[amluto]

That cooling system is … aggressive. 110m^2 of radiator to dissipate 120kW average heat. That’s about 1.1kW/m^2, which works out to very close to 100C at the radiator under absolutely perfect conditions (absolute zero ambient temperature, emissivity 1, no adverse geometric effects).

Radiating into 300K ambient, it’s 134C. (300K ambient is about what you get if the sun is visible or if a large fraction of what the radiator can see is the Earth.)

You can slightly fudge the 300K case with a spatially or specially selective system, which would add weight and complexity. (Well, you can’t get rid of the problem of the Earth being warm by spectral selectivity — it’s the same spectrum as the radiator.) You cannot fudge the absolute zero case — the Stefan-Boltzmann law is extremely unforgiving. [0] And you need some headroom for the system that gets the cooling fluid to the radiator.

The thermal qualification temperature of an H100 is 87C and the associated HBM is 95C.

So I don’t see how this can work short of using higher-temp chips. I have no idea how SpaceX expects to source any such thing in any meaningful volume.

[0] This includes heat pumps. A heat pump makes it worse.

[yread]

Maybe they count them twice? That would work out to 41C if both sides are in shade (or 69C if one is shaded and one on the sunny side)

[hparadiz]

I assume the radiators will be in the shadow behind the solar panels and never facing the sun. That's seems like the easiest quick win.

[amluto]

This isn’t that big a win. If you put the radiator in the shadow of the solar panels then a good fraction (which depends on the geometry) of the radiated heat from the side facing the panels hits the panels and warms the panels, and the radiated heat from the back of the panels warms the radiator. And the panels themselves are less efficient when they’re warmer.

On the flip side of all this, the Starlink satellites work, and I would expect SpaceX to have some idea what they’re doing. Starlink satellites have largish power systems (smaller than these proposed AI satellites, but not outrageously so). They presumably turn a smaller fraction of their power into low-temperature heat: the ion thrusters and the various transmitters emit a good deal of non-thermal power. A good fraction of Starlink’s electronics way well function at rather higher junction temperatures than 100C. And I imagine that Starlink satellites are economical to operate at an average of much less than 100% power. So I don’t really know what’s going on. It’s plausible that Starlink gets away with a cooling system that’s not so great for a compute satellite.

[fc417fc802]

Is the equilibrium temperature in orbit not somewhere between freezing and room temperature? If so spreading the heat evenly across the solar panels must necessarily be sufficient. Issues only arise if you try to get away with a smaller radiator or expose the radiator to direct sunlight or commit some other own goal.

[orwin]

The radiators then need to be protected from earth's heat/light if you want to reach 0K. I agree with GP, it doesn't seem great.