Why does the ISS need Thermal Control Systems like radiators? What’s generating so much heat that it needs to be dissipated?

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  • ?
    Lv 5
    1 month ago
    Favourite answer

    The ISS collects all the power it needs from the Sun.  However, since our electrical and electronic systems are not particularly efficient, much of that energy turns up inside the ISS in the form of heat.  Heat is a particular problem in spacecraft because they aren't touching anything - there's no air around them to carry excess heat away, so heat just builds up inside them.  Under such conditions, even the heat generated by the human crew's metabolism becomes a significant problem.

    You might recall that heat travels by conduction, convection, and radiation.  In spacecraft since there is nothing touching them as they orbit, conduction and convection are OUT.  We can only dump the excess heat by radiation.  Unfortunately, radiation is pretty much fixed to unmasked surface area and the ISS offers only so much of that.

    So the function of the Thermal Control Systems is to gather heat from where the greatest amount of excess occurs, and transport it to the exterior of the spacecraft at locations where it has a clear shot at radiating away.  For example, if you have electronic components that get hot, you don't just put them in a rack with a fan blowing air through them, as you would here in the atmosphere.  On the ISS that would just heat up the cabin air and it would require additional heavy equipment to remove the heat from the cabin.  Instead, you use plumbing in your hot electronics, to draw the heat into an exchange fluid that is then pumped to the radiating surfaces outdoors.

    On craft such as supersonic and hypersonic vehicles the same problem exists, even when they are in the atmosphere, because their skins get so hot there is no way to collect internal heat and remove it via ANY of the three means.  (If you build a radiator exposed to the slipstream, it will simply become as hot as the rest of the hull due to atmospheric friction, and become useless.)  So internal heat has to be collected and then dumped into the fuel as it moves toward the engines.  That's how the SR-71 could fly without melting, even with skin temperatures above the liquification temperature of steel.  (Obviously if you're in orbit, you don't have fuel and engines that you can use to get rid of your heat, so Thermal Control Systems are necessary.)

  • 1 month ago

    The humans aboard are a major source.  Pound for pound the human body generates more heat than the Sun!  (Always amused myself proving that to classes)  But on board electronic equipment generates plenty, and the ISS spends more than half its time in sunlight.

  • ?
    Lv 7
    1 month ago

    Every motor and circuit on the space station generates heat.

    The humans on board generate heat.

    The ISS absorbs sunlight for part of its orbit, that generates heat.

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