Countdown began on Saturday at the Kennedy Space Center in Florida toward Tuesday's launch of the

Space Endeavour, less than three weeks after the last shuttle flight.

The National Aeronautics and Space Administration will launch the shuttle at 2:28 a.m. from the Kennedy Space Center at Cape Canaveral. Meteorologists predicted clear skies and light breezes, with a 90 percent chance conditions would be suitable for liftoff.

The mission will last 16 day, making it NASA's longest space station trip ever and will include five spacewalks, the most ever performed while a shuttle is docked there.

The seven-man crew includes two veteran NASA astronauts: commander Dominic Gorie and lead spacewalker Richard Linnehan; rookies Greg Johnson, Michael Foreman, Robert Behnken and Garrett Reisman; and Japan's Takao Doi, who flew on a shuttle research mission in 1997.

The astronauts will deliver the first section of a new Japanese laboratory known as Kibo to the station, along with an eerily human-looking robot, called Dextre.

Endeavour's astronauts will install the first part of Japan's Kibo complex and use up the Canadian-made robot to help with station maintenance and other service works. The main part of Kibo, which is Japanese for hope, is due to arrive in May.

The station components come from all of the station's international partners — the United States, Russia, Canada, Europe and Japan — and will finally be joined in orbit.

For years we've been calling it an international space station and now we're truly there, said Dominic L. Gorie, the flight commander and a retired Navy captain.

Endeavour, which will be NASA's 122nd shuttle mission, is the second of six shuttle flights NASA plans for 2008.