Russian cosmonaut Salizhan Sharipov and US astronaut Leroy Chiao had planned to spend six hours outside the station but finished 90 minutes early. "The hatch has now been closed," a mission control spokesman said. "They managed to do everything -- they finished early because they were very well prepared."

The orbiting laboratory was left unmanned while the astronauts installed antennas that form part of the docking mechanism for a European Space Agency cargo craft.  

The astronauts also launched an experimental satellite -- by simply "throwing it like a basketball" while they were outside.

The satellite will be used to gather information on earthquakes, floods and fires.

Most of the spacewalk was taken up by working on the docking system ahead of the arrival of the first unmanned European cargo craft named Jules Verne, which is due to be launched in 2006.

The European crafts can carry more food, equipment and fuel than Russia's Progress cargo ships -- currently the only way to get supplies to the astronauts.

They will provide a helping hand as Russia struggles with having to launch all craft to the station while US shuttles are grounded after the deadly Columbia accident in 2003.

Russia has launched all manned and cargo vehicles to keep the station running for more than two years.

NASA has said it plans to return the shuttles to service in May or June.

The expedition was the last planned space walk for Sharipov and Chiao before they leave the station in April after six months in orbit.

They will be replaced by another US-Russian crew, scheduled to blast off from the Baikonur cosmodrome in Kazakhstan on April 15 for their six-month stint.

The new crew will be accompanied for 10 days by European Space Agency astronaut Roberto Vittori, who will conduct experiments and prepare the ground for longer European missions once the US shuttles are back in service.

Vittori will return to earth with Sharipov and Chiao.

Complicating the space walk this time was a seriously hampered stabilization system.

Two weeks ago, a circuit breaker popped open and cut power to one of the gyroscopes needed to keep the space station stable and pointed in the right direction.

The breakdown left the station running on only two gyroscopes, the bare minimum.

Flight controllers expected the two functioning gyroscopes to become overloaded, but said the space station would be fine drifting around the earth and pitching over, almost like a slow-motion cartwheel, for up to two orbits.

Engineers have yet to identify the source of the mysterious force that tilts the space station during space walks and causes the American-made gyroscopes to lose steering control.

(China Daily via agencies March 29, 2005)