US astronaut Michael Finke and Russian cosmonaut Gennady Padalk spent around five hours outside the station carrying out maintenance work and installing equipment to enable a European cargo vessel to dock alongside next year, said Vladimir Solovyov, a senior official at mission control.

"The spacewalk was completed ahead of schedule because the astronauts carried out their tasks faster than planned," Solovyov was quoted by Interfax news agency as saying in Moscow.

Scientists are still trying to work out why the station briefly lost radio contact with mission control and veered off its regular orbit during the operation, he added.

The Automated Transfer Vehicle (ATV), a 20-tonne unmanned vessel, will bring fuel, oxygen, water and provisions for the crew. The vessel will also correct the station's orbit and compensate for its regular losses of altitude, the control centre said earlier.

The ATV will be launched into orbit from an Ariane-5 rocket which will blast off from Kourou in French Guiana in October 2005, the European Space Agency's representative in Russia, Alain Fournier-Sicre, told AFP earlier.

Since the Columbia shuttle disaster in February 2003, Russia's Progress cargo ships have been the only way to send supplies to the ISS.

Tuesday's spacewalk is the third to be undertaken by the current crew who have been in orbit since April. It will be followed by another spacewalk on September 3, Solovyov said.

SPACE.WIRE