Space station alarm delays Atlantis crew spacewalk

Atlantis crew members Michael Foreman and Randy Bresnik floated outside the International Space Station for an abbreviated six-hour spacewalk after a false alarm disrupted their sleep. The spacewalkers halted a body-conditioning sleepover in a low-pressure chamber on the station after a false depressurization 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 realized 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 beginning the shortened spacewalk. Atlantis arrived at the station on Wednesday to deliver spare parts for the station.NASA is stocking the outpost 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. During Saturday's spacewalk, Foreman and Bresnik worked to install communications antennas and set up a cargo attachment mechanism to the station's truss.Bresnik, making his first spaceflight, was still awaiting word about the birth of his second child. His wife was due to deliver a baby girl on Friday.