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Either this is a straight up con, or Musk found a glitch in physics. It's extremely difficult to keep things cold in space.
by alangibson 8mo ago
Either this is a straight up con, or Musk found a glitch in physics. It's extremely difficult to keep things cold in space.
- pantalaimon 8mo agoExisting satellites manage to keep their equipment that already can consume several kW cool just fine. You might need space for radiators, but there is plenty space in space.
- alangibson 8mo agoSeveral kW is nothing for a bank of GPUs. Radiators in space are extremely inefficient because there's no conduction. Also you have huge heat inputs from the sun. So you need substantial cooling before you get around to actually cooling the GPUs.
- DoctorOetker 8mo agoyou put the radiators and the rest of the satellite within the shade of the solar panels, you can still make the area arbitrarily large EDIT: people continue downvoting and replying with irrelevant retorts, so I'll add in some calculations Let's assume 1. cheap 18% efficient solar panels (though much better can be achieved with multijunction and quantum-cutting phosphors) 2. simplistic 1360 W/m^2 sunlight orthogonal to the sun 3. an abstract input Area Ain of solar panels (pretend its a square area: Ain = L ^ 2) 4. The amount of heat generated on the solar panels (100%-18%) * Ain * 1360 W / m ^ 2, the electrical energy being 18% * Ain * 1360 W / m ^ 2. The electrical energy will ultimately be converted to computational results and heat by the satellite compute. So the radiative cooling (only option in space) must dissipate 100% of the incoming solar energy: the 1360 W / m^2 * Ain. 5. Lets make a pyramid with the square solar panel as a base, with the apex pointing away from the sun, we make sure the surface has high emissivity (roughly 1) in thermal infrared. Observe that such a pyramid has all sides in the shade of the sun. But it is low earth orbit so lets assume warm earth is occupying one hemisphere and we have to put thermal IR reflectors on the 2 pyramid sides facing earth, so the other 2 pyramid sides face actual cold space. 6. The area for a square based symmetric pyramid: we have 6.a. The area of the base Ain = L * L. 6.b. The area of the 4 sides 2 * L * sqrt( L ^ 2 / 4 + h ^ 2 ) 6.c. The area of just 2 sides having output Area Aout = L * sqrt( L ^ 2 / 4 + h ^ 2 ) 7. The 2 radiative sides not seeing the sun and not seeing the earth together have the area in 6.c and must dissipate L ^ 2 * 1360 W / m ^ 2 . 8. Hello Stefan-Boltzmann Law: for emissivity 1 we have the radiant exitance M = sigma * T ^ 4 (units W / m ^ 2 ) 9. The total power exited through the 2 thermal radiating sides of the pyramid is then Aout * M 10. Select a desired temperature and solve for h / L (to stay dimensionless and get the ratio of the pyramid height to its base side length), lets run the satellite at 300 K = ~26 deg C just as an example. 11. If you solve this for h / L we get: h / L = sqrt( ( 1360 W / m ^ 2 / (sigma * T ^ 4 ) ) ^ 2 - 1/4 ) 12. Numerically for 300K target temperature we get: h/L = sqrt((1360 / (5.67 * 10^-8 * 300 ^ 4)) ^ 2 - 1/4) = 2.91870351609271066729 13. So the pyramid height of "horribly poor cooling capability in space" would be a shocking 3 times the side length of the square solar panel array. As a child I was obsessed with computer technology, and this will resonate with many of you: computer science is the poor man's science, as soon as a computer becomes available in the household, some children autodidactically educate themselves in programming etc. This is HN, a lot of programmers who followed the poor man's science path out of necessity. I had the opportunity to choose something else, I chose physics. No amount of programming and acquiring titles of software "engineer" will be a good substitute for physicists and engineers that actually had courses on the physical sciences, and the mathematics to follow the important historical deductions... It's very hard to explain this to the people who followed the path I had almost taken. And they downvote me because they didn't have the opportunity, courage or stamina to take the path I took, and so they blindly copy paste each others doomscrolled arguments. Look I'm not an elon fanboy... but when I read people arguing that cooling considerations excludes this future, while I know you can set the temperature arbitrarily low but not below background temperature of the universe 4 K, then I simply explain that obviously the area can be made arbitrarily large, so the temperature can be chosen by the system designer. But hey the HN crowd prefers the layers of libraries and abstractions and made themselves an emulation of an emulation of an emulation of a pre-agreed reality as documented in datasheets and manuals, and is ultimately so removed from reality based communities like physics and physics engineering, that the "democracy" programmers opinions dominate... So go ahead and give me some more downvotes ;) If you like mnemonics for important constants: here's one for the Stefan Boltzman constant: 5.67 * 10^-8 W / m^2 / K ^ 4 thats 4 consecutive digits 5,6,7,8 ; comma or point after the first significant digit and the exponent 8 has a minus sign.
- alangibson 8mo ago> arbitrarily large Space is not empty. Satellites have to be boosted all the time because of drag. Massive panels would only worsen that. Once you boosters are empty the satellite is toast.
- inglor_cz 8mo ago"Satellites have to be boosted all the time because of drag." On Low Earth Orbits (LEOs), sure, but the traces of atmosphere that cause the drag disappear quite fast with increasing altitude. At 1000 km, you will stay up for decades.
- DoctorOetker 8mo agothe point wasn't that a 1 m^2 solar panel could theoretically be kept reasonably cool at the cost of a miles long radiator... nono, the point was that you could attain any desirable temperature this way, arbitrarily close to 4K. for a reasonable temperature (check my comment for updated calculations) the height of a square based pyramidal satellite would be about 3 times the side length of its base, quite reasonable indeed. Thats with the square base of the pyramid as solar panel facing the sun, and the top of the pyramid facing away, so all sides are in the shade of the base. I even halved my theoretical cooling power to keep calculations simple: to avoid a long confusing calculation of the heat emitted by earth, I handicapped my design so 2 of the pyramidal side surfaces are reflective (facing earth) and the remaining 2 side triangles of the pyramid are the only used thermal radiative cooling surfaces. Less pessimistic approaches are possible, but would make the calculation less didactic for the HN crowd.
- alangibson 8mo agoIt seems straightforward to you because you're ignoring everything that makes this not work. Here's a big one: you can't put radiators in shadow because the coolant would freeze. ISS has system dedicated to making sure the radiators get just enough sunlight at any given time.
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- TheGRS 8mo agoI'm not big on this subject, but I understand that heat transfer is difficult in space, because there's little to transfer to. If the solution is just making large radiators, then that means you're sending some big payloads full of radiators. Not to mention all the solar panels needed. I wanna live in sci-fi land too, but I don't see how it makes any sense compared to a terrestrial data center.
- eldenring 8mo agothe radiators would be lighter compared to the solar panels, and slightly smaller surface area so you can line them back to back
- TheGRS 8mo agoIf someone has a design out there where this works and you can launch it economically on a rocket today, I wanna see that. And then I wanna compare it to the cost of setting up some data centers on earth (which BTW, you can service in real time, it sounds like these will be one-and-done launches).
- queenkjuul 8mo agoThe radiators are full of ammonia, they would be the heaviest thing involved. Thousands of gallons of ammonia would have to be launched into space.
- nerdsniper 8mo ago5,000 Starship launches to match the solar/heat budget of the 10GW "Stargate" OpenAI datacenter. The Falcon 9 family has achieved over 600 launches. The ISS power/heat budget is like 240,000 BTU/hr. That’s equivalent to half of an Nvidia GB200 NVL72 rack. So two international space stations per rack. Or about 160,000 international space stations to cool the 10GW “Stargate” datacenter that OpenAI’s building in Abilene. There are 10,000 starlink satellites. Starship could probably carry 250-300 of the new V2 Mini satellites which are supposed to have a power/heat budget of like 8kW. That's how I got 5,000 Starship launches to match OpenAI’s datacenter. Weight seems less of an issue than size. 83,000 NVL72’s would weigh 270 million lbs or 20% of the lift capacity of 5000 starship launches. Leaving 80% for the rest of the satellite mass, which seems perhaps reasonable. Elon's napkin math is definitely off though, by over an order of magnitude. "a million tons per year of satellites generating 100 kW of compute power per ton" The NVL72's use 74kW per ton. But that's just the compute, without including the rest of the fucking satellite (solar panels and radiators). So that estimate is complete garbage. One note: If you could afford to send up one of your own personal satellites, it would be extremely difficult for the FBI to raid.
- wat10000 8mo agoThere's plenty of space in space, but there isn't plenty of space in rocket fairings, nor is there plenty of lift capacity for an unlimited amount of radiators.
- Aurornis 8mo ago> keep their equipment that already can consume several kW cool just fine That's equivalent to a couple datacenter GPUs. > You might need space for radiators, but there is plenty space in space. Finding space in space is the least difficult problem. Getting it up there is not easy.
- eldenring 8mo agoYou can line the solar panels and radiators facing away from each other, and the radiators would take up less surface area. I think maybe the tricky part would be the weight of water + pipes to move heat from the compute to the radiators.
- umeshunni 8mo ago> It's extremely difficult to keep things cold in space. This is one of those things that's not obvious till you think about it.
- dahinds 8mo agoThis isn't really true, though? The ISS does it with radiators that are ~1/2 the area of its solar panels, and both should scale linearly with power?
- wild_egg 8mo agoThe ISS creates radically less heat than a datacenter
- wongarsu 8mo agoMoving electricity long distance is a lot easier than moving coolant long distances, which puts a soft limit on the reasonable size of the solar array of these satellites. But as long as you stay below that and pick a reasonable orbit it's indeed not too bad, you just have to properly plan for it
- deleted 8mo ago[deleted]
- FireBeyond 8mo agoThe ISS isn't consuming and generating megawatts+ of power.
- dahinds 8mo agoYes but if the solar panel area scales linearly with radiator area, the problem doesn't get worse?
- manquer 8mo agoWouldn't the panels themselves need cooling too? The ones on earth generate heat while being in the sun. There are commercial systems that can use open loop cooling (i.e. spray water) to improve efficiency of the panel by keeping the panel at a optimal temp of ~25C and the more expensive closed loop systems with active cooling recovers additional energy from the heat by circulating water like a solar heater in the panel back.
- 8mo ago
- nutjob2 8mo agoIt's a con, his AI business is failing, so he's rolling it up into the profitable business. Did a similar thing with Twitter. This is so obvious, but it's so stupid and at this scale that people find it hard to believe.
- DoesntMatter22 8mo agoIf they AI business is failing why did they just do a successful large raise?
- krige 8mo agoIf the AI business is successful why does it keep changing hands? Where are the profits?
- DoesntMatter22 8mo agoNo ai companies have profits yet.
- nutjob2 8mo agoYour implication is that investors are in some way infallible? Hilarious.
- yandie 8mo agoWeWork or Theranos. Have we forgotten about them?
- pupppet 8mo agoJust put a fan in a window.
- DoctorOetker 8mo agowhat makes you believe this? radiators can be made as long as desirable within the shade of the solar panels, hence the designer can pracitically set arbitrarily low temperatures above the background temperature of the universe.
- deleted 8mo ago[deleted]
- ares623 8mo agowhat? the heat is coming from inside the house
- DoctorOetker 8mo agowhich house?
- eldenring 8mo agothese same comments pop up every time someone brings up satellite data-centers where people just assume the only way of dissipating heat is through convection with the environment.
- wat10000 8mo agoNo, we just "assume" (i.e. know) that radiation in a vacuum is a really bad way of dissipating heat, to the point that we use vacuum as a very effective insulator on earth. Yes, you can overcome this with enough radiator area. Which costs money, and adds weight and space, which costs more money. Nobody is saying the idea of data centers in space is impossible. It's obviously very possible. But it doesn't make even the slightest bit of economic sense. Everything gets way, way harder and there's no upside.
- eldenring 8mo agoThe radiators would be lighter compared to the solar panels, and slightly smaller surface area so you can line them back to back I don't think dissipating heat would be an issue at all. The cost of launch I think is the main bottleneck, but cooling would just be a small overhead on the cost of energy. Not a fundamental problem.
- darth_avocado 8mo agoHe buys twitter at an inflated valuation. Runs it to the ground to a much lower valuation of $9B. [1] Then, his company Xai buys Twitter at a $33B, inflating the valuation up. Then SpaceX merges with Xai for no particular reason, but is expected to IPO at a $1T+ in the upcoming years. [3] I’m not that smart, but if I were, I would be thinking this is an extended way to move the losses from the Twitter purchase on to the public markets. [1] https://www.axios.com/2023/12/31/elon-musks-x-fidelity-valuation-cut https://www.axios.com/2023/12/31/elon-musks-x-fidelity-valua... [2] https://www.reuters.com/markets/deals/musks-xai-buys-social-media-platform-x-45-billion-2025-03-28/ https://www.reuters.com/markets/deals/musks-xai-buys-social-... [3] https://www.cnbc.com/amp/2026/02/02/elon-musk-spacex-xai-ipo.html https://www.cnbc.com/amp/2026/02/02/elon-musk-spacex-xai-ipo...
- SilverElfin 8mo agoIt also makes it impossible for Twitter/X to die, as it deserves. It is by far the most toxic mainstream social network. It has an overwhelming amount of far right supremacist content. So bad that it literally resulted in Vivek Ramaswamy, a gubernatorial candidate in Ohio, to quit Twitter/X - nearly 100% of replies to his posts were from far right racists. Obviously advertisers have not been fans. And it is a dying business. But rather than it dying, Elon has found a clever (and probably illegal) way to make it so that SpaceX, which has national security importance, is going to prop up Twitter/X. Now our taxpayer dollars are paying for this outrageous social network to exist.
- RIMR 8mo agoI am with you 100%. It was easy to support SpaceX, despite the racist/sexist/authoritarian views of its owner, because he kept that nonsense out of the conversation. X is not the same. Elon is actively spewing his ultraconservative views on that site. Now that these are the same company, there's no separation. SpaceX is part of Musk's political mission now. No matter how cool the tech, I cannot morally support this company, and I hope, for the sake of society, it fails. This announcement, right after the reveal that Elon Musk reached out to Jeffrey Epstein and tried to book a trip to Little St. James so that he could party with "girls", really doesn't bode well. It's a shame you can't vote these people out, because I loved places like Twitter, and businesses like SpaceX and Tesla, but Elon Musk is a fascist who uses his power and influence to attack some of the most important pillars of our society.
- FloorEgg 8mo agoSetting aside the possibility it's window dressing for a financial bailout, there would be two ways compute in space makes sense: 1) new technology improves vacuum heat radiation efficiency 2) new technology reduces waste heat generation from compute All the takes I've seen have been focused on #1, but I'm starting to wonder about #2... Specifically spintronics and photonic chips.
- brandonlovesked 8mo agoIf you solve 2, heat dissipation goes away on earth too, so what’s the advantage of space
- FloorEgg 8mo agoI'm not the best person to make that case as I can only speculate (land cost, permitting, latency, etc). /Shrug In all the conversations I've seen play out on hacker news about compute in space, what comes up every time is "it's unviable because cooling is so inefficient". Which got me thinking, what if cooling needs dropped by orders of magnitude? Then I learned about photonic chips and spintronics.
- tadfisher 8mo agoIf you're considering only viability, the obvious concern would be cooling, yes; because increasingly large radiative cooling systems dominate launch costs because of all the liquid you need to boost into orbit. And one 100MW installation would be 500 times the largest solar power/radiative cooling system we've ever launched, which is the ISS. So get that down 2 orders of magnitude and you're within the realm of something we _know_ is possible to do instead of something we can _speculate_ is possible. After that frankly society-destabilizing miracle of inventing competitive photonic processing, your goal of operating data centers in space becomes a tractable economic problem: Pros: - You get a continuous 1.37 kW/m^2 instead of an intermittent 1.0 kW/m^2 - Any reasonable spatial volume is essentially zero-cost Cons: - Small latency disadvantage - You have to launch all of your hardware into polar orbit - On-site servicing becomes another economic problem So it's totally reasonable to expect the conversation to revolve around cooling, because we know SpaceX can probably direct around $1T into converting methane into delta-V to make the economics work, but the cooling issue is the difference between maybe getting one DC up for that kind of money, or 100 DCs.
- nhq1298 8mo agoMaybe Karpathy has been hired to design a Full Self Cooling system.
- JeremyNT 8mo agoIt's such bullshit that we've decided this moron and others in his cohort can unilaterally reallocate such vast portions of humanity's labor at their whims. This is an extremely stupid idea, but because of our shared delusion of capitalism and the idea that wealth accumulation at the top should be effectively limitless, this guy gets to screw around and divert actual human labor towards insane and useless projects like this rather than solving real world problems.
- Wilder7977 8mo agoI wanted to come and express this thought, but you did that already very well, thanks for that. I am saddened too by the fact that the system is designed so that people like him can waste a large amount of economic and human capital.
- kristjansson 8mo agoThe physical constraints aren’t insane for black body radiators. The engineering to run radiators at 90C in space OTOH…