Space Shuttle On Track for Sunday Launch

The space shuttle Discovery is on track for a planned Sunday evening launch, pending the successful repair of a hydrogen gas leak that prevented an attempted liftoff earlier this week, NASA officials said today.

Engineers have been studying the problem, a hydrogen gas leak from a vent line connected to the vehicle's external fuel tank, that thwarted a launch attempt on Wednesday. Ground crews are in the process of replacing the connector segments between the vent line and the tank in hopes that this will enable Discovery to liftoff on Sunday at 7:43 p.m. EDT (2343 GMT).

"We're going to replace these components and get into a launch attempt Sunday," said shuttle launch director Mike Leinbach during a morning briefing at NASA?s Kennedy Space Center in Cape Canaveral, Fla. "If it doesn?t leak, we're going to fly. If it does leak again we're going to stand down."

Discovery had already begun its launch countdown last Wednesday when ground crews at NASA's Kennedy Space Center in Cape Canaveral, Fla. noticed the gas leak coming off a cable that allows excess pressure to vent from the fuel tank. The leak forced NASA to immediately begin unloading fuel from the tank and cancel the launch that day.

Finding the problem

Shuttle engineers have been examining the connection between the shuttle's tank and the faulty vent line since Wednesday and believe the issue to be with a seal there.

"We're into the detailed inspection of the components right now," Leinbach said. "We don?t have any smoking guns yet."

NASA hopes to fix the leak by replacing a connector segment of the 7-inch (18-cm) hydrogen vent line, which siphons flammable gaseous hydrogen away from safely the launch pad, so it does not pose an explosion risk to the shuttle or crew. The hydrogen gas builds up in the fuel tank as shuttle's super-chilled liquid hydrogen propellant is loaded in and then boils off over time.

Shuttle technicians will do a series of leak checks on the newly-configured system before launch, but they won't really know if the repaired vent line is leak free until it is tested under the super-cooled temperatures it will experience Sunday night when the tank is fueled for launch.

Shortened mission

NASA has until Tuesday to try and launch Discovery?s space station construction flight before the liftoff of a previously scheduled crew change mission aboard a Russian-built Soyuz spacecraft on March 26.

If Discovery successfully launches on Sunday, there will still be enough time for its seven-astronaut crew to complete most of its mission plan, shuttle managers said. The mission, originally slated to last 14 days, with four spacewalks, will be shortened by one day with one spacewalk eliminated, to make room for an incoming Russian Soyuz spacecraft set to launch March 26.

"Effectively, we'd accomplish most of the major objectives," said mission management chair Mike Moses.

If Discovery cannot launch until Monday, then two days and two spacewalks would likely be cut. A Tuesday liftoff would most likely mean an 11-day mission with only one spacewalk. If the shuttle cannot launch by Tuesday, it will stand down until April 7 to let the Soyuz mission fly. NASA wants to avoid docking the shuttle and Soyuz simultaneously at the station to avoid crew workload and spacecraft concerns.

Discovery's delay has also hindered plans to launch a new U.S. military communications satellite from the Cape Canaveral Air Force Station near Discovery?s seaside pad at the Kennedy Space Center. The Wideband Global SATCOM-2 satellite was due to launch Saturday atop an Atlas 5 rocket, but will stand down until next week after Discovery?s planned liftoff.

Discovery's trip

Discovery's STS-119 crew, commanded by Lee Archambault, is set to launch toward the International Space Station to drop off the station's remaining backbone-like girder segment and final set of solar array panels. The shuttle?s STS-119 mission will also deliver Japanese astronaut Koichi Wakata, who is due to serve as Japan's first long-duration astronaut when he replaces NASA astronaut Sandra Magnus as part of the space station's Expedition 18 crew.

The gas leak delay is only the most recent setback for Discovery's mission, which had previously been pushed back about a month due to concerns with suspect fuel valves on the orbiter.

SPACE.com is providing continuous coverage of STS-119 with reporter Clara Moskowitz and senior editor Tariq Malik in New York. Click here for mission updates and SPACE.com's live NASA TV video feed.

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