Where is my von Braun wheel?
85 comments
·July 3, 2025PaulHoule
perihelions
Ceres is very far away orbitally. It's three times further than Mars, but also has no braking atmosphere or gravity. If you send a payload to Ceres, that payload has 5 km/s of relative velocity that can only be zeroed out with rocket propulsion. (That's a lot).
It's not coincidence the first Ceres orbiter was also a flagship prototype for advanced electric propulsion. It's a deceptively remote target.
PaulHoule
Granted. I don't see it as a Muskian "send 10,000,000 people and keep sending them supplies" kind of thing but rather "send 100 people, 1,000,000 eggs and the closest thing to a Drexler machine that we can make" kind of thing. The latter is what I think the BoM for a successful Mars colony looks like too.
tim333
I'd imagine, given the rate of progress with AI and robots, the most practical would be to send robots ahead and have them build the infrastructure for some people to maybe visit later?
jandrese
I had a back of the napkin design that was basically a sleeve that fitted over Starship and could be launched into orbit. Those sleeves had angled ends that could then be bolted together in orbit to make a station with an octagon shape that could be spun at 2 or 3 rpm to get 1/2 Earth gravity. Obviously still an enormous engineering challenge, but one that I think is solvable using today's tech. Well, tomorrows tech, but nothing that requires a breakthrough in materials science or basic physics or anything like that.
My plan was to fit the inside with huge water bags that would help to reduce cosmic radiation, provide thermal mass, and slow any micrometeorites that puncture the hull. The water could be launched on cheaper rockets and transferred in orbit. The water could also be pumped between sections to keep the wheel balanced. The central hub area would be more of a challenge, probably having to be assembled (or at least unfolded) in orbit.
Probably the biggest downside is that you wouldn't be able to spin it up until the entire structure was somewhat balanced, which means installing things like solar panels and radiators in pairs and the docking bit of the central hub would probably need to be on bearings so it can counter rotate to be effectively stationary or you wouldn't be able to dock more than 2 spacecraft at a time. The ISS was built in sections over the course of decades, this would need to be built all in one go, which is a huge commitment.
NASA's plans for two tethered stations (or one station and a counterweight) are probably more feasible, but much less cool.
mr_toad
> large amounts of nitrogen or some other inert gas
You could ship liquid ammonia and then burn it to produce nitrogen and water.
TMEHpodcast
Starship feels like the ultimate engineering gamble, so many moving parts (literally) that getting it right might be as hard as building the habitats it’s meant to launch.
On nitrogen, I keep wondering: if in-space manufacturing matured, couldn’t we generate atmosphere by cracking water for oxygen and synthesizing nitrogen analogues through hydrogen-based pathways? Or is Earth’s air mix so specific that importing nitrogen stays unavoidable?
PaulHoule
Starship to LEO is technologically conservative -- it's hard for me to believe that something like that couldn't be made to work. The uncertainty is that there's not a big market right now for launching things that size but the hope is that the low cost creates the market and maybe Starlink bootstraps it. If it succeeds as an LEO cargo hauler it can be successful without getting man rated or perfecting refueling.
Refueling to go father is technically risky and the performance often not that exciting. If you aren't able to refuel on the Moon, Starship lands and returns roughly 3.5 tons, not better than the Apollo LEM which a much larger vehicle that is tall and tippy -- landing on inner solar system bodies that it is covered with boulders.
Now it might make sense to put a full load of cargo on it, leave it on the Moon and use it as living space, storage tanks or something, but that's not the plan right now. Refueling on the Moon looks tough: water on the moon looks like a good bet, if we're lucky we find frozen carbon sources at the poles or in asteroid residues on the surface [1], but a hydrogen-oxygen rocket looks like a surer thing.
As for alternatives to local nitrogen there is: (1) producing it by nuclear processes which looks tough and (2) various other alternative breathing gases such as Argon, Helium, SF6, etc.
[1] Not clear though if we want to spend any of those on reaction mass or incorporate them in a circular economy. Actual colonists would see it differently than flatlanders. (See The Moon is a Harsh Mistress and The Martian Way)
dylan604
> The uncertainty is that there's not a big market right now for launching things that size
Is that true? It seems like there have been the want of lifting large payloads that must be shrunk to fit the actual launch capabilities. This usually means sacrificing so the thing that is launched is not what was really wanted originally. I think the market is there and just waiting for the thing to work.
boznz
Hard challenges are good and setbacks are to be expected if you are pushing every limit. I would love to be on such a fast moving team with such a massive payoff if they succeed.
bryanlarsen
> the ultimate engineering gamble
It's a no-lose gamble though. If they fail we still end up with SuperHeavy as a massive, cheaper Falcon like architecture. If it succeeds, finally our space dreams can start to be realized.
null
jitl
Where are you going to get the water? What makes water mass cheaper to orbit compared to nitrogen mass?
TMEHpodcast
Closed-loop systems like on the ISS already reclaim water from humidity, sweat, and urine, and could be scaled up for larger habitats. Air works similarly: CO₂ is scrubbed, oxygen is regenerated from electrolysis, and trace gases are filtered. I realize you still need an initial stock of oxygen and nitrogen, but isn’t this a problem that could be solved eventually with science?
dylan604
Hang out a big butterfly net and capture the dirty snowballs that float past.
There have been lots of new releases of frozen water discoveries on various bodies. Typically in craters that pretty much stay in shadow. Water doesn't seem to be that scarce. It's just not as abundant as on Earth
schiffern
>What makes water mass cheaper to orbit compared to nitrogen mass?
Nitrogen needs a high-pressure bottle which is wasted mass, whereas water you can send to orbit in thin plastic and fabric bags like they do on ISS.
Often on ISS they're actually shipping oxygen as water, but still the wasted mass of water being 11% hydrogen plus the wasted mass of the bag is more efficient than a high pressure gas cylinder.
lukan
"(5) Colonization of Ceres dominates all other space colonization opportunities in the solar system because there is no shortage of water and no shortage of nitrogen."
What about gravity?
PaulHoule
Rotation. You don’t live on the surface but you build a beanstalk and build a big framework of small O’Neill’s cylinders. See
https://arxiv.org/abs/2011.07487
I’d say this paper thoroughly debunks all other space colonization plans in comparison. For instance it is not sustainable to use rockets for routine transformation. The moon doesn't have enough volatiles. Who knows if gravity on the Martian surface is enough to be healthy.
Even if you could take, say, Mercury, apart it would be silly to build a ‘Dyson swarm’ but rather you would build a big framework like that or a ‘Dyson foam’ (e.g. if you took Mercury apart and turned it into a solar collecting structure 1m thick you could capture enough energy to make a few tons of antimatter a second for interstellar travel)
Animats
All the things worth doing in space turned out to be do-able without humans. Telescopes, radio relays, etc. The ISS doesn't really have much of a mission. Here's the list of current ISS experiments.[1] Many are aimed at the problems of keeping humans alive long term without gravity.
[1] https://www.nasa.gov/mission/station/research-explorer/searc...
avmich
The was a long discussion about benefits of human space exploration. A comparison was made between that and basic science: just like the basic science doesn't bring immediate benefits, so do humans in space. However over long periods of time both could prove to be worthwhile.
pimlottc
> Popularised by von Braun in his 1949 sci-fi novel, Project Mars
Von Braun's novel was written in 1949 but wasn't published until 2006. Perhaps the author means the technical appendix "The Mars Project" [0] which was published in 1952, which spawned a series of articles [1] in the popular magazine Collier's from 1952 to 1954.
0: https://en.wikipedia.org/wiki/The_Mars_Project
1: https://en.wikipedia.org/wiki/Man_Will_Conquer_Space_Soon!
PicassoCTs
Could a automated factory melt moon regolith into ringsegments, which are then send into moon orbit, assembled and spun up? So far the problem seems to be the launch cost with heavier, durable materials, or m i misunderstanding the problem?
bryanlarsen
Long term zero gravity experience and experiments were very important information for future space flight. Now we know a lot more about the muscle atrophy, bone loss, and vision problems that the author complains of. Having the first space station be zero-g was probably the right move.
But for the second one, more information on artificial gravity through centripetal force makes a lot of sense.
lupusreal
The problem is the ISS wasn't the first station and we already knew zero-g fucks people up long before the ISS was built. Building the ISS anyway so we can waste more time studying the minutia of exactly how badly and quickly it fucks people up was a mistake. In truth the ISS exists for political reasons, not because it was a sound investment from a science and research perspective.
bryanlarsen
Congratulations, your alternate history has delayed Mars colonization by several decades.
Because of the ISS we know that stays of greater than 12 months in zero gravity have real but minor impacts on the human body. So 3-4 month trips to Mars in zero-g are feasible.
If we assume they aren't, those trips would be far more resource intensive.
lupusreal
And another thing:
We still have no idea what long term stays in Martian or even Lunar gravity does to a human body. We don't know because we have spent the past half a century fucking around with useless zero-g space stations instead of building von Braun wheels which could easily be used to simulate those conditions. Because forget about Mars colonization, merely finding the political willpower to do something as conceptually simple as spinning in space is evidently impossible for us.
lupusreal
We didn't learn any of that from the ISS which we didn't already know from Salyut 6 and 7, and Mir. The ISS, aka Mir 2, hasn't taught us anything new. The reason it exists is because decades ago, for a few years, manned space stations made sense for orbital reconnaissance because putting unmanned cameras in space was complicated. Salyut and MOL were born from this transient strategic necessity. Unmanned recon satellites soon became practical though, so MOL was canceled but the Soviets carried on with Salyut because if there was anything they were good at, it was continuing to make something long after anybody else would have canceled it. Even when they did get recon satellites they did it with Vostok capsules, they never stopped making those after launching Yuri Gragarin in one. They just kept on making them because they were already tooled up for it, finding new excuses to keep making the same old stuff. And so it was with Salyut, the program was obsolete for orbital reconnaissance but they were already making them so they kept at it, turning it into a national prestige program. Mir was a direct descendant of it, built around the DOS-7 module which was a Salyut module with 6 docking ports instead of the two on DOS-6. It never had a good reason for existing besides Soviet politics. (By the way, Skylab never had a good reason for existing either, just politics. NASA trying to hold onto their funding as Apollo was wound down.)
The ISS is nothing more than Mir 2, built around the DOS-8 module, it's a Salyut with American funding because this time America wanted to keep the Russian space program solvent to make it harder for Iran/etc to recruit that Soviet talent. And because NASA likes long term projects that require around the clock staffing because that's great for budgets and careers. That's why the ISS exists.
Also we aren't going to Mars. Sorry. A lot of individuals are passionate about that but at an organization level there is no drive for it. NASA likes to use the talk of it for fundraising but never makes progress on it and Congress won't ever greenlight it, and SpaceX uses it to keep their employee moral up but all they are demonstrably working towards is being the king of launching satellites. The only money to be made in space is with stuff pointed at Earth. There is no economic case for Mars colonization. It's not happening. I wish it weren't so because I'm a sci-fi junky, but it is what it is.
dan-robertson
People begin from the premise that there should be lots of primates living away from earth, and then work backwards from there. I don’t think governments should be paying so much for such activities.
In my opinion it is not a good use of public money relative to other space projects, and crude missions to mars would likely destroy any hope of finding life there should it have existed, making them actively harmful.
It seems sometimes that for NASA, the big goal is to have a large source of steady funding is the goal, and a space station is the best way to get that (hence the insane space station in the lunar mission plan). I get some vague impression that politicians like talking about missions to the moon or mars more than space stations, telescopes or probes.
avmich
> People begin from the premise that there should be lots of primates living away from earth, and then work backwards from there.
No, people begin with interest in all things around them and from that conclude that being closer to them would be more convenient. This idea is perhaps as old as the human race itself.
Modern robots aren't as capable as humans, so if the project is big enough, human involvement is reasonable.
aidenn0
What about an "I" (or H if your font is sans-serif) shaped system? Like the Vast "stick" but with two sticks attached to the end. Seems like that would multiply the livable area by a much greater factor than it would multiply the number of launches. If I understand correctly the Vast is already a multi-launch system, so it seems like the obvious change.
schiffern
If you can tolerate +/- 5% gravity level (which should be doable), instead of a stick for the habitable area you can rearrange the modules into a more compact blob, which should reduce radiation shielding. In LEO it doesn't really matter but it's more important in deep space.
I sometimes hear this called a "barbell" design.
Someone
> For example, one of von Braun’s designs called for a massive 75 metre diameter wheel
That’s a radius of about 5% of the length of a human body, so I guess we would soon find out how humans react to living in an environment where ‘gravity’ at eye height is about 5% lower than at toe height or do we already know something about that?
lupusreal
Some people would lose their lunch, but that's nothing new for space flight. It's just a much more mellow version of classic carnival rides.
Someone
I know it’s nothing vs a rollercoaster, but people don’t regularly spend 24 × 7 in rollercoasters.
silverquiet
Not regularly, but there have been contests to see how long people will stay on a rollercoaster. Speaking from some experience, after you've gone around a few times, it can actually get rather boring.
glitchc
The first and best place to build a permanent station is the moon. The wheel could spin on the surface at a very low rpm given the Moon's existing gravity, giving us the launchpad need to build and deploy a permanent space station.
Until we settle on the moon, our forays into space will always be limited by pesky things such as Earth's gravity and atmosphere.
cosmic_cheese
I am fully in favor of doing things on the moon, but have a theory that its relative convenience is actually detrimental. Without going into a lengthy spiel, convenience means low commitment, which translates into a high likelyhood of projects getting the plug pulled.
Elsewhere, the hurdles to clear to get something started are higher, but once you’re out there it’s a lot less justifiable to reverse course.
It could very well be true that it’s necessary to settle the Moon before doing anything else, though, which could spell bad news for any endeavor involving crewed spaceflight. We might end up with a series of false starts on the Moon (due to events like funding getting pulled as a result of changing politcal winds) that end up going nowhere which then puts crewed spaceflight in a state where it's stuck in LEO perpetually.
apples_oranges
Wait would this even work? Can you add moon gravity to centrifugal space station gravity? I can’t imagine a setup where the wheel is always pushing inhabitants out in such a way that they are moved towards the center of the moon.
avmich
Yes, you add accelerations as vectors. Say, a centrifugal ring flatly lays on the Moon surface and rotates (around the axis of ring symmetry perpendicular to the ring plane) so that the artificial gravity on the centrifuge is about Earth. Moon gravity, about 1.42 m/s^2 , adds perpendicularly to that, so the total gravity is still about the Earth one. The level surface on the centrifuge is slightly tilted away from local vertical, but in essence you just added Moon gravity, vectorally, to the rotational acceleration.
kevin_thibedeau
The unitized concepts were proposed by people who didn't know the microprocessor, sophisticated electronic control systems, and compact robotics would be developed in the future. Furthermore, what rocket was going to launch that six cylinder monstrosity?
Avshalom
https://en.wikipedia.org/wiki/NERVA had already been in development for several years by 1961.
Project Orion had been proposed as early as '46.
rich_sasha
> Made from soft materials, like rubber and nylon, there were concerns that collisions with micrometeorites could puncture the station with fatal outcomes.
I fixed many an inner tube punctures, but I'd rather not be blowing at glue while my precious oxygen is hissing out towards outer space!
dylan604
Just send up a case of Flex Seal. Maybe the spreadable version instead of a spray on version. Not sure what zero-G would do to an aerosol can like that.
craig_s_bell
Even better: Make the entire structure out of Flex Seal.
tokai
I bet something like tubeless sealant could be utilized for automatic sealing.
XorNot
I mean, tapered rubber bung stoppers are a commonly used technology in day to day life...
abe94
Great read,
One question i've had is if its given that we care about making humans space faring, why focus on getting to new planets and colonisation and not instead on building the massive megastructures mentioned in the article as an end in itself?
(1) Assuming Starship makes it to orbit, it enables a range of structures larger than the ISS but smaller than the O'Neill colonies. A mission to Luna or Mars involves 12-20 launches of fuel tankers, for the same cost you can put up a lot of mass to LEO. A really flashy space hotel seems practical, as would simulation environments for Lunar, Mars and Asteroidal technology development.
(2) O'Neill colonies with large airspaces seem impractical because you'd need large amounts of nitrogen or some other inert gas: you can find oxide rocks everywhere in space but pure oxygen environments aren't safe. On the other hand, the atmosphere for an LEO baby Bernal sphere would be about 15 Starship loads and probably worth it for the visual appeal.
(3) The later work of O'Neill's students focused a lot on manufacturing. The proposal to build large structures by vapor deposition of metals onto a balloon still looks feasible. The solar power satellites shrank considerably in mass and it seemed that they could be built more practically from terrestrial materials.
(4) Any space colonization effort runs into the problem that it needs to be self-sufficient in terms of manufacturing (especially Mars) which led Eric Drexler to go off and develop his vision of molecular assemblers. Drexler's proposals haven't aged well but something equivalent that combines 3-d printing with flow chemistry, synthetic biology, fermentation and other technologies is probably possible -- and I think is the critical path. That flashy space hotel, however, really is about rocketry and space assembly of large structures which really is the unique application of space manufacturing; I don't think space manufacturing can ever be competitive for the terrestrial market but it can be competitive for things that can only be made in space.
(5) Colonization of Ceres dominates all other space colonization opportunities in the solar system because there is no shortage of water and no shortage of nitrogen. It seems possible to take the whole thing apart and build a colony with more floor space and a larger population than Earth. You don't get the 0.2 cubic kilometers of ocean that we get, but I think you can culture all the fish you can eat anyway.