How to Cool a Space Station

17 February 2015

Last month astronauts at the International Space Station (ISS) were forced to evacuate the American section after an alarm indicated a possible ammonia leak.

Used in the cooling and heating of this outer-space orbiting outpost, ammonia is an essential part of the ISS’s complex airconditioning system. 

While a broken airconditioning unit at home or work can cause some inconvenience, out there in space, a faulty airconditioner can be a life and death situation.

It’s not the first time the ISS airconditioning has broken down but, according to US space agency NASA, this latest alarm was a false one – thankfully!

Without thermal controls, the temperature of the ISS’s sun-facing side would rise to 121 degrees Celsius, while its dark side would fall to -157 degrees Celsius.

In space, heating and cooling occurs through radiation – objects are warmed by solar rays and cool off by emitting infrared energy. So, for the ISS to maintain a comfortable, middle-of-the-range temperature for its astronauts, it requires a pretty clever cooling solution.

Firstly, the space station’s metal skin is protected from extreme heat and bitter cold using special Mylar insulation (a highly reflective blanket called Multi-Layer Insulation).

For the internal temperatures, however, NASA engineers designed the Active Thermal Control System, or ATCS, to remove the waste heat (given off by active machinery and human bodies inside the space station) in two ways.

Air and water heat exchangers cool and dehumidify the spacecraft’s internal atmosphere while high heat generators are attached to custom-built cold plates. To keep everything cool, cold water circulated by a 17,000-rpm impeller (about the size of a 10c coin!) courses through the heat-exchanging devices.

The heat is then carried outside the space station, to circulate through a grid of coiled pipes, much like a giant radiator, and rejected into space.

But rather than containing water, which would freeze once outside the space station, these pipes contain ammonia. The heated ammonia circulates through the huge radiators and the heat is released into the atmosphere as infrared radiation.

And if you think that’s complicated, just imagine what’s involved in controlling air quality and air flow! To read more about how the ISS stays cool visit Motherboard.

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