> There is to little matter in space to absorb excess heat.
If that were true the Earth would have overheated, molten and turned to plasma long ago. Earth cools by.... radiative cooling. Dark space is 4 K, thats -267.15 deg C or -452.47 deg Fahrenheit. Stefan-Boltzmann law can cool your satellite just fine.
> You'd need thermal fins bigger than the solar cells.
Correct, my pessimistic calculation results in a factor of 3,...
but also Incorrect, there wouldn't be "fins" thats only useful for heat conduction and convection.
That wasn't the original question. The head of this thread was quoting Musk's claim, which I repeat here:
> it is possible to put 500 to 1000 TW/year of AI satellites into deep space
This is 500-1000 times as much as current global production.
Musk is talking about building on the Moon 500-1000 times as much factory capacity as currently exists in aggregate across all of Earth, and launching the products electromagnetically.
Given how long PV modules last, that much per year is enough to keep all of Earth's land area paved with contiguous PV. PV doesn't last as long in space, but likewise the Moon would be totally tiled in PV (and much darker as a consequence) at this production rate.
In fact, given it does tile the moon, I suspect Musk may have started from "tile moon with PV" and estimated the maximum productive output of that power supply being used to make more PV.
I mean, don't get me wrong, in the *long term* I buy that. It's just that by "long term" I mean Musk's likely to have buried (given him, in a cryogenic tube) for decades by the time that happens.
Even being optimistic, given the lack of literally any experience building a factory up there and how our lunar mining experience is little more than a dozen people and a handful of rovers picking up interesting looking rocks, versus given how much experience we need down here to get things right, even Musk's organisation skills and ability to enthuse people and raise capital has limits. But these are timescales where those skills don't last (even if he resolves his political toxicity that currently means the next Democrat administration will hate his guts and do what they can to remove most of his power), because he will have died of old age.
> Clearly this person was referencing a financial efficiency predominantly through uptime.
I read the person you are quoting differently, as them misunderstanding and thinking that the current 1 TW-peak/year manufacturing was 1 TW-after-capacity-factor-losses/year.
if the thermal radiation panels have ~3 x the area of the solar panels, the temperature of the satellite can be contained to about 300 K (27 deg C). Ctrl+F:pyramid to find my calculations.
I looked, and you outlined a solution that would be hard to achieve in a vacuum chamber on earth. Now we're going to launch it into orbit and it will work great?
Building data centers in Antarctica with nuclear power would be easier. And still way harder than necessary.
Yes, how would you simulate a 4K background in a vacuum chamber on earth... or you could just trust a law that has withstood 150 years the test of time by physicists...
for solar panels that are say 25% efficient, that means 75% of optical energy is turned into heat, whereas the sand had a relatively high albedo, its going to significantly heat up the local environment!
No. It is enough for me to see such a single ridiculous statement of such magnitude to discount the rest of your voluminous contributions to this thread.
I'm dumbfounded, most light incident on a solar panel is not reflected, so logically photons were absorbed, some generated useful electron hole pairs pushing current around the load loop, others recombined and produced heat.
Its an entirely reasonable position in solar panel discussions to say that a 20% solar panel will heat as if 80% of the optical energy incident on the panel was turned into heat. Conservation of energy dictates that the input energy must equal the sum of the output work (useful energy) and output heat.
Not sure what you are driving at here, and just calling a statement ridiculous does not explain your position.
You have not done any real world verification on any of this, you are arguing from a very flawed and overly simplistic lay-persons theoretical model of how solar panels must function in space and then you draw all kinds of conclusions from that model, none of which have been born out by experiment. 25% efficiency for a solar panel means that 25% of the sunlight incident on a panel was turned into electricity. It has nothing to do with how big a fraction is turned into heat, though obviously the more of it is turned into electricity the less there is available to be converted into heat. And it does not account for other parts of the spectrum that are outside of the range that the panel can capture.
That 25% is peak efficiency. It does not take into account:
(1) the temperature of the panel (higher temp->lower efficiency), hence the need for passive cooling of the panels in space due to a lack of working fluid (air).
(2) the angle of the incidence: both angles have to be 'perfect' for that 25% to happen, which in practice puts all kinds of constraints on orientation, especially when coupled with requirements placed on the rest of the satellite.
(3) the effects of aging (which can be considerable, especially in space), for instance, due to solar wind particles, thermal cycling and so on
(4) the effect of defects in the panels causing local failure that can cascade across strings of cells and even strings of panels
(5) the effects of the backing and the glass
(6) in space: the damage over time due to mechanical effects of micro meteorite impact on cells and cover; these can affect the panels both mechanically and electrically
To minimize all of these effects (which affect both operational life span of panels as well as momentary yield) and effectively to pretend they do not exist is proof that you are clueless, and yet you make these (loud) proclamations. Gell-Mann had something to say about this, so now your other contributions suffer from de-rating.
1) yes solar panels should be cooled, but this is feasible with thermal radiation (yes it takes surface area)
2) pointing the panels straight at the sun for a sun-synchronous orbit is not exactly unobtainium technology
3) through 6) agreed, these issues need to be taken into account but I don't see how that meaningfully invalidates my claim that a solar panel operated at 25% efficiency turns ballpark ~75% of incident photons into heat. Thats basic thermodynamics.
OK I read the story (it was shorten than expected).
So simplistically put there are 3 periods:
1) the grassy period before overgrazing, lot of wind
2) the overgrazed period, loss of moisture retained by plants and loss of root systems, lot of wind results in soil run-away erosion without sufficient root systems
3) the solar PV period: at higher heights still lots of wind, but the installation of the panels unexpectedly allowed the grass to regrow, because wind erosion is halted.
The PV panels actually increase the local heating, but that doesn't need to directly equate to temperature: the wind just carried away the heat so it's someone else's problem :). Also the return of soil moisture thanks to the plants means a return of a sensible heat buffer, so the high temperature in the overgrazed period before solar panel introduction may not actually be an average temperature increase, but an increase in peak temperature during the summer. Imagine problematic summer temperatures, everybody would be talking about the increased temperature, when they are really just experiencing the loss of a heat buffer.
> > absolutely massive radiator here, many times larger than the solar panels
> A_radiator / A_PV = ~3;
Seems like you're in agreement. There's a couple more issues here--
1. Solar panels are typically big compared to the rest of the satellite bus. How much radiator area do you need per 700W GPU at some reasonable solar panel efficiency?
2. Getting the satellite overall to an average 27C temperature doesn't necessarily keep the GPU cool; the satellite is not isothermal.
My back of the envelope estimate says you need about 2.5 square meters of radiator (perhaps more) to cool a 700W GPU and the solar panel powering the GPU. You can fit about 100 of these GPUs in a typical liquid-cooled rack, so you need about 250 square meters of radiator to match one rack. And, unfortunately, you can't easily use an inflatable structure, etc, because you need to conduct or convect heat into that radiator.
This assumes that you lose no additional heat in moving heat or in power conversion.
And they’re going to mass a -lot-. Not that anyone would use a pyramid— you would want panels with the side facing the sun radiating too. There are plenty of surfaces that radiate more than they absorb at reasonable temperatures in sunlight.
First of all a note on my calculations: they appear very simple, and its intentional, its not actually optimized, its intended to give programmers (who enjoyed basic high school physics but not more) the insight that cooling in space while hard, is still feasible. If you look around the thread you'll find categorical statements that cooling in space is essentially impossible etc.
The most efficient design and the most theoretically convincing one are not in general the same. I intentionally veer towards a configuration that shows it's possible without requiring radiating surface with an area of a square Astronomical Unit. Minimizing the physics and mathematics prerequisites results in a suboptimal but comprehensible design. This forum is not filled with physicists and engineers in the physical sciences, most commenters are programmers. To convince them I should only add the absolute minimum and configure my design to eliminate annoying integrals (for example the heat radiated by earth on the satellite is sidestepped by simply sacrificing 2 of the triangular sides of the pyramid to be mere reflectors of emissivity ~0, this way we can ignore the presence of a nearby lukewarm earth). Another example is the choice of a pyramid: it is convex and none of the surfaces are exactly parallel to the sun rays (which would result in ambiguity or doubt, or make the configuration sensitive to the exact orientation of the satellite), a more important consequence of selecting a convex shape is that we don't have to worry about heat radiated from one part of the satellite surface, being reabsorbed by another surface of the satellite (in view of the first surface), a convex shape insures no surface patch can see another surface patch of the satellite. And yes I pretend no heat is radiated by the solar panel itself, which is entirely achievable. So I intentionally sacrifice a lot of opportunities for more optimal design to show programmers (who are not trained in mathematical analysis, and not trained with physics textbook theorem-proof-theorem-proof-definition-theorem-proof-...) that physically it is not in the real of the impossible and doesn't result in absurdly high radiator/solar panel area ratios.
To convince a skeptic you 1) make pessimistic suboptimal estimates with a lot of room for improvement and 2) make sure those estimates require as little math and physics as possible, just the bare minimum to qualitatively and quantitatively understand the thermodynamics of a simple example.
You are asking the right questions :)
Given the considerations just discussed I feel OK forwarding you to the example mini cluster in the following section:
It describes a 230 kW system that can pretrain a 405B parameter model in ~17 days and is composed of 16x DGX B200 nodes, each node carrying 8x B200 GPUs. The naive but simple to understand pyramid satellite would require a square base (solar PV) side length of 30 m. This means the tip of the pyramid is ~90m away from the center of the solar panel square. This gives a general idea of a machine capable of training a 405B parameter model in 17 days.
We can naively scale down from 230 kW to 700 W and conclude the square base PV side length can then be 1.66 m; and the tip being 5 m "higher".
For 100 such 700 W GPU's we just multiply by 10: 16.6 m side length and the tip of the pyramid being 50 m out of the plane of the square solar panel base.
Why bother with all this crazy geometry? Why not just area as I've done above? You can design a radiator so that barely any of the light shines back on the spacecraft.
Your differences from my number: A) you're working based on spacecraft average temperature and not realizing you're going to have a substantial thermal drop; B) you're assuming just one side of the surface radiates. They're on the same order of magnitude. Both of us are assuming that cooling systems, power systems, and other support systems make no heat.
You can pick a color that absorbs very little visible light but readily emits in infrared-- so being in the sun doesn't matter so much, and since planetshine is pulling you towards something less than room temperature, it's not too bad either.
None of these numbers make me think "oh, that's easy". You're proposing a structure that's a big fraction of the size of the ISS for one rack of GPUs.
I don't really think cooling in space is easy. The things I have to do to get rid of an intermittent load of 40W on a small satellite are very very annoying. The idea of getting rid of a constant load of tens of kilowatts, or more, makes me sweat.
As I said, my geometry and properties are chosen to be easy to understand with a minimum of knowledge and mathematics.
Yes, I could make more optimistic calculations: use the steradians occupied by earth, find and use the thermal IR emissivities of solar panels place many thin layers of glass before the solar panel allowing energy generating photons through and forming a series of thermal IR black body radiators as a heat shield in thermal IR, the base also radiates heat outwards and at a higher temperature, use nonsquare base, target a somewhat higher but still acceptable temperature, etc... but all of those complicate the explanation, risking to lose readers in the details, readers that confuse the low net radiative heat transfer between similar temperature objects and room walls in the same room as if similar situation applies for radiative heat transfer when the counterbody is 4 K. Readers that half understand vacuum flasks / dewars: no or fewer gas particles in a vacuum means no or less energy those particles can collectively transport, that is correct but ignores the measures taken to prevent radiative heat loss. For example if the vacuum flask wasn't mirror coated but black-body coated then 100 deg C tea isolated from room temperature in a vacuum flask is roughly 400 K versus 300 K, but Stefan Boltzmann carries it to the fourth power (4/3) ^ 4 = 3.16 ! That vacuum flask would work very poorly if the heat radiated from the tea side to the room-temperature side was 3 times higher than the heat radiated by the room temperature side to the tea-side. The mirroring is critical in a vacuum flask. A lot of people think its just the vacuum effect and blindly generalize it to space. Just read the myriad of comments in these discussions. People seriously underestimate the capabilities of radiative cooling because the few situations they have encountered it, it was intentionally minimized or the heat flows were balanced by equilibrium, not representative for a system optimized to exploit radiative heat transfer.
Some small corrections:
>Both of us are assuming that cooling systems, power systems, and other support systems make no heat.
I do not make this assumption! all heat generated in the cooling, power and other support systems stem from electrical energy used to power them, and that energy came from the solar panels. The sum of the heat generated in the solar panel and the electrical energy liberated in the solar panel must equal the unreflected incident optical power. So we can ignore how efficient the solar panel is for the rest temperature calculation, any electrical energy will be transformed to heat and needs to be dissipated but by conservation of energy this sum total of heat and electrical energies turned into heat must simply equal the unreflected energy incident on the solar panel... The solar panel efficiencies do of course matter a lot for the final dimensions and mass of the satellite, but the rest temperature is dictated by the ratio of the height of the pyramid to the square base side length.
>You can pick a color that absorbs very little visible light but readily emits in infrared-- so being in the sun doesn't matter so much, and since planetshine is pulling you towards something less than room temperature, it's not too bad either.
emissivity (between 0 and 1) simultaneously dials how well it absorbs photons at that wavelength as well as how efficiently it sheds energy at that wavelength. A higher emissivity allows the solar panel to cool faster spontaneously, but at the cost of absorbing thermal photons from the sun more easily! Perhaps you are recollecting the optimization for the thermal IR window of our atmosphere, the reason that works is because it works comparatively to solar panels that don't exploit maximum emissivity in this small window. The atmospheric IR window location in the spectrum is irrelevant in space however.
> A) you're working based on spacecraft average temperature and not realizing you're going to have a substantial thermal drop;
of course I realize there will be a thermal gradient from base to apex of the pyramidal satellite, it is in fact good news: near the solar panel base the triangular sides have wider area and hotter temperature, so it sheds heat faster than assuming a homogenous temperature (since the shedding is proportional to the fourth power of temperature). When I ignore it it's not because I'm handwaving it away, it's because I don't wish to bore computer science audience with integral calculations, even if they bring better news. Before bringing the better news you need to bring the good news that its possible with similar order of magnitude areas for the radiator compared to the solar panels, without their insight that its feasible first, its impossible to make them understand the more complicated realistic and better news picture, especially if they want to not believe it... Without such proof many people would assume the surface of the radiator would need to be 10's to 100's of times the surface area of the solar panels...
> B) you're assuming just one side of the surface radiates.
No, I even explicitly state I only utilize 2 of the 4 side triangles of the pyramid (to sidestep criticisms that earth is also radiating heat onto the satellite). So I make a more pessimistic calculation and handicap my didactic example just to show you get non-extreme surface ratios even when handicapping
the design. If you look at history of physics, you will often find that insights were obtained much earlier by prior individuals, but the community only accepted the new insights when the experimental design was simplified to such an extent that every criticism is implicitly encoded in the design by making it irrelevant in the setup, this is not explicitly visible in many of the designs.
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 all basically boils down to: in order to dissipate heat, you need something to dissipate heat into, e.g. air, liquid, etc. Even if you liquid cool the GPUs, where is the heat going to go?
On Earth, you can vent the heat into the atmosphere no problem, but in space, there's no atmosphere to vent to, so dissipating heat becomes a very, very difficult problem to solve. You can use radiators to an extent, but again, because no atmosphere, they're orders of magnitude less effective in space. So any kind of cooling array would have to be huge, and you'd also have to find some way to shade them, because you still have to deal with heat and other kinds of radiation coming from the Sun.
What you're describing is one of two mechanisms of shedding heat which is convection, heating up the environment. What the long comment above is describing is a _completely_ different mechanism, radiation, which is __more__ efficient in a vacuum. They are different things that you are mixing up.
that page has not a single calculation of radiative heat dissipation, seems like he pessimistically designed the satellite avoiding use of radiative cooling which forces him to employ a low operational duty cycle. Kind of a shame to be honest, given the high costs of launching satellites, his sat could have been on for a larger fraction of time...
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.
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.
Not so. Look at the construction of JWST. One side is "hot", the other side is very, very cold.
I am highly skeptical about data centers in space, but radiators don't need to be unshaded. In fact, they benefit from the shade. This is also being done on the ISS.
"I meant they would need a clear path to open space not blocked by solar panels, but yes, a hot and cold side makes sense."
This is precisely why my didactic example above uses a convex shape, a pyramid. This guarantees each surface absorbs or radiates energy without having to take into account self-obscuring by satellite shape.
The goal of JWST is not to consume as much power as possible, and perform useful computations with it. A system not optimized for metric B but for metric A scores bad for metric B... great observation.
this makes no sense, the radiation of heat from the GPU's came from electrical energy, the electrical energy came from the efficient fraction of solar panel energy, the inefficient fraction being heating of the solar panel, the total amount of heat that needs to be dissipated is simply the total amount of energy incident on the solar panels.
at ~20% solar panel efficiency, we need 1.15 MW of optical power incident on the solar panels.
The required solar panel area becomes 1.15 * 10^6 W / 1.360 * 10^3 W / m ^ 2 = 846 m ^ 2.
thats about 30 m x 30 m.
From the center of the square solar panel array to the tip of the pyramid it would be 3x30m = 90 m.
An unprecedented feat? yes. But no physics is being violated here. The parts could be launched serially and then assembled in space. Thats a device that can pretrain from scratch LLaMa 3.1 in 16.8 days. It would have way to much memory for LLaMa 3.1: 16 x 8 x 192 GB = ~ 25 TB of GPU RAM. So this thing could pretrain much larger models, but would also train them slower than a LLaMa 3.1.
Once up there it enjoys free energy for as long as it survives, no competing on the electrical grid with normal industry, or domestic energy users, no slow cooking of the rivers and air around you, ...
We're talking past each other I think. In theory we can cool down anything we want, that's not the problem. 8 DGX B200 isn't a datacenter, and certainly not anywhere close to the figures discussed (500-1000tw of ai satellites per year)
Nobody said sending a single rack and cooling it is technically impossible. We're saying sending datacenters worth of rack is insanely complex and most likely not financially viable nor currently possible.
Microsoft just built a datacenter with 4600 racks of GB300, that's 4600 * 1.5t, that alone weights more than everything we sent into orbit in 2025, and that's without power nor cooling. And we're still far from a single terawatt.
it is instructive to calculate the size and requirements for a system that can pretrain a 405B parameter transformer in ~ 17 days.
a different question is the expected payback time, unless someone can demonstrate a reasonable calculation that shows a sufficiently short payback period, if no one here can we still can't exclude big tech seeing something we don't have access to (the launch costs charged to third parties may be different than the launch costs charged for themselves for example).
suppose the payback time is in fact sufficiently short or commercial life sufficiently long to make sense, then the scale didn't really matter, it just means sending up the system described above repeatedly.
I mean yeah if you consider the "scale" to not be a problem there are no problems indeed. I argue that the scale actually is the biggest problem here... which is the case with most of our issues (energy, pollution, cooling, heating, &c.)
The real question is not scale, but if it makes financial sense, I don't have sufficient insight into the answer to that question.
Either it does or it doesn't make financial sense, and if it does the scale isn't the issue (well until we run into material shortages building Elon's Dyson sphere, hah).
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.
the point wasn't that a 1 m^2 solar panel could theoretically be kept reasonably cool at the cost of a miles long radiator... nono, the point was that you could attain any desirable temperature this way, arbitrarily close to 4K.
for a reasonable temperature (check my comment for updated calculations) the height of a square based pyramidal satellite would be about 3 times the side length of its base, quite reasonable indeed. Thats with the square base of the pyramid as solar panel facing the sun, and the top of the pyramid facing away, so all sides are in the shade of the base. I even halved my theoretical cooling power to keep calculations simple: to avoid a long confusing calculation of the heat emitted by earth, I handicapped my design so 2 of the pyramidal side surfaces are reflective (facing earth) and the remaining 2 side triangles of the pyramid are the only used thermal radiative cooling surfaces. Less pessimistic approaches are possible, but would make the calculation less didactic for the HN crowd.
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.
The ISS goes into Earth's shadow for ~45 minutes and then in the sun for 45 minutes, in 24/7 repeat;
this system would not be given such an orbit. Its trivial to decrease the cooling capacity of the radiators: just have an emissivity ~0 shade (say an aluminum foil) curtain obscure part of the radiator so that it locally sees itself instead of cold empty space. This would only happen during 2 short periods in the year.
The design issues of the ISS are totally different from this system.
"Satellites have to be boosted all the time because of drag."
On Low Earth Orbits (LEOs), sure, but the traces of atmosphere that cause the drag disappear quite fast with increasing altitude. At 1000 km, you will stay up for decades.
> 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
The larger you make the area, the more solar energy you are collecting. More shade = more heat to radiate. You are not actually making the problem easier.
no the radiator planes are in the shade, so you can increase the height of a pyramidal shaped satellite for a constant solar panel base, and thus enjoy arbitrarily low rest temperatures, check my calculation which I added.
for a target temperature of 300K that would mean the pyramid height would be a bit less than 3 times higher than the square base side length h=3L.
I even handicapped my example by only counting heat radiation from 2 of the 4 panels, assuming the 2 others are simply reflective (to make the calculation of a nearby warm Earth irrelevant).
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.
When a physicist says arbitrarily large it could even be in a dimensionless sense. It doesn't matter how small or large the solar panel is:
for a 4 m x 4 m solar panel, the height of the pyramid would have to be 12 m to attain ~ 300 K on the radiator panels. Thats also the cold side for your compute.
for a 4 km x 4 km solar panel the height of the pyramid would be 12 km.
https://news.ycombinator.com/item?id=46862869
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