NASA officials postponed the launch of Orbital Sciences' unmanned cargo resupply mission to the International Space Station to no later than mid-January as engineers and crew members continue to work to repair a faulty pump module on the outside of the station.

A series of spacewalks are planned to replace the pump found on one of the orbiting lab's two external cooling loops. The systems are responsible for circulating ammonia outside the station in order to keep equipment both inside and outside the station cool.

The problem started Dec. 11 when the pump automatically shutdown after reaching its preset temperature limit. NASA followed by releasing a statement saying both the crew and lab were in stable condition, but that the glitch "does remove redundancy, which could make a second failure a far more serious concern."

Several non-critical systems were powered down in response to the pump's failure.

NASA astronauts Rick Mastracchio and Mike Hopkins have been tasked with removing the failed pump module with a spare throughout three spacewalks scheduled for Dec. 21, 23 and 25.

In an interview with The Associated Press, Mastracchio said the situation was a mix of pros and cons.

"Of course, the bad news is the station's having problems and we have to go out and do a repair," he said. "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."

Each spacewalk will begin at 7:10 a.m. EST and is expected to last for six and a half hours. NASA TV will offer coverage of the walks starting at 6:15 a.m. all three days.

"Everything we can do is being done," ISS Mission Operations Integration Manager Kenny Todd said in a statement Dec. 12. "The system is good and stable. The crew is in good shape. All the right folks on the ground are looking at the problem and trying to assess exactly what the root cause is and what our options are to continue moving forward."

Originally planned for Dec. 18, the mission represents Orbital's first cargo mission following a successful test run carried out in September, and is part of a $1.9 billion contract between the space agency and aerospace firm.