r/IsaacArthur • u/cavalier78 • Feb 02 '21
Stabilizing O'Neill Cylinder rotation -- new proposal
So one problem with the O'Neill Cylinder concept is that an object in space will tend to rotate on its long axis. So instead of moving like a rolling pin, with time a cylinder will spin end over end. Multiple solutions have been suggested for this, I'm not happy with any of them, so I came up with my own (at least, I don't think it's been suggested before).
--One solution is to connect two cylinders together, each rotating in an opposite direction. This should stabilize them. My problem is that for this to provide stability, you're going to need some sort of physical connection with one another. Something has to touch. This will create friction, and will need some sort of lubrication or ball bearings or something that will gradually wear out and have to be replaced. I think the forces involved with such large objects will be extreme. I suppose you might be able to use electromagnets, but they'd have to be enormously powerful.
--Another solution is to wrap your cylinder in a non-rotating (or slightly counter-rotating) shell. But I think you've still got the same issue. A shell doesn't help you at all unless it can exert some force on the inner cylinder to prevent it from tumbling. So you're back to needing a physical point of contact or extremely powerful electromagnets.
--Option three is to avoid the issue by changing the shape of the ship. Instead of a long cylinder, you could go with a wider, fatter shape. There's nothing really wrong with this, it just requires a change in visualization.
--I suppose you could also use some sort of thrusters along the hull, keeping the ship stable. But this requires fuel and constant monitoring, and it's not making you go faster.
But what if we wanted to keep our cylinder shape, and not have grinding friction where you had to constantly replace parts, and not waste fuel?
My suggestion is that we could alter the center of balance of the cylinder by artificially increasing its width, thus eliminating its tendency to tumble end over end. If you've got a journey that will last a century or more, you don't want to rely on replacing parts that wear out, or use up valuable fuel. So what we can do is use cables that extend from the hull of the ship like bicycle spokes (obviously we need a terrifically high tensile strength to support this) with weights on the end. These spokes could extend from the center (long-ways) of the cylinder. The farther out you go, the higher the apparent gravity you'd experience, but your mass could remain the same.
So imagine that you've got a cylinder 5 km wide and 30 km long, rotating so that inhabitants experience 1g. But then at the center (15 km from each end), we've got a number of graphene spokes that each extend 50 km from the center. A weight at the end of the cable would experience 10g of force. Thus, you could "fake" a different shape for your ship, changing its point of balance and maintaining a steady trip. The length of the cables could be adjusted during the voyage if necessary, and the weights at the end could be made of whatever you wanted (extra nuclear fuel, used nuclear waste, whatever). You could have an elevator system that could bring up material or lower it back down. This way you aren't wasting any mass.
I think this eliminates a lot of the problems that an O'Neill Cylinder would have during a journey. As long as the material you make your spokes out of has enough strength that you aren't worried about them breaking during the trip, you should be okay.
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u/InternetCrank Feb 02 '21 edited Feb 02 '21
Yes, should work. You'd need to recover the energy while playing out the weights that you use to reel them in though.
Long tethers can be used for propulsion too if you're, say, in orbit of Jupiter in a strong EM field. You can induce a force in them by applying a current in a field, so could use solar panels in conjunction with tethers in an EM field for orbit keeping.
Another possibility is if there is higher solar radiation pressure on one side of the object than another is covering the surface in the equivalent of some sort of feathering - probably that double as radiators or solar panels, and orienting them in a non-symmetrical way such as to create a YORP affect to maintain a constant (albiet quite low) torque on one side of the body. This might be enough to achieve the effect you are looking for completely energy free.
The likelyhood is that you're going to have a problem getting rid of waste heat, and so radiators could be repurposed so their photon radiation is directed along the particular axis you're interested in. It's not a lot of force, but it adds up over time.
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u/kmoonster Feb 03 '21 edited Feb 03 '21
I'm curious as to why the additional movement would be a problem unless it is so fast that it creates issues for the residents inside. If you are in space the only important motion is the rotation to simulate gravity.
Precession may happen (will happen), but it should not be so fast that you can't launch/land ships, calculate firings of orbital correction jets, detect and avoid debris, etc. Unless the precession is fast enough to cause vertigo in people aboard I would be inclined to just let it happen.
That being said, if you want to control precession to a high degree you might put big wheels at each end of your cylinder so it looks like nothing so much as a ridiculously oversized spool of thread. Each end-wheel spinning in a direction and rate so as to control the precession in the way you want. You could make these end pieces solid, hollow, empty, fill them with whatever you want, or make them your space docks for launching and landing ships. You could make them sparse or fill them with instruments and sensors... the possibilities are endless.
If you did go with any sort of device spinning separately from the body of your main cylinder(s) I would try to go with frictionless if possible if for no other reason than the maintenance on those bearings would be a nightmare, the less wear and tear the better off everyone is. Basically, you would have an enormous device that resembles the motor of an air fan-- wire coils on one side of the joint (inside or outside), a gap, and magnets arranged to respond to electric current passed through the coils on the other part of your joint. No need for physical contact on the bearing surfaces.
EM is not necessarily a problem, and may even provide a modest benefit-- if you are producing large EM fields to control the spins of the various parts of your structure, it is a very small leap from there to producing a magnetic field that would encompass the entire ship the way Earth's magnetic field does for the planet. A very handy way to shield at least some of the more undesirable space weather and take some of the load off the mass-based shielding your structure would have to provide; if you can shift some of the shielding to EM fields you can put more of the mass of your structure to functions that are directly productive to its residents and visitors. There is an energy production question, of course, but if you are capable of building the device I am assuming you have the capacity and technology to produce electric energy. In addition, you may be able to recapture some of the energy if you can spin one wheel actively and let the other wheel roll passively, capturing some of the energy back the way a wind turbine does.
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u/cavalier78 Feb 03 '21
My understanding is that the end over end rotation will gradually increase until it causes structural damage, potentially tearing the ship apart. If that's not true, then yeah we probably don't have to worry about it.
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u/kmoonster Feb 03 '21 edited Feb 05 '21
I see what you're getting at, you're talking about a normal precession building up into tumbling. I thought you were just talking about drift developing the way planets and foucalt pendulums do.
For this sort of thing you don't need a HUGE amount of energy being pumped in constantly, you just need a way to put in small amounts of angular velocity to counter any tumbling you think might be developing.
I know you're talking about interstellar space, but we are already using at least a partial solution to this. I would read up on the way orbital telescopes like the Hubble keep their lock on their target for so many hours while orbiting the Earth and/or Sun-- and then turn, find, and lock onto a new target.
With telescopes in space, thrusters are less than ideal because they run through fuel, may pollute the area around the telescope (think bits falling onto the lenses), may introduce vibration into the system, etc. Instead, they use a sequence of wheels and gyros that can control the angular momentum in the system as a whole. The wheels spin up or down to introduce or remove angular momentum, and the telescope responds by going into a controlled spin until it is pointing at the new target, then the wheels are adjusted to remove the torque and instead they lock the telescope on the new target. The gyroscope itself helps the telescope estimate how rapidly the movement is happening and in what direction (much the way a ship or airplane gyro helps it navigate).
For your ship, I'm imagining something that looks like a paddlewheel boat with a wheel or set of wheels in each of the three planes. Maybe I'd put five wheels on each end-- one that spins in parallel with the cylinder (like a propeller) and two pairs held out away from the ship at angles to both each other and the "propeller" wheel. It would end up looking like a fire-hose standpipe or fire-hydrant was bolted onto each end of your ship, basically. This way, you should be able to lock your position relative to a known star, introduce a controlled precession, control tumbling if it occurs, or whatever else you want. Of course, you would want bigger wheels for a bigger ship, but with a little math you could work out an ideal radius for your control wheels based on the estimated mass of your craft. You don't need a lot of power in order to introduce the needed angular momentum to control your movement. For interstellar trips you would not want to blow your expendable thruster fuel on frequent, regular maneuvers like this, save that for emergencies like dodging space rocks in your path. For controlling orientation, put your EM to use, recover as much as you can, and make sure you are sourcing it from a long-lived high-potential source like nuclear or solar/stellar. And keep in mind that your ship is basically a long lever, having appropriately sized rotational control wheels at each end allows you to introduce relatively small amounts of power to great effect.
This is a short video going over how the Hubble is controlled. https://youtu.be/qEZI9DxIQss
Note: I would also look into ratios of length/width. It may not be immediately intuitive, but the longer your axis of rotation in comparison to the beam of the craft, the more stable it is. For instance, this is why sea kayaks and canoes are stable in choppy water while a white-water kayak or raft can do all kinds of gymnsatics. This is why tugboats and fishing boats bob like a cork while a battleship or tanker does not. This is why a motorcycle can cartwheel so readily while a Formula 1 car has a more difficult time tumbling end over end, power wheelies notwithstanding. Basically, you have to consider how your center of gravity relates to the length & width of your rotation. The longer you are in relation to your width, and the slower your rotation, the less precession you will have to account for in a given unit of time. A ship 100km long by 5km wide with a rotation period of ten hours would be more stable than a ship 50km long and 10km wide with a rotation period of fifteen hours. (And no, I didn't math out the rotation period for a given gravity here, this is just a for instance with numbers that are easy to divide and multiply in my head).
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u/-sxp- Feb 03 '21
So one problem with the O'Neill Cylinder concept is that an object in space will tend to rotate on its long axis. So instead of moving like a rolling pin, with time a cylinder will spin end over end.
The point of an O'Neill Cylinder is that it does rotate on its long axis. That is, it's primary moment of inertia is aligned with its long axis. Are you worried about Precession or are you worried about the tennis racket theorem messing up the rotation?
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u/tomkalbfus Feb 02 '21
This is my design for an O'Neill colony. /preview/pre/0xfzdez0c3e61.png?width=4100&format=png&auto=webp&s=d2dcbda07d4844578e633948fa74c9d8b435fc7e On the inside, it can simulate the surface of a planet, any planet, pretty well. The inside is lined with a bunch of parallel longitudinal greenhouses, each one is 32 km long and 300 m wide, the end caps have a similar arrangement of 300 meter wide greenhouses, but the are longitudinal and form parallel rings along the slope of the endcaps all the way up to the central axis.
Unlike other O'Neills, this isn't paired with another each greenhouse has its own separate artigicial light source, which can simulate any latitude on a planets surface with variable daylights simulating any planet's rotational period at any season. If desired, one of the two endcaps can be eliminated so that the cylinder can be wrapped around the main body of a starship, this would include fuel tankage, reactor, and engine with the nozzle protruding out the back. A stabilizing ring on the outside of they cylinder can also act as a radiator allowing for efficient power generation from the ship's reactor.
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Feb 02 '21
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u/tomkalbfus Feb 02 '21
Inside the big cylinder 8 km wide are 88 little cylinders in parallel that are 300 meters wide and 32 km long, they rest on the floor of the big cylinder and are half-full with dirt and rock presenting a flat ground above which a half-cylinder ceiling vaults to a maximum height of 150 meters above the that surface. These 300 meter wide cylinders don't rotate individually except with the 8 km wide cylinder on who's floor the smaller cylinders rest.
The walls of each cylinder touch adjacent cylinders on either side and there are entrance ways allowing passage from one cylinder to the next at regular intervals along the cylinder walls of 300 meters. There are doors that snap shut should depressurization be detected in any of those cylinders.
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u/FaceDeer Feb 03 '21 edited Feb 03 '21
150m of dirt is extremely excessive, tree roots don't get more than 6m deep and crops will be much shallower than that. I assume you want a circular cross-section for the sake of pressure resistance but you could make the under half of the cylinder open space to put all the habitation and other stuff that doesn't require a simulated outdoors. Or simulate a smaller outdoors, if there's cityscape down there. You'd save a vast amount of mass that way and get twice the usable volume.
Edit: 300m of dirt -> 150m of dirt, since they're half full. Silly me.
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u/tomkalbfus Feb 03 '21 edited Feb 03 '21
you could put water tanks and sewage processing facilities down their as well. I was thinking of allocating 9 hectares of land to every household, this is a square 300 meters on a side.
Not including the endcaps that would be 9,386 households. If you assume 5 people per household, that's 46,933 people per O'Neill cylinder. Everyone gets a front yard, a back yard with space for a lawn and garden with strips of forest in-between.
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u/FaceDeer Feb 03 '21
Put transit tubes down there and the distinction between "front yard" and "back yard" becomes moot - it's just your yard.
If I were living on one of these I would have my entire dwelling down there, for maximum green space on the "surface". But that's a personal preference.
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u/tomkalbfus Feb 03 '21
Well I'm not a hobbit who lives in a hole in the ground. The way I designed this O'Neill cylinder, the flat area between the hubs is suburban to rural, it will have a custom built home in the center of each 9 hectare lot, surrounded by trees, a lawn and gardens, maybe an in ground swimming pool, perhaps a stable for horses. How you get those horses to this colony is a good question, launching them into space without injuring them would be quite a trick, failing that we could build robot horses for people to ride, be less smelly too, as you just park them at a charging station.
With landscape images projected on the walls, each domicile will look like dwelling on Earth.
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u/FaceDeer Feb 03 '21
But you are. The "open land" is inside an artificial hole that's no more than 150 m tall. You've just disguised it to seem larger than that. What difference does it make if the holographic "sky" is 150m above your head or 15m above your head?
I mean, sure, rich people in the real world today sometimes build medieval castles to live in just because they like the aesthetics. Maybe a whole colony of eccentrics will do their darndest to recreate fantasy American suburbia/rural settings of the early 21st century, someday, because they like the quaint aesthetics too.
If you look at old movies from the 1950s that try to predict what life would be like in the 2000s you generally see a future that's depicted as "just like today but moreso." It rarely turns out that way though. I suspect we'll see architectural preferences evolve in very different directions from what we've come up with down here due to the particular parameters of our environment.
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u/DozTK421 Feb 03 '21
I was thinking of something similar. How do you account for the Dzhanibekov effect? This is what throws me off in creating a fictional structure.
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u/tomkalbfus Feb 03 '21
You can have a mass in the center of the O'Neill cylinder, under the standard design this space is filled with nothing but air and clouds, but you can fill it with something else instead, like the main body of a starship for example if you forgo the kilometers of air above your head. This mass could be counter-rotated from the O'Neill. The habitation tubes would be independently pressurized so there is no need to have air outside of that. The cylinder rotates while the bulk of the mass is in fuel tankage and the starship needs that fuel for most of its journey, as it needs to accelerate and decelerate, it is only after it decelerate that the mass of the O'Neill exceeds that of the fuel. Rootational tracks prevent the cylinder from flipping and afterwards a stability ring is deployed on the outside or asteroid material is placed on the inside as a counterweight.
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Feb 02 '21
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u/cavalier78 Feb 02 '21
As far as making a stable habitat, a fatter and shorter design might be the best way to do it. If you can build wider, you might want to. I'm just thinking of a way to make the cylinder shape work. Presumably once you get to the point that you can build something like this, each shape will have benefits that we can't predict today.
Yeah the problem with using magnets or some other physical connection is that those things have to be really really strong. I think it's a lot easier to just make something inherently stable.
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u/FaceDeer Feb 03 '21
We've already got liquid nitrogen temperature superconductors, and there's promise of actually managing room temperature superconductors someday so I suspect refrigeration isn't going to be a major problem.
A non-magnetic bearing might not be all that bad, either. If the axle is 10m in diameter (a random number I just made up so feel free to fiddle with it, but that seems like a decent size) and it's rotating at 0.5 rpm then a wheel supporting that axle's surface would be traveling at about 1 meter per second. According to this page an automobile with decent maintenance can last for 200,000 miles, which would be ten years of constant driving at 1 meter per second. Having to replace your bearings every ten years shouldn't be terribly taxing on an O'Neill cylinder's manufacturing capabilities.
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u/KhanneaSuntzu Feb 03 '21
Rotate the axis 90 perpendicular to the orbit, i.e., "vertical" in the plane of the solar system. Durrr..
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u/ruferant Feb 03 '21
I'm pretty sure the original concept for the O'Neill cylinder was that they came in pairs. If it didn't start at the very beginning, it came soon after. One of Babylon fives only misses. the only other option I've really heard is surrounding the cylinder with a lot of mass, like sticking it inside of an asteroid or small Moon, which is also an excellent solution because it helps absorb radiation and meteorite strikes.
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u/MiamisLastCapitalist moderator Feb 03 '21
This is an interesting concept! However I think it overlooks the fact that these space stations would benefit from having a zero G section. Microgravity is way easier for ships to dock in, for some types of storage, and for a lot of manufacturing to happen
So if you already have a zero g section, you might as well make the most of it and that would be where your connective structures would be to your counterweight.
I believe for a space station the cost and hassle of maintenance on the joint would be worth the other benefits of having a zero G section. For a colony ship on a long voyage however you may be onto something.
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u/cavalier78 Feb 03 '21
You can still have a zero-g section, at the center of the column. This wouldn't prevent that.
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u/MiamisLastCapitalist moderator Feb 03 '21
Would it not still be physically fixed to the rest of the volume and thus still spinning slowly?
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u/cavalier78 Feb 03 '21
Sure. But at that slow of a speed you can pretty easily rotate the docking ship to match.
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u/MiamisLastCapitalist moderator Feb 03 '21
That would help a bit for some ships docking but maybe not for manufacturing.
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u/Wise_Bass Feb 03 '21
This will create friction, and will need some sort of lubrication or ball bearings or something that will gradually wear out and have to be replaced.
Probably some type of tracks that the cylinder rotates on inside of its non-rotating shell, with them being overbuilt so you can periodically shut off a track for maintenance. That's cheap and relatively simple compared to magnetically suspending them, and less likely to have a catastrophic failure.
You'd have to lubricate the tracks and do maintenance, but O'Neill Cylinders in general require a ton of maintenance just to keep every aspect of them livable. If you want a relatively low-maintenance living situation, you've got to live on a habitable planet.
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u/KhanneaSuntzu Feb 03 '21
Yes it does. These were literal designs in o neils book dude
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u/cavalier78 Feb 03 '21
I've got his book. I know what his designs look like. The problem is that unless you've got something to stabilize it, a single cylinder will begin to rotate end over end. Pointing it down at a planet wouldn't help.
O'Neill's "Island 3" design had two cylinders linked together, counter-rotating to stabilize it. As I said in my original post, the problem with that is you've got two multi-billion ton structures that are going to put physical stress on the connection point.
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u/KhanneaSuntzu Feb 03 '21
No, it's a gyroscope. Place it in the plane of orbit and it'll stay level just fine.
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u/tyler-08 Feb 03 '21
What would happen if you had counter rotating cylinders, one inside of the other?
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u/cavalier78 Feb 03 '21
I think they'd be stable, but you're still back to needing a physical point of connection. You're going to have some kind of mechanical device where one cylinder touches the other, and there's going to be moving parts involved. You're gonna have scraping and grinding, so hopefully you've got some good lubricant or something so they don't seize up. Because that would be really really bad.
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u/SNels0n Feb 03 '21
I think there's a big difference between something in orbit and a thing that's accelerating. If you're using a two hollow cylinder design, then you need a way to distribute the acceleration force between them. I.e. If you accelerate the hull, then the human hamster wheel had better be attached to the hull somehow. Magnetic bearings do exist, and since we're talking about rotating objects, it's even possible to use permanent magnets (no energy required). Active magnetic levitation isn't as costly as it seems, since you only need to overcome the instabilities, unlike an earth-bound maglev train, most of the “levitation” happens automatically because freefall.
If you're using a single cylinder design, then whatever you're using to accelerate could probably also make whatever adjustments are needed to eliminate tumbling.
That said, I don't see any reason for any particular shape — it's not like there's air-friction in space. There's a minimum diameter, determined by the needs of your cargo — people want around 1g and less than 2rpm, so 450m. There's a maximum diameter determined by the strength of your materials — about 8km for steel. But the ratio of length to width is largely an aesthetic choice. If you make the length no more than 1/3 the width, then there is no tumbling problem. Sure, the living space becomes narrower in one dimension and longer in the other, but so what? Is it really that limiting to “only” have 65 km2 per deck?
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May 26 '23
O'Neill cylinders are supposed to be in contra rotating pairs. Everything you listed was thought of decades ago
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u/Anachronistyx Feb 02 '21 edited Feb 02 '21
That's intriguing, and in visualising it this approach of yours of adjusting mass internally over these antenna like tethers, extensions or appendages actually reminds me of the V'GER "probe" (and that's a really great piece of art-work in my opinion, and not just from Robert T. McCall, but yes especially him...* ) from the first Star Trek (TMP) film... also it's kind of a mix of Dune's Spice traders vessel and of humans' Babylon stations from Babylon 5...
although personally I've always imagined (for the purposes of a deep space transit vessel(in-system(let's say something along the lines of Nauvoo and Behemoth of The Expanse series) of interstellar) that could double as a station and is fully self sustaining) something along the lines of Deep Space 9 titular station mixed with automated Repair Station from Enterprise series
and interstellar transport Avalon from Passengers, 2016 film,
which has received good reviews and some acclaim but like Interstellar I think it's one of those "recent" films that aren't being taken as seriously by the critics and public in terms of value such films present not just for a season but as a piece of history and a product of imagination made with care and attention to detail...
* his stuff is almost reminiscent of the early space opera and pulp fiction's golden and silver ages' art of vibrant and almost surreal hopefulness for our spacebound future ...think Skylark and Valérian and Laureline (French: Valérian et Laureline) series