The US space shuttle Endeavour was poised to blast off from its Florida home port on Tuesday to deliver the first part of a huge Japanese laboratory to the International Space Station.
The newest of NASA's three remaining space shuttles, Endeavour and its seven-man crew was scheduled to lift off at 2:28 am EDT (0628 GMT) on a rare night launch and spend 16 days in orbit, 12 of them at the space station.
That will be the longest planned visit to date by a shuttle to the orbital outpost, a $100 billion project that is finally living up to its multinational billing with last month's installation of Europe's first permanent space lab and now Japan's.
In addition to a storage and equipment module for Japan's double-decker bus-sized space lab, the main part of which will be hoisted to space in late May, Endeavour will carry a Canadian two-armed robotic system.
The final section of the $2.4 billion Japanese lab called Kibo, a Japanese word for "hope," will be launched into space next year, culminating a 20-year effort by Japan to build a facility in space.
Space around the station will be more crowded than usual during Endeavour's mission. Europe's first cargo ship, an unmanned Automated Transfer Vehicle called Jules Verne, was launched from French Guiana on Saturday and will be hovering near the station during the shuttle's visit, waiting for its turn to berth.
The weather appeared almost perfect for launch, with a 90 per cent chance conditions will be suitable for an on-time liftoff.
NASA technicians began filling the shuttle's 15-story-tall tank at around 5:15 pm EDT (2115 GMT) with more than 500,000 gallons (1.9 million litres) of supercold liquid oxygen and liquid hydrogen.
The fuel will feed Endeavour's three main engines, which, together with two solid rocket boosters that will be jettisoned on the way up, will take the shuttle to a speed of more than 17,000 mph (28,000 kph) by the time it reaches orbit.
Looking relaxed, Endeavour's crew headed for the launch pad just before 11 pm EDT on Monday (0300 GMT Tuesday) in a shiny, oval-shaped bus of the type that has transported astronauts since the shuttle program began 27 years ago. A helicopter with sharpshooters, a precaution introduced after the September 11 attacks, hovered overhead.
The shuttle mission will include five spacewalks, two of which will be dedicated to constructing a robotic pair of hands for the station's crane.
The Canadian addition, called Dextre, spans 30 feet (9 meters) from the tip of one arm to the other and will be able to install and service components as small as a phone book or as large as a phone booth.
Astronauts also plan to test on a spacewalk a heat shield repair technique designed after the 2003 Columbia accident.
Debris damaged Columbia's wing at launch, causing the ship to break up during its fiery descent through the atmosphere for landing. All seven astronauts aboard were killed.
The experimental repair technique could prove useful during a planned maintenance flight this year to the Hubble Space Telescope, when the space station will not be within reach as a refuge should the shuttle be too damaged to return to Earth.
The United States and Russia lead the 15-nation space station partnership, which includes Canada, Japan and 11 members of the European Space Agency.
NASA has two years to finish constructing the station before the space shuttle fleet is retired.