[pclmulqdq]

I am referring to the "using a heat pump to make the radiator hotter than the GPU" as "creating a thermal gradient." No matter the technology, moving heat like this is always pretty expensive in power terms, and the price goes way up if you want the radiator hotter that the thing it's cooling.

Can you point to a terrestrial system similar to what you are proposing? Liquid cooling and phase change cooling in computers always has a radiator that is cooler than the component it is chilling.

You can do this in theory, but it takes so much power you are better off with some heat pumping to much bigger passive radiators that are cooler than your silicon (like everything else in space).

[fnordpiglet]

Yah but the key is that it’s not the power draw that’s the issue is the dissipation of thermal energy through pure radiation. The heat of the radiator is really important because it reduces the required surface area immensely as it scales up.

However the radiators you’re discussing are not pure radiance radiators. They transfer most heat to some other material like forced air. This is why they are cooler - they aren’t relying on the heat of the material to radiate rapidly enough.

I would note an obvious terrestrial example though is a home heat pump. The typical radiator is actually hotter than the home itself, and especially the heads and material being circulated. Another is any adiabatic refrigerator where the coils are much hotter than the refrigerated space. Peltier coolers even more so where you can freeze the nitrogen in the air with a peltier tower but the hot surface is intensely hot and unless you can move the heat from it rapidly the peltier effect collapses. (I went through a period of trying to freeze air at home for fun so there you go)

For radiation of heat the equation is P = \varepsilon \sigma A T^4

P = radiated power • A = surface area • T = absolute temperature (Kelvin) • \varepsilon = emissivity • \sigma = Stefan–Boltzmann constant

This means the temperature of the material increases radiation by the fourth power of its value. This is a dramatic amount of variance at it scales. If you can expend the power to double the heat it emits 16x the heat. You can use a much lower mass and surface area.

This is why space based nuclear reactors are invariably high temperature radiators. The idea radiators are effectively carbon radiators in that they have nearly perfect emissivity and extraordinarily high temperature tolerances and even get harder at very high temperatures. They’re just delicate and hard to manufacture. This is very different than conduction based radiators where metals are ideal.

[pclmulqdq]

Making your radiator hotter than the thing you're pulling heat out of is very, very expensive in energy terms. This is why home AC is so expensive and why nobody uses systems like this to cool computers. All that energy has to come from a solar panel you fly, too, so you're not saving mass by doing this. You're just shifting it from cooling to power. If you need 200W to cool 100W of compute, you're tripling the amount of power you need to do that work.

Also, peltiers are less energy-efficient than compressors. That is why no home AC uses a peltier.