuz flight to ferry the new Expedition 19 crew to the space station. If the shuttle cannot launch by March 17, NASA plans to stand down until after the space station crew change, with the next launch window opening on April 7.

SPACE.com is providing continuous coverage of STS-119 with reporter Clara Moskowitz at Cape Canaveral and senior editor Tariq Malik in New York. Click here for mission updates and SPACE.com's live NASA TV video feed. Live launch coverage begins at 4:00 p.m. EDT (2000 GMT).

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