Astronauts begin spacewalk to repair ISS

First of three spacewalks aims to fix broken cooling system on the International Space Station.

Two American astronauts have floated outside the International Space Station on the first of a series of urgent spacewalks to repair a broken cooling line at the research outpost. Astronauts Rick Mastracchio and Mike Hopkins began their spacewalk at 7:01am (1201 GMT) on Saturday to remove a failed ammonia pump that caused the shutdown of the ISS cooling system for more than a week. "Today's spacewalk has officially begun," said a NASA commentator during the US space agency's live broadcast of the operation, which is expected to last six hours. O n December 11 a broken valve caused the failure in one of the station's two external cooling loops, which circulate ammonia outside the station to keep both internal and external equipment cool. The breakdown forced the six-man crew to turn off all nonessential equipment aboard, including some science experiments, but the crew was not in any danger, NASA said. Mastracchio is making his seventh career spacewalk, while Hopkins is venturing outside the ISS for the first time, a $100bn research lab that flies some 400km above Earth. Japanese astronaut Koichi Wakata is operating the station's 15-meter robotic arm, which is hoisting Mastracchio and hefty equipment from one section of the lab to another. NASA ordered three spacewalks to complete the job, which was attempted only once before, in 2010. The team's second spacewalk is set for Monday, when the astronauts will remove the cooling pump so it can be replaced with a spare that was already stowed at the ISS. The broken pump will be shuttled away during a third spacewalk scheduled for Christmas Day, but there is a chance the astronauts will be able to complete the work in only two spacewalks, NASA said. The repair job has sidelined Orbital Sciences Corp's first cargo run to the ISS. Orbital Sciences is one of two companies hired by NASA to fly supplies to the outpost after the retirement of its 30-year space shuttle programme in 2011. The flight, the first of eight under a $1.9bn NASA contract, will be rescheduled for no earlier than January 7.

Source: Agencies