Six astronauts currently aboard the International Space Station will start a series of spacewalks this weekend to fix the orbital outpost's cooling system, NASA confirmed this week.

The spacewalks will delay a cargo resupply flight until January as well.

One of the station's ammonia cooling systems shut down on Dec. 11, causing astronauts to power down "unnecessary equipment." The crew was not in any danger as is doing fine, according to NASA.

The cooling systems shut down due to an apparent faulty valve inside a pump, located outside the station. Engineers on the ground attempted to avoid the spacewalks, but by Dec. 16, the cooling system was still down.

The U.S. space agency then decided to have two astronauts currently aboard the station replace the pump with a spare. Three spacewalks are planned to complete the work, according to NASA.

The first spacewalk has been scheduled for Saturday by flight engineers Rick Mastracchio and Michael Hopkins. Two additional spacewalks could take place on Dec. 23 and Dec. 25.

"Of course, the bad news is the station's having problems and we have to go out and do a repair," said Mastracchio, according to the Associated Press. "The good news is we have the spare parts. We have the training. We have the skills and, of course, going out and doing a spacewalk is always very exciting, yet very challenging."

Mastracchio and Hopkins will attempt to get the spare pump from a storage location outside the station and replace the defective pump.

The cooling system issue will sideline Orbital Sciences Corp's first cargo run to the ISS. The $100 billion research lab was set to fly about 250 miles above Earth sometime before Christmas to bring supplies to the six-person crew.

The spacewalks will be the first by NASA astronauts since July.

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