Comment by utopiah
4 hours ago
> space compute
Heard anybody remotely competent about space talk the topic? It's pretty much a literal laugh every time.
4 hours ago
> space compute
Heard anybody remotely competent about space talk the topic? It's pretty much a literal laugh every time.
Some of the proposals are laughable, some of the example calculations are. The idea of running AI training sounds extremely challenging. But the idea of inference in space doesn't seem absurd
The power budget of a starlink v2 mini satellite is estimated at around 20kW based on the known solar panel size. That also matches what a satellite of that size would roughly dissipate without dedicated radiators, using just some heat pipes to spread the heat evenly over the satellite's surface. There is nothing fundamentally preventing you from taking the same satellite design, remove most of the comms payload and instead put 15kW of GPUs there. Or about 10 GB200 including the CPUs, networking, etc that you need along with the GPUs
Now, do the economics work out for $300k worth of compute for each satellite, in an environment where maintenance is impossible and degradation will be higher than on the ground? Probably not right now, but in a couple years they might
The starlink satellites have hall effect thrusters, and presumably beefy laser and radio comms systems that will account for a lot of the energy budget. Also, they are sometimes in the earth's shadow, a naive calculation says they have 2x the solar budget they need, in order to charge up batteries for shade-time operations. There is no where near 20kw of compute in a single satellite, and thus no where near 20kw of heat to get rid of.
Furthermore, xAI's colossus supercomputer is specced at 250MW. And this seems to be a number that'll just increase over the coming years with new bigger DCs.
To match this level of performance they will have to launch what, ~15k satellites _per_ equivalent datacentre?
Regarding cooling: you can't just cover the outer surface with pipes. You cant't dissipate the heat, you need to _radiate_ it away. You need to point that surface to the deep dark cold of space. If you point it to the sun, you will heat your satellite. Think a massive "reverse solar panel" that works with infrared. You need surface area, and loads of it.
I'm not saying this is impossible. Obviously elon will prove us all wrong because he's stubborn like that. But there is no way this will ever be economically viable when competing with terrestrial based systems.
The assumption behind "spread the heat over the size of the satellite" is radiative cooling. Admittedly my numbers were a bit off, you need to make the satellite a bit bigger, or use some of your solar panels. A starlink v2 mini has 8m² of area per side, so 16m² total. To dissipate 20kW to space, at a surface temperature of 80°C and emissivity of 0.85, you need about 28m² of space. So you need to increase size a bit, or add 12m² of dedicated radiators. A bit more to deal with the real live complications (the sun exists, the earth is actually warmer than space and covers a significant portion of the sky if you are in leo, etc.).
The actual Starlink V2 Mini is has estimates for solar generation that range up to 35kW. We need a bit more, but not much more.
My numbers are a bit optimistic, but they are in the right order of magnitude. Power and cooling are very achievable in the area of putting one server on one satellite. It's the "putting one DC on one mega satellite" ideas that run into feasability issues, and for inference those aren't needed. The economics are the bigger issue, and launch costs are only moving in one direction
The terrestrial based systems getting protested, blocked, and demonized everywhere? Those ones?
How is this not absurd? What is the benefit? Space is a harsh environment, with issues due to solar radiation etc, etc. And it's permanently 100ms away from any user.
Tl;dr — but it’s too heavy
You’re making some decent points here, but you’re either forgetting or ignoring the major thing that people usually neglect to mention when they want to make a case for this (crazy) idea — weight. Unless SpaceX is going to completely redesign hardware such that it is optimized entirely for its mass, it requires many (many) launches to even get a small set of racks into space. I don’t normally get up in arms about the CO2 emissions of data centers, I think there is offsetting value created by their use, but I would absolutely protest trying to put data centers in space and do my best to shut down the hundreds, if not thousands of launches it would take to achieve even a tiny fraction of an AI data center.
Have you calculated the CO2 output of Terran datacenters run on natural gas vs. space datacenters run on solar? The launch CO2 usage is one time, the datacenter energy is for the life of the equipment.
It is absolutely baffling to me how frequently I hear people talk about this around me. There is no way this is happening anytime in the near future.
But if the US isn’t the first to put an AI on the moon, we’ll lose the AI space race!
Mr. President, we must not allow a mine-shaft gap!
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You don't have to actually have an orbiting datacenter for the idea to work. You just have to convince enough people. Once you've done that, you can claim that regional regulations don't apply to your data because the data is in orbit. Its not like somebody is gonna go up there and catch you in the lie.
Out-of-regulatory-reach is what they'll actually be selling. It can be on earth, it just has to be sufficiently hidden such that you can claim that it's in space.
I don't think that's the purpose and if it is, it's obviously trivially solvable. The US can and does simply assert jurisdiction all over the globe. There's no reason it can't or wouldn't extend that to orbit.
That conversation goes like this:
US: Stop doing that thing with your data center
X: It's in space, you can't tell us what to do
US: Yes we can
X: <Say OK> or <Go to jail>
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The US already claims jurisdiction on all launches from US and NZ (Rocket Lab). Every one of these had to get approval from the US to launch.
While I agree with you on the merit of the idea, rockets that can take off and then land vertically without damage were also laughable pre-SpaceX.
NASA had literally done it. It was never laughable, just thought to be an incredibly difficult engineering challenge.
I think compute in space suffers less from being "impossible" and more from being "impractical". It is plenty easy to put compute in space. It is just still silly expensive and by the time your equipment makes up the cost of putting it in space, it will be well out of date.
The non-deterministic nature of LLMs will get a whole lot more fun when we add randomly flipping bits to the situation.