CAPE CANAVERAL, Fla. - NASA officials today cleared the space shuttle Discovery to blast off Tuesday as the weather outlook improved for the planned predawn launch.
Mike Moses, head of Discovery?s mission management team, said the shuttle and its seven-astronaut crew are ready for their 1:36 a.m. EDT (0536 GMT) launch toward the International Space Station on Tuesday from a pad here at NASA's Kennedy Space Center.
?We are go for launch,? Moses told SPACE.com late Sunday.
The shuttle now has an 80 percent chance (up from 70 percent yesterday) for good weather at launch time, but only if lightning doesn?t delay fueling operations, said Kathy Winters, NASA?s shuttle weather officer.
There is a slight chance that lightning could stall efforts to fuel Discovery?s tank with liquid hydrogen and liquid oxygen propellant late Monday afternoon. A similar weather concern delayed the launch of the shuttle Endeavour last month. NASA does not fuel shuttle tanks if there?s a 20 percent chance of lightning within 5 miles (8 km) of the launch pad to avoid the risk of an explosion.
NASA could delay fueling Discovery?s external tank by up to three hours and still try to launch early Tuesday, mission managers said.
?Overall, the weather is looking good,? Winters added.
Discovery?s six-man, one-woman crew is poised to fly a 13-day resupply mission to the space station. The astronauts are hauling about 15,200 pounds (6,894 kg) of new science gear, supplies and spare parts to the orbiting laboratory. Three spacewalks are planned for the mission.
The only issue facing Tuesday?s launch was a failed power controller on Discovery that was replaced last week. An analysis found that a connector in the 30-year-old device was bent, causing the failure.
NASA engineers are not sure if other power controllers on Discovery may be vulnerable to similar malfunctions, including the replaced one. If they fail in orbit, some systems could be stuck on or off depending on which state they were in at the time of the glitch, but mission managers said there are workarounds in place to handle those failures.
The power controllers route power to payload heaters, reaction control thrusters and other systems, so engineers plan to leave them on for the duration of the flight - with the exception of the thrusters - avoid a failure. Multiple failures would be required to affect all of Discovery?s thrusters, Moses said.
Moses said that the malfunction will also be reviewed for NASA?s next shuttle launch in November.
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SPACE.com is providing complete coverage of Discovery's STS-128 mission to the International Space Station with Managing Editor Tariq Malik in Cape Canaveral, Fla., and Staff Writer Clara Moskowitz in New York. Click here for shuttle mission updates and a link to NASA TV.