Taking a system which was conceptualized about a quarter of a century ago and serves much different needs than what a datacenter in space needs (e.g. very strict thermal band, compared to acceptable temperature range from 20 to 80 degrees) isn't ideal.

The physics is quite simple and you can definitely make it work out. The Stefan Boltzman law works in your favor the higher you can push your temperatures.

If anything a orbital datacenter could be a slightly easier case. Ideally it will be in an orbit which always sees the sun. Most other satellites need to be in the earth shadow from time to time making heaters as well radiators necessary.

That exactly. It's not that it's impossible. It's that it's heavy to efficiently transport heat to the radiators or requires a lot of tiny sats, which have their with problems.

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

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, except those for their own heat.

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)

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.

I think otherwise.

I saw that too but wonder if it's different for the sparse matter in the interstellar medium, excluding the visible objects.

That proposal I've seen a few times too, basically put up a constellation up there, linked with laser comms and then transfer data to the illuminated sats in a loop. That sounds possible, but I have doubts. First of all if we take 400 km orbit, the "online" time would be something like 50 minutes. We need to boot up the system fully, run comm apps, locate a peer satellite and download data from it (which needs to be prepared in a portable form), write it locally and start calculations, then by the end of the 50 min repeat. All these operations are slow, especially boot time of the servers (which could be optimized of course). It would be great if some expert could tell us if it is feasible or not.

You can use everything as a radiator, but you can't use everything as a radiator sufficiently efficient to cool hot chips to safe operating temperature, particularly not if that thing is a thin panel intentionally oriented to capture the sun's rays to convert them to energy. Sure, you can absolutely build a radiator in the shade of the panels (it's the most logical place), but it's going to involve extra mass.

You can rivet people onto the outside of the ISS to radiate heat, too, but it may be detrimental to the overall system.

> Could the compute be distributed instead?

For electrons that would dramatically increase latency, and lower bandwidth, slowing down compute.

Maybe dense optical connects could work?

It's easier to shield the GPUs if they're all grouped up.

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.

You need 50sqm of solar panels just for a tiny 8RU server. You also forgot any overhead for networking, control etc. but let's even ignore those. Next at the 400km orbit you spend 40% of the time in shade, so you need an insulated battery to provide 5kWh. This would add 100-200kg of weight to a server weighing 130kg on its own. Then you need to dissipate all that heat and yes, 50sqm of radiators should deal with the 10kW device. We also need to charge our batteries for the shade period, so we need 100sqm of solar panels. And we also need to cool the cooling infrastructure - pumps, power converters, which wasn't included in the power budget initially.

So now we have arrived to a revised solution: a puny 8RU server at 130 kg, requires 100sqm and 1000 kg of solar panels, then 50-75 sqm of the heat radiators at 1000-1500 kg, then 100-200 kg of batteries and then the housing for all that stuff plus station keeping engines and propellant, motors to rotate all panels, pumps, etc. I guess at least 500kg is needed, maybe a bit less.

So now we have a 3 ton satellite, which costs to launch around 10 million dollars at an optimistic 3000/kg on F9. And that's not counting cost to manufacture the satellite and the server own cost.

I think the proposal is quite absurd with modern tech and costs.

Especially if with the radiators you can just roll out as rolls of aluminum foil, which is very light and very cheap.

Maybe you should re-read the "do things that don't scale" article. It is about doing things manually until you figure out what you should automate, and only then do you automate it. It's not about doing unscalable things forever.

Unless you have a plan to change the laws of physics, space will always be a good insulator compared to what we have here on Earth.

The transistors are experimental, and no one is building high-performance chips out of them.

You can't just scale current silicon nodes to some other substrate.

Even if you could, there's a huge difference between managing the temperature of a single transistor, managing temps on a wafer, and managing temps in a block of servers running close to the melting point of copper.

Lift costs are not quite dropping like that lately. Starship is not yet production ready (and you need to fully pack it with payloads, to achieve those numbers). What we saw is cutting off most of the artificial margins of the old launches and arriving to some economic equilibrium with sane margins. Regardless of the launch price the space based stuff will be much more expensive than planet based, the only question if it will be optimistically "only" x10 times more expensive, or pessimistically x100 times more expensive.

I don't get this "inevitable" conclusion. What is even a purpose of the space datacenter in the first place? What would justify paying an order of magnitude more than conventional competitors? Especially if the server in question in question is a dumb number cruncher like a stack of GPUs? I may understand putting some black NSA data up there or drug cartel accounting backup, but to multiply some LLM numbers you really have zero need of extraterritorial lawless DC. There is no business incentive for that.

He didn't use 20C as the temperature of space. He used the OP's example of comparing the radiative cooling effectiveness of a heat SOURCE at 90C (chosen to characterize a data center environment) and 20C (chosen to characterize the ISS/human habitable space craft).

The background temp at Earth's orbit is due to the incidence of solar flux, which I took account of.

I'm assuming the radiators are shaded from that flux by the rest of the satellite, for efficiency reasons, so we don't need to account for solar flux directly heating up the radiators themselves and reducing their efficiency.

In the shade, the radiators emission is relative to the background temp of empty space, which is only 2.7 K[0]. I did neglect to account for that temperature, that's true, but it should be negligible in its effects (for our rough estimate purposes).

[0] https://sciencenotes.org/how-cold-is-space-what-is-its-tempe...

These satellites will certainly be above the themosphere. The temperature of the sparse molecules in space is not relevant for cooling because there are too few of them. We're talking about radiative cooling here.

The Sun is also not 10 C. Luckily you have solar arrays which shade your radiators from it, so you can ignore the direct light from it when calculating radiator efficiency. The actual concern in LEO is radiation from the Earth itself.