Space Shuttle to Make Second Launch Attempt Tonight

CAPE CANAVERAL, Fla. - The space shuttle Discovery is primed for asecond launch attempt tonight after engineers repaired a gas leak that kept thespacecraft from lifting off last week.

Discovery and herseven-astronaut crew are poised to blast off at 7:43 p.m. EDT (2343 GMT)from Launch Pad 39A here at NASA's Kennedy Space Center.

The weather outlook for this evening is promising, with a roughly 80percent chance of favorable conditions for launch, shuttle weather officerKathy Winters said.

Since last Wednesday's foiledlaunch attempt, ground crews have completely replaced a suspect connectorbetween the shuttle's external fuel tank and a vent line that carries flammablehydrogen gas away from the launch pad. Technicians discovered a leak in theline after Discovery's tank began fueling last week, prompting mission managersto call off the launch.

Crews have since worked around the clock to replace the connector sealand investigate the problem. Though no smoking-gun explanation has yet beenfound, mission managers are hopeful that swapping out the offending part will stopoff the leak. If the leak persists today, NASA will call off the launchattempt, mission managers said.

Discovery is slated for a 13-daymission to space, featuring three spacewalks to deliver and install thelast section of the International Space Station (ISS)'s backbone-like maintruss. The final segment, called Starboard-6, comes with a complement of newsolar panel wings that should boost the station's power generation capabilityby 25 percent.

The shuttle is also set to carry up Japan Aerospace Exploration Agencyastronaut Koichi Wakata to replace NASA astronaut Sandra Magnus as a spacestation Expedition 18 flight engineer. Wakata will become Japan's firstlong-duration astronaut when he stays aboard the orbiting laboratory untillater this summer.

Veteran spaceflyer Lee Archambault will command Discovery?s STS-119mission, with pilot Tony Antonelli and mission specialists Joseph Acaba, SteveSwanson, Richard Arnold, and John Phillips completing its crew.

"These crewmates have been absolutely tremendous to workwith," Archambault said of his team in a preflight NASA interview. "Ilook at this crew and I say, 'Boy, you really stacked the deck in my favor andI?m very appreciative for each one of these guys.'"

If the shuttle launches today, the astronauts' original 14-day missionwill be cut short by one day and one spacewalk, to make room for an incomingRussian Soyuz mission to the space station launching March 26. If the shuttleis unable to launch today, NASA can try again Monday and Tuesday, thoughlaunching then will necessitate shortening the mission even further.

Today's launch attempt comes more than a month after Discovery's initialFeb. 12 launch target. NASA delayed the shuttle's launch for weeks due tosuspect fuel control valves in the orbiter's main engines. The shuttle?s threevalves were each replaced twice, with mission managers clearing Discovery forlaunch earlier this month.

NASA?s STS-119 mission will mark the 125th shuttle launch and the 27th missionfor the Discovery spacecraft. The spaceflight is the first of at least fiveNASA shuttle missions planned for 2009 to continue space station constructionand perform one last overhaulof the Hubble Space Telescope.

SPACE.com is providing continuous coverage of STS-119 with reporterClara Moskowitz in Cape Canaveral and senior editor Tariq Malik in New York. Click here for missionupdates and SPACE.com's live NASA TV video feed. Live Coverage begins at2:30 p.m. EDT (1830 GMT) today.

• New Video - Meet Discovery's STS-119 Shuttle Astronauts
• New Video - Discovery's Mission: Space Station Power Up!
• New Show - NewSpace: The Orbital Industrial Revolution