While many people may spend Christmas Eve doing last-minute shopping, two American astronauts have 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 on Tuesday morning to repair part of the International Space Station's cooling system.
It is the second Christmas Eve spacewalk in history, according to NASA.
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.
The two astronauts spent about 5 1/2 hours outside the space station on Saturday working to remove the problematic pump. They are stepping out again Tuesday to install a new one.
If everything goes according to plan, the spacewalk will last 6 1/2 hours and the repair job will be completed Tuesday.