Wednesday February 4 2026

Hacker Times

xAI joins SpaceX

Discussion

There are a class of people who may seem smart until they start talking about a subject you know about. Hank Green is a great example of this.

For many on HN, Elon buying Twitter was a wake up call because he suddenly started talking about software and servers and data centers and reliability and a ton of people with experience with those things were like "oh... this guy's an idiot".

Data centers in space are exactly like this. Your comment (correctly) alludes to this.

Companies like Google, Meta, Amazon and Microsoft all have so many servers that parts are failing constantly. They fail so often on large scales that it's expected things like a hard drive will fail while a single job might be running.

So all of these companies build systems to detect failures, disable running on that node until it's fixed, alerting someone to what the problem is and then bringing the node back online once the problem it's addressed. Everything will fail. Hard drives, RAM, CPUs, GPUs, SSDs, power supplies, fans, NICs, cables, etc.

So all data centers will have a number of technicians who are constantly fixing problems. IIRC Google's ratio tended to be about 10,000 servers per technician. Good technicians could handle higher ratios. When a node goes offline it's not clear why. Techs would take known good parts and basically replacce all of them and then figure out what the problem is later, dispose of any bad parts and put tested good parts into the pool of known good parts for a later incident.

Data centers in space lose all of this ability. So if you have a large number of orbital servers, they're going to be failing constantly with no ability to fix them. You can really only deorbit them and replace them and that gets real expensive.

Electronics and chips on satellites also aren't consumer grade. They're not even enterprise grade. They're orders of magnitude more reliable than that because they have to deal with error correction terrestial components don't due to cosmic rays and the solar wind. That's why they're a fraction of the power of something you can buy from Amazon but they cost 1000x as much. Because they need to last years and not fail, something no home computer or data center server has to deal with.

Put it this way, a hardened satellite or probe CPU is like paying $1 million for a Raspberry Pi.

And anybody who has dealt with data centers knows this.

solid_fuel•about 21 hours ago

It's just the thought process that comes with shallow understanding:

    "I can buy a server"
    "We can put things in space"
    "What do you mean I can't get a server in space?!"

throw0101a•about 13 hours ago

> Contrary to the narrative of the internet being about sharing science, ARPANET was pushed by the DoD as a means of maintaining comms during nuclear war.

[citation needed]

Because according to Bob Taylor, who initially got the funding for what became ARPANET:

> Taylor had been the young director of the office within the Defense Department’s Advanced Research Projects Agency overseeing computer research, and he was the one who had started theARPANET . The project had embodied the most peaceful intentions—to link computers at scientific laboratories across the country so that researchers might share computer resources. Taylor knew theARPANET and its progeny, the Internet, had nothing to do with supporting or surviving war—never did.Yet he felt fairly alone in carrying that knowledge.

> Lately, the mainstream press had picked up the grim myth of a nuclear survival scenario and had presented it as an established truth. When* Time magazine committed the error, Taylor wrote a letter to the editor, but the magazine didn’t print it. The effort to set the record straight was like chasing the wind; Taylor was beginning to feel like a crank.

* https://www.goodreads.com/book/show/281818.Where_Wizards_Sta... § Prologue

> Taylor told the ARPA director he needed to discuss funding for a networking experiment he had in mind. Herzfeld had talked about networking with Taylor a bit already, so the idea wasn’t new to him. He had also visited Taylor’s office, where he witnessed the annoying exercise of logging on to three different computers. And a few years earlier he had even fallen under the spell of Licklider himself when he attended Lick’s lectures on interactive computing.

> Taylor gave his boss a quick briefing: IPTO contractors, most of whom were at research universities, were beginning to request more and more computer resources. Every principal investigator, it seemed, wanted his own computer. Not only was there an obvious duplication of effort across the research community, but it was getting damned expensive. Computers weren’t small and they weren’t cheap. Why not try tying them all together? By building a system of electronic links between machines, researchers doing similar work in different parts of the country could share resources and results more easily. […]

* Wizards § Chapter 1

The first four IMPs were UCLA, SRI, UCSB, and Utah. Then BBN, MIT, RAND, System Development Corp., and Harvard. Next Lincoln Laboratory and Stanford, and by the end of 1970 Carnegie-Mellon University and Case Western Reserve University.

It was only "later in the 1970s" that command and control was considered more (Lukasik):

* https://en.wikipedia.org/wiki/ARPANET#Debate_about_design_go...

But the first two people who get the project going, Taylor and Herzfeld, were about the efficient use of expensive computer resources for research. Look at the firs >dozen sites and they were about linking researchers: the first DoD site wasn't connected until 3-4 years after things go going, and there was nothing classified about it. MILNET didn't occur until 1984:

* https://en.wikipedia.org/wiki/ARPANET#Operation

rkagerer•about 24 hours ago

Thanks for putting words to that; the paragraph which most stuck out to me as outlandish is (emphasis mine):

    The basic math is that launching a million tons per year of satellites generating 100 kW of compute power per ton would add 100 gigawatts of AI compute capacity annually, *with no ongoing operational or maintenance needs*.

I'm deeply disillusioned to arrive at this conclusion but the Occam's Razor in me feels this whole acquisition is more likely a play to increase the perceptual value of SpaceX before a planned IPO.

DoctorOetker•1 day ago

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.

vidarh•about 16 hours ago

Just scratching at the surface, assuming the increase in production capacity is only realistically possible if you can bring prices down (or this "project" would start to consume a proportion of economic output large enough to seem implausible), you can address the intermittency problem in several ways:

Driving down the cost makes massive overprovision a means of reducing the intermittency because you will be able to cover demand at proportionally far lower output, which also means you'll be able to cover demands in far larger areas, even before looking at storage.

But lower solar costs would also make storage more cost effective, since power cost will be a lower proportion of the amortised cost of the total system. Same with increasing transmission investments to allow smoothing load. Ever cost drop for solar will make it able to cover a larger proportion of total power demand, and we're nowhere near maximising viable total capacity even at current costs.

A whole lot of industrial costs are also affected by energy prices. Drive down this down, and you should expect price drops in other areas as well as industrial uses where energy expensive processes are not cost-effective today.

The geopolitical consequences of a dramatic acceleration of the drop in dependency on oil and gas would also take decades to play out.

At the same time, if you can drive down the cost of energy by making solar so much cheaper, you also make earth-bound data centres more cost-competive, and the cost-advantage of space-bound data centres would be accordingly lower.

I think it's an interesting idea to explore (but there's the whole issue of cooling being far harder in space), but I also think the effects would be far broader. By all means, if Musk wants to poor resources into making solar cheap enough for this kind of project to be viable, he should go ahead - maybe it'll consume enough of time to give him less time to plan a teenage edgelor - because I think the societal effects of driving down energy costs would generally be positive, AI or not, it just screams of being a justification for an xAI purchase done mostly for his personal financial engineering.

robocat•1 day ago

From [2] (abridged):

  NASA contracts alone have exceeded $13 billion since 2015, with $1.1 billion expected for 2025.

  The U.S. Space Force awarded $845 million for 2025 and $733 million for 2024.

  Commercial satellite operators are estimated to contribute between $2.5 billion and $3 billion in 2025.

schiffern•1 day ago

  >We can make ten or hundred times the number of solar cells we make right now

Tomorrow?

The limit isn't just about the current capacity or the maximum theoretical capacity, it's also about the maximum speed you can ramp.

schiffern•1 day ago

  >just use even more solar panels

I think it's because at this scale a significant limit becomes the global production capacity for solar cells, and SpaceX is in the business of cheaper satellites and launch.

jacquesm•about 16 hours ago

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.

DoctorOetker•about 10 hours ago

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:

https://news.ycombinator.com/item?id=46867402

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.

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benzible•about 11 hours ago

You are arguing against something I didn't say. I never claimed bias doesn't exist. My point is that having previously criticized someone is not evidence of bias. You are treating "this person has been critical before" as inherently discrediting, when it is just as likely they were right before and are right again now. Conversely, "I used to support him so I am not biased" is given unearned credibility when really it just means you were late to noticing the obvious, or got it wrong previously.

As for dismissing the article: the author has a PhD in space electronics, worked at NASA, and spent a decade at Google including on AI capacity deployment. He walks through power, thermal, radiation, and communications constraints with actual numbers. You do not get to hand-wave that away with "he is anti-Elon" and then defer to "the team spending the most money." That is not rational analysis, that is fandom.

And the idea that SpaceX's experts looked at this and concluded the combination makes strategic sense - seriously? This is the same playbook Musk has run repeatedly: SolarCity into Tesla, X into xAI, now xAI into SpaceX. Every time there is a struggling asset that needs a lifeline, it gets folded into a healthier entity with Musk negotiating on both sides. xAI is burning $1B/month. There is already a fiduciary duty lawsuit over Tesla's $2B investment in xAI. The "space data centers" rationale is a pretext for giving xAI investors an exit through SpaceX's upcoming IPO. This is not a strategic vision, it is financial engineering solving an obvious problem for Elon.

Meanwhile, Grok has been generating sexualized images of children, the California AG has opened a formal investigation, the UK Internet Watch Foundation found CSAM attributed to Grok on the dark web, Musk personally pushed to loosen Grok's safety restrictions after which three safety team members quit, and xAI's response to press inquiries was the auto-reply "Legacy Media Lies." This is the company whose judgment you are trusting over a domain expert's detailed technical analysis.

DoctorOetker•about 5 hours ago

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.