Space shuttle Discovery was undocked from the International Space Station on Monday to end an eventful 11-day stay that included delivery of a new room for the space outpost and a risky repair to a power-producing solar panel.

Discovery, with pilot George Zamka at the helm, gently pulled away from the station which was 348 km above the Pacific Ocean at the beginning of its two-day journey back to Earth. “Shuttle departing,” space station commander Peggy Whitson said as she rang a ship's bell in a naval salute which is a tradition on the station.

“Thank you guys for the (Harmony) module and all your help,” she radioed to Discovery, referring to an Italian-built module delivered by the shuttle.

Discovery was to fly around the station to take photographs for NASA engineers to study, then move about 64 km away to perform a final inspection of the shuttle's heat shield. The shuttle was launched from Kennedy Space Center in Florida on October 23 and is scheduled to land there on Wednesday afternoon.

The seven shuttle astronauts bid a weepy farewell to the three space station crew members on Sunday. The shuttle crew includes returning space station flight engineer Clay Anderson, who was replaced by astronaut Dan Tani.

The seven metre Harmony module delivered by Discovery was the first new room added to the outpost in six years. It adds 2,600 cubic feet of space to the 15,000 cubic feet that the station had before its arrival.

Harmony also will be the berthing port for European and Japanese laboratories scheduled for delivery starting in December as NASA pushes to finish the outpost before the shuttle fleet is retired in 2010.

Station expansion plans may have been saved by a risky repair improvised by NASA after a solar power panel critical for the station's growing electricity needs ripped in two places while it was being unfurled on October 30.

Astronaut Scott Parazynski, on the fourth spacewalk of the mission, rode the station's robot arm, extended by a boom borrowed from the shuttle, out to the partially unfolded panel to thread it with hand-fashioned cables so it would not tear further.