Spacewalkers on Tuesday treated the International Space Station, or ISS, with a Christmas gift, a new ammonia-pump module that would fully restore the station’s critical coolant system.

Flight Engineers Mike Hopkins and Rick Mastracchio completed the mission of replacing a refrigerator-sized faulty coolant pump with a spare unit in two spacewalks conducted on Dec. 22 and Dec. 24.

“Houston, you got yourself a new pump module, congratulations,” one of the spacewalkers radioed to NASA’s Mission Control in Houston, Texas, after making the final electrical connections.

“It’s the best Christmas ever, thanks guys,” Doug Wheelock, an astronaut working with the crew from mission control replied.

Flight engineers removed the degraded pump module during a 5-hour 28-minute spacewalk on Saturday, and they retrieved a spare pump module from an external stowage platform near the end of the station’s truss, or backbone. The duo installed the module during a 7-hour 30- minute spacewalk on Dec. 24, NASA said in a statement.

The coolant module is believed to be fully functional after the repairs, but its full reintegration with the ISS’s two-loop external cooling system is expected to be completed on Christmas Day, Dec. 25, NASA said.

The only hitch faced by the spacewalkers was getting one of the four ammonia fluid lines disconnected from a temporary jumper box that was installed to enable ammonia flow during the repair spacewalks. However, with some difficulty the crew was able to disconnect the line, but in the process their space suits were sprayed with frozen ammonia flakes -- some tiny, some big snow-like chunks -- from a valve.   

The spacewalkers underwent ammonia decontamination procedures on their spacesuits once they reached the vacuum room of the orbiting space station.

On Wednesday, teams at mission control hoped to reactivate noncritical systems that were shut down following the malfunction in the coolant system on Dec 11.   

It was NASA’s second Christmas Eve spacewalk, following one conducted in 1999 to service the Hubble Space Telescope. The crew at 15-year-old ISS so far has performed 176 spacewalks devoted to the station’s assembly and maintenance and Tuesday’s space outing marks tenth such event this year.

One more space walk this year is scheduled for Dec. 27 for Russian cosmonauts Oleg Kotov and Sergey Ryazanskiy, who will install a pair of high-resolution cameras on the exterior of the Russian segment of the station.