This story was updated at 7:32 p.m. EDT.
The sevenastronauts set to launch aboard the space shuttle Discovery on Sunday are fillingsome free time caused by their latest flight delay with some last-minutetraining and visits with family.
NASA shuttlemission managers plan to launch Discovery on Sunday night at 7:43 p.m. EDT(2343 GMT) after a hydrogen gas leak thwartedan attempted liftoff on Wednesday.
Discoverycommander Lee Archambault and pilot Tony Antonelli planned to fill the downtimecaused by the launch delay with landing rehearsals in a modified jet that mimics thereturn 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?regoing to be reviewing theirmission objectives and spending time with their families,? NASAspokesperson Laura Rochon told SPACE.com on Thursday.
NASAofficials said engineers have a good understanding of the leak in a hydrogenvent line that forced mission managers to call off Discovery?s late Wednesdaylaunch from a seaside launch pad at the agency?s Kennedy Space Center in CapeCanaveral, Fla.
?They thinkthey have a decent understanding [of the leak] to do the troubleshooting at the pad,? NASAspokesperson Candrea Thomas said from the Florida spaceport.
Engineerswill 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 propellantduring fueling, is siphoned away to a safe distance where it does not pose anexplosion risk to the Discovery and its crew during launch, NASA officialssaid.
Archambaultand his crewmates plan to launch toward the International Space Station todeliver the outpost?s final set of U.S.-built solar arrays and swap out onemember of its three-astronaut crew. Japanese astronaut Koichi Wakata - Japan?sfirst long-duration astronaut - will launch aboard Discovery to replace NASA astronautSandra Magnus as part of the space station?s Expedition 18 crew.
The missionhas been delayed more than a month, first due to concerns with suspect fuelvalves on Discovery and later by Wednesday?s gas leak.
WhileDiscovery?s crew prepared for a Sunday launch, the three astronauts aboard theInternational Space Station were also eager for the shuttle?s arrival.
Earliertoday, station commander Michael Fincke of NASA, Magnus and Russian flightengineer Yury Lonchakov hadto 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, atiny part of an outdated satellite motor, flew past the station at distance of about2.4 miles (4 km), too close for comfort, but did not damage the orbitallaboratory.
After theincident, NASA?s Mission Control in Houston radioed Fincke and his crew to tellthem that Discovery remained on track for a Sunday night launch.
?We?rehappy to have it up here if they can get up here safely,? Fincke said of theshuttle. ?Thanks for the update.?
SPACE.comis providing continuous coverage of STS-119 with reporter Clara Moskowitz andsenior editor Tariq Malik in New York. Click here for missionupdates and SPACE.com's live NASA TV video feed.
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