Repairs to the International Space Station's external cooling system are on hold, while astronauts work through a space suit problem.

Hours after the end of a spacewalk Saturday, during which the two Americans on the station's current crew removed an old space station pump as part of a critical effort to revive a faultering cooling line, Mission Control delayed the second scheduled spacewalk until Tuesday, Christmas Eve, to allow enough time for one of the astronauts to prepare a spare suit.

The original suit, worn by National Aeronautics and Space Administration Astronaut Rick Mastracchio, was left unusable after a water switch was mistakenly switched on at the end of Saturday's walk.

NASA officials announced Saturday night that, considering the speed and success of the first outside repair session, they're not sure if a third spacewalk will be needed --- although a third walk had been initially planned for Christmas Day.

The space agency requires a day between spacewalks in order for astronauts to get enough rest.

Mastracchio and fellow Astronaut Michael Hopkins successfully detached and removed an ammonia pump with a bad valve, ahead of schedule, since that specific task had been planned for the second spacewalk.

If the repair duo keep up their pace, two spacewalks may be all that's needed to finish the replacement of a spare pump.

The space station's cooling system broke down about 10 days ago, causing one of two cooling loops to get too cold, after which the station's six-man crew needed to turn off all nonessential equipment inside the orbiting laboratory.

That dramatically slowed all scientific research to a near-halt and left the station vulnerable.

Mission Control hoped to extend Saturday's spacewalk, but after 5-and-a-half hours, Mastracchio, whose suite had been repeatedly blasted by frozen ammonia flakes during the repair, felt uncomfortable and asked to go back inside the station.

An Italian astronaut nearly drowned in his suit last summer when his helmet filled with water. So, in an effort to avoid a repeat incident, NASA had Mastracchio and Hopkins wear snorkels in their suits and water-absorbent pads in their helmets.

Then, as if the spacewalk wasn't exciting enough, a smoke alarm went off in the space station as the repair crew worked outside. It was determined in short order to be a false alarm.

The station's 780-pound (354-kilogram) coolant pump is about the size of a double-door refrigerator and extremely awkward to handle, as the entire coolant system is full of toxic ammonia.

Following the Dec. 11 breakdown, flight controllers tried to fix the valve through remote commands. When that didn't work, they tried using a different valve to regulate the station system's temperature.

Up until Saturday, U.S. spacewalks had been on hold since the helmet flooding issue in July.

Besides the two Americans, three Russian and one Japanese astronaut are serving on the space station.