NEW: NASA: The spacewalk has concluded, lasting 7 hours and 30 minutes
The astronauts are trying to fix a problem on the International Space Station
A malfunctioning pump in the station's cooling system needed to be replaced
It's the second Christmas Eve spacewalk in history, NASA says
While many people spent Christmas Eve doing last-minute shopping, two American astronauts had a more challenging matter to attend to Tuesday.
In orbit more than 200 miles above Earth, flight engineers Rick Mastracchio and Mike Hopkins embarked on a spacewalk Tuesday morning to repair part of the International Space Station’s cooling system.
The spacewalk ended at 2:23 p.m. ET Tuesday and lasted 7 hours and 30 minutes, NASA said.
More than four hours into the job, the two astronauts had successfully bolted a replacement ammonia pump module into its location and were working to connect lines to allow the ammonia to flow, NASA said in a tweet.
There was a slight kink in the work when one of the fluid lines tangled. The astronauts untangled it, but when they did, the line released some ammonia flakes that landed on their space suits.
It was not a leak, but some residue, NASA spokesman John Ira Petty said. The ammonia that landed on the spacesuits will require the spacewalkers to air out their suits before going back into the station, but is otherwise not a big deal, he said.
The two engineers were carrying out the second in a series of expeditions needed to replace a malfunctioning pump, which circulates ammonia through loops outside the station to keep equipment cool.
The pump developed problems December 11 when an internal valve stuck in an incorrect position. The space station’s life support system remains up and running, but operations were cut back as a result of the problem, NASA said.
It is the second Christmas Eve spacewalk in history, according to NASA.
Two American astronauts spent 5 hours, 28 minutes working outside the International Space Station on Saturday in the first in a series of spacewalks needed to replace a malfunctioning ammonia pump module.
The pump circulates ammonia through loops outside the station to keep equipment cool. The space station’s life support system is up and running, but ISS operations were cut back as a result of the failure, NASA said.
CNN’s John Zarrella reported that NASA had concerns about the excursion because water built up in a European astronaut’s helmet in July, causing that spacewalk to be cut short.
“Both Mastracchio and Hopkins reported dry conditions repeatedly throughout Saturday’s activities and the two were never in danger,” the agency said.
NASA installed new safeguards, including snorkels inside the space suits that would allow astronauts to take breaths if water formed and they had to return to the space station, Zarrella said. Mastracchio and Hopkins reported no problems Saturday.
Tuesday’s spacewalk was the 176th to support the space station’s assembly and maintenance, according to NASA.
The previous Christmas Eve spacewalk took place in 1999, the agency said, when Discovery astronauts Steve Smith and John Grunsfeld spent more than eight hours refitting parts of the Hubble Space Telescope.
The others on the space station include Russian cosmonauts Mikhail Tyurin, Sergey Ryazanskiy and Oleg Kotov and Japanese astronaut Koichi Wakata.
CNN’s Ashley Corum, Ralph Ellis and John Zarrella contributed to this report.