Question Musings about Oneil cylinders

jedidia

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So my brain lately started of its own accord to pick together bits and pieces for a science fiction setting in a run-down dyson swarm. I find the idea appealing since it offers a lot of common space opera tropes like world hopping, exotic cultures and ancient abandoned ruins packed with high-tech treasures without bending physics and logic out of shape too much (no super-drives, no FTL, and "planets" of hats suddenly make a lot more sense too).

Naturally this got me interested into orbital megastructures like ONeil cylinders, but there's a few things about those that I don't quite get, and some people here might explain to me a bit better.

First off, there's them mirrors... I get that they're supposed to get sunlight in, but I can't quite figure out the benefits of that versus just sticking on solar panels and do the lighting with electrical power.
As I understand it, the actual interior of the cylinder is not used for farming, since that would require a ridiculous amount of soil and rather cumbersome irrigation systems. So the only benefit would be for people to enjoy actual sunlight, which we know is important for human health, but I figure if we can build an Oneil cylinder, we should be able to build a lamp that can emulate sunlight well enough for that.
On the downside we have transparent sections in the cylinder walls. What material would they be made of? Transparent Aluminium would be a candidate I guess, since that is an actual thing now, but that's a lot of very expensive material just to let the sun in.
You'd lose a lot of living area too, at least judging by the concept drawings, and then there's micrometeorites and space debries to consider, and people might get nausea from seeing the spinning starscape (though that probably wouldn't last more than a generation).
Radiation shielding would also be a concern, though probably not so much if you can keep cylinder facing the sun reliably enough (which is why, as I understand it, ONeil cylinders were originally proposed to come in coupled pairs, so you could control their attitude with slight manipulations in the spinrate of the cylinders.
But all in all, is there any significant advantage to the mirror/window design that I'm missing? You would still need solar panels anyways because you'll want electricity, so all in all they seem pretty useless for the effort.

Another point I'm a bit unclear about is armor... You'd need some form of it. Just having a steel cylinder won't cut it in the long run. But you also don't want to spin up megatons of dead mass. So now I'm wondering if it wouldn't be a much better idea to melt down some asteroids to form a protective shell, and then having the actual habitat cylinder spinning inside it. Might also be a nice idea to line that outer shell with a water tank or maybe a layer of ice, and you have radiation shielding and seizable water reserves. Having a static outer shell instead of spinning the whole thing also makes for a good dock, attachment points for all those solar panels and anything else you might prefer to do in a non-spinning frame of reference.

So the picture forming in my mind does not quite match the cool concept art... From the outside, this thing would be a still cylindrical block made out of molten down and reshaped silicates with a large solar farm, "surface" docks and possibly some factories and labs for zero-G specialised stuff sticking out of its surface, while on the inside it's an enclosed, window-less cylinder with an oversized neon tube equivalent running down its axis. Does that make sense?

The next thing I can't quite wrap my head around is how one would actually transit convieniently between the spinning interior and the outside. As far as I can see that's not just a problem of the design I outlined above, but a general one. It's my understanding that in the original oneil cylinder vessels aren't docking directly to the spinning part either, but maybe I'm wrong.
Now the problem here is not so much how you would get a person, or a couple of persons, through there. What about freight? If 10 million people are living in there, there would be some traffic. While it's technically possible to run such a thing as an enclosed ecology, if there's a swarm of such and similar structures it's hard to imagine there wouldn't be a decent amount of trade going on between them, though usually only limited to manufactured high-tech goods or maybe highly specialised agricultural produces (patents can be a female dog even in a dyson swarm, I imagine...). So how would you efficiently get a few tons of cargo per day in and out of such a thing without messing up its rotation in the long run?

And finally, there's those pesky farming modules of the original oneil cylinder. I have not found any clarification of why they have to be outside the cylinder, and why they take the shape of small cylinders arrayed in a ring much larger in diameter than the actual colony itself, though maybe the concept drawings are just misleading that way.
The drawings also make it look like that ring is not part of the spinning section of the cylinder, but rather part of the static structure connecting the two cylinders. That would excarbate the transition problem outlined above, as now you have to get the entire food supply for 10 million people in there each day (and presumably, at some point, a whole lot of garbage out of there again).
Wouldn't it be more sensible to have the whole agricultural "section" somewhere in the cylinder itself? Does anybody know the reason for their particular shape and positioning?

Anyways, it would be nice to discuss these things with some fellow geeks. And what better place than this? :cheers:

EDIT - appended a question I had but completely forgot when writing this initial post

Wind... To produce one G, the floor of the habitat will be spinning at about 9 m/s, which is a lot slower than we move on earth, but there's no rotating gravitational field pulling the air along with it... Would that mean that you'd essentially get a constant stiff breeze? If no, why not? And if yes, what are the possibilities to mitigate that?
 
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Ravenous

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Somewhere on the web is a very large PDF version of the early design studies. I saw is a few years ago. They include basic mechanical stresses on the hull, arrangements for the hydroponic gardens, etc...

Edit: this might be the one I'm thinking of (a bit slow to load):

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19790024054.pdf

---------- Post added at 04:21 PM ---------- Previous post was at 04:08 PM ----------

Another point I'm a bit unclear about is armor... You'd need some form of it. Just having a steel cylinder won't cut it in the long run. But you also don't want to spin up megatons of dead mass. So now I'm wondering if it wouldn't be a much better idea to melt down some asteroids to form a protective shell, and then having the actual habitat cylinder spinning inside it.

I saw this idea somewhere - possibly in documents from the O'Neill studies. The idea was I think a shell of moon rock (waste from the processes that built the Island) surrounding the actual hull. This shell would not rotate, but would be quite close to the walls of the rapidly rotating hull... eek...
 
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Urwumpe

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The mirrors make more sense in terms of effectivity - Remember, even a good solar array just converts 35% of the sunlight into electricity.
 

jedidia

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Edit: this might be the one I'm thinking of (a bit slow to load):

https://ntrs.nasa.gov/archive/nasa/c...9790024054.pdf

Not specifically about giant rotating habitats, but definitely lots and lots of extremely interesting stuff that is applicable. Thanks a lot for that!

This shell would not rotate, but would be quite close to the walls of the rapidly rotating hull... eek...

Well, I guess how close you want to cut it depends mostly on how much material you have available for the shell. If the material is easy enough to supply, which I think would be reasonable to expect when building say a fifth generation habitat (a "finished" swarm consists of millions of habitats, so at some point supply of materials has to become very very routine), you could put quite a margin in between there. So maybe older habitats in the swarm could well be unshielded steel cylinders (or comparable materials), while after a few generation they'd switch to rotating cylinders in a shell. I'm not sure what the chances are of the "pioneer habitats" surviving the first thousand years, though.

The mirrors make more sense in terms of effectivity - Remember, even a good solar array just converts 35% of the sunlight into electricity.

True... so you'd have the mirrors for heating and lighting, but I guess the bulk of the colony's energy requirement would still have to be supplied in electric form. So it seems to me you'd need sizable solar arrays anyways. Unless you have fusion of course, but then you definitely wouldn't need to bother with mirrors. Fission would be rather impractical I think, since the fuel is hard to come by and a pain to work with.
On the topic of heating I guess I'll have to do some math, but on the first glance i'd guess that a steel shell in a vacuum containing a few million people and being at approximately the orbital radius of earth would have more trouble with cooling, but I haven't run the numbers yet. In any case, if the tendency went the wrong way round and you'd lose more heat than you generate, you could just build it closer to the sun...

---------- Post added at 10:30 PM ---------- Previous post was at 10:15 PM ----------

I appended another question to the initial post that I wanted to ask, but completely forgot when writing the post.
 
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jedidia

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So I'm starting to get some questions answered from that paper provided by Ravenous. Might as well summarise some of them here for general consumption.

The reason for building the farms as modularly and not include them in the overall structure seems to be that every single one of them seems to be intended to be a self-contained unit. They might not be perfectly redundant, since they might have different specialisations, but the idea seems to be that each of them is an ecosystem in its own right, in order to prevent catastrophic cascades through the entire colony's ecosystem in case something went terribly wrong.
I'd argue that on the other hand a single large ecosystem can take a lot more abuse before it collapses, but I guess it makes sense to prefer "maintenance-heavy, but recoverable" to "largely self-balancing, but if you miss the train you might as well be under it".
Also, I learned that volume per person is calculated in two different sections, one for low recyclability and one for high recyclability, and the volume for high-recylable space seems to be over twice as much... In other words, if you'd build the general living space to the same standards as the farms, where you want to recycle every drop of dew, you could fit a lot less people. I guess that makes sense.


I also learned a lot about mirrors/windows/lighting. Something that honestly shocked me was that actual window glass is proposed for the windows, at a thickness of a mere 5.65 cm (well, transparent aluminium was still science fiction back then...). But they would be relatively small. So those square-kilometers of windows you see in the concept art of oneil cylinders? Yeah, that would be thousands upon thousands of individual glass panes built into a lattice, and apparently they intended to shield them with chevrons built from moon rocks. Also, the mirrors would only reflect the visible light to reduce the thermal load on the habitat, so I guess I was right about the cooling concerns.

And the reason for the whole thing seems to be, as Urwumpe pointed out, that it's cheaper than the alternative. In case of lighting for agricultural area apparently up to 6 times cheaper. Still, if you would plan for the thing to be inhabited for geological timespans, that would probably be saving on the wrong end. So adjustments to these concepts have to be made if you plan a swarm that should serve as the living space for the larger part of the future human race...
 
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Urwumpe

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Well, I like the modularity concept for the farms, but I would not design them as independent units. I would rather have something like resource management there - managing demands of animals, humans or plants vs available production, storage or industrial capacity.

I agree, such a small ecosystem like a O'Neill cylinder must be treated more like a zoo than a farm, you can't hope for nature fixing itself in a way that prefers human survival.
 

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Wind... To produce one G, the floor of the habitat will be spinning at about 9 m/s, which is a lot slower than we move on earth, but there's no rotating gravitational field pulling the air along with it... Would that mean that you'd essentially get a constant stiff breeze? If no, why not? And if yes, what are the possibilities to mitigate that?

The air on Earth is *not* pulled along by gravity. You don't get significant frame dragging unless an object is very close to being a black hole (or actually a black hole) and rotating very quickly. The air on Earth is kept rotating with the solid surface by plain old friction, which would apply to an O'Neil cylinder as well.
 

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The air on Earth is *not* pulled along by gravity. You don't get significant frame dragging unless an object is very close to being a black hole (or actually a black hole) and rotating very quickly. The air on Earth is kept rotating with the solid surface by plain old friction, which would apply to an O'Neil cylinder as well.

Yes, if the cylinder rotates long enough, the air would be rotating with it. Initially it might be different. But some small amount of longitudinal wind might be useful to allow a better transport of gases there.

---------- Post added at 22:55 ---------- Previous post was at 22:54 ----------

The whole paper about how to construct a Orbital habitat might make a nice Orbiter add-on, don't you think?
 

jedidia

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I would rather have something like resource management there - managing demands of animals, humans or plants vs available production, storage or industrial capacity.

They do have that, of course, though they don't seem to go into too great detail (i.e. no hard numbers). But there's an ecosystem flowchart on page 15 explaining the circulation, though it seems to me that it's incomplete for briefness' sake.
 

Ravenous

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There's a "1983 O'Neill OMNI Interview" at this location:

http://www.askmar.com/Massdrivers/

On page 6 of that PDF he talks about food a little. He likes the idea of agriculture being separate to allow a lower oxygen concentration, different temperature/humidity etc.

Also there's a NASA document SP-413, HTML (text only) version is here:
https://settlement.arc.nasa.gov/75SummerStudy/Design.html
Pretty pictures for this:
https://settlement.arc.nasa.gov/70sArt/art.html
(There's also a big PDF version of this on the net somewhere but I've lost the link I'm afraid. It does contain a lot of simpler line drawings not included in the HTML version I've linked though.)

Chapter 4 of SP-413 mentions putting the agricultural areas outside the main area would reduce the overall shielding mass required - presumably they reckoned less shielding would be needed for the agri areas. (Note the document seems to be talking about the smaller Torus habitat, not the enormous cylinders, but the same reasoning might well have applied at the time.)

So these are probably the reasons they went for farms outside of the main habitat.

The summer study was in the '70s... there seems to be newer stuff below, which I haven't read yet (again, doesn't necessarily apply to your specific questions but may be worth considering):
https://settlement.arc.nasa.gov/
 

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Another thing on mirrors vs. solar panels, regardless of efficiency, recall that when the concept was first proposed, solar cells were a relatively new technology, and cost around $100/watt.
 

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Although the O'Neil cylinder sounds like totally awesome concept, I can't see any reason to build Dyson swarm out of these. Why would anyone do it? Wouldn't it be cheaper and more rational for an advansed civilization to change species itself to fit different environments rather than creating environment to fit species' capabilities absolutely useless outside of this environment? I find the O'Neil cylinder a developmental dead end in the long term, but an exciting experiment for the nearest future (nearest on the scale of centuries of course). I'm afraid the Dyson swarm will rather consist of robotized facilities, and planets will be inhabited by quite a diverse species not necessarily resembling their human ancestors.
In my thinking the problem of all the space operas is that there are people of XX-XXI centuries playing with toys of XXII-inf. And I expect us to change together with our toys.
 
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Ravenous

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Although the O'Neil cylinder sounds like totally awesome concept, I can't see any reason to build Dyson swarm out of these. Why would anyone do it?

You're quite right, it's a very far-out concept that might work in theory but would be incredibly costly.

I think of these things as a really interesting bit of engineering speculation, done when the world was very different, and of course in the 40 years since we know a lot more about our own physiology as well as things like ecology, launch systems, etc.

Personally I watch the idea because I like it, simple as that. Pretty sure nobody will actually spend the money in the next half century! Ultimate long-term technologies beyond a few million years will no doubt be very different :)
 

jedidia

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Wouldn't it be cheaper and more rational for an advansed civilization

To be honest, I have little hope that humanity will ever get rational, no matter how advanced...
But I do agree with the general point of your argument. It's not a probable future. But a possible one, at least for a dialectic definition of possible. The trouble is, foreseeing an actually probable future is almost impossible. It will always be wild guessing based on reasonable conjectures that can never consider all of the factors, and even less consider future technological capabilites.
 
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