Original URL: http://www.theregister.co.uk/2013/12/12/nasa_iss_spacewalk/

Hot Stuff! NASA mulls 'urgent' space walk as ISS cooler conks out

In space, no one can hear you sweat

By Iain Thomson

Posted in Science, 12th December 2013 01:29 GMT

NASA has ordered a partial shutdown of the International Space Station after one of the two cooling systems stopping the astronauts broiling stopped working unexpectedly.

The ISS has two ammonia-based cooling loops placed outside the orbiting station that suck out the heat generated by equipment and personnel. On Wednesday one of these loops began to heat up and had to be shut down for safety reasons, possibly due to a dodgy flow control valve in the cooling system pump, and the agency is still trying to work out how to fix the problem.

"At no time was the crew or the station itself in any danger, but the ground teams did work to move certain electrical systems over to the second loop," NASA said in a statement. "The crew is safe and preparing to begin a normal sleep shift while experts on the ground collect more data and consider what troubleshooting activities may be necessary."

The second cooling loop on the ISS isn’t powerful enough to cool the station on its own, so "non-critical systems" have been shut down in the Harmony node (containing electrical and computing systems), and the Kibo and Columbus laboratory modules.

Early indications are that the cooling system valve may be fixed with a software upgrade, but if not, NASA is getting ready for some of the ISS' six-person crew to suit up and take a space walk to check out if the problem can be fixed from the outside of the platform.

The ISS has had repeated problems with its cooling systems over the last year, with unscheduled space walks to effect repairs last November and in May this year. Both of those issues were with coolant leaks, rather than the current mechanical failure.

Cooling is vital to the ISS. Without thermal control systems the side of the station catching the Sun's rays would heat up to 250°F (121°C), while temperatures on the shadow side of the ISS fall to -250°F (-157°C). The cooling system not only keeps the astronauts comfortable, but also eases the thermal stresses on the module's structure.

Within the ISS itself most of the thermal control systems use water cooling but that's not going to work for exterior cooling – the fluid would quickly freeze, so ammonia is used instead. These coolers act not only on the shell of the ISS but also regulate the temperature of its solar panels.

NASA's mission control in the Johnson Space Center is running through preset routines to check out the cooling systems telemetry before making any decisions on a space walk. The ISS does have backup pumps in orbit if some DIY is required and it's highly unlikely that more serious measures will have to be taken. ®