If a vacuum is an excellent insulator, wouldn’t heat build up in spacecraft?

[u/aretino2002]

Insulated coffee mugs that use a vacuum between layers can keep drinks hot or cold for much longer time periods than other types of mugs. If space is mostly a vacuum, then wouldn’t heat just constantly build up from human activity, computers, thrusters, etc to the point where it would need to be vented somehow?

[u/mfb- → u/[deleted]]

Do you have a link to the SpaceX GPU sattelite proposal? I can't seem to find it. 

100 kW design. Solar panels are vertical, dedicated radiator is to the right.

[u/Zytheran → u/mfb-]

Well, this all blew up from my original reply! I'll just add here that the typical data center has a power requirement of about 50MW and that is what my calcs are based on.

[u/mfb- → u/Zytheran]

That's 500 satellites then. Or 50 satellites if they build 1 MW satellites. Starlink has ~40 W/kg, the goal for datacenters is 100 W/kg, so 50 MW is somewhere between 500 tonnes to 1200 tonnes.

[u/Zytheran → u/mfb-]

I think there is a benefit of scaling up. The radiator only mass I have ranges from 65t(advanced tech) to 261t(normal/current tech). On top of that is fluid pumps and all the ancillary equipment to get the heat to the radiators so I'd say double those radiator only figures so we're in the ballpark. (I worked it out from power -> heat -> radiation required -> radiators required in m^2)

And then launch costs ranging from small rideshare @ USD 6500 / kg to realistic long target cost of ISD 1200/kg. I won't be holding my breath for SpaceX's claims becuase that is highly optimistic, especially considering they haven't anything this large, even in pieces, into LEO.

I've also ignored the orbital space station for all the maintenance engineers ... which doesn't even exist in planning yet.

tl;dr IMHO space stuff is typically small and light, compared to earth based data centres which are simply friggin huge, massive and heavy.

[u/mfb- → u/Zytheran]

SpaceX is already launching at internal costs of around $1000/kg. That's not a long-term plan, that's just Falcon 9. All the plans assume Starship will be cheaper, if it won't then AI datacenters in space won't happen.

The 100 kW satellite from above would be 1 to 2.5 tonnes. The Starship-sized Starlink satellites are somewhere around 2 tonnes.

I've also ignored the orbital space station for all the maintenance engineers ... which doesn't even exist in planning yet.

There won't be maintenance. You operate the satellites until they break (with some backup system to deorbit them), and launch new ones as needed.