NASA clears shuttle for launch, weather improving

August 23, 2009 By MARCIA DUNN , AP Aerospace Writer

(AP) -- NASA has cleared space shuttle Discovery for liftoff Tuesday, and the weather looks promising as long as thunderstorms stay away during fueling.

After meeting Sunday afternoon, managers decided Discovery is in good shape to fly to the international space station. A power controller issue - one had to be replaced a week ago in the shuttle - did not stand in the way of the launch.

The chairman of the mission management team, Mike Moses, said there is no way of knowing with certainty whether the new power controller in Discovery might break like the old one did. To minimize the risk of a power failure, some equipment will be left on longer than usual - rather than shutting it down and then turning it back on, he said.

Two other power controllers failed in the lab at Johnson Space Center earlier this summer, adding to NASA's concern. Engineers are comfortable with the workaround for Discovery, Moses said.

Forecasters, meanwhile, said there is an 80 percent chance the weather will cooperate for Discovery's 1:36 a.m. liftoff. That's better than previous forecasts.

But there is a 40 percent chance that thunderstorms could interfere with Monday afternoon's fueling. A fueling delay of more than three hours would bump the flight into the next day.

"Obviously, the weather is going to be one of our challenges," Moses told reporters.

Discovery and seven astronauts will deliver about 17,000 pounds of space station supplies and equipment. Three spacewalks are planned during the 13-day flight.

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