5 ms·

> 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 p

> 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 9mo ago
Is it the required size of the wings for radiative cooling then?
- DoctorOetker 9mo ago
  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.
  - oliv5900 9mo ago
    Some people on here are such NPCs, you can give them all calculations, numbers and diagrams as to how this is not an impossible concept, and all they will say is "Thermal radiation is not efficient". You can prove that the lower efficiency can be managed, and they will still say the only thing they know: "Thermal radiation is not efficient".
    - DoctorOetker 9mo ago
      don't give up on them ;) as an example my points almost instantly fell down 15 points, but over the last 11 hours it has recuperated back to just a 1 point drop. it's not because they don't like to write an apology (which I don't ask for) that they aren't secretly happy they learnt something new in physics, and in the end thats what matters to me :)
    - wat10000 9mo ago
      Cooling is being presented as an advantage of putting these things in space. Of course the lower efficiency can be managed. But it’s not an advantage. If cooling is harder (which it is) the what’s the point of this whole thing?
  - queenkjuul 9mo ago
    So how big are you proposing the solar panel be to be able to provide 1GW to the GPUs? Nearly a square kilometer? With an additional 3 square kilometers of radiators? Yeah doesn't sound particularly feasible, sorry. Glad you know all the math though!
    - DoctorOetker 9mo ago
      I made an example calculation at https://news.ycombinator.com/item?id=46867402 https://news.ycombinator.com/item?id=46867402 For a 230 kW cluster: 16 x DGX (8x)B200; we arrived at a 30m x 30m solar PV area, and a 90 meter distance from the center of the solar array to the tip of the pyramid. 1 GW = 4348 x 230 kW sqrt(4348)= ~66 so launch 4348 of the systems described in the calculation I linked, or if you insist on housing them next to each other: the base length becomes 30 m x 66 = 1980 m = ~ 2 km. the distance from center of square solar array to the tip of the pyramid became 6 km... any of these systems would need to be shipped and collected in orbit and then assembled together. a very megalomaniac endeavor indeed.

defrost 9mo ago

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

DoctorOetker 9mo ago
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.
- oliv5900 9mo ago
  Some people on here are such NPCs, you can give them all calculations, numbers and diagrams as to how this is not an impossible concept, and all they will say is "Thermal radiation is not efficient". You can prove that the lower efficiency can be managed, and they will still say the only thing they know: "Thermal radiation is not efficient".
  - DoctorOetker 9mo ago
    don't give up on them ;) as an example my points almost instantly fell down 15 points, but over the last 11 hours it has recuperated back to just a 1 point drop. it's not because they don't like to write an apology (which I don't ask for) that they aren't secretly happy they learnt something new in physics, and in the end thats what matters to me :)
  - wat10000 9mo ago
    Cooling is being presented as an advantage of putting these things in space. Of course the lower efficiency can be managed. But it’s not an advantage. If cooling is harder (which it is) the what’s the point of this whole thing?
- queenkjuul 9mo ago
  So how big are you proposing the solar panel be to be able to provide 1GW to the GPUs? Nearly a square kilometer? With an additional 3 square kilometers of radiators? Yeah doesn't sound particularly feasible, sorry. Glad you know all the math though!
  - DoctorOetker 9mo ago
    I made an example calculation at https://news.ycombinator.com/item?id=46867402 https://news.ycombinator.com/item?id=46867402 For a 230 kW cluster: 16 x DGX (8x)B200; we arrived at a 30m x 30m solar PV area, and a 90 meter distance from the center of the solar array to the tip of the pyramid. 1 GW = 4348 x 230 kW sqrt(4348)= ~66 so launch 4348 of the systems described in the calculation I linked, or if you insist on housing them next to each other: the base length becomes 30 m x 66 = 1980 m = ~ 2 km. the distance from center of square solar array to the tip of the pyramid became 6 km... any of these systems would need to be shipped and collected in orbit and then assembled together. a very megalomaniac endeavor indeed.