Hacker News Reader

Comment by GMoromisato | Hacker News Reader

Huh? Radiators are known technology. They have them on ISS; they have them on every Starlink satellite. This isn't like warp drive or antigravity.

Moreover, you can easily calculate how big of a radiator you need for a given power level and temperature. You can use the Stefan–Boltzmann law:

  A ~ (1000 P) / (2 e k T^4)

Where

  A is the radiator area in square meters
  P is the power in kilowatts
  e is emissivity (usually 0.9)
  k is the constant 5.67e-8

For a 1 kW test like Googles, you just need 1 square meter of radiators (assuming two-sided).

For SpaceX's 175 kW satellites, they will need ~170 square meters of radiators.

None of this is impossible or even difficult to calculate. That's why I think this is the laziest argument against space data centers. There are so many other more reasonable arguments (like whether they will be economically competitive) but people love to latch on to this one for some reason.

View on HN

I think you misunderstand the argument of the people worrying about cooling. I don’t think most people think it’s literally physically impossible, they just think that this will be the thing that makes it economically uncompetitive. It’s a combined argument.

That may be the argument, but it's a dumb argument. Most of the cost is going to go to chips, solar panels, and launch. Radiators are probably one of the cheapest parts of the satellite: it's a hunk of metal with some pumps for liquid cooling.

People use that argument because it takes zero thought to make and significant effort to refute.

Again you’re missing the combined argument, the cooling will increase launch costs because your hunk of metal will increase the weight of the satellite.

People use that argument because one of the chief bullshit arguments put forward by proponents of space based datacentres is "space is cold", when what they actually mean is "space lacks the possibility of using relatively efficient conductive cooling, so we need to expensively launch large amounts of additional mass to use radiative cooling, consider the extent to which we can shield our miles of active cooling loops from impact, and under current plans all of this mass must be replaced on the same cycles as the chips"

"Space is cold" is classic zero effort to make, significant effort to refute stuff: proponents imply complete nonsense about vacuums being optimal for cooling and anyone who understands why this is a lie to gull retail investors ends up getting bogged down in "sure, but Boltzmann equations proving it's prohibitively expensive doesn't prove it isn't possible"...

To your last paragraph: when opposing something, it makes sense to use the laziest argument first. Only if that doesn't achieve your goals, would you move towards less lazy arguments. I forget what the term for this is, it's generally criticized ("you should just put your strongest arguments first").

sure, the physics is solved: we know how radiators work, and we can calculate the area needed, blah blah. but we haven't put sustained-AI-computer systems into space yet - heat is a genuine concern, and personally I'm curious if they are developing something beyond simple radiators. if a ~1m^2 radiator works, great. but if the current test can only run the TPUs for ~15-minute bursts before it has to stop and dump heat, this issue isn't exactly "solved" in my book.

I don't understand your argument. Sounds like you're saying, "In theory it should work, but what if there are space pixies that keep rebooting the TPUs? What do we do then?"

The 15-minute figure is what they currently designed for because they have mass constraints. If they wanted a different figure (like forever) they could do it with a larger radiator.

As you said, the physics is solved! We know exactly how much heat a surface radiates in space--there is literally an equation for it. We know how to cool stuff in space. Will the price be low enough to make a profit? That's the real question. But stop worrying about cooling in space.

No one thinks we don't know how to cool things in space. Everyone is saying that it's not feasible because you'd have to put too much mass up. Stop derailing the conversation please.

If you have something useful to contribute regarding how to actually reasonably put up enough mass to make this remotely a feasible idea then please contribute. We have the technology to prevent global warming, and doing that is far easier than this, and yet even that is apparently not feasible for humanity.

I honestly don't get that. The current SpaceX design is for a ~4 ton satellite with 160 m^2 radiator with peak 250 kW output. You can launch 25 of those satellites on a single Starship launch. 160 Starship launches and you get 4,000 satellites with peak 1 GW compute.

What's unfeasible about that? SpaceX has already launched 10,000 Starlink satellites. Falcon 9 launches 150 times per year.

> For SpaceX's 175 kW satellites

That's like a quarter of a rack of modern AI hardware. Modern AI datacenters are now in the multi-GW range.

Okay, so you agree the cooling problem has a solution.

Now the argument is, what, you can't launch that many satellites?

The argument is that launching and operating those satellites is more expensive than just using the same silicon on the ground.

I don't think that is the argument, or if so it's an odd one because it's just a fact right now. Instead, people are claiming that it will never be feasible from a purely physics standpoint, which is something debatable.

Saying it’s impossible isn’t debatable because it obviously is. What would stop you from a physics standpoint to just launch 100 ISS with Server racks in each? A few kW of installed power in space is already reality, it’s just really expensive.

How sure are you of that? How much does each satellite cost? How much will silicon on the ground cost in 2030?

How can anyone be certain of any of those numbers without (a) knowing how the technology will evolve, and (b) doing the math?

I'm just astounded that people can have such confidence.

We know such thing as physics and economics. That dictate the fundamental limits.

They are showing that space-based DCs only make sense for criminal enterprises. Which probably IS what's going on here.

While I really don’t trust Google, I’m not sure I call them a criminal enterprise.

Reply on news.ycombinator.com