Astronauts Rick Mastracchio and Mike Hopkins successfully concluded Saturday their first spacewalk to repair the damaged cooling system of the International Space Station, NASA said.

The astronauts were almost six hours outside the ISS and managed to work faster than expected, entirely removing the cooling pump with the faulty valve so they could return to the space station with much of the job done.

This operation was not expected to be finished until Monday, but the good work of Mastracchio and Hopkins allowed NASA's Mission Control in Houston to give them the go-ahead to completely remove the broken pump.

Now they can finish replacing the faulty cooling pump with a new one on Monday, and will not have to make a third spacewalk on Wednesday, Christmas Day.

The two astronauts were aided by Japan's Koichi Watkata, who lifted his colleagues and heavy equipment with a robotic arm from inside the ISS.

The damage to the cooling system, reported by NASA earlier this week after detecting a temperature anomaly in one of the external ammonia pumps, has had no serious impact on the operations of the ISS up to now, but required the suspension of all non-essential activities of the research laboratory in the spacecraft, in orbit some 450 kilometers (260 miles) from the Earth.

The damage also forced Orbital Science Corp. to postpone until mid-January the launch of its capsule Cygnus with supplies for the ISS that had been scheduled for this week.

Besides Mastracchio, Watkata and Hopkins, the ISS Expedition 38's six-person crew is made up of Russians Oleg Kotov, with the rank of commander, Mikail Tyurin and Sergey Ryazanskiy. EFE