NASA

This image from a NASA space shuttle mission shows the International Space Station in orbit. The space station is the size of a football field and home to six astronauts. (Image was taken on Feb. 10, 2010.)

By Clara Moskowitz Space.com

Astronauts on the International Space Station have discovered a leak of ammonia coolant on their orbiting habitat, and NASA is looking into the problem, though it poses no immediate danger to the crew, officials said Thursday.

The space station uses chilled liquid ammonia to cool down the power systems on its eight giant solar array panels. A minor leak of this ammonia was first noticed in 2007, and NASA has been studying the issue ever since. In November 2012 two astronauts took a spacewalk to fix the problem, rewiring some coolant lines and installing a spare radiator due to fears the original radiator was damaged by a micrometeorite impact.

At the time, those measures appeared to fix the problem, but today astronauts on the football field-size space station noticed a steady stream of frozen ammonia flakes leaking from the area of the suspect coolant loop in the Photovoltaic Thermal Control System (PVTCS). [Gallery: Building the International Space Station]

"It is in the same area, but we don't know whether it's the same leak," NASA spokesman Kelly Humphries of the Johnson Space Center in Houston told Space.com. Humphries said the agency was taking the leak seriously because it affects an important system if they loose the ability to cool that particular solar array, it won't be able to generate power for the station. In fact, the leak has worsened to the point that Mission Control expects that particular loop to shut down within the next 24 hours.

However, "the crew is in no danger," Humphries stressed. It's too soon to speculate on a possible spacewalk or other measure to deal with the issue, he added.

Mission Control has been discussing the problem with the astronauts on the station throughout the afternoon.

"What you guys have provided in the way of imagery and video has been just like gold to us on the ground," astronaut Doug Wheelock from Mission Control radioed to space station commander Chris Hadfield, a Canadian Space Agency astronaut. "We are fairly confident that it's coming from the vicinity of the TCS." However, flight controllers noted they were still unable to pinpoint the leak's exact location.

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Space station leaking coolant