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Economics of Orbital vs. Terrestrial Data Centers

andrewmccalip.com

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Re: Economics of Orbital vs. Terrestrial Data Centers

#261

Post by Nevermark »

jaywee wrote: post #205
Nevermark wrote: post #131

Earlier quoted context omitted.

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 mor…

Well, divide et impera. Fairly straightforward for AI inference (not training): The existing Starlink constellation: 3491 V1 sats × 22.68 m² = 79176 m² 5856 V2-mini sats × 104.96 m² = 614 646 m² Total: 0.7 km² of PERC Mono cells with 23% efficiency. At around 313W/m² we get 217MW. But half the orbit it's in shade, so only ~100MW. The planned Starship-launched V2 constellation (40k V3 sats, 256.94 m²) comes out at 10…

Take those 40,000 satellites, and combine their solar panels, and combine the cooling panels, and centralize all the compute.

Distances are not our friend in orbit. Efficiency hyperscales down for many things, as distances and area scale up.

Things that need to hyperscale when you scale distance and area:

• Structural strength.

• Power and means to maneuver, especially for any rotation.

• Risk variance, with components housed together, instead of independently.

• Active heat distribution. Distance is COMPOUNDING insulation. Long shallow heat gradients move heat very slowly. What good does scaling up radiative surface do, if you don't hyperscale heat redistribution?

And you can't hyperscale heat distribution in 2D. It requires 3D mass and volume.

You can't just concatenate satellites and get bigger satellites with comparable characteristics.

Alternatives, such as distributing compute across the radiative surface, suffer relative to regular data centers, from intra-compute latency and bandwidth.

We have a huge near infinite capacity cold sink in orbit. With structural support and position and orientation stabilization for free. Let's use that.

Re: Economics of Orbital vs. Terrestrial Data Centers

#262

Post by DoctorOetker »

adrian_b wrote: post #251
DoctorOetker wrote: post #235

Earlier quoted context omitted.

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…

Making the pyramid arbitrarily long and sharp will arbitrarily diminish the heat conductance through the pyramid, so the farther from the pyramid base, the colder it will be and the less it will radiate. So no, you cannot increase too much the height of the pyramid, there will be some optimum value at which the pyramid will certainly not be sharp. The optimum height will depend on how much of the pyramid is solid and…

we are not discussing a schoolbook exercise, we are not calculating passive heat conduction of a pyramid heated to a base, since it's not a schoolbook exercise we can decide on the condition, we could put in heat pipes etc.

its CPU/GPU clusters, so we don't have 0 control on where to locate what heat generators, but even if we had 0 control over it, the shape and height of the pyramid does not preclude heat pipes (not solid bars of metal, but having a hot side where latent heat of a gas condensing to a liquid on the cold side and then evaporating on the hot side).

heat pipes have enormous thermal conductivities

Re: Economics of Orbital vs. Terrestrial Data Centers

#263

Post by DoctorOetker »

yetihehe wrote: post #244
DoctorOetker wrote: post #235

Earlier quoted context omitted.

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…

> The rest of the satellite must be within the shade of the solar panel, Problem is with solar panels themselves. When you get 1.3kW of energy per square meter and use 325w of that for electricity (25% efficiency) that means you have to get rid of almost 1kW of energy for each meter of your panel. You can do it radiatively with back surface of panels, but your panels might reach equilibrium at over 120°C, which means…

no matter how inefficient the solar panels, even with 1% efficiency, you could make the pyramid sharp enough to dissipate the heat stabilizing at any arbitrary low temperature (well, must still be above the temperature of CMB)

Re: Economics of Orbital vs. Terrestrial Data Centers

#264

Post by DoctorOetker »

adrian_b wrote: post #252
yetihehe wrote: post #244

Earlier quoted context omitted.

> The rest of the satellite must be within the shade of the solar panel, Problem is with solar panels themselves. When you get 1.3kW of energy per square meter and use 325w of that for electricity (25% efficiency) that means you have to get rid of almost 1kW of energy for each meter of your panel. You can do it radiatively with back surface of panels, but your panels might reach equilibrium at over 120°C, which means…

When the cost of the solar panels does not matter you can reach an efficiency close to 50% (with multi-junction solar cells) and the panels will also be able to work at higher temperatures. Nevertheless, the problem described by you remains, the panels must dissipate an amount of heat at least equal with the amount of useful power that is generated. Therefore they cannot have other heat radiators on their backside, e…

the point is that even with 100% INefficient solar panels the pyramidal sides can be made to have an arbitrarily large area, and due to convexity of the pyramid each infinitesimal surface element of the radiating sides can emit the full hemisphere, so given any target temperature, we can design the pyramid sharp enough (same base, different height, so that heat absorbed is constant and heat emitted must equal it in steady state, then by basic thermal radiation math, the asymptotic temperature it will settle at can be made arbitrarily close to temperature of the universe, by making the pyramid sharper.)

Re: Economics of Orbital vs. Terrestrial Data Centers

#265

Post by bigbadfeline »

Great article, with dollars and numbers as it should be.

The proponents of orbital wunderbars may have different calculations and there's only one way to resolve the differences - make them pay for their space-centers themselves, making sure no public money is spent on the project which is also required to carry zero default risk and pay regular taxes without the right to claim deductions or write-offs for any losses. All this is necessary to avoid the usual corporate tax games.

I can sketch a contract to that end in like 10 minutes. Everything else is a waste of time.

Re: Economics of Orbital vs. Terrestrial Data Centers

#266

Post by fc417fc802 »

yetihehe wrote: post #241
torginus wrote: post #226

Earlier quoted context omitted.

Out of curiosity, I plugged in the numbers - I have solar at home, and a 2 m2 panel makes about 500w - i assume the one in orbit will be a bit more efficient without atmosphere and a bit more fancy, making it generate 750w. If we run the radiators at 80C (a reasonable temp for silicon), that's about 350K, assuming the outside is 0K which makes the radiator be able to radiate away about 1500W, so roughly double. Depen…

> 2 m2 panel makes about 500w It receives around 2.5kW[0] of energy (in orbit), of which it converts 500W to electric energy, some small amount is reflected and the rest ends up as heat, so use 1kW/m^2 as your input value. > If we run the radiators at 80C (a reasonable temp for silicon), that's about 350K, assuming the outside is 0K which makes the radiator be able to radiate away about 1500W, so roughly double. 1500…

You can't just omit the 500 W of electric. That ultimately ends up as heat too.

Re: Economics of Orbital vs. Terrestrial Data Centers

#267

Post by fc417fc802 »

bee_rider wrote: post #214
zeofig wrote: post #139

Earlier quoted context omitted.

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.

I think your second sentence is what they were referencing. Space has a temperature. But because the matter is so sparse and there’s so little thermal mass to carry heat around as a result, we don’t have an intuitive grasp on what the temperature numbers mean.

To rephrase it slightly. It's not a perfect vacuum, but compared to terrestrial conditions it's much closer to the former than the latter. The physics naturally reflects that fact.

To illustrate the point with a concrete example. You can heat something with the thermal transfer rate of aerogel to an absurdly high temperature and it will still be safe to pick up with your bare hand. Physics says it has a temperature but our intuition says something is wrong with the physics.

Re: Economics of Orbital vs. Terrestrial Data Centers

#268

Post by danpalmer »

verzali wrote: post #180
danpalmer wrote: post #103

Earlier quoted context omitted.

My understanding was that anything at ~500km needed readjustments every few months in order to not come down. Much less than 2-3 years. I'd be interested to know what the average lifespan or failure rate of Starlink has been. That's good that some are still up there 6+ years later, but I know many aren't. I'm not sure how many of those ran out of fuel, had hardware failures, or were simply obsolete, but an AFR would…

The atmosphere is still thick enough to drag you down at 500km. You would last typically last a few years before burning up - the rate of fall is pretty low at 500km. But you do need fuel to do collision avoidance manoeuvres and for attitude control (otherwise your panels will no longer face the Sun and your antennas will not face the ground).

Thank you, I think it might have been collision avoidance and/or attitude control that I was thinking of then, rather than actually burning up. I remember reading about this in relation to the ISS which needs frequent adjustments, although is a bit lower than 500km.

Re: Economics of Orbital vs. Terrestrial Data Centers

#269

Post by lurquer »

JoeAltmaier wrote: post #197
TheOtherHobbes wrote: post #196

Earlier quoted context omitted.

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.

Lift costs dropping geometrically. Cost and weight of solar decreasing similarly. The trend makes space-based centers nearly inevitable. Reminds me of "Those darn cars! Everybody knows that trains and horses are the way to travel."

> Reminds me of "Those darn cars! Everybody knows that trains and horses are the way to travel."… … said nobody ever.

Re: Economics of Orbital vs. Terrestrial Data Centers

#270

Post by sawjet »

DoctorOetker wrote: post #235
PeterHolzwarth wrote: post #132

Earlier quoted context omitted.

"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…

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…

The sun is not the only radiative body in the solar system.
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