Two Nasa astronauts wrapped up successful repairs at the International Space Station on Tuesday after a rare Christmas Eve spacewalk to fix an equipment cooling system.
Americans Rick Mastracchio, 53, and Mike Hopkins, 44, floated outside the orbiting lab for seven and a half hours to replace an ammonia pump whose internal control valve failed on December 11.
"We have a pump that is alive and well," said Nasa commentator Rob Navias on the US space agency's live television feed after a successful jumpstart test on the newly installed pump module, a bulky piece of gear the size of a refrigerator.
More checks need to be done, but the pump appeared to be "in good shape" and would be fully activated in the coming hours, Navias said from mission control in Houston.
Despite recent concerns about leaking spacesuits, neither astronaut reported any problems.
The suits "have functioned perfectly and have been bone dry throughout the course of today's spacewalk", Navias said.
Hopkins, making his second career spacewalk, rode the 15-metre robotic arm, operated from inside the station by Japanese astronaut Koichi Wakata.
With his boots affixed to the Canadian-made arm, Hopkins grasped the bulky pump module as Wakata maneuvered him over to its installation location.
Then, Mastracchio, who was making his eighth career spacewalk, helped push the module into its slot and the pair began affixing it in place.
Five electrical connections and four fluid connections followed, and a brief test, like a jumpstart, was done to test the pump's connections and electronics.
The pump would later be pressurized with nitrogen and fully activated. In the meantime, Nasa said it appeared "healthy".
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.
Orchestrating the spacewalks from inside the station's Destiny laboratory was Wakata of the Japan Aerospace Exploration Agency.
Wakata 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.
Meanwhile, Mastracchio was 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 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.
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.
On Wednesday, the six-man crew at the station will be off duty to enjoy a quiet Christmas, Nasa said.
On Friday, Russian cosmonauts Oleg Kotov and Sergey Ryazansky will embark on a spacewalk to install a pair of high-fidelity cameras on the Zvezda service module and to do maintenance on the Russian segment of the station.