Washington: Two NASA astronauts stepped out Tuesday on a rare Christmas Eve spacewalk to wrap up repairs to an equipment cooling system at the International Space Station.
Americans Rick Mastracchio, 53, and Mike Hopkins, 44, floated outside the orbiting lab on a second outing to replace an ammonia pump module whose internal control valve failed December 11.
Their task was to retrieve a spare pump module from an external stowage platform and install it and, despite recent concerns about leaking spacesuits, the spacewalk got off to a smooth start.
After about two hours of maneuvers outside the station, Hopkins, riding a 57-foot (15-meter) robotic arm operated from inside the station by Japanese astronaut Koichi Wakata, managed to unhook all the connectors on the spare pump module.
"Okay, my friend you have yourself a pump module," said a NASA official at mission control in Houston, overheard in footage broadcast live on the space agency's online television station.
With his boots affixed to the Canadian-made arm, Hopkins' next adventure was to grasp the refrigerator-sized pump module as Wakata maneuvered him over to its installation location.
The team made swift work of the first spacewalk on Saturday, disconnecting and pulling out the old cooling pump that regulates the temperature of equipment at the orbiting space lab.
They managed to complete what had been seen as almost two days' worth of work in a single outing that lasted just five and a half hours, ending an hour earlier than planned.
Wakata, of the Japan Aerospace Exploration Agency, arrived at the space station in November for a half-year stay as part of the six-member international crew.
In March, he will become the first Japanese commander of the space station, NASA said.
Mastracchio is wearing a different spacesuit than the one he donned on Saturday, a backup that was stored at the station and was resized to fit him over the weekend.
On Saturday, a "small amount of water" had entered his suit's cooling system in the space station airlock after he finished the spacewalk, NASA said.
But the US space agency said the problem was not related to the water leak in a helmet that cut short Italian astronaut Luca Parmitano's spacewalk in July and risked drowning him.
NASA is still investigating what went wrong in that case.
As a backup measure, the astronauts are now outfitted with emergency snorkels in their spacesuits and extra pads to absorb any leaking water in their helmets.
NASA officials have said the suits, which were designed 35 years ago, are safe, and stressed that Saturday's problem did not put Mastracchio in any danger.
Tuesday's spacewalk was expected to last six and a half hours, which the US space agency estimated would be enough time to complete the repair job.
Hopkins and Mastracchio must complete five electrical connections and four fluid connections before the pump can be activated.
NASA said tests will be done on the new pump later Tuesday to see how well it is working.
The spacewalk marks the second of Hopkins' career, and the eighth for Mastracchio.
NASA said the last time astronauts embarked on a Christmas Eve spacewalk was 14 years ago, when space shuttle Discovery astronauts Steve Smith and John Grunsfeld stepped out to install upgrades and new insulation on the Hubble Space Telescope.
Later this week, Russian cosmonauts Oleg Kotov and Sergey Ryazanskiy will make a spacewalk on December 27 to install a pair of high-fidelity cameras on the Zvezda service module and to do maintenance on the Russian segment of the station.
