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by wkat424220 hours ago |
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upvoteby Robotbeat13 hours ago|
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This isn’t true. The radiators on ISS are MUCH smaller than the solar panels. I know it’s every single armchair engineer’s idea that heat rejection is this impossible problem in space, but your own example of ISS proves this is untrue. Radiators are no more of a problem than solar panels.
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upvoteby 0xTJ3 hours ago|
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The radiators are significantly smaller than the PV arrays, but not by a massive ratio; looks like about 1:3.6 based on the published area numbers that I could find.

It looks like the ISS active cooling system has a maximum cooling capacity that could handle the equivalent of a single-digit number of racks (down to 1 for an AI-focused rack).

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upvoteby e_y_9 hours ago|
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The heat load of the ISS is a handful of astronauts and some equipment and whatever it absorbs from the sun. Not an entire data center or a nuclear rocket which is where the radiator discussion comes into play.
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upvoteby Robotbeat4 hours ago|
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The heat load is equal to the load from the solar panels, to first order. So actually yeah, you CAN compare the size of solar panels to the size of the radiators.
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upvoteby PaulDavisThe1st17 hours ago|
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seems oddly paradoxical. ISS interior at some roughly livable temperature. Exterior is ... freakin' space! Temperature gradient seems as if it should take of it ...

... and then you realize that because it is space, there's almost nothing out there to absorb the heat ...

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upvoteby thwarted15 hours ago|
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There's nothing paradoxical about it. There's no such thing as a temperature gradient in a vacuum, there's nothing to hold or measure temperature against. And thus a vacuum is a really good insulator. Which is why a vacuum flask, which ultimately became one of Thermos' most well known products, is used to control temperature both in and outside the lab.
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upvoteby Robotbeat13 hours ago|
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Except a thermos has a really low emissivity, otherwise (if it had high emissivity), it’d be a poor insulator due to thermal radiation, the same reason why ISS’s radiators are much smaller than its solar panels.
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upvoteby throwawaymaths17 hours ago|
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there literally is nothing to absorb the heat. Conduction and convection are out, all you got is radiation.

new vc rule: no investing in space startups unless their founders have 1000 hours in KSP and 500 hours in children of a dead earth

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upvoteby dismalpedigree15 hours ago|
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I’d settle for at least a high school physics education. This idea seemed insane when I first heard about it a few weeks back. This analysis just makes it that much more crazy.

If YC is hell bent on lighting piles of money on fire, I can think of some more enjoyable ways.

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upvoteby throwawaymaths14 hours ago|
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they got the sun synchronous orbit part right.
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upvoteby Robotbeat13 hours ago|
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Radiation is not actually a problem unless you're trying to do super high power nuclear electric propulsion (i.e. in your videogame). Classic armchair engineer mistake, tbh.

Radiators work great in space. Stefan-Boltzmann's law. The ISS's solar panels are MUCH smaller than the radiators. Considering datacenters on Earth have to have massive heat exchangers as well, I really think the bUt wHaT aBoUt rAdiAtOrs is an overblown gotcha, considering every satellite still has to dump heat and works just fine.

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upvoteby semi-extrinsic12 hours ago|
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The problem is not that radiators don't work. The problem is the need for liquid cooling. The heat prduced per area in the GPU/CPU is much bigger than the cooling capacity per area of your radiator.

Even here on earth, contemporary GPU racks for AI have had to move to liquid cooling because it is the only way to extract enough heat. At 120 kW for 18x 1U servers (GB200 NVL72), the power density is waaay beyond what you can do with air even.

The last time Starcloud was doing the rounds on HN, I estimated that they need to be pumping water at a flow rate of 60 000 liters per second, if you use the numbers in their whitepaper. That's a tenth of the Sacramento river, flowing in space through a network with a million junctions and hoping nothing leaks.

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upvoteby fennecfoxy8 hours ago|
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There's a difference between a couple humans (n150W) and say JUST one H200 DGX (8700W).
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upvoteby throwawaymaths1 hours ago|
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yes. in general as a rule of thumb your radiator size must scale proportionally to your solar panel size, as parent says:

> The ISS's solar panels are MUCH smaller than the radiators.

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upvoteby ThrowawayTestr16 hours ago|
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A great interactive example of this is the game Oxygen Not Included. By the late game, you're biggest problem is your base getting too hot from the waste heat of all your industry.
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