Comment by pantalaimon
11 hours ago
Existing 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.
11 hours ago
Existing 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.
5,000 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.
Several 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.
you 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.
It's really not that simple. See this for a good explanation of why: https://taranis.ie/datacenters-in-space-are-a-terrible-horri...
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It 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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That helps with the heat from the sun problem, but not the radiation of heat from the GPUs. Those radiators would need to be unshaded by the solar panels, and would need to be enormous. Cooling stuff in atmosphere is far easier than in vacuum.
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> 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.
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I’ve got a perpetual motion machine to sell you.
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arbitrarily large means like measured in square km. Starcloud is talking about 4km x 4km area of solar panels and radiative cooling. (https://blogs.nvidia.com/blog/starcloud/)
Building this is definitely not trivial and not easy to make arbitrarily large.
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I'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.
the radiators would be lighter compared to the solar panels, and slightly smaller surface area so you can line them back to back
If 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).
> 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.
You 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.
Water is not needed to move heat. Heat pipes do it just fine. There's one in your laptop and one in your phone too. It does scale up.
Interesting, That could surely simplify things.
There'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.