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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