Comment by trhway
6 hours ago
>you can also spread those sub-units on desert land with no water or electricity and cool them radiatively.
no, you can't.
>attacking up is easier than attacking down.
no.
6 hours ago
>you can also spread those sub-units on desert land with no water or electricity and cool them radiatively.
no, you can't.
>attacking up is easier than attacking down.
no.
Asserting the contrary is not an argument.
Nothing prevents SpaceX or anyone else from buying up the right to put these things on cheap desert land. They don't even need to own the land, just the right to wheel these things out on a trailer or a helicopter and leave them there.
A desert is significantly less harsh than space. If your radiator is sized for space, it's overkill in an atmosphere.
And for your edit: https://www.youtube.com/watch?v=xNmbvaUzC8Q
>If your radiator is sized for space, it's overkill in an atmosphere.
no. Again totally wrong.
The 20-40C air surrounding the radiator radiates at the radiator too. This is why a human immediately gets stone cold in space while not in the atmosphere - our body radiates away about 900W and receives 800W+ back from the atmosphere - our internal heat 'generation has to cover only the difference - less than 100W usually.
You probably meant forced convection cooling. That requires additional machinery. And that additional machinery is a significant part why ground based datacenters such expensive to build and operate.
To the comment below:
>The planet underneath anything in low orbit also does this, making this argument irrelevant.
no. Again, totally wrong. You've just stated that a human in LEO wouldn't get immediately cold when exposed to space. Just think about it for a second. And after that plug the numbers in thermodynamic calculator. You'll see your error.
>Likewise, the fact that convection exists even without the adjective "forced".
no. Again, wrong. Non-forced convection is pretty small. Use the calculator. And you'll understand why datacenters use forced convection.
The planet underneath anything in low orbit also does this, making this argument irrelevant. There's even cheap paints specifically made to be most emissive in the wavelength window the atmosphere is mostly transparent to rather than itself emitting at.
As does the fact that humans are only slightly warmer than their surroundings. A human-sized object at the operating temperature of a GPU would have a net radiative loss in Earth's atmosphere of around 0.9-1.3 kW.
Likewise, the fact that convection exists even without the adjective "forced". Again, replace a human with an identically shaped android at maximum GPU operating temperatures of 80-100 °C, normal (non-forced) convection goes from ~117 W (human) to 0.9-1.3 kW (80 °C) to 1.2-2 kW (100 °C).
> > The planet underneath anything in low orbit also does this, making this argument irrelevant.
> no. Again, totally wrong. You've just stated that a human in LEO wouldn't get immediately cold when exposed to space. Just think about it for a second. And after that plug the numbers in thermodynamic calculator. You'll see your error.
I already did before previous comment. I was also considering adding "don't forget evaporative cooling for human bodily fluids" to previous comment, but it seemed an irrelevant tangent to discussing data centres.
Now, if you plug the mass of a human and the specific heat capacity of water into a thermodynamic calculator, tell me how long it would take for a human to cool one degree?
https://www.wolframalpha.com/input?i=%2870+Kg+*+%28specific+...
And that's with the 1 kW radiative losses from being in shadow far enough from Earth to not get meaningful thermal radiation from the planet itself. Even at 500 km, thermal radiation from Earth will still add 200 W/m^2. This is comparable to the thermal paint previously mentioned, whose peak emissivity (and by extension absorption) is chosen to be a different wavelength than the thermal emission of air temperature.
> >Likewise, the fact that convection exists even without the adjective "forced".
> no. Again, wrong. Non-forced convection is pretty small. Use the calculator.
I did, for both humans and GPUs, you saw the results. Humans are the wrong reference class.
In your own words, "Just think about it for a second": a human in humid 40°C air is in immediate danger because then all the sources of cooling have been blocked off. Radiation becomes balanced, I said humid to block off evaporation. Conduction and convection there have the same problem there as radiation. A GPU wouldn't have a problem with 40°C ambient, because it will still be radiating heat, conducting heat, and by conducting heat to the air specifically also convecting it away.
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