[OneDonOne]

This borders on science fiction. 88,000-and 1-million satellite clusters (as claimed in your link) are hard to take seriously, especially with the possibility of Kessler Syndrome. Also:

1. How do you cool your chips? Vacuum is a thermal insulator, so radiators are required to remove heat. nVidia (or even ASICs) require much and specialised cooling.

2. How does one radiation harden a H100?

3. I'm also seeing where TCO for these are 78x their terrestrial equivalents [0]. Is that financial sustainable?

And there still remain issues with power supply, regulations, and bandwidth. This feels more like a thought experiment rather than an actual serious engineering or business case.

[0] https://www.abiresearch.com/blog/data-centers-in-space

[alephnerd]

The projections are questionable, but this is something the US and China are experimenting with as well.

1 and 2 are still open questions, but these are not aimed to be commercial grade DCs - this is basically edge compute (think a handful of racks). 3 is not a problem for defense usecases. (EDIT: Discussion here seems to point out that data OP is using might be flawed [1]).

Ignoring the fact that just about every orbital data center startup in the US is funded by IQT and China's CMF has been doing something similar is bad from a defense perspective.

Based on dealflow, these aren't being targeted for consumer usecases in the short-term and whoever has been saying that is misleading.

> especially with the possibility of Kessler Syndrome...

India, Russia, China, and the US don't care about Kessler Syndrome - they have already launched and deployed ASATs. This also comes after India and China had a near collision in 2024 that was treated as an offensive action [0].

[0] - https://www.bloomberg.com/news/articles/2025-09-22/india-pla...

[1] - https://news.ycombinator.com/item?id=49039873

[AlotOfReading]

    3 is not a problem for defense usecases.

Cost is the critical constraint for defense programs. Yes, militaries spend a shit-ton of money, but that's usually in a penny wise and pound foolish way. A dollar spent on your project is a dollar that's not spent on the innumerable things generals think are critical to their future wars like boondoggles, missiles, planes, ships, missile defense systems, etc.

The exception is if you're one of those rare projects. A starlink type constellation or launch capabilities certainly could be, but it's hard to imagine generals getting excited about compute in space just for the sake of it.

[taneq]

It is critical to avoid a boondoggle gap.

[OneDonOne]

This reminds me of the railgun. Basic math and physics tells us that not only would the (very expensive) barrels wear out very quickly, but that it would have had to be fitted on on a nuclear-powered pocket battlecruiser.

Worse, the technology for firing any meaningful payloads from an electric gun (8" Small Diameter Bomb equivalents, guided, airburst, incendiary) simply does not exist.

Same as with Musk's California Vacuum Tunnel (which diverted attention from passenger rail). And his Neuralink. In the 1980s, it was nuclear pumped space-based lasers and Soviet particle beam weapons.

All of the above can be debunked with 2 years undergrad physics and a Casio calculator. Yet they were still taken seriously by high-level politicians and business, some of whom were deeply connected with the military-industrial complex.

People have shrugging of questions like 1 and 2, only for 3 to hit them very hard. But we will see if they can launch 600 of these satellites as they claim.

[alephnerd]

As raynier and pfdietz pointed out [0], the assumptions you are using aren't necessarily correct.

[0] - https://news.ycombinator.com/item?id=49039873

[OneDonOne]

Ah yes. The heat pump.

My response:

Carnot's theorem and refridgeration cycles rear their head. Your heat pump still needs power to pump heat uphill., negating any savings from a smaller radiator. And what happens when you shrink a radiator? It becomes a high temperature radiator, meaning the GPU must operate outside its operational tmperature of about 70 degrees C. So small radiator = big pump + extra solar panels and batteries + dead GPU

Also, how do you deal with the added cost and complexity for the solar tracking mechanisms for the "edge-on-to-the-Sun" radiator?

[pfdietz]

Yes, that was your response. It was a terrible and obviously invalid response, as I explained.

You never explained why the GPU temperature had to increase. Could you explain that now? The GPU would be on the cold side of the heat pump, not the hot side.

> Also, how do you deal with the added cost and complexity for the solar tracking mechanisms for the "edge-on-to-the-Sun" radiator?

We ignore that issue, because we were debunking a bad argument about "the laws of physics". The laws of physics say nothing about budgets or complexity.

[selimthegrim]

Soviets definitely experimented with airborne CO2 lasers.

[OneDonOne]

It just goes to show magical thinking isn't just an American thing.

[kulahan]

I can’t imagine how inefficient a country would be if they tamped down all their magical thinking. FFCS, SMILE, and EUVL are all magical thinking if you ask me. Some of the craziest things humans have ever conceived of.

[avmich]

Full-flow staged combustion is a rather logical - and not even particularly useful, we're talking about small percentage points - extension of staged flow combustion, and staged combustion is a rather obvious change to open-cycle schema - and I'm hyperbolizing just a little bit here.

Yes, it brings effects, and it's a cool technology. But saying that at least idea - or results - are fundamentally changing rocket engines... I think that's a stretch.

[selimthegrim]

laser enrichment of uranium

[TeMPOraL]

> 1. How do you cool your chips? Vacuum is a thermal insulator, so radiators are required to remove heat.

This is space 101 and honestly, at this point, I consider bringing this up as disqualifying from giving criticism on the topic.

> nVidia (or even ASICs) require much and specialised cooling.

Whatever. They generate N kW of heat, you need to shed N kW of heat, and you need to fit that within your budget. End of worry.

Pro tip: if you can slice your problem so that individual satellite needs to shed less than M kW of heat, where M corresponds to how much heat some existing, deployed satellite platform handles, you can just do your initial design around that satellite platform, replacing the "business payload" with yours.

This is e.g. how the unfairly criticized recent "satellite swarm TPUs" paper from Google handled it. Everyone who brought up cooling revealed themselves as not having read the first page and not having thought about it seriously for more than 30 seconds.

> 2. How does one radiation harden a H100?

See that paper for some ideas and considerations, as this is part of what they focused on, after solving cooling by sizing the per-satellite payload power needs to Starlink.

[Alive-in-2025]

Yeah, there's no solution for heat dissolution at this time.

You can run a few cpus in space, you are a few seconds closer to the data to figure out something basic, but you cant do that much calculation. If you do much cpu intensive stuff, you just get hot quickly and you can't dissipate the heat. I'm sure new ways to cool down will be developed, but there's not even any experimental techniques, right?

[avmich]

ISS collects ~250 kW solar power. All of that needs eventually to be dissipated - the energy removed by communication radiowaves is small. ISS routinely handles this thermal question for decades.

There is nothing magical with cooling in space. Just a different environment - a rather well studied already, we send satellites to space for some 70 years almost. Saying there is no solution is incorrect - we have options, we have numbers, we can point to concrete questions and answers.

[LargoLasskhyfv]

1. By using some form of liquid droplet radiator, as described in these:

https://en.wikipedia.org/wiki/Liquid_droplet_radiator

https://ntrs.nasa.gov/citations/19850005591

https://ntrs.nasa.gov/citations/19810062992

https://spectrum.ieee.org/orbital-data-centers-heat

2. By producing them on intel 18A, like Starfire:

https://duckduckgo.com/?q=intel+foundry+18A+starfire

( Or going for different substrates, like Gallium-arsenides, Gallium-nitrides, Silicon on Sapphire, by using https://en.wikipedia.org/wiki/Heterojunction_bipolar_transis... on https://en.wikipedia.org/wiki/Indium_phosphide 's , enabling insane speeds & photonics.

To be fabbed here, possibly:

https://www.nist.gov/news-events/news/2026/06/department-com...

Or whichever other new metamaterial may come along. )

Now imagine the medium of these liquid droplets to directly flow through micro-capillaries in on-die cooling channels.

Good Morning! Ring, Ding, Ding, Rrrrriiiinnnnng!

[taneq]

(1) seems to be the big question to me. Surely it would be much cheaper to simply stick a data centre up in the mountains somewhere, low enough to be fairly easy to reach but high enough to be nice and chilly?

[holoduke]

Why do you need radiation hardening? We don't need hyper deterministic systems in those setups.

[amluto]

You need your chip to not completely fail. Latch-up can destroy things. A complete failure of a SERDES may dramatically reduce the utility of the whole system.

[NetMageSCW]

Explain to the class why Kessler Syndrome isn’t possible with large LEO constellations.

[SiempreViernes]

It is in fact possible to have the Kessler syndrome in LEO, the debris doesn't just immediately fall out of the sky so in practice you just need to put more satellites into a specific orbit to reach the critical density where one satellite breaking leads to a runaway chain reaction.

In actual reality it's estimated that several segments of LEO have already reached criticality, especially around 600 km: https://conference.sdo.esoc.esa.int/proceedings/sdc9/paper/3...

[mayama]

In case of collision in LEO, wouldn't the debris have chance to go high altitude and cause further collisions?

[cyberax]

No. It'll stay in essentially the same orbit.

During collision, some of the energy will be lost, so the fragments will necessarily have a lower orbit.

The only thing that can accelerate fragments into a substantially higher orbit is the energy of elastic deformation of material during the explosion.

[lanstin]

Can’t two solid object with equal kinetic energy collide in such a way that most of the energy goes into one of them, giving it a velocity that boosts its orbit while the other one has lower velocity and de-orbits?

Or one object explode into two fragments, equal and opposite relative velocity, again pushing the one half into a higher orbit and de-orbiting the other half?

(Honest question, math major, never took orbital mechanics or played KSP much).

[cyberax]

> Can’t two solid object with equal kinetic energy collide in such a way that most of the energy goes into one of them, giving it a velocity that boosts its orbit while the other one has lower velocity and de-orbits?

Sure, you can. Imagine shooting a bullet into a tungsten cube. The cube will go into a higher orbit, and the bullet will bounce back (and maybe de-orbit).

But the kicker here is that for this to work, the bullet has to be in a _higher_ orbit than the cube initially. So the end result is still fewer objects in higher orbits.

Another option is momentum transfer via elastic deformation - you shoot a bullet into a 45-degree facet of that tungsten cube, and the bullet then ricochets into a higher orbit. It ultimately works by momentarily storing the energy of the projectile as a plastic deformation of the facet. So it can't accelerate more than a few small fragments.

[crewindream]

In a form of a question: does low earth orbit has big enough drag to be effectively do automatic cleanup every several years?

[nine_k]

The answer is positive. LEO satellites need orbital corrections every few weeks, and some, several times a week.