The seven astronauts on the U.S. space shuttle Discovery scrambled aboard their spaceship on Tuesday to await blastoff on a construction mission to the International Space Station.
Liftoff remained targeted for 11:38 a.m. (1538 GMT) although forecasters predicted a 60 percent chance of a delay due to clouds and rain.
Discovery is carrying a connection hub to the space station so NASA can attach laboratories owned by Europe and Japan to the orbital outpost. The new module, called Harmony, will be the first expansion to the station's living space since 2001.
If Discovery's 14-day mission unfolds with few problems, NASA plans to launch the European Space Agency's Columbus laboratory on December 6.
Earlier Tuesday, technicians filled Discovery's fuel tank with 500,000 gallons of liquid oxygen and liquid hydrogen to feed the ship's three main engines during the 8.5-minute climb to orbit.
NASA then dispatched a team of inspectors to survey Discovery for signs of ice or cracks in the tank's foam insulation.
"There are no technical issues that would preclude launch at this time," said launch commentator Mike Curie.
Both ice and foam pose a threat to the shuttle if pieces fly off during liftoff, as happened during Columbia's launch in 2003.
The impact damaged the ship's heat shield, which failed during the descent through Earth's atmosphere for landing, causing the shuttle's breakup and the deaths of seven astronauts.
For Discovery's flight, NASA carved an hour off the amount of time the tank is filled before launch in the hope of minimizing ice buildups.
After Discovery's mission, NASA has 11 construction flights to the station remaining and two resupply flights before the $100 billion outpost is finished.
NASA needs to have the work completed within three years when the shuttle fleet is due to be retired.
Image Above: STS-120 commander Pamela Meroy gets strapped into space shuttle Discovery. Image credit: NASA TV
Technicians working at Launch Pad 39A at NASA's Kennedy Space Center in Florida have closed the hatch, or doorway, leading into space shuttle Discovery's crew compartment. The shuttle's seven astronauts are running through pre-launch tests and checks. Technicians are putting the finishing touches on the white room itself so it can safely fold away from Discovery in the last few minutes before launch.
The countdown is proceeding towards an 11:38 a.m. EDT liftoff.