CAPE CANAVERAL, Fla. - NASA has cleared Discovery for a launch Monday morning to the International Space Station, the last scheduled liftoff in darkness for the soon-to-retire shuttle program.

Mission managers met Saturday and gave the "go" to proceed toward liftoff. The unanimous decision came after engineers determined there were no booster rocket safety concerns. Two booster problems recently cropped up when the parts were tested off-site.

Forecasters expect an 80 percent chance of good weather for the 6:21 a.m. liftoff, close to an hour before sunrise.

Discovery is loaded with spare parts and science experiments for the space station. A crew of seven will deliver the gear and conduct three spacewalks to set everything up.

Only three shuttle flights remain after this one. President Barack Obama will visit the Cape Canaveral area April 15 - while Discovery is in orbit - to elaborate on his post-shuttle plans. He created a furor in the aerospace community in February when he killed NASA's Constellation program, which had been aimed at returning astronauts to the moon.

That will mean more lost jobs for Kennedy Space Center and NASA's other hubs for human spaceflight operation.

Launch manager Mike Moses told reporters that even as the shuttle program winds down, the workforce remains as loyal and dedicated to the job as ever.

"But I don't want to take away from the fact that this is a very human space program, not just with the humans flying in the shuttle, but the folks building it and preparing it and getting ready to launch it," he said.

The shuttle crew includes three women. Combined with the woman already in the space station, the launch will lead to the most women in space at the same time.

The women astronauts include a former schoolteacher, a chemist who once worked as an electrician, and two aerospace engineers. Three are American; one is Japanese.

Discovery will spend 13 days in orbit, on its next-to-last flight.

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