Astronauts aboard the International Space Station are planning a second and final spacewalk to fix the outpost's cooling system early on Tuesday, a NASA official said.

NASA astronauts Rick Mastracchio and Mike Hopkins are expected to leave the station's Quest airlock to install a new ammonia pump, space station flight director Judd Frieling said during an interview on NASA Television on Monday.

During an initial spacewalk on Saturday, Mastracchio and Hopkins removed a failed pump, accomplishing about half the work planned for the second spacewalk. That prompted the National Aeronautics and Space Administration to drop plans for a third spacewalk, provided no problems occur on Tuesday.

"It's apparent now that we'll be able to get most of our critical objectives done [Tuesday]," Frieling said.

One of two cooling systems on the U.S. side of the space station, a $100-billion project of 15 nations, shut down on Dec. 11 due to a faulty valve. Engineers tried software patches to control the flow of ammonia, which is used to dissipate heat from equipment aboard the station and radiate it into space.

International Space Station

Astronauts aboard the International Space Station hope to complete repairs on Tuesday. (Associated Press/NASA)

With time running short before the position of the sun causes complications, NASA managers decided to have astronauts replace the pump with one of three spares stored outside the permanently staffed research complex which flies about 400 kilometres above Earth.

The spacewalks were the first since July when a spacesuit problem caused the helmet worn by Italian astronaut Luca Parmitano to fill with water, a condition that could have caused him to drown.

Suspect components replaced

Suspect components in the spacesuit were replaced. As a precaution, Mastracchio and Hopkins also outfitted their helmets with absorbent pads and makeshift snorkels that would allow them to draw air from the belly of their spacesuits if the helmet leaks reoccurred.

"The suits worked as expected," Frieling said.

However, an unrelated suit problem prompted NASA to delay the second spacewalk until Tuesday.

Mastracchio, a veteran of seven spacewalks, apparently accidentally hit a switch once he and Hopkins were back in the airlock on Saturday that allowed water to get inside his suit's sublimator, a device that regulates the suit's cooling system.

As a precaution, that spacesuit will be dried out for about a week, Frieling said.

Mastracchio and Hopkins used the extra day to piece together a new spacesuit from spare components aboard the station.

Also on Monday, station commander Oleg Kotov and flight engineer Sergey Ryazanskiy prepared for a Russian spacewalk slated for Friday. The cosmonauts plan to install two high-fidelity cameras on the Zvezda service module and replace several experiments mounted to the outside of the station.

On Monday, Kotov and Ryazanskiy put on their Russian spacesuits and went into the Russian Pirs airlock as part of a practice run.