Nasa astronauts completed a spacewalk on Saturday at the International Space Station that had been delayed after a false alarm woke the crews of the station and the visiting space shuttle Atlantis.
Atlantis crewmembers Michael Foreman and Randy Bresnik installed communications antennae and set cargo attachment mechanisms to the station's truss during their excursion which lasted a little over six hours.
Earlier they had halted a body-conditioning sleepover in a low-pressure chamber on the station after a false depressurisation alarm shut down ventilation fans.
The problem, which interrupted the sleep of crews on the station and the shuttle Atlantis for a second consecutive night, appeared to stem from a new Russian docking module that arrived at the station on November 12.
Foreman and Bresnik were sleeping inside the station's Quest airlock when alarms indicated a rapid depressurization of the station.
Flight controllers quickly realised it was a false alarm but the system automatically shut down ventilation fans, which in turn allowed dust to swirl in the microgravity environment, triggering false smoke detection alarms.
It took the crew about an hour to get the fans working again, prompting Nasa to cancel the spacewalkers' sleepover that was intended to purge nitrogen from their bodies to prevent a dangerous condition known as the 'bends'.
Instead, Foreman and Bresnik put on oxygen masks and exercised vigorously on stationary bicycles to rid their bodies of nitrogen before floating outside the station.
Atlantis arrived at the station on Wednesday to deliver spare parts for the outpost.
Nasa is stocking it with equipment in hopes of keeping it operational after the US space agency's shuttles stop flying next year.
The Russian, European and Japanese cargo craft that will keep the station supplied with food, water and fuel after the shuttles are retired cannot haul the heavy pumps, tanks and gyroscopes carried aboard the shuttles.
Station crewmembers will fly on Russian Soyuz capsules.
Bresnik, making his first spaceflight, was still awaiting word about the birth of his second child.
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