[eldenring]

The 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.

[lm28469]

If you solved this problem apply at nasa because they still haven't figured it out.

Either that or your talking out of your ass.

FYI a single modern rack consumes twice the energy of the entire ISS, in a much much much much smaller package and you'll need thousands of them. You'd need 500-1000 sqm of radiator per rack and that alone would weight several tonnes...

You'll also have to actively cool down your gigantic solar panel array

[DoctorOetker]

eldenring is slightly wrong: for reasonable temperatures the area of the radiating panels would have to be a bit more than 3 times the area of the solar panel, otherwise theres nothing wrong.

No need to apply at NASA, to the contrary, if you don't believe in Stefan Boltzmann law, feel free to apply for a Nobel prize with your favorite crank theory in physics.

[eldenring]

Whats your definition for reasonable temp? my envelope math tells me at 82 celsius (right before h100s start to throttle) you'd need about 1.5x the surface area for radiators. Not exactly back to back, but even 3x surface area is reasonable.

Also this assumes a flat surface on both sides. Another commenter in this thread brought up a pyramid shape which could work.

Finally, these gpus are design for earth data centers where power is limited and heat sinks are abundant. In the case of space data centers you can imagine we get better radiators or silicon that runs hotter. Crypto miners often run asics very hot.

I just don't understand why every time this topic is brought up, everyone on HN wants to die on the hill that cooling is not possible. It is?? the primary issue if you do the math is clearly the cost of launch.

[DoctorOetker]

I am the person who gave the pyramid shape as a didactic example (convexity means we can ignore self obscuration, and giving up 2 of the 4 triangular side surfaces of the pyramid allows me to ignore the presence of lukewarm earth).

My example is optimized not for minimal radiator surface area, but for minimal mathematical and physical knowledge required to understand feasibility.

Your numbers are different because you chose 82 C (355 K) instead of my 26 C (300 K).

Near normal operating temperatures hardware lifetime roughly doubles for every 10 deg C/K decrease in temperature (this does not hold indefinitely of course).

You still need to move the heat from the GPU to the radiator so my example of 26 deg C at the radiator just leaves a lot of room against criticism ;)

[wat10000]

Who’s saying cooling is not possible? Cooling gets brought up because it’s presented as an advantage of putting stuff in space. But it’s not an advantage, cooling is harder in space than on the ground.

[eldenring]

I've never seen this argument brought up by anyone serious, not in the above post, not in the space datacenter blog by Google, etc.

The main benefit is that solar panels go from a complicated mess of batteries + permitting to a very stable, highly efficient energy source.

[wat10000]

Search "data centers in space" and it gets mentioned constantly. Cooling is even mentioned in this announcement. It's not explicitly described as an advantage for putting things in space, but it states that terrestrial data centers "require immense amounts of power and cooling," and that heavily implies that cooling is less of a problem in space.

[wat10000]

The pertinent thing is that it’s not an advantage. It may be doable but it’s not easier than cooling a computer in a building.

[DoctorOetker]

The distinction is that you don't need to compete for land area, that you don't cause local environmental damage by heating say a river or a lake, that you don't compete with meatbags for energy and heat dissipation rights.

Without eventually moving compute to space we are going to have compute infringe on the space, energy, heat dissipation rights of meatbags. Why welcome that?!?

[defrost]

How efficient is thermal radiation through a vacuum again?

Sure, it occurs, but what does the Stefan–Boltzmann law tell us about GPU clusters in space?

[DoctorOetker]

> How efficient is thermal radiation through a vacuum again?

I provided the calculation for the pyramidal shape: if the base of a pyramid were a square solar panel with side length L, then for a target temperature of 300K (a typical back of envelope substitute for "room temperature") the height of the pyramid would have to be about 3 times the side length of the square base. Quite reasonable.

> Sure, it occurs, but what does the Stefan–Boltzmann law tell us about GPU clusters in space?

The Stefan-Boltzmann law tells us that whatever prevents us from putting GPU clusters in space, it's not the difficulty in shedding heat by thermal radiation that is supposedly stopping us.

[defrost]

Is it the required size of the wings for radiative cooling then?

[DoctorOetker]

Just picture a square based pyramid, like a pyramid from egypt, thats the rough shape. Lets pretend the bottom is square. For thermodynamic analysis, we can just pretend the scale is irrelevant, it could be 4 cm x 4 cm base or 4 km x 4 km base. Now stretch the pyramid so the height of the tip is 3 times the length of the sides of the square base, so 12 cm or 12 km in the random examples above.

If the base were a solar panel aimed perpendicular to sun, then the tip is facing away and all side triangles faces of the pyramid are in the shade.

I voluntarily give up heat dissipation area on 2 of the 4 triangular sides (just to make calculations easier, if we make them thermally reflective -emissivity 0-, we can't shed heat, but also don't absorb heat coming from lukewarm Earth).

The remaining 2 triangular sides will be large enough that the temperature of the triangular panels is kept below 300 K.

The panels also serve as the cold heat baths, i.e. the thermal sinks for the compute on board.

Not sure what you mean with wings, I intentionally chose a convex shape like a pyramid so that no part of the surface of the pyramid can see another part of the surface, so no self-obstruction for shedding heat etc...

If this doesn't answer your question, feel free to ask a new question so I understand what your actual question is.

The electrical power available for compute will be approximately 20% (efficiency of solar panels) times the area of the square base L ^ 2 times 1360 W / m ^ 2 .

The electrical power thus scales quadratically with the chosen side length, and thus linearly with the area of the square base.

[wat10000]

The land area and heating is completely insignificant on a terrestrial scale.