Astronauts aboard the International Space Station are prepped for a spacewalk Saturday morning to inspect and possibly repair a leak in the station's cooling system.

"We are absolutely, 100 per cent ready for the EVA .... It's the right thing to do and everybody on board is gearing up for it," Canadian astronaut Chris Hadfield told Mission Control at a planning conference Friday morning.

EVA, which stands for extra-vehicular activity, is the technical name for a spacewalk, in which astronauts perform manoeuvres outside the safety and controlled environment of the space station.

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Chris Cassidy, one of two NASA astronauts scheduled to perform the spacewalk, prepared the equipment required, including space suits, inside the space station's Quest airlock Friday. (NASA TV)

Astronauts Chris Cassidy and Tom Marshburn are scheduled to step outside the space station at 8:15 a.m. ET to inspect an ongoing ammonia leak in one of the coolant loops outside the space station that help keep the station's power system running properly.

The spacewalk is scheduled to last six hours and 15 minutes.

ISS manager Mike Suffredini said the EVA's main goal was to locate the source of the leak, but says the crew will also replace a pump which he expects will "likely solve the problem."

NASA spokesman Norm Knight called the EVA "precedent-setting" in terms of its quick turnaround. Between detecting the leak Thursday and stepping outside Saturday morning, it's the most abrupt spacewalk ever orchestrated on the ISS.

Asked to assess the seriousness of the problem, Suffredini characterized the leak as an "annoyance," strictly due to the time and manpower involved in fixing it. He said the cause of the leak remains unclear, but a visual inspection should provide answers, including the possibility of a meteorite strike.

The area has had a small leak for several years, but proved too difficult to detect.

"You're talking a very, very, very small hole," Suffredini said .

Hadfield coming home on schedule

Hadfield is scheduled to be the "spacewalk choreographer," assisting Cassidy and Marshburn from inside the space station NASA said.

Hadfield, who took command in March, is the first Canadian to oversee the crew of the space station. The ammonia leak is the first notable glitch at the space station since he took command, and comes just days before he is scheduled to return to Earth. He seemed keen to meet the challenge.

"What a fun day!" he tweeted Friday afternoon. "This type of event is what the years of training were for. A happy, busy crew, working hard, loving life in space."

Hadfield, Marshburn and Russian cosmonaut Roman Romanenko are scheduled to undock their Soyuz TMA-07M spacecraft at 7:08 p.m. ET Monday and land in Kazakhstan at 10:31 p.m.

'Serious situation'

Hadfield had contacted NASA Mission Control at 11:30 a.m. ET Thursday after crew reported seeing a "very steady stream" of small white flakes floating away from a particular area of the station. A few hours later, he tweeted that it was "a serious situation, but between crew and experts on the ground it has been stabilized."

The crew's reports, along with related imagery and space station data, confirmed that ammonia, which is used to cool the power channels that provide electricity to the station, was leaking more and more quickly from the area of the space station where the flakes were spotted.

Suffredini emphasized that the crew is not in danger and said NASA is expediting the EVA because the flakes represent a unique opportunity to pinpoint the source of the elusive leak.

NASA said the affected cooling loop, which is linked to a particular solar array, was the same one that spacewalkers tried to troubleshoot during a spacewalk on Nov. 1, 2012. It wasn't known, however, whether the leak — which wasn't visible in November — was the same one. NASA said work was underway Friday to reroute power channels to maintain full operation of systems normally powered by the affected solar array.

Cassidy and Marshburn have each performed three previous spacewalks. Hadfield performed two spacewalks in 2001 to install the space station's Canadarm2 robotic arm.

A view of the flakes coming from the leak