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This is such a hypebeast paragraph. Datacenters in space are a TERRIBLE idea. Figure out how to get rid of the waste heat and get back to me.

by esseph 9mo ago

fnord77 9mo ago
I agree that data centers in space is nuts. But I think there's solutions to the waste heat issue https://www.nasa.gov/centers-and-facilities/goddard/engineers-solve-excessive-heat-removal-from-nasas-webb-telescope/ https://www.nasa.gov/centers-and-facilities/goddard/engineer...
- boutell 9mo ago
  That's a solution for minuscule amounts of heat that nevertheless disturb extremely sensitive scientific experiments. Using gold, no less. This does not scale to a crapton of GPU waste heat.
- OneDeuxTriSeiGo 9mo ago
  The distinction is that what they are doing for Webb is trying to dissipate small amounts of heat that would warm up sensors past cryogenic temperatures. Like on the order of tens or hundreds of watts but -100C. Dissipating heat for an AI datacenter is a different game. A single AI inference or training rack is going to be putting out somewhere around 100kW of waste heat. Temps don't have to be cryogenic but it's the difference between chiselling a marble or jade statue and excavating a quarry.
  - fnord77 9mo ago
    got it - thanks
elihu 9mo ago
That's not a new problem that no one has dealt with before. The ISS for instance has its External Active Thermal Control System (EACTS). It's not so much a matter of whether it's an unsolvable problem but more like, how expensive is it to solve this problem, what are its limitations, and does the project still makes economic sense once you factor all that in?
- OneDeuxTriSeiGo 9mo ago
  It's worth noting that the EACTS can at maximum dissipate 70kW of waste heat. And EEACTS (the original heat exchange system) can only dissipate another 14kW. That is together less than a single AI inference rack. And to achieve that the EACTS needs 6 radiator ORUs each spanning 23 meters by 11 meters and with a mass of 1100 kg. So that's 1500 square meters and 6 and a half metric tons before you factor in any of the actual refrigerant, pumps, support beams, valve assemblies, rotary joints, or cold side heat exchangers all of which will probably together double the mass you need to put in orbit. There is no situation where that makes sense. ----------- Manufacturing in space makes sense (all kinds of techniques are theoretically easier in zero G and hard vacuum). Mining asteroids, etc makes sense. Datacenters in space for people on earth? That's just stupid.
  - marcus_holmes 9mo ago
    I'm a total noob on this. I get that vacuum is a really good insulator, which is why we use it to insulate our drinks bottles. So disposing of the heat is a problem. Can't we use it, though? Like, I dunno, to take a really stupid example: boil water and run a turbine with the waste heat? Convert some of it back to electricity?
    - ikr678 9mo ago
      Harder to direct waste heat in space if you dont have gravity for convection.
    - jdyer9 9mo ago
      It's a good question, but in a closed system (like you have in space) the heat from the turbine loop has to go somewhere in order to make it useful. Let's say you have a coolant loop for the gpus (maybe glycol). You take the hot glycol, run it through your heat exchanger and heat up your cool, pressurized ammonia. The ammonia gets hot (and now the glycol is cool, send it back). You then take the ammonia and send it through the turbine and it evaporates as it expands and loses pressure to spin the turbine. But now what? You have warm, vaporized, low pressure ammonia, and now you need to cool it down to start over. Once it's cool you can pressurize it again so you can heat it up to use again, but you have to cool it, and that's the crux of the issue. The problem is essentially that everything you do releases waste heat, so you either reject it, or everything continues to heat up until something breaks. Developing useful work from that heat only helps if it helps reject it, but it's more efficient to reject it immediately. A better, more direct way to think about this might be to look at the Seebeck effect. If you have a giant radiator, you could put a Peltier module between it and you GPU cooling loop and generate a little electricity, but that would necessarily also create some waste heat, so you're better off cooling the GPU directly.
everfrustrated 9mo ago
Just have to size radiators correctly. Not a physics problem. Just an economic one. Main physics problem is actually that the math works better at higher GPU temps for efficiency reasons and that might have reliability trade off.
- kadoban 9mo ago
  Anything is possible here, it's just there's no goddamn reason to do any of this. You're giving up the easiest means of cooling for no benefit and you add other big downsides. It's scifi nonsense for no purpose other than to sound cool.
  - everfrustrated 9mo ago
    It's about creating a flywheel for scale. Getting better at creating and erecting solar panels & AI datacenters on earth is all well and good, but it doesn't advance SpaceX or humanity very much. At lot of the bottlenecks there are around moving physical mass and paperwork. Whereas combining SpaceX & xAI together means the margins for AI are used to force the economies of scale which drives the manufacturing efficiencies needed to drive down launch etc. Which opens up new markets like Mars etc. It is also pushing their competitive advantage. It leaves a massive moat which makes it very hard for competitors. If xAI ends up with a lower cost of capital (big if - like Amazon this might take 20 years horizon to realize) but it would give them a massive moat to be vertically integrated. OpenAI and others would be priced out. If xAI wants to double AI capacity then it's a purely an automation of manufacturing problem which plays to Elons strengths (Tesla & automation). For anyone on earth doubling capacity means working with electricity restrictions, licensing, bureaucracy, etc. For example all turbines needed for electricity plants are sold years in advance. You can't get a new thermal plant built & online within 5 years even if you had infinite money as turbines are highly complex and just not available.
    - amluto 9mo ago
      Hmm, Elon really did run that flywheel pretty well. He built the Roadster to drum up some cash and excitement so he could develop the Model S, then he used that success to do the Model X, and then he expanded capacity to develop the 3 and Y, and he reinvested the profits to develop the Model 2, finally bringing EVs to the masses, displacing ICEs everywhere, and becoming the undisputed leader of both EV and battery manufacturering. Oh wait, that didn’t actually happen, because he got distracted or something? He doesn’t really have battery capacity worth writing home about, the Chinese are surpassing Tesla in EV manufacturing, and Waymo is far ahead in self-driving. The amazing space computation cost reduction process sounds rather more challenging than the Model 2, and I’m not sure why anyone should bet on Elon pulling it off.
typ 9mo ago
It makes sense to target a higher operating temperature, like 375K. At some point, the energy budget would reach an equilibrium. The Earth constantly absorbs solar energy and also dissipates the heat only by radiative cooling. But the equilibrium temperature of the Earth is still kind of cool. I guess the trick lies in the operating temperature and the geometry of the satellites.
- golem14 9mo ago
  Asking for a friend (who sucks at thermodynamics:) could you use a heat pump to cool down the cold end more and heat up the hot end much higher? Heat radiation works better the higher the temperature?
  - typ 9mo ago
    Not sure about the effectiveness of a heat pump in this use case. >Heat radiation works better the higher the temperature? The power output is proportional to T^4 according to the Stefan-Boltzmann law.
    - golem14 9mo ago
      https://www.mdpi.com/1996-1073/16/10/4010 https://www.mdpi.com/1996-1073/16/10/4010 40% isn't much in the grand scheme of things, but maybe they can reach higher reduction with more research/materials. Mass and power are pretty cheap for spaceX, so shipping more solar panels and a heap pump might not be a deal breaker. Would e.g. a reduction of 90% in radiator area change the overall picture on the overall feasibility? I think not, it would still be ludicrous, but I'd be happy to be proven wrong.
      - typ 9mo ago
        The radiator area is probably not what they need to worry about that much as we thought. When the energy input comes from solar 100%, they just need to optimize the ratio of the sectional area facing the sun over the total surface area of the satellite. If the ratio is low enough, like a fin or cone shaped object, it will be harder to be hot.
jonners00 9mo ago
Heat exchanger melts salts, salts boil off? Some kind of potential in there to use evaporants for attitude/altitude correction. Spitballing. Once your use case also has a business case, scope to innovate grows.

This is such a hypebeast paragraph. Datacenters in space are a TERRIBLE idea. Figure out how to get rid of the waste heat and get back to me.

by esseph 9mo ago

This is such a hypebeast paragraph. Datacenters in space are a TERRIBLE idea. Figure out how to get rid of the waste heat and get back to me.

fnord77 9mo ago

I agree that data centers in space is nuts. But I think there's solutions to the waste heat issue https://www.nasa.gov/centers-and-facilities/goddard/engineers-solve-excessive-heat-removal-from-nasas-webb-telescope/ https://www.nasa.gov/centers-and-facilities/goddard/engineer...

boutell 9mo ago
That's a solution for minuscule amounts of heat that nevertheless disturb extremely sensitive scientific experiments. Using gold, no less. This does not scale to a crapton of GPU waste heat.
OneDeuxTriSeiGo 9mo ago
The distinction is that what they are doing for Webb is trying to dissipate small amounts of heat that would warm up sensors past cryogenic temperatures. Like on the order of tens or hundreds of watts but -100C. Dissipating heat for an AI datacenter is a different game. A single AI inference or training rack is going to be putting out somewhere around 100kW of waste heat. Temps don't have to be cryogenic but it's the difference between chiselling a marble or jade statue and excavating a quarry.
- fnord77 9mo ago
  got it - thanks

elihu 9mo ago

That's not a new problem that no one has dealt with before. The ISS for instance has its External Active Thermal Control System (EACTS). It's not so much a matter of whether it's an unsolvable problem but more like, how expensive is it to solve this problem, what are its limitations, and does the project still makes economic sense once you factor all that in?

OneDeuxTriSeiGo 9mo ago
It's worth noting that the EACTS can at maximum dissipate 70kW of waste heat. And EEACTS (the original heat exchange system) can only dissipate another 14kW. That is together less than a single AI inference rack. And to achieve that the EACTS needs 6 radiator ORUs each spanning 23 meters by 11 meters and with a mass of 1100 kg. So that's 1500 square meters and 6 and a half metric tons before you factor in any of the actual refrigerant, pumps, support beams, valve assemblies, rotary joints, or cold side heat exchangers all of which will probably together double the mass you need to put in orbit. There is no situation where that makes sense. ----------- Manufacturing in space makes sense (all kinds of techniques are theoretically easier in zero G and hard vacuum). Mining asteroids, etc makes sense. Datacenters in space for people on earth? That's just stupid.
- marcus_holmes 9mo ago
  I'm a total noob on this. I get that vacuum is a really good insulator, which is why we use it to insulate our drinks bottles. So disposing of the heat is a problem. Can't we use it, though? Like, I dunno, to take a really stupid example: boil water and run a turbine with the waste heat? Convert some of it back to electricity?
  - ikr678 9mo ago
    Harder to direct waste heat in space if you dont have gravity for convection.
  - jdyer9 9mo ago
    It's a good question, but in a closed system (like you have in space) the heat from the turbine loop has to go somewhere in order to make it useful. Let's say you have a coolant loop for the gpus (maybe glycol). You take the hot glycol, run it through your heat exchanger and heat up your cool, pressurized ammonia. The ammonia gets hot (and now the glycol is cool, send it back). You then take the ammonia and send it through the turbine and it evaporates as it expands and loses pressure to spin the turbine. But now what? You have warm, vaporized, low pressure ammonia, and now you need to cool it down to start over. Once it's cool you can pressurize it again so you can heat it up to use again, but you have to cool it, and that's the crux of the issue. The problem is essentially that everything you do releases waste heat, so you either reject it, or everything continues to heat up until something breaks. Developing useful work from that heat only helps if it helps reject it, but it's more efficient to reject it immediately. A better, more direct way to think about this might be to look at the Seebeck effect. If you have a giant radiator, you could put a Peltier module between it and you GPU cooling loop and generate a little electricity, but that would necessarily also create some waste heat, so you're better off cooling the GPU directly.

everfrustrated 9mo ago

Just have to size radiators correctly. Not a physics problem. Just an economic one. Main physics problem is actually that the math works better at higher GPU temps for efficiency reasons and that might have reliability trade off.

kadoban 9mo ago
Anything is possible here, it's just there's no goddamn reason to do any of this. You're giving up the easiest means of cooling for no benefit and you add other big downsides. It's scifi nonsense for no purpose other than to sound cool.
- everfrustrated 9mo ago
  It's about creating a flywheel for scale. Getting better at creating and erecting solar panels & AI datacenters on earth is all well and good, but it doesn't advance SpaceX or humanity very much. At lot of the bottlenecks there are around moving physical mass and paperwork. Whereas combining SpaceX & xAI together means the margins for AI are used to force the economies of scale which drives the manufacturing efficiencies needed to drive down launch etc. Which opens up new markets like Mars etc. It is also pushing their competitive advantage. It leaves a massive moat which makes it very hard for competitors. If xAI ends up with a lower cost of capital (big if - like Amazon this might take 20 years horizon to realize) but it would give them a massive moat to be vertically integrated. OpenAI and others would be priced out. If xAI wants to double AI capacity then it's a purely an automation of manufacturing problem which plays to Elons strengths (Tesla & automation). For anyone on earth doubling capacity means working with electricity restrictions, licensing, bureaucracy, etc. For example all turbines needed for electricity plants are sold years in advance. You can't get a new thermal plant built & online within 5 years even if you had infinite money as turbines are highly complex and just not available.
  - amluto 9mo ago
    Hmm, Elon really did run that flywheel pretty well. He built the Roadster to drum up some cash and excitement so he could develop the Model S, then he used that success to do the Model X, and then he expanded capacity to develop the 3 and Y, and he reinvested the profits to develop the Model 2, finally bringing EVs to the masses, displacing ICEs everywhere, and becoming the undisputed leader of both EV and battery manufacturering. Oh wait, that didn’t actually happen, because he got distracted or something? He doesn’t really have battery capacity worth writing home about, the Chinese are surpassing Tesla in EV manufacturing, and Waymo is far ahead in self-driving. The amazing space computation cost reduction process sounds rather more challenging than the Model 2, and I’m not sure why anyone should bet on Elon pulling it off.

typ 9mo ago

It makes sense to target a higher operating temperature, like 375K. At some point, the energy budget would reach an equilibrium. The Earth constantly absorbs solar energy and also dissipates the heat only by radiative cooling. But the equilibrium temperature of the Earth is still kind of cool. I guess the trick lies in the operating temperature and the geometry of the satellites.

golem14 9mo ago
Asking for a friend (who sucks at thermodynamics:) could you use a heat pump to cool down the cold end more and heat up the hot end much higher? Heat radiation works better the higher the temperature?
- typ 9mo ago
  Not sure about the effectiveness of a heat pump in this use case. >Heat radiation works better the higher the temperature? The power output is proportional to T^4 according to the Stefan-Boltzmann law.
  - golem14 9mo ago
    https://www.mdpi.com/1996-1073/16/10/4010 https://www.mdpi.com/1996-1073/16/10/4010 40% isn't much in the grand scheme of things, but maybe they can reach higher reduction with more research/materials. Mass and power are pretty cheap for spaceX, so shipping more solar panels and a heap pump might not be a deal breaker. Would e.g. a reduction of 90% in radiator area change the overall picture on the overall feasibility? I think not, it would still be ludicrous, but I'd be happy to be proven wrong.
    - typ 9mo ago
      The radiator area is probably not what they need to worry about that much as we thought. When the energy input comes from solar 100%, they just need to optimize the ratio of the sectional area facing the sun over the total surface area of the satellite. If the ratio is low enough, like a fin or cone shaped object, it will be harder to be hot.

jonners00 9mo ago

Heat exchanger melts salts, salts boil off? Some kind of potential in there to use evaporants for attitude/altitude correction. Spitballing. Once your use case also has a business case, scope to innovate grows.