Comment by lopsotronic
7 hours ago
For real. It's an enormous problem solved only with 1) sheer scale, and 2) Science Fiction.
Both of those are expensive as hell, by the way.
Cooling via radiation follows Stefan–Boltzmann: P = εσAT⁴. Let's assume a good surface (emissivity ~0.9) at 300 K (27 °C) at 400 W per square meter per side. A flat panel radiating from both faces into deep space gets 800 W/m, not including the losses from, say, the Sun, or from IR coming off the Earth. Now, input power. Sunlight in orbit ~1,360 W/m², assume ~22% cell efficiency, we got 300 W/m². So each 1 MW compute, 3,300 m² of solar panel and minimum 1,200–1,500 m² of radiator.
In case ya didn't know - 1 MW is tiny from a present-day-datacenter perspective. It's like 8 racks. So we're talking orbital megastructures here, many many many square kilometers, and this is with all the best case assumptions, and magic radiator panels that never see the sun, or the earth, or the moon.
This is just the basic numbers here, by the way. There's a garbage truck full of other unsolvable problems if you poke your head in there.
Aside from the "Avoid Regulations" aspect, and the "Everything That Burns Deorbiting is Depreciation" aka "The Starlink Trick", I'm not sure what the hell the draw is.
Cooling in space is hard but not impossible - while current (IMHO stupid without advanced in space infra) space data center projects work with a couple MW, many advanced space propulsion concepts might have to reject hundreds of MW if not a couple GW.
For that you might need more advanced stuff like liquid droplet radiators (https://en.wikipedia.org/wiki/Liquid_droplet_radiator), heat sinks & pulsed operation. Still, it should be eventually doable.
As for space data centers - I think the main issue is the complete lack of in space infrastructure for resource mining, processing and manufacturing & maintenance. It is kinda like building your first practical steam locomotive & the deciding to build directly an airliner. No suitable materils, experience, work force, material sources, etc.
We eventually went from locomotives to airliner, in an incremental manner & expanding the supporting infrastructure to support the ever more ambitious projects.
It might be eventually doable, as an experiment or as a flex, sure. But it's never going to come close to being cost-reasonable versus the equivalent infrastructure here on earth.
> But it's never going to come close
never? I doubt that.
Technology will improve over time. Eventually I bet it will become cheaper.
Have you tried building in the U.S.? Why do you think it's so expensive to build in the U.S.? It's due to regulation and red tape.
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The security advantages are enormous since access to space is so tightly restricted and controlled, compared to the access potential of a land based data center. Only risk in space is maybe we start WWIII with china and the US directly trading blows. On the ground, any insurgent group can disable your infrastructure. Nothing is truly safe on the surface of the earth. Anyone can strap a bomb on a drone now. See examples from the currently active wars.
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According to Wikipedia this reduces weight and not the required area. Also AI said the same thing, but I can't trust in it this blindly. So, how smaller would be the required surface area?
> Now, input power. Sunlight in orbit ~1,360 W/m², assume ~22% cell efficiency, we got 300 W/m². So each 1 MW compute, 3,300 m² of solar panel and minimum 1,200–1,500 m² of radiator.
We need > 2x more solar panels than we need radiators. Doesn't this imply radiation isn't really the limiting factor here?
Getting the energy back from the solar panel is easy via copper cables. Getting the heat back out there to the radiators is a bit harder, you needed fluids and pumps and heat exchangers which have lots of moving parts and need maintenance.
This has all been covered over and over again. It’s actually not that big of a deal
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Glad you are on the case before these companies foolishly waste their money sending datacenters to space.
Radiating 1MW at 500K (227C) with a 0.4MW heat pump takes about 200 m^2 flat sheet surface. Inputs - solar+nuclear for double fun. So - quite feasible.
Moves 1 MW of heat with 0.4 MW of work? I.e. 2.5 COP {coefficient of performance). That's insane, and I mean that in a good way. Could you dig me up a cite for that?
That's thumping the Carnot limit: [[T_cold / (T_hot − T_cold)]].
2.5, while rejecting at 500 K, cold side's at least 357 K (eeehhhhhhh 84 °C) . . . and that's an absolutely perfect Carnot machine. At 50% Carnot -- a pretty good heat pump, real world performance is 40-60 -- cold side's at 417 K (144 °C). 417k, feeding your GPU coolant loops.
And if you look at SpaceX's Starmind sats, they will have a 160 m^2 liquid radiator for 175kw/250kw peak compute.
Do we even _have_ semiconductors that can work at 220C? And if you're thinking about using some kind of refrigeration cycle, its efficiency is going to be bad.
1) The chips don't reach 220C. The 220C is the temperature at the hot end of the heat pump. The chips are on the cold end of the heat pump.
2) The International Space Station has used a dual-loop ammonia/water-based heat pump to cool the station temperatures. It's been in place for several decades. Heat pumps are a proven technology.
Other satellites have also used heat pumps, such as SES-17 in geostationary orbit https://www.esa.int/Applications/Connectivity_and_Secure_Com...
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Getting this all up into orbit it obviously the hard part, but if you're already building so much solar capacity the cooling actually doesn't seem unreasonable?
Surface area is a materials problem? Folded microstructure, atomic-scale textured surface or some other science-fiction solution could have square kilometers of surface area in a shoebox.
Imagine you have two blackbody radiators with the same bulk properties, except one has surface area shenanigans like aerogels. In the far field as a whole, it seems like both should radiate essentially the same regardless of the internal details. You can shape emissive direction, or improve efficiency of non-ideal materials, but even ideal materials don't fix the issues pointed out by the parent.
It needs to be facing open space instead of other parts of itself, otherwise the radiation is just reabsorbed.
Great read, thanks for sharing. I am interested in reading some more about the other unsolvable problems that exist in this space, do you have any recommendations that you wouldn't mind pointing me at? It would be greatly appreciated, and thank you :)
Is it possible for one side of panel to be used for solar power and other side for radiating heat?
Wouldn't this be solved like similar problems on earth by making small structures with large surface areas?
I don't think so. Large surface area helps with convective cooling I think by increasing the surface area that participates in heat exchange with the air (or other thermally conducting material), radiative cooling wouldn't benefit from this because you can't concentrate light beyond the source that it's emitted from (etendue).
Though I do wonder if it would be possible to have some kind of internal heat pump driven by electrical power to juice up the temperature of the radiators to increase the power being radiated away? E.g., run a heat pump to increase the temperature of a working fluid and then run high temperature radiators? I think it would work and I don't immediately see that it would violate the laws of thermodynamics? (this is ignoring all practically, I'm sure the engineering would be devilishly hard, although if you're already shooting for the moon you might as well throw in some artificial gravity to boot, it's not like the robots get motion sickness)
You can use heatpumps to increase radiator temperature but then you need a heatpump and need to power it. But the principle is sound.
Don’t you get 4 faces to radiate away, assuming a long rectangular tube.
It would be a shame if a rock came out of nowhere and hit that many square kilometers stucture
Luckily, there are almost no rock in space.
Almost no rocks, but they're going 10 to 30 km/s
I assume the kilometer-size array would not be series-wired.
there are two arguments for it.
one is marketing.
the other is that you could make tiny datacenters and flood the sky with them. in effect, not datacenters at all, but some kind of dataswarm coordinating at literal lightspeed via lasers.
they'd still be wildly expensive to deploy, and probably litter the orbit zone with fast-moving debris.
Your "other" makes no sense. It doesn't matter if you make a few big or a lot smaller, in space you will still need the same space for the same amount of megawatt. Or did you miss the scale of parent's post ? Because in that dream scenario of "let's ignore all the issues except that" and "the earth and the sun don't have any impact", it's still 3 THOUSANDS square meters for a MW of 8 racks.
You want to go smaller and go one rack only sure, it's still hundreds of square meters. Check the size of current orbital structure for a point of reference, you can't dwarf those and call it a "dataswarm of tiny datacenters flooding the sky".