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Economics of Orbital vs. Terrestrial Data Centers

andrewmccalip.com

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Re: Economics of Orbital vs. Terrestrial Data Centers

#191

Post by Yizahi »

wmf wrote: post #81
cmgbhm wrote: post #59

Earlier quoted context omitted.

Doing like an 8xh200 server ( https://docs.nvidia.com/dgx/dgxh100-user-guide/introduction-... ) is 10.2kW. Let’s say you need 50m^2 solar panels to run it, then just a ton of surface area to dissipate. I’d love to be proven wrong but space data centers just seem like large 2d impact targets.

Yeah, you need 50m^2 of solar panels and 50m^2 of radiators. I don't see why one is that much more difficult than the other.

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.

Re: Economics of Orbital vs. Terrestrial Data Centers

#192

Post by merman »

uplifter wrote: post #160
terminalshort wrote: post #76

Earlier quoted context omitted.

But space isn't actually cold, or at least not space near Earth. It's about 10 C. And that's only about a 10 C less than room temperature, so a human habitable structure in near earth space won't radiate very much heat. But heat radiated is O(Tobject^4 - Tbackground^4), and a computer can operate up to around 90C (I think) so that is actually a very big difference here. Back of the envelope, a data center at 90C will…

It's actually only about 3x. As you intimated, the radiated heat Energy output of an object is described by the Stefan-Boltzmann Law, which is E = [Object Temp ]^4 * [Stefan-Boltzmann Constant] However, Temp must be in units of an absolute temperature scale, typically Kelvin. So the relative heat output of a 90C vs 20C objects will be (translating to K): 383^4 / 293^4 = 2.919x Plugging in the constant (5.67 * 10^-8 W…

You use arbitrary temps to prove at some temps it’s not as efficient. Ok? What about at the actual temps it will be operating in? We’re talking about space here. Why use 20 degC as the temperature for space?

Re: Economics of Orbital vs. Terrestrial Data Centers

#193

Post by noosphr »

baq wrote: post #183
noosphr wrote: post #150

Earlier quoted context omitted.

Space hardware needs to be fundamentally different from surface hardware. I don't mean it in the usual radiation hardenrining etc, but in using computing substrates that run over 1000c and never shut down. T^4 cooling means that you have a hell of a time keeping things cool, but keeping hot things from melting completely is much easier.

if you have a compute substrate at 1300K you don't have a cooling problem - you have an everything else problem

There are very high temperature transistors.

We don't use them on earth because we expect humans to be near computers and keeping anything extremely hot is a waste of energy.

But an autonomous space data center has no reason to be kept even remotely human habitable.

Re: Economics of Orbital vs. Terrestrial Data Centers

#194

Post by TheOtherHobbes »

uplifter wrote: post #170
jcattle wrote: post #166

Earlier quoted context omitted.

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…

These data centers are solar powered, right? So if they are absorbing 100% of the energy on their sun side, by default they'll be able to heat up as much as an object left in the sun, which I assume isn't very hot compared to what they are taking in. How do they crank their temperature up so as to get the Stefan Boltzmann law working in their favor? I suppose one could get some sub part of the whole satellite to a hi…

σ is such a small number in Stefan-Boltzman that it makes no difference at all until your radiators get hot enough to start melting.

You not only need absolute huge radiators for a space data centre, you need an active cooling/pumping system to make sure the heat is evenly distributed across them.

I'm fairly sure no one has built a kilometer-sized fridge radiator before, especially not in space.

You can't just stick some big metal fins on a box and call it a day.

Re: Economics of Orbital vs. Terrestrial Data Centers

#195

Post by TheOtherHobbes »

noosphr wrote: post #193
baq wrote: post #183

Earlier quoted context omitted.

if you have a compute substrate at 1300K you don't have a cooling problem - you have an everything else problem

There are very high temperature transistors. We don't use them on earth because we expect humans to be near computers and keeping anything extremely hot is a waste of energy. But an autonomous space data center has no reason to be kept even remotely human habitable.

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.

Re: Economics of Orbital vs. Terrestrial Data Centers

#196

Post by TheOtherHobbes »

davedx wrote: post #161
jofer wrote: post #39

What really worries me is that I keep hearing "cooling is cheap and easy in space!" in a lot of these conversations, and it couldn't be farther from the truth. Cooling is _really_ hard and can't use efficient (i.e. advection-based air or water cooling) approaches and are limited to dramatically less efficient radiative cooling. It doesn't matter that space is cold because cooling is damned hard in a vacuum. The artic…

I think the point is, yes, cooling is a significant engineering challenge in space; but having easy access to abundant energy (solar) and not needing to navigate difficult politically charged permitting processes makes it worthwhile. It's a big set of trade offs, and to only focus on "cooling being very hard in space" is kind of missing the point of why these companies want to do this. Compute is severely power-const…

Of course you can build these things if you really want to.

But there is no universe in which it's possible to build them economically.

Not even close. The numbers are simply ridiculous.

And that's not even accounting for the fact that getting even one of these things into orbit is an absolutely huge R&D project that will take years - by which time technology and requirements will have moved on.

Re: Economics of Orbital vs. Terrestrial Data Centers

#197

Post by JoeAltmaier »

TheOtherHobbes wrote: post #196
davedx wrote: post #161

Earlier quoted context omitted.

I think the point is, yes, cooling is a significant engineering challenge in space; but having easy access to abundant energy (solar) and not needing to navigate difficult politically charged permitting processes makes it worthwhile. It's a big set of trade offs, and to only focus on "cooling being very hard in space" is kind of missing the point of why these companies want to do this. Compute is severely power-const…

Of course you can build these things if you really want to. But there is no universe in which it's possible to build them economically. Not even close. The numbers are simply ridiculous . And that's not even accounting for the fact that getting even one of these things into orbit is an absolutely huge R&D project that will take years - by which time technology and requirements will have moved on.

Lift costs dropping geometrically. Cost and weight of solar decreasing similarly. The trend makes space-based centers nearly inevitable.

Reminds me of "Those darn cars! Everybody knows that trains and horses are the way to travel."

Re: Economics of Orbital vs. Terrestrial Data Centers

#198

Post by Gazoche »

Cons of orbital data centers:

- Ludicrously expensive to setup

- Need radiation-hardened silicon

- Ludicrously expensive maintenance requiring highly specialized operators (a.k.a astronauts)

- High risk of losing the entire equipment to a rocket failure (not infrequent even for modern launch vehicles)

- Supplying enough electrical power would be extremely difficult

- Cooling would be extremely difficult

- Geosynchronous orbits have at least 200ms of communication latency

- Lower orbits means the data center would not stay in place and require complicated tracking antennae and/or a communication mesh a la Starlink, again increasing latency and complexity

Pros of orbital data centers:

- ??????

...why are we doing this again?

Re: Economics of Orbital vs. Terrestrial Data Centers

#199

Post by coffeebeqn »

notahacker wrote: post #186
viraptor wrote: post #149

Earlier quoted context omitted.

Only on a short distance. To effectively radiate a significant amount of heat, you need to actually deliver the heat to the distant parts of the radiator first. That normally requires active pumping which needs extra energy. So now you need to unfold sonar panels + aluminium + pipes (+ maybe extra pumps)

Orbital assembly of a fluid piping system in space is a pretty colossal problem too (as well as miles of pipes and connections being a massive single point failure for your system). Dispersing the GPUs might be more practical, but it's not exactly optimal for high performance computation...

It’s a fun problem to think about but even if all the problems were solved we would have very quickly deprecating hardware in orbit that’s impossible to service or upgrade
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