[jofer]

What really worries me is that I keep hearing "cooling is cheap and easy in space!" in a lot of these conversations, and it couldn't be farther from the truth. Cooling is _really_ hard and can't use efficient (i.e. advection-based air or water cooling) approaches and are limited to dramatically less efficient radiative cooling. It doesn't matter that space is cold because cooling is damned hard in a vacuum.

The article makes this point, but it's relatively far in and I felt it was worth making again.

With that said, my employer now appears to be in this business, so I guess if there's money there, we can build the satellites. (Note: opinions my own) I just don't see how it makes sense from a practical technical perspective.

Space is a much harder place to run datacenters.

[yabones]

Yeah, I don't see a way to get around the fact that space is a fabulous insulator. That's precisely how expensive insulated drink containers work so well.

If it was just about cooling and power availability, you'd think people would be running giant solar+compute barges in international waters, but nobody is doing that. Even the "seasteading" guys from last decade.

These proposals, if serious, are just to avoid planning permission and land ownership difficulties. If unserious, it's simply to get attention. And we're talking about it, aren't we?

[eldenring]

You should read the linked article, they talk about it there. You radiate the heat into space which takes less surface area than the solar panels and you can just have them back to back.

In general I don't understand this line of thinking. This would be such a basic problem to miss, so my first instinct would be to just look up what solution other people propose. It is very easy to find this online.

[kristianbrigman]

But heat = energy, right? So maybe we don’t really want to radiate it, but redirect it back into the system in a usable way and reduce how much we need to take in? (From the sun etc)

[PeterHolzwarth]

"space is cold"

I've always enjoyed thinking about this. Temperature is a characteristic of matter. There is vanishingly little matter in space. Due to that, one could perhaps say that space, in a way of looking at it, has no temperature. This helps give some insight into what you mention of the difficulties in dealing with heat in space - radiative cooling is all you get.

I once read that, while the image we have in our mind of being ejected out of an airlock from a space station in orbit around Earth results in instant ice-cube, the reality is that, due to our distance from the sun, that situation - ignoring the lack of oxygen etc that would kill you - is such that we would in fact die from heat exhaustion: our bodies would be unable to radiate enough heat vs what we would receive from the sun.

In contrast, were one to experience the same unceremonious orbital defenestration around Mars, the distance from the sun is sufficient that we would die from hypothermia (ceteris paribus, of course).

[zeofig]

A perfect vacuum might have no temperature, but space is not a perfect vacuum, and has a well-defined temperature. More insight would be found in thinking about what temperature precisely means, and the difference between it and heat capacity.

[DoctorOetker]

Assuming merely attitude control, sure only radiative cooling is available, but its very easy to design for arbitrary cooling rates assuming any given operating temperature:

Budget the solar panel area as a function of the maximum computational load.

The rest of the satellite must be within the shade of the solar panel, so it basically only sees cold space, so we need a convex body shape, to insure that every surface of the satellite (ignoring the solar panels) is radiatively cooling over its full hemisphere.

So pretend the sun is "below", the solar panels are facing down, then select an extra point above the solar panel base to form a pyramid. The area of the slanted top sides of the pyramid are the cooling surfaces, no matter how close or far above the solar panels we place this apex point, the sides will never see the sun because they are shielded by the solar panel base. Given a target operating temperature, each unit surface area (emissivity 1) will radiate at a specific rate, and we can choose the total cooling rate by making the pyramid arbitrarily long and sharp, thus increasing the cooling area. We can set the satellite temperature to be arbitrarily low.

Forget the armchair "autodidact" computer nerds for a minute

[teeray]

> Temperature is a characteristic of matter. There is vanishingly little matter in space. Due to that, one could perhaps say that space, in a way of looking at it, has no temperature.

Temperature: NaN °C

[pfdietz]

Temperature is a property of systems in thermal equilibrium. One such system is blackbody radiation, basically a gas of photons that is in thermal equilibrium.

The universe is filled with such a bath of radiation, so it makes sense to say the temperature of space is the temperature of this bath. Of course, in galaxies, or even more so near stars, there's additional radiation that is not in thermal equilibrium.

[fulafel]

Related: what color is space?

[vessenes]

Jusssst had this conversation two nights ago with a smart drunk friend. To his credit when I asked "what's heat?" and he said "molecules moving fast" and I said "how many molecules are there in space to bump against?" He immediately got it. I'm always curious what ideas someone that isn't familiar with a problem space comes up with for solutions, so I canvased him for thoughts -- nothing novel, unfortunately, but if we get another 100 million people thinking about it, who knows what we'll come up with?

[BobaFloutist]

I got really annoyed when I first realized that heat and sound (and kinetic energy) are both "molecules moving," because they behave so dramatically differently on a human scale.

And yes, obviously they aren't moving in the same way, but it's still kind of weird to think about.

[fanf2]

This article assumes that no extra mass is needed for cooling, i.e. that cooling is free. The list of model assumptions includes:

• No additional mass for liquid cooling loop infrastructure; likely needed but not included

• Thermal: only solar array area used as radiator; no dedicated radiator mass assumed

[Yizahi]

Author also forgot batteries for the solar shade transition period and then additional solar panels to charge these batteries during the solar "day" period. then insulation for batteries. Then power converters and pumps for radiators and additional radiators to cool the cooling infrastructure.

Overall not a great model. But on the other hand, even an amateur can use this model and imagine that additional parts and costs are missing, so if it's showing a bad outlook even in the favorable/cheating conditions for space DCs, then they are even dumber idea if all costs would be factored in fully. Unfortunately many serious journalists can't even do that mental assumption. :(

[davedx]

Yeah that's just flat out wrong then: you can't use the solar array as a radiator.

[pavon]

Cooling isn't anymore difficult than power generation. For example, on the ISS solar panels generate up to 75 W/m², while the EATCS radiators can dissipate about 150 W/m².

Solar panels have improved more than cooling technology since ISS was deployed, but the two are still on the same order of magnitude.

[Nevermark]

So just 13.3 million sq. meters of solar panels, and 6.67 million sq. meters of cooling panels for 1 GW.

Or a 3.651 km squared and 2.581 km squared butterfly sattelite.

I don't think your cooling area measures account for the complications introduced by scale.

Heat dissipation isn't going to efficiently work its way across surfaces at that scale passively. Dissipation will scale very sub-linearly, so we need much more area, and there will need to be active fluid exchangers operating at speed spanning kilometers of real estate, to get dissipation/area anywhere back near linear/area again.

Liquid cooling and pumps, unlike solar, are meaningfully talked about in terms of volume. The cascade of volume, mass, complexity and increased power up-scaling flows back to infernal launch volume logistics. Many more ships and launches.

Cooling is going to be orders of magnitude more trouble than power.

How are these ideas getting any respect?

I could see this at lunar poles. Solar panels in permanent sunlight, with compute in direct surface contact or cover, in permanent deep cold shadow. Cooling becomes an afterthought. Passive liquid filled cooling mats, with surface magnifying fins, embedded in icy regolith, angled for passive heat-gradient fluid cycling. Or drill two adjacent holes, for a simple deep cooling loop. Very little support structure. No orbital mechanics or right-of-way maneuvers to negotiate. Scales up with local proximity. A single expansion/upgrade/repair trip can service an entire growing operation at one time, in a comfortable stable g-field.

[wmf]

None of it is easy but neither is cooling impossible as many people are saying.

[cmgbhm]

Doing like an 8xh200 server (https://docs.nvidia.com/dgx/dgxh100-user-guide/introduction-...) is 10.2kW.

Let’s say you need 50m^2 solar panels to run it, then just a ton of surface area to dissipate. I’d love to be proven wrong but space data centers just seem like large 2d impact targets.

[mjhay]

There’s a big difference between “impossible” (it isn’t) and “practical” (it isn’t).

[jmyeet]

I've done some reading on how they cool JWST. It's fascinating and was a massive engineering challenge. Some of thos einstruments need to be cooled to near absolute zero, so much so that it uses liquid helium as a coolant in parts.

Now JWST is at near L2 but it is still in sunlight. It's solar-powered. There are a series of radiating layer to keep heat away from sensitive instruments. Then there's the solar panels themselves.

Obviously an orbital data center wouldn't need some extreme cooling but the key takeaway from me is that the solar panels themselves would shield much of the satellite from direct sunlight, by design.

Absent any external heating, there's only heating from computer chips. Any body in space will radiate away heat. You can make some more effective than others by increasing surface area per unit mass (I assume). Someone else mentioned thermoses as evidence of insulation. There's some truth to that but interestingly most of the heat lost from a thermos is from the same IR radiation that would be emitted by a satellite.

[Turskarama]

The computer chips used for AI generate significantly more heat than the chips on the JWST. The JWST in total weighs 6.5 tons and uses a mere 2kw of power, which is the same as 3 H100 GPUs under load, each of which will weight what, 1kg?

So in terms of power density you're looking at about 3 orders of magnitude difference. Heating and cooling is going to be a significant part of the total weight.

[IncreasePosts]

Who says that?

Every conversation I've seen is despite how many serious organizations with talented people, the "uhhh how do you cool it?" Is brought up immediately

[BobbyTables2]

Indeed. If cooling in space was that easy then we would have just built datacenters in hermetically sealed terrestrial containers…

[moralestapia]

Maybe hang out with different people?

Everyone I talked to (and everyone on this forums) knows cooling is hard in space.

It is always the number one comment on every news piece that is featured here talking about "AI in space".

[renewiltord]

For some decades now I’ve heard the debunk many times more than the bunk. The real urban myth appears to be any appreciable fraction of people believe the myth.

[noosphr]

Space hardware needs to be fundamentally different from surface hardware. I don't mean it in the usual radiation hardenrining etc, but in using computing substrates that run over 1000c and never shut down. T^4 cooling means that you have a hell of a time keeping things cool, but keeping hot things from melting completely is much easier.

[baq]

if you have a compute substrate at 1300K you don't have a cooling problem - you have an everything else problem

[davedx]

I think the point is, yes, cooling is a significant engineering challenge in space; but having easy access to abundant energy (solar) and not needing to navigate difficult politically charged permitting processes makes it worthwhile. It's a big set of trade offs, and to only focus on "cooling being very hard in space" is kind of missing the point of why these companies want to do this.

Compute is severely power-constrained everywhere except China, and space based datacenters is a way to get around that.

[TheOtherHobbes]

Of course you can build these things if you really want to.

But there is no universe in which it's possible to build them economically.

Not even close. The numbers are simply ridiculous.

And that's not even accounting for the fact that getting even one of these things into orbit is an absolutely huge R&D project that will take years - by which time technology and requirements will have moved on.

[panick21_]

The idea that its faster and cheaper to launch solar panels then get local councils to approve them is insane. The fact is those Data Center operates simply don't want to do it and instead want politicians to tax people to build the power infrastructure for them.

[terminalshort]

But space isn't actually cold, or at least not space near Earth. It's about 10 C. And that's only about a 10 C less than room temperature, so a human habitable structure in near earth space won't radiate very much heat. But heat radiated is O(Tobject^4 - Tbackground^4), and a computer can operate up to around 90C (I think) so that is actually a very big difference here. Back of the envelope, a data center at 90C will radiate about 10x the heat that a space station at 20C will. With the massive caveat that I don't know what the constant is here, it could actually be easy to keep a datacenter cool even though it is hard to keep a space station cool.

[uplifter]

It's actually only about 3x.

As you intimated, the radiated heat Energy output of an object is described by the Stefan-Boltzmann Law, which is E = [Object Temp ]^4 * [Stefan-Boltzmann Constant]

However, Temp must be in units of an absolute temperature scale, typically Kelvin.

So the relative heat output of a 90C vs 20C objects will be (translating to K):

383^4 / 293^4 = 2.919x

Plugging in the constant (5.67 * 10^-8 W/(m^2*K^4)) The actual values for heat radiation energy output for objects at 90C and 20C objects is 1220 W/m^2 and 417 W/m^2

The incidence of solar flux must also be taken into account, and satellites at LEO and not in the shade will have one side bathing in 1361 W/m^2 of sunlight, which will be absorbed by the satellite with some fractional efficiency -- the article estimates 0.92 -- and that will also need to be dissipated.

The computer's waste heat needs to be shed, for reference[0] a G200 generates up to 700W, but the computer is presumably powered by the incident solar radiation hitting the satellite, so we don't need to add its energy separately, we can just model the satellite as needing to shed 1361 W/m^2 * 0.92 = 1252 W/m^2 for each square meter of its surface facing the sun.

We've already established that objects at 20C and 90C only radiate 1220 W/m^2 and 417 W/m^2, respectively, so to radiate 1252 W per square meter coming in from the sun facing side we'll need 1252/1220 = 1.026 times that area of shaded radiator maintained at a uniform 90C. If we wanted the radiator to run cooler, at 20C, we'd need 2.919x as much as at 90C, or 3.078 square meters of shaded radiator for every square meter of sun facing material.

[0] Nvidia G200 specifications: https://www.nvidia.com/en-us/data-center/h200/

[modeless]

The temperature that you raise to the fourth power is not Celsius, it's Kelvin. Otherwise things at -200 C would radiate more heat than things at 100 C. Also the temperature of space is ~3 K (cosmic microwave background), not 10 C.

[ithkuil]

Pressure matters