So like I don't get to use my degree except to tutor kids and answer physics questions and the like, so indulge me for a second because this doesn't make much sense to me. So like the endgame is to create a new Pryor, OK facility in space, right? It doesn't make sense if we're not shipping something that's about the same as what you can build on Earth.
Epoch.AI says that this facility has 100,000 TPU chips, eats 370 megawatts of electricity, but designed to get rid of up to 480 megawatts of heat. Sun power is 1.36 kW/m^2, which is something like 7 megawatts per football field (assuming ~5000 m^2), but you have to put up something like 3-5x that because solar panels are only 20-30% efficient, right? Assume that you can arrange it so that the solar panels are one side, the radiators on the other, you can maybe get away with only 300-400 football fields maybe? So like 1.5 million m^2 or 1.2 km wide, right? At LEO, 650 km, you have (1.2km)/(650 km) * 180 degrees/pi is 0.11 degrees or 6.6 arcminutes of visual size. The moon is only like 30 arcminutes. And the paper talks about how they're going to not do one big monolithic construction but an oval of fridge-sized objects separated out 2-3 times this size -- so like I don't see how you get another Pryor, OK size data center in LEO without basically having it look like a second, smaller moon flying across the sky 10 times per day.
And if this were a wildly successful idea are we talking about having like 5-10 of them, a few for each big frontier lab? This just sounds like we're talking about the most profound shift to our night skies since we started having to deal with light pollution in our cities.
There's a lot of different designs besides this one.
So far as I can work out, literally all of the plans are bad. The "why" varies, but they're all bad.
I'm too tired to double check your maths, so I will assume correct: one likely difference even for this plan is a terminator following sun-synchronous orbit, which means you'll only see it twice a day despite the orbital period being about 90-100 minutes, and when you see it will be specifically at sunrise and sunset.
Visibility is also a question of reflection, not just size. Terminator following orbits are worse than normal satellites, because one of the tricks for reducing e.g. Starlink visibility is to tilt them as they cross the terminator and you can't do that if they're always on the terminator.
The SpaceX plans (a million small ones) becomes a glitter band in some parts of the sky and will appear visually contiguous in other parts, though I need to double check my maths and assumptions about visibility given this happens during sunrise and sunset so the sky itself is pretty bright.
I think there are at least a few problems with the math’s assumptions:
1) Don’t the radiators need to have more surface area than the solar? (Unless the chips run very hot.)
2) The datacenter will have the pesky earth between it and the sun some fraction of the time, and have to either shut down or run off batteries. ~50%, assuming LEO, right? If you leave LEO, then the latency sucks, so they’re training-only clusters. At 50% the solar doubles and you need 370 megawatt hours per hour of darkness, or you run the machines 50% of the time, rebooting for each orbit. If you make the orbit shorter (so you can have smaller batteries), then they wear out faster. The batteries also emit heat. Plus, you need to double the solar so they charge while the workload is running.
3) How do they cope with cosmic rays? The standard approach is still to duplicate or triplicate all computation, or use larger/slower processes, right?
The obvious answer to each question makes the engineering design at least twice as dumb, and they stack. There are many other problems like these.
1) Not even if the PV was 100% efficient, which is impossibly good.
Imagine this side on, as a T-shape: the top bar is the PV, sunlight coming downwards, and because of that only one side is illuminated. The radiator is the vertical bar, in shadow, but crucially it's two-sided, so 1m^2 of material is 2m^2 of surface. If they're the same area of material, thanks to that 2:1 advantage the radiator has naturally, this would only need to run at 58°C: <a href="https://www.wolframalpha.com/input?i=%281361+watt+%2F+%281*σ*2m%5E2%29%29%5E%281%2F4%29" rel="nofollow">https://www.wolframalpha.com/input?i=%281361+watt+%2F+%281*σ...
(Adjust as you prefer for power, area, emissivity is 1 here which isn't possible either but realistic radiators are more like 0.8-0.95 and even 0.8 only raises the above to 77°C)
One of the bigger problems for radiator size is putting them in LEO. Earth is warm and a big fraction of the sky at that altitude. Less of a problem as you get hotter, because radiated power is proportional to the fourth power of temperature in Kelvin, but the closer you operate to Earth's temperature the worse it is.
However, one of the things I am trying to sort out for the blog post is what happens exactly, as a function of temperature, if you just put this all on the ground, because down here you have convection as well as radiation; I'm sure I've seen someone do this and their conclusion was that any radiator good enough to work in space will actually work better on the ground for realistic operating temperatures.
If that rings a bell for anyone else, and you can remember a link to who already worked that out, please let me know :)
2) Not necessarily, but different people pursuing this have different plans: that's why I said the thing about terminator-following sun synchronous orbit, it's a special class of orbits that are always on the edge between day and night at all times.
If you don't do use that class of orbit, then yes, you lose half the supposed benefit on the power front.
3) The current plans seem to be "wing it". Given how resilient LLMs are to noise, this might even work.
crdrost · · focus · HN ↗
Epoch.AI says that this facility has 100,000 TPU chips, eats 370 megawatts of electricity, but designed to get rid of up to 480 megawatts of heat. Sun power is 1.36 kW/m^2, which is something like 7 megawatts per football field (assuming ~5000 m^2), but you have to put up something like 3-5x that because solar panels are only 20-30% efficient, right? Assume that you can arrange it so that the solar panels are one side, the radiators on the other, you can maybe get away with only 300-400 football fields maybe? So like 1.5 million m^2 or 1.2 km wide, right? At LEO, 650 km, you have (1.2km)/(650 km) * 180 degrees/pi is 0.11 degrees or 6.6 arcminutes of visual size. The moon is only like 30 arcminutes. And the paper talks about how they're going to not do one big monolithic construction but an oval of fridge-sized objects separated out 2-3 times this size -- so like I don't see how you get another Pryor, OK size data center in LEO without basically having it look like a second, smaller moon flying across the sky 10 times per day.
And if this were a wildly successful idea are we talking about having like 5-10 of them, a few for each big frontier lab? This just sounds like we're talking about the most profound shift to our night skies since we started having to deal with light pollution in our cities.
ben_w · · focus · HN ↗
So far as I can work out, literally all of the plans are bad. The "why" varies, but they're all bad.
I'm too tired to double check your maths, so I will assume correct: one likely difference even for this plan is a terminator following sun-synchronous orbit, which means you'll only see it twice a day despite the orbital period being about 90-100 minutes, and when you see it will be specifically at sunrise and sunset.
Visibility is also a question of reflection, not just size. Terminator following orbits are worse than normal satellites, because one of the tricks for reducing e.g. Starlink visibility is to tilt them as they cross the terminator and you can't do that if they're always on the terminator.
The SpaceX plans (a million small ones) becomes a glitter band in some parts of the sky and will appear visually contiguous in other parts, though I need to double check my maths and assumptions about visibility given this happens during sunrise and sunset so the sky itself is pretty bright.
hedora · · focus · HN ↗
1) Don’t the radiators need to have more surface area than the solar? (Unless the chips run very hot.)
2) The datacenter will have the pesky earth between it and the sun some fraction of the time, and have to either shut down or run off batteries. ~50%, assuming LEO, right? If you leave LEO, then the latency sucks, so they’re training-only clusters. At 50% the solar doubles and you need 370 megawatt hours per hour of darkness, or you run the machines 50% of the time, rebooting for each orbit. If you make the orbit shorter (so you can have smaller batteries), then they wear out faster. The batteries also emit heat. Plus, you need to double the solar so they charge while the workload is running.
3) How do they cope with cosmic rays? The standard approach is still to duplicate or triplicate all computation, or use larger/slower processes, right?
The obvious answer to each question makes the engineering design at least twice as dumb, and they stack. There are many other problems like these.
ben_w · · focus · HN ↗
Imagine this side on, as a T-shape: the top bar is the PV, sunlight coming downwards, and because of that only one side is illuminated. The radiator is the vertical bar, in shadow, but crucially it's two-sided, so 1m^2 of material is 2m^2 of surface. If they're the same area of material, thanks to that 2:1 advantage the radiator has naturally, this would only need to run at 58°C: <a href="https://www.wolframalpha.com/input?i=%281361+watt+%2F+%281*σ*2m%5E2%29%29%5E%281%2F4%29" rel="nofollow">https://www.wolframalpha.com/input?i=%281361+watt+%2F+%281*σ...
(Adjust as you prefer for power, area, emissivity is 1 here which isn't possible either but realistic radiators are more like 0.8-0.95 and even 0.8 only raises the above to 77°C)
One of the bigger problems for radiator size is putting them in LEO. Earth is warm and a big fraction of the sky at that altitude. Less of a problem as you get hotter, because radiated power is proportional to the fourth power of temperature in Kelvin, but the closer you operate to Earth's temperature the worse it is.
However, one of the things I am trying to sort out for the blog post is what happens exactly, as a function of temperature, if you just put this all on the ground, because down here you have convection as well as radiation; I'm sure I've seen someone do this and their conclusion was that any radiator good enough to work in space will actually work better on the ground for realistic operating temperatures.
If that rings a bell for anyone else, and you can remember a link to who already worked that out, please let me know :)
2) Not necessarily, but different people pursuing this have different plans: that's why I said the thing about terminator-following sun synchronous orbit, it's a special class of orbits that are always on the edge between day and night at all times.
If you don't do use that class of orbit, then yes, you lose half the supposed benefit on the power front.
3) The current plans seem to be "wing it". Given how resilient LLMs are to noise, this might even work.