The shuttle is to lift off at 2:29 a.m. EDT Tuesday from the Kennedy Space Center in Florida. The shuttle's seven astronauts will, among other things, deliver the first section of the Japanese-built Kibo laboratory and the Canadian Space Agency's two-armed robotic system called Dextre.
At 6 a.m. Monday, the rotating service structure that provides access and weather protection for Endeavour was retracted, clearing the way for loading about 500,000 gallons of liquid oxygen and liquid hydrogen propellants into the shuttle's external fuel tank Monday evening.
NASA said the weather forecast called for a 10 percent chance that atmospheric conditions would delay the launch, although meteorologists said they were concerned about the slight chance of a low cloud ceiling around Kennedy at launch time.
STS-123 will be commanded by Dominic Gorie with Gregory Johnson serving as shuttle pilot. The crew includes astronauts Rick Linnehan, Robert Behnken, Mike Foreman, Garrett Reisman and Japanese astronaut Takao Doi.