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(CNN) -- While many people may spend Christmas Eve doing last-minute gift shopping, two American astronauts have a more challenging matter to attend to Tuesday.

In orbit more than 200 miles above the planet, Flight Engineers Rick Mastracchio and Mike Hopkins are set to embark on a spacewalk to repair part of the International Space Station's cooling system.

It will be the second Christmas Eve spacewalk in history, according to NASA.

The two engineers will be 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.

NASA Delays Emergency Spacewalk

This week in space

NASA posted this snap of astronaut James H. Newman on November 20, 1998, to celebrate the 15th anniversary of the International Space Station.

A #nofilter image of the surface of Mars, courtesy NASA's Mars Curiosity Rover.

Super Typhoon Haiyan lashing the Philippines, taken from NASA's Aqua satellite on November 7.

There it goes! A still camera on a sound trigger captured this intriguing photo of an airborne frog in the foreground as NASA's Lunar Atmosphere and Dust Environment Explorer spacecraft lifts off toward the moon. This foreground photobomber stole the show, earning this snap almost 25,000 likes.

This one went viral too: a new view of Saturn taken by NASA's Cassini spacecraft. It's a natural color image that shows the view as it would be seen by a human observer.

A throwback to 2010 for the International Space Station's 15th anniversary: NASA astronaut Tracy Caldwell Dyson looks down at Earth through a window on the ISS.

NASA astronaut Karen Nyberg takes a selfie with Russian cosmonaut Fyodor Yurchikhin and European Space Agency astronaut Luca Parmitano behind her.

From the Hubble telescope: the crowded center of the Milky Way, showing the constellation Sagittarius. Right in the center of the image is a supermassive black hole called Sagittarius A*, consuming clouds of dust as it affects its environment with its enormous gravitational pull.

A historic image of Earth from the moon, taken on July 20, 1969, from Apollo 11.

A view of spiral galaxy IC 2560 captured from the Hubble Space Telescope.

To celebrate the launch of Mars probe MAVEN on November 18, NASA showed off this mosaic from the Viking 1 Orbiter, which passed by the planet over 30 years ago, on February 22, 1980.

A Soyuz spacecraft carrying new International Space Station residents Oleg Kotov, Mike Hopkins and Sergey Ryazanskiy arrives at the space station in September.

Earth on September 7, as seen by the Geostationary Operational Environmental Satellites, which looks out for atmospheric "triggers" for severe weather conditions such as flash floods and hurricanes.

Drifting away: three nanosatellites, known as Cubesats, are deployed from the ISS airlock.

Expedition 36 flight engineer Chris Cassidy of NASA is carried to the medical tent shortly after landing in Kazakhstan on September 11, having spent five and a half months on the International Space Station.

Out-of-this-world photos from Nasa's Instagram

Out-of-this-world photos from Nasa's Instagram

Out-of-this-world photos from Nasa's Instagram

Out-of-this-world photos from Nasa's Instagram

Out-of-this-world photos from Nasa's Instagram

Out-of-this-world photos from Nasa's Instagram

Out-of-this-world photos from Nasa's Instagram

Out-of-this-world photos from Nasa's Instagram

Out-of-this-world photos from Nasa's Instagram

Out-of-this-world photos from Nasa's Instagram

Out-of-this-world photos from Nasa's Instagram

Out-of-this-world photos from Nasa's Instagram

Out-of-this-world photos from Nasa's Instagram

Out-of-this-world photos from Nasa's Instagram

Out-of-this-world photos from Nasa's Instagram

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15 out-of-this-world photos from NASA's Instagram

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 failure, NASA said.

The two astronauts spent about five and half hours outside the space station on Saturday working to remove the problematic pump. They are scheduled step out again Tuesday at 7:10 a.m. ET to install a new one.

If everything goes according to plan, the repair job will be completed Tuesday.

Spacesuit problem

Mastracchio will be using a different spacesuit after a small amount of water leaked into the cooling system of the one he wore on Saturday.

NASA said the issue with the suit, which happened at the end of the spacewalk, was unrelated to a problem experienced in July, when water pooled in an Italian astronaut's helmet, causing a 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 had installed new safeguards, including snorkels inside the spacesuits that would allow astronauts to take breaths if water formed and they had to return to the space station.

Tuesday's spacewalk will be 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 other people in the International Space Station at the moment include Russian cosmonauts Mikhail Tyurin, Sergey Ryazanskiy and Oleg Kotov and Japanese astronaut Koichi Wakata.

CNN's Ralph Ellis and John Zarrella contributed to this report.