Discovery, with pilot George Zamka at the helm, gently pulled away from the station 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 that is 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 launched from Kennedy Space Center in Florida on Oct 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 when they closed the hatch between the spacecraft in preparation for departure.

The shuttle crew includes returning space station flight engineer Clay Anderson, who was replaced by astronaut Dan Tani.

The 7 metre Harmony module delivered by Discovery was the first new room added to the outpost in six years. It adds 74 cubic metres of space to the 425 cubic metres 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. -- REUTERS