Two U.S. astronauts successfully removed an old pump on the International Space Station on Saturday, completing the first of a number of planned spacewalks to repair the broken cooling line.

An ammonia pump with a faulty valve was removed by Rick Mastracchio and Michael Hopkins ahead of schedule.

The removal of the valve -- initially expected to come out on Monday – prompted Mission Control to state that it was "an early Christmas."

While three space walks were initially planned for the procedure,  two sojourns may now be enough to finish installing a spare pump on the ISS.

Several hours after the pump was removed, NASA pushed the second spacewalk from Monday to Tuesday -- Christmas Eve -- to size a new suit for Mastracchio.

At the end of Saturday's spacewalk, Mastracchio's suit was compromised when he inadvertently turned on a water switch.

He wasn't in any danger, but mission control decided to switch to a backup suit.

Saturday's spacewalk took approximately six hours and saw some minor dramas, including a smoke alarm going off inside the ISS. It was, however, quickly declared a false alarm.

In an effort to prevent a repeat of an incident from last summer, when Luca Parmitano’s helmet flooded nearly drowning the Italian astronaut, Mastracchio and Hopkins were outfitted with extra safety gear. The two had snorkels in their suits and water-absorbent pads in their helmets.

Still, cold temperatures were a factor, causing Mastracchio to crank up the heat in his space boots to protect his toes. Eventually, on his request, Mission Control called the astronauts back to the space station after the old pump was secured in its temporary position.

Replacing the pump is a significant task. It has only been attempted once, in 2010, by the same astronauts who were guiding Mastracchio and Hopkins from Mission Control on Saturday.

The 354-kilogram pump is roughly the size of a double-door fridge. In addition to being difficult to handle, the pump's plumbing is full of toxic ammonia.

After the pump broke down on Dec. 11, attempts were made to fix the faulty valve remotely. While flight controllers were partially successful, NASA decided that spacewalks were required to replace the valve.

Spacewalks have been on hold since the last one in July nearly ended in disaster, when Parmitano's helmet flooded with water and he barely got back inside the ISS alive.

It was eventually determined that the flooding was caused by a contaminated device in his suit. It is still not known how it was contaminated.

In addition to Mastracchio and Hopkins, three Russian astronauts and one Japanese astronaut are living on the ISS.