The new crew of the International Space Station have completed the longest spacewalk in the 20-year history of the space shuttle programme.

American astronauts Jim Voss and Susan Helms ventured out to do some exterior work on the evolving platform, less than 24 hours after arriving at the orbiting complex.

The return of the astronauts was delayed until flight controllers determined their help was not needed to relocate a docking port that had to make way for a module filled with supplies.

The spacewalk lasted eight hours and 56 minutes. The longest previous spacewalk in the shuttle programme, in May 1992, lasted eight hours and 29 minutes.

'Uh, oh'

The spacewalkers had to deal with a few minor glitches during their walk, which began shortly after midnight Saturday and had been scheduled to last about seven and a half hours.

ISS: Expedition Two's home until July

The first words spoken by Helms on her spacewalk were "Uh, oh". A plastic bag holding a hydrazine-detection kit was drifting away, after breaking loose from Discovery.

Jim Voss tried to grab the bag but it was just outside his reach. He finally brought it under control by getting a quick lift on the shuttle's robot arm. But a portable attachment device needed for a work platform did get away when Voss accidentally let go of it.

His shuttle crewmates told him not to worry about it and that a spare was available.

Return journey

The Discovery space shuttle is delivering the first replacement crew for the space station, made up of Voss, Helms and Russian cosmonaut Yuri Usachev.

The three-member crew, known as Expedition Two, will remain aboard the space station until late July. Usachev has already moved into the space station, while the Americans will join him over the next few days.

They will relieve Expedition One made up of commander Bill Shepherd and two Russian cosmonauts. The current crew have been on the space station since 2 November.

They are due to return on Discovery, when it heads back to Earth next weekend.