(Reuters) - NASA planned to try again on Saturday to launch the shuttle Discovery on a mission to rewire the International Space Station, but the weather forecast kept the nighttime launch in doubt.
Low clouds, strong crosswinds and isolated showers threatened to ground the spacecraft and its seven-member crew, scheduled to blast off from the Kennedy Space Center in Florida at 8:47:34 p.m. EST, reports Trend.
NASA said there was only a 30 percent chance the weather would clear enough for liftoff Saturday night, and the odds rose only slightly -- to 40 percent -- on Sunday night.
Shuttle managers planned to decide by around 11 a.m. (1600 GMT) whether to start filling the shuttle's external tank with 500,000 gallons of super-chilled fuel for the ride into space.
The crew was strapped in and ready for an initial launch attempt Thursday night but the thick ceiling of clouds failed to part before the Earth rotated out of position for the shuttle to reach the space station.
NASA needs good visibility to track the shuttle at liftoff, and the winds have to be calm enough to permit landing in an emergency.
Discovery's astronauts are to rewire the space station's electrical grid during their 12-day mission, a necessary step in NASA's plan to finish building the orbiting outpost before the aging shuttles are retired in 2010.
Commander Mark Polansky leads a crew that includes Sweden's first astronaut, Christer Fuglesang, along with pilot William Oefelein, flight engineer Robert Curbeam, and mission specialists Nicholas Patrick, Joan Higginbotham and Sunita Williams.
The launch will be NASA's first after sunset since before the 2003 Columbia disaster. Managers recently lifted the ban on night launches, imposed to ensure cameras had good lighting to spot any debris falling off the shuttle's fuel tank.
Debris damaged Columbia and caused it to break apart, killing its seven astronauts, as it re-entered Earth's atmosphere. The fuel tank has since been redesigned.