The US space shuttle Endeavour was due to blast off from Florida on Wednesday (this morning Beijing time) on its first mission in nearly five years, carrying a former teacher who trained with the ill-fated Challenger crew and gear for the International Space Station.

The mission will be the second of four that the US space agency plans this year as it presses to finish construction of the $100 billion space station before the three remaining US shuttles are retired in 2010.

Florida's weather, often marked by afternoon thunderstorms during the state's steamy summer, was expected to cooperate, with an 80 percent chance of clear skies for the 6:36 pm EDT/2236 GMT launch, NASA said.