Setting Background I'm working on an admittedly silly sounding setting. Technologically advanced space fairing humans become stranded on a ring of asteroids in orbit around a large planet. They have lost the vast majority of their technology in the process of becoming stranded, but the existing stations keep them alive. They rebuild slowly. The micro-gravity that they live in makes space travel accessible at a far lower level of technological process, and so by the time they have reached what we might consider medieval tech, they are scooting around the vacuum of space in resin-laminated wooden ships propelled by compressed air.

Mechanical Power I've got most of this figured out already. Don't worry about how the ships work, don't worry about how life support works. What I need to know is what these people use as a source of mechanical energy for tasks like milling, air circulation, etc.

Constraints No electricity. No non-human animals of any kind. And no offense to people who are into this, but I am desperately trying to avoid steam power in order to keep this from getting too "Steam Punk". Like the ancient Greeks and many other peoples from antiquity, these folk understand that pressurized steam has force to it, but lack the mechanical precision to make an efficient steam engine - something that took a long time to figure out!

Materials Cast iron, low quality steal, copper alloys, dandelion sap rubber, wood, plant fiber cloths, and leather from human skin. Open to other materials if they make sense for the setting.

Ideas so far

  1. Temperature differential. Exploiting the dark side/light side of the asteroids.

  2. Tidal force. The planet that these asteroids orbit presumably has a very strong tidal force on these little asteroids. Would some sort of crank ratchet pendulum be able to generate a sufficient amount of power?

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    $\begingroup$ They do have muscles, don't they? They push the spokes which turn the wheels which turn the mill. (And air circulation is part of the life support system, so that it's magically taken care of.) (And I don't get the part about the tidal force. Tidal force is basically due to the difference between gravitational acceleration here and there: it depends on the size of the object; it may be quite large across a hundred kilometer asteroid, but it will be negligible across a two meters long human.) $\endgroup$ – AlexP Nov 18 '20 at 19:10
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    $\begingroup$ Do the habitats have nanotechnology-fused self-repair capabilities? Otherwise they will become uninhabitable in decades at best, due to wear and tear. $\endgroup$ – vsz Nov 19 '20 at 10:47
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    $\begingroup$ Where are they getting the gases for compressed-gas thrusters? Only thing I can think of is their own atmosphere...which would be limited in volume and tend to escape anyway, over time. Not saying a bad idea (I love it), but this is my hangup with it. Also, reminds me of a short story I read long ago (can't remember the name), where humans turned "right" at the industrial revolution, and others turned "left" to find a low-tech mechanism of FTL travel that we missed, but the rest of their tech was stuck at a medieval stage. They got a rude awakening when they arrived to conquer Earth... $\endgroup$ – Doug R. Nov 19 '20 at 16:00
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    $\begingroup$ @DougR. : The road not taken. (but they travel planet to planet, so they can replenish their air, which gets very stale during the journey) $\endgroup$ – vsz Nov 19 '20 at 16:22
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    $\begingroup$ Feudal is a type of societal organization. It has nothing whatever to do with the level of technology. You could easily have a feudal society with a very high level of technology (and could probably find any number of SF stories built on such a premise :-)) I think the word you want is medieval. $\endgroup$ – jamesqf Nov 19 '20 at 17:01

Asteroid wheel.



Saturns moon Daphnis cruises along in a gap that it has cleared in one of the rings. The rings are made of smaller stuff. Your medievals live on a similar rock and have erected wheels about the circumference of their rock. Like a waterwheel, these extract energy from impacting icy rubble as they pass by the slower ring on the outside and the faster on the inside.

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    $\begingroup$ After trying to write my own answer, I realized I was expressing the same idea you are. Those big rocks are already in motion - they just need something to create drag that could then translate into mechanical energy. Like your waterwheel idea. +1! $\endgroup$ – JBH Nov 18 '20 at 22:21
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    $\begingroup$ Worth noting that this solution slowly destroys itself as it sweeps out an ever-wider channel. Fun plot hooks! $\endgroup$ – Joe Bloggs Nov 18 '20 at 22:48
  • $\begingroup$ Interesting! For this solution, would it help to make this a very young solar system? As Joe notes, eventually the debris would be cleared. $\endgroup$ – Pink Sweetener Nov 18 '20 at 23:50
  • $\begingroup$ @JBH - this does seem like your kind of answer. Now I want to read your version. As regards young solar system not necessarily. If the ring is made of pulverized moonlets you can regenerate them to some degree by having moonlets in the rings grind against each other. $\endgroup$ – Willk Nov 19 '20 at 3:11

I’m shamelessly stealing from the late, great Sir Terry Pratchett here but:


Nobody knows how they were made. Like the Habitats, they are relics of a bygone age. A Device does nothing but turn, or reciprocate, or wiggle, with impossible torque and seemingly endless energy. Though they might have previously had some purpose they are now naught but motive curiosities.

Your people have hoarded what devices they can find, amassing some thousands of them. They have learnt the secrets of starting/stopping them and figured out methods to harness their immeasurable power using only primitive materials. One ship can get all the mechanical power it needs from a single Device, but as the supply is limited and nobody knows how to make more they are inconceivably valuable.

After all, how can one mill grain without the help of an unstoppable, indestructible, unfathomable, ancient motor?

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    $\begingroup$ If all the device does is turn, the people would only have to invent a clutch, not figure out how to stop and start it. $\endgroup$ – Charles Bamford Nov 20 '20 at 2:09

Solar Powered Stirling Engine or Solar Sail "Wind"mills

This can depend on the star your planet and asteroids orbit, but you can have the light heat a black surface to create the temperature differential of a Stirling engine.

Stirling engines only need small differences in temperature to work

Solar Sails are large, thin sails used by small spacecraft. They operate off the miniscule amount of momentum delivered by photons, it may be small, but it is constant acceleration over a long period of time. These are used to move low mass objects to high speeds. You could set up solar mills that instead of sails moved by the wind, the photons move your massive sails.

Both of these would be best paired with Cast-Iron Flywheels with magnetic bearings. The heat differential and the photon momentum will be delivering low energy, but these can be built up to useable levels with a flywheel.

This is where the micro-gravity and vacuum help you out. If you are lucky enough to have some magnetic material, you can create an almost frictionless flywheel that has constant energy fed into it as long as the star shines. Your only real limits would be how much light your asteroids receive and the strength of cast iron. If you receive too much light, your flywheel could rip itself apart.

  • $\begingroup$ @PinkSweetener, your choice is ultimately your own, but given your stated stance on steam engines and precision, a Stirling engine is comparatively harder to machine. I only bring this to your attention so you have the opportunity to keep your world's workings consistent - if your people have reasonable lathes and drills they can build pistons for most any engine configuration. $\endgroup$ – Sean Boddy Nov 21 '20 at 5:29

Look at H. Beam Piper's novel Space Viking.

Piper was always pessimistic about human government. In this novel he posits an Industrial Feudal society. feudal does not have to equal low tech. Economically each company/fiefdom is in essence a company town, with services and employment provided by the fief holder. Individuals may have subfiefs within the fief. Each has oaths of fealty to the level above, and fief holders have duties and obligations to those below.

Another example is Larry Niven's novel Oath of Fealty which amounts to a feudal micro society within a broader capitalistic one.

At it's core feudalism is a set of non equal but symmetric set of duties and obligations.

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    $\begingroup$ Can you provide more details? At the moment this answer looks like a "link only" answer, without the hyperlink. $\endgroup$ – L.Dutch - Reinstate Monica Nov 19 '20 at 3:18
  • $\begingroup$ I thought about this set of novels, but dismissed them because they didn't match the tech level requested. So I'm glad you brought them up. :-) $\endgroup$ – Doug R. Nov 19 '20 at 15:57
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    $\begingroup$ "feudal does not have to equal low tech." What's the motivation for a landlord to provide high-tech equipment to hereditary tenant-farmers? If you say "higher productivity!", that leads to fewer tenant farmers. Since they must go somewhere, they head to cities, and that breaks down the feudal system. $\endgroup$ – RonJohn Nov 19 '20 at 16:47

Maybe you could harness a cryovolcano or geyser? I think those typically have methane in them, though, so I can't imagine why they wouldn't just burn that if their habitat is somehow still giving them enough of an earth-like atmosphere to burn wood and cast iron.

  • $\begingroup$ No atmosphere on asteroids! They're living in habitats with big big greenhouses. Do asteroids have geysers? $\endgroup$ – Pink Sweetener Nov 18 '20 at 19:21
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    $\begingroup$ en.m.wikipedia.org/wiki/Ahuna_Mons The actual level of cryovolcanic activity in the asteroid belt is unknown. There's still a whole lot in general we don't know about them. Ahuna Mons was only discovered in 2015. I know Ceres is a dwarf planet, but it's in the asteroid belt and presumably other solar systems could have belts with even more dwarf planets. $\endgroup$ – Morgan Nov 18 '20 at 19:42

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