Comment by ben_w
19 hours ago
My draft blog post about all the things that are up with space data centres keeps getting bigger and bigger.
"The other half of the MS model is data centres. “Orbital compute deployments” start in 2028, reach cost parity with their earthbound equivalents by 2031, and put 364GW of rigs in space by 2040."
With 25% efficient cells, at 500 km altitude, in a terminator-tracing SSO, this is enough to occupy a *contiguous* ring roughly 25 m tall, all the way around that orbit.
Also, from other statements they're clearly copying Alphabet's study which said cost parity in 2035, if they can actually launch 370,000 tons and maintain their learning rate.
https://arxiv.org/pdf/2511.19468
"A $668bn funding obligation to 2034 that delivers free cash flow that year of negative $48bn sounds less than ideal, though FCF might flip positive to $138bn in 2035 if everything goes to plan, so that’s nice. The SpaceX CEO presumably has a long history of delivering products on time and to the required specification that can support such confidence."
I love the snark here.
"Helium-3 is one of the clearest examples of why lunar infrastructure could matter. The isotope is extremely rare on Earth, with current supply largely tied to tritium decay, but the Moon has accumulated helium-3 for billions of years because it lacks Earth’s atmosphere and magnetic field. NASA mining concepts often assume concentrations around 20 parts per billion, meaning helium-3 is abundant in total but painfully diffuse, requiring hundreds of tons of regolith to be mined and heated to recover small quantities."
Ugh. This will need a separate blog post for why it's stupid. At 20 ppb, even if we could fuse He3, that makes lunar regolith marginally less energy dense than firewood. Also, anyone with a fusion reactor can make He3, even highschool students with home-made fusors can already do this. I'll have to check sources and maths to make sure I've not missed something important about which would be cheaper, *currently existing* neutron sources like fusors or going to the moon, but regardless, we can't currently use this stuff for fusion and the moment we can we won't need to mine it.
(I have not yet formed an opinion about non-fusion uses for He3).
I just skimmed that linked paper. Only mention I found of cooling is:
> Cooling would be achieved through a thermal sys- tem of heat pipes and radiators while operating at nominal temperatures.
Isn't that drastically underselling potentially one of the harder parts of this whole endeavor?
> Isn't that drastically underselling potentially one of the harder parts of this whole endeavor?
Everything in space is hard; but these are Alphabet researchers not NASA researchers, and honestly even the NASA papers I've been skimming through have a lot of simplifying assumptions in them, so that's not something to hold against them here.
They are just saying when they think it's worth considering, after all, not giving a detailed all-aspect proposal for how to make one.
I view articles like that as a kind of roleplaying, essentially. The authors are pretending to be space hardware engineers, but the results are not remotely realistic.
Very drastically, the ISS solar panels can generate up to 120kW of power, look at the size of its radiators needed to cool it down.
Scaling that to the hundreds of GW range is quite laughable.
https://x.com/SawyerMerritt/status/2064108916611420273?lang=...
While I'd suspect the design is still in flux, the current design is for a 120kw satellite with 110 square meters of radiators. Scaling to hundreds of gigawatts is intended to be by repeatedly launching smaller designs.
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I'm not very informed on SpaceX plans, but one thing I think people gloss over is how much maintenance a data center requires. Parts fail, computers get stuck on crash loops, etc. A space data center would need workers - computer people, not astronauts - and a constant supply of parts tob replace hardware. Whoever wrote this proposal doesn't understand neither space nor data centers.
Is a data center satellite really that different from a communications satellite? Starlink sats must have some significant processing power and nontrivial control system, and they work without physical maintenance. One data center sat is like one server rack, if it fails, it's fully lost and you just deorbit it, as it's done with Starlink sats. They sent 12443 Starlink sats to space, deorbited 1684. The thing that matters is failure rate, and the economics resulting from that. And also the cost of specialized resilient hardware.
Communications satellites don't have nearly as much long-term rewritable storage needed.
I'm also writing a blogpost on orbital datacentres, maybe we should compare notes!
Dotnetrocks did an excellent breakdown https://www.dotnetrocks.com/details/2007
He3 is needed as a cryogenic for quantum systems, not fusion fuel.
As I understand it, He3 is also used in nuclear materials detectors.
Morgan Stanley list both.
Not a coincidence that both technologies aren’t going to live up to the proponents’ claims, and both want materials we don’t really have.
The cost of fuel is not the problem. We have unlimited uranium and thorium, and there is no reason a fusion should be cheaper. Sure its more dense then fission but fission is absurdly dense already and the economics don't improve that much.
The idea that it makes sense to use moon based He3 compared to using thorium that is already mined in waste quantities is absurd. Thorium is free energy already and the machine that turns it into energy is simpler the any fusion reactor we can come up with.