The crew of the US space shuttle Discovery was preparing for a return to Earth Monday.

The US space agency NASA expects the shuttle to land at 1314 hrs GMT Monday at Kennedy Space Centre on Cape Canaveral, Florida, ending a 13-day mission.

The shuttle decoupled Saturday from the International Space Station (ISS) to start the two-day return flight to Earth.

The undocking manoeuvre occurred about 400 kilometres above the Earth.

The ISS orbits the earth every 92 minutes at a speed of 28,000 kilometres per hour.

German astronaut Thomas Reiter, 48, remained aboard the ISS, where he will stay for the next six months with US astronaut Jeffrey Williams and Russian Pavel Vinogradov.

Without Reiter, Discovery began its return flight to Earth with six astronauts aboard. It is transporting 2.3 tonnes of rubbish, waste and unneeded parts for the ISS.

Discovery's heat shield did not sustain any apparent external impact damage during take-off.

In 2003, the space shuttle Columbia broke apart as it re-entered Earth's atmosphere, killing all seven crewmembers.

Investigators found that the disaster was caused by insulating foam falling from the external fuel tank during launch, striking the shuttle's wing and compromising the heat shield required to protect it during re-entry.

A year ago, heat-shielding tiles were again damaged during the first shuttle launch since the Columbia disaster. External repairs were made on the 2005 mission while the shuttle was docked to the ISS.

The next space shuttle launch is scheduled for August 28, when the Atlantis is to lift off with four huge solar energy panels bound for the ISS.