NASA aimed to launch shuttle Endeavour in the early morning darkness today with the last major pieces of the International Space Station.
Stiff wind rattled the launching site on Saturday afternoon, but forecasters were hopeful the gusts would subside in time for the 4:39 a.m. (0939 GMT) liftoff. The odds of good weather were 80 per cent.
Endeavour is loaded with a new room for the space station, as well as an observation deck. Once both of those are installed, the orbiting complex will be 98 per cent complete.
The six astronauts assigned to the mission slept through the afternoon. They will work the graveyard shift during the 13-day flight.
It was expected to be the last shuttle launch in darkness.
NASA Administrator Charles Bolden, an ex-astronaut, met with journalists on the eve of the launch and noted there are only five shuttle missions left.
"You're going to have to figure out what else you're going to do, along with us," he said.
In an hourlong news conference, Bolden accepted the blame for the way the NASA work force was informed of President Barack Obama's plans to dismantle the Constellation moon exploration programme. In the proposed budget that was released on Monday, Obama set NASA on a new post-shuttle path.