Five trips to the International Space Station are scheduled for this year, along with a final servicing call to the Hubble Space Telescope.

The space station, a US$100 billion (S$149 billion) project of 16 nations, is nearing completion after more than a decade of construction.

Discovery and a crew of seven will deliver and install the last of the U.S.-built solar wing panels and radiators, which are needed to bring the orbital complex up to full power.

The panels are folded up inside a 45-foot- (14-metre) long, 15-tonne aluminum girder that completes the station's exterior backbone.

Riding atop a slow-moving Apollo-era transport system, the shuttle's trek to the launch pad began before sunrise on Wednesday. The 3.4-mile (5.5-km) journey took about six hours.

Discovery's crew plans to climb aboard the shuttle at its seaside launch pad in central Florida for a final dress rehearsal before the scheduled blastoff.

The crew includes Japan's Koichi Wakata, who will become the first from his country to live aboard the outpost. He replaces Nasa astronaut Sandra Magnus, who has been one of the station's flight engineers since mid-November. -- REUTERS