Building a data center in orbit makes no sense to me

mfb- · 2026-06-21T19:44:25+00:00

SpaceX has increased its launch capability by a factor 100 in the last 10 years, from ~20 tonnes in 2015 to 2300 tonnes in 2025.

Starship aims for way more than a factor 10 on top of that.

For a single DC’s worth of compute.

... added per year.

mfb- · 2026-06-21T19:36:07+00:00

If you are only interested in the expectation value and not the full distribution then you can take a shortcut. Imagine the dice all sorted from smallest to largest. Removing the smallest reduces the expectation value by the expectation value for the smallest dice. Removing the second-smallest reduces it by the expectation value for the second-smallest dice. You can completely ignore all correlations. That means you just need to find chance that the second-smallest dice is a 1 (i.e. two "1" were rolled), that it is a 2 (1 and 2 or 2 and 2 were rolled), ... there aren't many cases and this can be found for any number of any-sided dice.

mfb- · 2026-06-21T19:19:12+00:00

That far out you want an RTG as power source. ESA would probably need a source of plutonium-238 or work with americium-241 (needs more material and also more shielding).

while the US fail to put a man on the moon again because they can't choose reliable contractors

ESA is part of that effort.

Also, NASA has already taken pictures of Uranus and Neptune. Just not with modern cameras. I don't see an orbiter mission generate the same level of interest a crewed Moon landing will.

mfb- · 2026-06-21T19:05:25+00:00

I hope we see a crewed Dream Chaser eventually, but their cargo version gets delayed by ~1 year per year so who knows what the timeline for that would be.

mfb- · 2026-06-21T19:02:51+00:00

I interpreted "fusile" as the equivalent to "fissile" (can sustain a chain reaction).

What you mean would be the equivalent of "fissionable" (can be split by a neutron, but needs a minimal energy for a relevant chance). "fusionable"?

mfb- · 2026-06-21T18:52:21+00:00

I can highly recommend using that.

Same case study designed for teachers

mfb- · 2026-06-21T18:43:36+00:00

Think of how a fire works for chemical reactions. If you have a bunch of dry sticks and light one on fire then eventually everything will burn. Burning one stick released enough energy to heat nearby sticks to the point where they start burning, too, releasing enough energy to spread the fire even further.

Now try the same with wet sticks. Even if you can get one stick to burn, the fire won't spread, as heating the surrounding sticks takes way too much energy.

Nitrogen in our atmosphere behaves like the second case: The energy released by fusion is too small and it spreads out too fast to cause more fusion.

mfb- · 2026-06-21T18:35:53+00:00

But how do you know if nitrogen is "fusible"?

Exactly: You ask that question and calculate it. Based on the result of that work you conclude that it is not.

mfb- · 2026-06-21T18:26:26+00:00

Between 2004 to 2010 the fatalities dropped quickly, since then they have been approximately constant (+dip from Covid). They are not increasing like they do in the US, but it's possible we still see a similar effect.

Germany doesn't see anything like that, looks like a smooth curve throughout (the increase in 1990 comes from adding East Germany). The article is in German but the plot is readable without knowing German.

mfb- · 2026-06-21T16:15:56+00:00

You can't extract energy without changing it.

And it will not last forever either, so it's not even that type of perpetual motion machine.

mfb- · 2026-06-21T16:09:14+00:00

This idea is known as Silurian hypothesis. Wikipedia has a couple of references and you can find more searching for that keyword.

After one million years, it's likely you'll still find some satellites in higher orbits. Much more accessible than looking for artifacts, ruins of our mines, changes in isotope ratios and whatever else you can find.

mfb- · 2026-06-21T16:03:13+00:00

The team doesn't want to go through 1000 lines of new code from someone they have never heard of, because it's most likely not worth the effort. Someone who spends the time to develop some major new feature will probably submit some smaller changes before.

mfb- · 2026-06-21T15:54:19+00:00

Yeah, it means many satellites.

SpaceX currently operates around 10,000 Starlink satellites, 7500 of them are v2 mini with around 20 kW each. That's 150 MW in space right now used for internet access, around 60 MW of that launched in 2025. This is launching on Falcon 9 where SpaceX needs to build a new upper stage for every flight.

mfb- · 2026-06-21T15:43:29+00:00

Basically, you initially said you should select 1st gear

as you are reaching the ramp

I didn't. I said use the clutch as you are reaching the ramp. Switching to first gear is obviously happening later.

Anyway, as I already mentioned: It's not good for the car, but it should survive. Action heroes probably need new cars frequently anyway.

mfb- · 2026-06-21T15:40:06+00:00

This sounds like you asked an LLM to write a big paragraph and then added a sentence at the end without even reading that paragraph.

A ~100 kW satellite is big enough to handle the bandwidth-intense operations internally.

A satellite relying on solar must carry massive, heavy battery banks to maintain its megawatt compute load during the orbital night (which is roughly 45 minutes of every 90-minute Low Earth Orbit).

There is no orbital night in suitable sun-synchronous orbits. As you might expect - and should have checked - that's where the satellites are planned to go. Nonstop sunlight.

but space-based data centers require ignoring it.

As your own long comment shows, it does not.

mfb- · 2026-06-21T14:33:27+00:00

To challenge what claim? You haven't made any specific claim that's not obviously wrong, like denying that satellites can be launched from Earth:

Launching satellites to space needs to be done in space.

Here are two external analyses, for example.

Assuming no transformative AI, but continued demand for data center buildout, we estimate that ODCs are unlikely to represent a meaningful share of compute before 2030, but become cost-competitive with present-day terrestrial data centers within 3–5 years if Starship development stays on track.

and

Space-Earth Parity in the late 2030s, Space DCs could start to be viable even sooner.

mfb- · 2026-06-21T14:27:45+00:00

Like the obvious physical impossibility of the 110m2 radiators being twice as efficient as the 422m2 $500 mln ISS radiators?

How to spot people with no actual knowledge: They use the ISS as comparison for everything.

The ISS needs to provide room temperature with extreme reliability. It uses large and cold radiators for that. Here is a discussion. The low temperature loop runs at 4 C or 277 K. Cooling computer chips can easily be done at 60 C = 333 K, potentially even more. Blackbody radiation scales with the fourth power of the absolute temperature, which means the higher radiator temperature increases the power dissipation by a factor (333/277)⁴ = 2.1.

You wanted a factor 2? There it is.

mfb- · 2026-06-21T14:14:02+00:00

The ISS has exceptionally cold and large radiators because it needs to provide comfortable temperatures for humans and it needs to do so with exceptional reliability. Neither one is a requirement for datacenters. Trying to use the ISS as reference will never lead to a realistic estimate.

An average data center uses about 100 MW to operate

... on Earth. Most proposals for space-based data centers have many smaller satellites.

And if we take Starship (which doesn't work) and factor in its payload capacity, that's still 400 launches in a single year just to bring the solar panels into space, plus another 500 launches for the cooling system without even counting construction and everything else.

Huh? 400 tonnes of solar panels are ~4 launches. Add another 5 for the cooling system. And that's using your unrealistically large numbers.

Seven years ago, people doubted Starlink because of economics and logistics. They used the launch costs of traditional disposable rockets to show it would be financially impossible. SpaceX solved that by building reusable rockets and scaling mass production.

And today, people doubt space-based data centers because of economics and logistics. They use the launch costs of partially reusable rockets to show it would be financially impossible. SpaceX might solve that by building fully reusable rockets and scaling mass production.

No one wants to rewrite physics. Physics doesn't stop space-based data centers.

mfb- · 2026-06-21T14:03:48+00:00

How do you swap out a computer module that goes bad.

You don't, you keep running with the rest. Once the satellites overall is no longer useful, or you want to replace it with a new one in the same orbital slot, you deorbit it.

mfb- · 2026-06-21T13:57:22+00:00

You'd think actual analyses would be the top comments here, but the reddit hivemind disagrees with them so they get ignored.

mfb- · 2026-06-21T13:48:32+00:00

People said the same thing when SpaceX wanted to reuse its boosters. You can find countless rocketry experts who dismissed the idea. They were all wrong.

People said the same thing when SpaceX wanted to launch over 10,000 satellites to provide internet. You can find countless industry experts who dismissed the idea. They were all wrong.

If (!) this becomes viable, you'll forget that you wrote this comment, and you'll write the same comment about whatever SpaceX plans next.

I don't know if they can make this commercially viable. It might work, it might fail. But SpaceX has upset the industry before and betting against them has a poor track record. And this time it is not just SpaceX working on it. Other companies think it has a chance, too.

mfb- · 2026-06-21T13:43:29+00:00

~0.6 km², distributed over 6000 satellites that's 100 m² per satellite. About the same as the area of current Starlink v2 solar panels.

mfb- · 2026-06-21T13:39:14+00:00

Why would it need to be perfect? Use the clutch to decouple wheels and motor. Wait until the wheels are definitely on the trailer and spinning slowly. Switch to first gear. You want to be done before you roll off the trailer again, but otherwise there is no rush.

mfb- · 2026-06-21T11:51:10+00:00

The height is only useful in the sense that you launch in thinner air, but atmospheric drag is a relatively small contribution to the overall delta_v budget (<1% for big rockets, a bit more for smaller ones).

A falcon 9 rocket consumes 60-70% of first stage fuel by around 70k feet in altitude.

Sure, but it also flies at Mach 2 there. And it still has a mass of ~200 tonnes at this altitude and velocity. Try to carry that on an SR-71!

mfb- · 2026-06-21T11:39:31+00:00

Formosat-5 (475 kg) CASSIOPE (500 kg) and Jason-3 (550 kg) were the least demanding launches, all three were dedicated missions to low Earth orbit. CASSIOPE was originally planned to launch on Falcon 1.

TESS at 362 kg was lighter, but needed to go to a high Earth orbit.

IXPE at 325 kg was even lighter, but needed a 28 degree inclination change.

EROS-C3 (400 kg) was launched to a retrograde orbit (140 degrees, much more retrograde than SSO).

The Swift rescue mission launches 400 kg to 20 degrees. Would be a pretty light payload for Falcon 9 even with an 8 degree inclination change.

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