ISS pump repair

US astronauts Rick Mastracchio and Michael Hopkins completed the first risky spacewalk on Saturday, NASA said, to replace the broken equipment cooling system.

They spent five and a half hours outside the station disconnecting the 350-gram pump that malfunctioned on December 11. According to NASA the astronauts completed the work an hour earlier than expected meaning they were also able to take on the extra task of removing the pump.

That task had originally been planned for the second spacewalk, which will take place on Monday - when they also hope to install the new pump. They plan to embark on a second spacewalk on Monday to install a new pump. A third walk, if necessary, is planned for Christmas Day.

The fault with one of two US ammonia systems, that regulates equipment temperature at the space station, forced the six-man crew to turn off non-essential equipment and shut down dozens of science experiments.

None of the crew are in danger, although the functioning cooling system is unable to support the three laboratories and other modules on the US side of the station. The Russian side has a separate cooling system.

The venture outside the station was the seventh for Mastracchio, 53, who has now logged 44 hours on spacewalks. It was the first, however, for 44-year-old Hopkins.

It was the first spacewalk for NASA since July, when a space helmet worn by Italian astronaut Luca Parmitano began filling with water, a malfunction which could have potentially forced him to drown. The cause of the leak is still under investigation.

Mastracchio and Hopkins both wore helmets equipped with water-absorbent pads and homemade snorkels in case there is a malfunction in the water pump.

cp/jm (AFP, Reuters, dpa)