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Comment by GMoromisato | Hacker News Reader

Emissivity is one factor, but it is dwarfed by the T^4 term. Sure, maybe if you use exotic materials you can get from 0.9 to 0.95 emissivity, but why bother? Just run the radiators a little hotter.

The equation is:

  A ~ (1000 P) / (2 e k T^4)

Where

  A is the radiator area in square meters
  P is the power in kilowatts
  e is emissivity (usually 0.9)
  k is the constant 5.67e-8

P and T are the dominating factors. Don't worry about emissivity.

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Emissivity is an important factor here because as I said, and as the sources I linked for you to reference clearly stated convective radiation is not taking place in space.

Both Google and NASA are worried about this for a reason, if you think they are wrong, you should offer your assistance to them, rather than debating me.

My point is you don't need fancy/expensive materials for your radiator. Anodized aluminum is at 0.8. With inexpensive coatings you can get to 0.9.

If your argument against space datacenters is "radiator materials are too expensive" then I just think that's not a very good argument.

Oh, sure yeah I agree with that. I was just making a point about the “big hunk of metal” comment and the fact that emissivity is important because the expense of radiator materials aren’t the problem - the surface area (and mass) of the radiator is.

And I agree with you on that. "Big hunk of metal" was too much of an exaggeration--SpaceX's design has liquid cooling, so I assume they have some channels or tubs running through the radiator, plus pumps, etc.

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