US astronauts begin spacewalk for station repairs

Two US astronauts on Saturday stepped outside the International Space Station for the first of three spacewalks to fix a broken equipment cooling system, NASA said. "Today's spacewalk has officially begun," said a NASA commentator as the space agency broadcast live images of Japanese astronaut Koichi Wakata leading the operation from inside the space station. Veteran spacewalker Rick Mastracchio is making his seventh career spacewalk, accompanied by rookie Mike Hopkins, who is making his first venture outside the global research lab. Wakata will operate the station's 50-foot (15-meter) robotic arm, hoisting Mastracchio and hefty equipment from one section of the lab to another. The men's first task is to disconnect the failed ammonia pump, which is about the size of a refrigerator. On the second spacewalk, set for Monday, the astronauts are to remove the pump so it can be replaced with a spare that was already stowed at the ISS. A third spacewalk is planned for Christmas Day, when the failed pump will be shuttled away and final installations made on its replacement. However, there is a chance the astronauts will be able to complete all their work in two spacewalks, NASA has said.