Shuttle Astronauts Await Sunday Launch Attempt

This story was updated at 7:32 p.m. EDT.

The seven astronauts set to launch aboard the space shuttle Discovery on Sunday are filling some free time caused by their latest flight delay with some last-minute training and visits with family.

NASA shuttle mission managers plan to launch Discovery on Sunday night at 7:43 p.m. EDT (2343 GMT) after a hydrogen gas leak thwarted an attempted liftoff on Wednesday.

Discovery commander Lee Archambault and pilot Tony Antonelli planned to fill the downtime caused by the launch delay with landing rehearsals in a modified jet that mimics the return flight of a 100-ton space shuttle, NASA officials said. Their crewmates, meanwhile, reviewed plans for the upcoming mission and took some personal time, they added.

?They?re going to be reviewing their mission objectives and spending time with their families,? NASA spokesperson Laura Rochon told SPACE.com on Thursday.

NASA officials said engineers have a good understanding of the leak in a hydrogen vent line that forced mission managers to call off Discovery?s late Wednesday launch from a seaside launch pad at the agency?s Kennedy Space Center in Cape Canaveral, Fla.

?They think they have a decent understanding [of the leak] to do the troubleshooting at the pad,? NASA spokesperson Candrea Thomas said from the Florida spaceport.

Engineers will replace a connector segment of the 7-inch (18-cm) hydrogen vent line, which funnels flammable gaseous hydrogen away from the launch pad. The hydrogen, which boils off from the shuttle?s super-cooled liquid hydrogen propellant during fueling, is siphoned away to a safe distance where it does not pose an explosion risk to the Discovery and its crew during launch, NASA officials said.

Archambault and his crewmates plan to launch toward the International Space Station to deliver the outpost?s final set of U.S.-built solar arrays and swap out one member of its three-astronaut crew. Japanese astronaut Koichi Wakata - Japan?s first long-duration astronaut - will launch aboard Discovery to replace NASA astronaut Sandra Magnus as part of the space station?s Expedition 18 crew.

The mission has been delayed more than a month, first due to concerns with suspect fuel valves on Discovery and later by Wednesday?s gas leak.

While Discovery?s crew prepared for a Sunday launch, the three astronauts aboard the International Space Station were also eager for the shuttle?s arrival.

Earlier today, station commander Michael Fincke of NASA, Magnus and Russian flight engineer Yury Lonchakov had to take refuge in their docked Soyuz spacecraft - which doubles as a lifeboat - when a small piece of space junk came too close to the station. The debris, a tiny part of an outdated satellite motor, flew past the station at distance of about 2.4 miles (4 km), too close for comfort, but did not damage the orbital laboratory.

After the incident, NASA?s Mission Control in Houston radioed Fincke and his crew to tell them that Discovery remained on track for a Sunday night launch.

?We?re happy to have it up here if they can get up here safely,? Fincke said of the shuttle. ?Thanks for the update.?

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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