According to Wikipedia, the solar panels of the ISS produce an average of about 120 kW of electrical energy, which is then used by the station's systems. Can it be converted into something other than heat? This would mean that the heat input of the systems is about 120 kW. Can I think about it this way or is it completely wrong?

Heat from the interior of the ISS is removed by heat exchangers, which then transfer the heat to the External Active Thermal Control System. The station is further heated by the sun. Is it really the case that all the heat is removed mainly with the help of these heat exchangers? If my previous reasoning is correct, they would have to take over 100,000 J per second from the air. Is it really like this or am I missing something important?


1 Answer 1


If my previous reasoning is correct, they would have to take over 100,000 J per second from the air.

All the heat resulting from the use of electricity does not end up in the cabin air. A lot of the equipment is mounted on coldplates which interface directly with the cooling loops.

Description of external equipment cooled by ammonia loop coldplates:

These electrical components are mounted on an interface known as a coldplate, which both connects the component to the truss and provides an interface for ETCS cooling (Figure 9). Each coldplate is a broad plate with narrow- set fins extending from it. Those fins interleave with fins extending from the electrical component such that heat from the electrical component fins radiates to the coldplate fins. This finned plate is bonded to a stainless steel flow plate, which is sealed to allow ammonia flow through the unit to pick up heat transferred through the aluminum fins.

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Note: Figure 9 is labeled incorrectly. The External Thermal Control System (ETCS) uses ammonia, not water.

Description of internal equipment cooled by water loop coldplates:

The cooled water flow then splits across many parallel paths to reach the equipment in racks throughout the module, is warmed by that equipment using coldplates, and returns to the pump to start the circuit again.

So the cabin air heat exchangers need not bear the total load.

Source: The International Space Station - Operating an Outpost in the New Frontier pp 204-205

  • $\begingroup$ Yeah, that's actually true. And is the relationship between electrical energy and thermal energy correct? $\endgroup$
    – Saturn V
    Mar 15, 2023 at 18:15
  • 2
    $\begingroup$ @SaturnV The thermal control system has to reject all heat generated from electrical power, crew metabolism, and incoming heat from the Sun and/or Earth. $\endgroup$ Mar 15, 2023 at 18:16
  • $\begingroup$ And don't you know roughly how much heat is removed by cold plates and how much by heat exchangers? $\endgroup$
    – Saturn V
    Mar 16, 2023 at 14:06
  • 1
    $\begingroup$ @SaturnV I am away from home now; I will look when I get back to see if I have that kind of detail. $\endgroup$ Mar 16, 2023 at 14:31

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