So, apparently, you need a lot of mass to shield from radiation. Something like 30 feet of water. And, while nobody knows how much gravity you actually need, you probably need somewhere between 0.5 to 1 G to avoid medical problems.
So you build a gigantic can-shaped structure. The distance between the inner and outer layers is about 30 feet. You fill the void with water or whatever radiation blocking materials are at hand. On the inner can, you build structural reinforcements - made of steel, carbon fiber, whatever is common.
Then, the actual habitat is shaped like an inner tube and it rides on maglev tracks on the inner can. The tube has some structural reinforcement made of lightweight carbon fiber, but most of the “weight” of the habitat is being supported by the non-spinning inner can.
There are a minimum of 2 habitats in any real station, and they have roughly the same mass and spin in opposite directions. There are 2 more “counterweight” rings that spin at variable speeds to balance the angular momentum of the station. You change the speed of these rings to turn the station on that axis. This way you keep the angular momentum of the station at zero and have the option of “de-spinning” the habitat rings for maintenance purposes.
There’s a transition ring between the habitats. It spins up and matches speed with one of the 2 habitats. You open hatches and get into acceleration couches inside the transition ring. You close the hatches (outside the habitats is vacuum to reduce friction) and the transition ring spins down and spins back up the opposite direction. The counterweight rings adjust speed when you do this.
Finally, there’s possibly a gigantic pressurized zero g area. One thing you might do is have a non spinning curved “ceiling” above the habitat rings. All this space in the hubs you can pressurize and construct spacecraft, etc inside this volume.
Is this roughly the right way to go? You keep the mass of the radiation shielding outside the centrifuge ring. Same with the main structural reinforcements, so you aren’t adding to the structural stress on the centrifuge rings by having structural mass in the rings itself and subject to spin… There’s no spinning bit of habit exposed to the “outside” for spacecraft to crash into. Finding enough water for 30 feet of shielding might be difficult, but if you are mining asteroids on a large scale, you could just use mine tailings.
I’m not sure what the problem is with the habitat having a net angular momentum. Allowing that takes away the extra layers of complication with the maglev tracks and the mismatched habitats.
The use of water as radiation shielding, as well as insulation and a thermal mass to regulate the energy balance, makes a lot of sense. Water is plentiful in comets and some types of asteroids, non-toxic, easy to work with, and also has some unique material and thermal properties that make it ideally suited for many uses, as well as being necessary for drinking, irrigation, and maintaining proper humidity. However, I would go further and get rid of the interior and exterior metallic shells entirely, and use the water as the bulk of your habitat structure with reinforcement using a wound fiber composite structure for large scale tensile strength and crystalline silicates for local stiffness as well as insulation. I’ve describe the design for such a habitat in several past threads, including [THREAD=495064]here[/THREAD] and [POST=14053719]here[/POST]. (The second link describes in some detail a presumed construction method and delineates many of the advantages, so I won’t reiterate it here.)
This concept obviates the need to either haul up mass quantities of metals and other heavy constituents from Earth’s surface or establish a complex mining, smelting, and manufacturing infrastructure in space, so the infrastructure in place to construct this would be minimized (though it is still orders of magnitude beyond the effort put into constructing the ISS). For a solar orbiting structure, orientation could be maintained by deploying a “keel”, e.g. a mass at the end of a long tether which is tensioned by tidal forces, keeping the sunshield/collector oriented toward the Sun at all times, thereby reducing the need for active altitude control. Primary power can be provided by using focused sunlight to work directly on a molten salt fluid, and additional sunlight could be routed through a large reflective tube or fiber optic cable running down the center of the habitat with apertures which could control the intensity and timing of illumination.
Counterrotating rings are useful if you anticipate the need to spin up and spin down the habitats, as the energy can be stored or applied without using any propellants, but it adds significant complication in both the dynamics of the structure and the necessity of having some kind of bearing to accept the Coriolis and Euler components from differential loads, and yet still maintain an essentially rigid connection which would presumably include some kind of pressurized tunnel to transit from one ring to another. That is workable for a smaller habitat like that on board an interplanetary ship or small space station, but will become unworkably large when dealing with large masses like a 30 m thick ring of water. The fewer actually moving parts of the structure the better, as anything that goes wrong on that scale is likely to cause the entire structure to come apart like a cheap gold watch.
I haven’t thought in detail, but it seems to me that building cables to support the rotating habitat (a maximum of one gee) isn’t that difficult – bridges support weight against one gee all the time, and given this is a tensile load, it’s even easier.
On the other hand, it’s going to be a royal pain maintaining the bearings between the rotating habitat and an outer, non-rotating structure that supports it.
Might be easier to let the habitat support itself with cables, and leave a gap between it and the shielding ?
Quercus - maglev tracks. Computer control. Accelerometers in the outer non spinning ring detect the slightest angular momentum transfer, and then regulate the current to the maglev tracks to speed up/slow down the counterweight ring to keep the outer habitat stationary.
There’s no bearings. Just a train riding above some coils embedded in the surface or the bottom of the train. Probably the active part would be in the track, so you can easily run electrical wires to the solar array which is also part of the non-rotating system. Superconductors would use the least power but require you keep the track cold.
You transfer electric power to the habitat rings via induction coils. You transfer liquids, gasses, etc by loading them into tanks on the transfer ring- that thing that spins up and spins down - when it is stationary with respect to the outer hub. The transfer ring is how you get between the 2 habitat rings and also get to the zero- g hub. No crazy bearings required.
Just because the bearings are magnetic doesn’t mean there are no bearings. But again, why have bearings at all? Why not just make the whole thing, outer wall included, rotate rigidly?
Because there’s structural stress from 30 feet - 30 meters of water. An enormous amount of it. Also, the structure to hold the structure itself adds to the structural stress. Dividing it up removes all this.
Somehow, the OP’s 30 feet of water shielding became 30 ft to 30 meters of water? Is there any actual research and more than just WAGs about how much water is needed for shielding?
A 30 meter thickness of water is about equivalent to the Earth’s atmosphere down to ~1 mile AMSL; in other words, it would provide a radiation condition similar to living in, say, Denver. This is important because also there are alternatives for shielding against heavy solar charged particles, there is literally nothing but mass that will slow the super high energy cosmic particle radiation (“cosmic rays”). The cosmic radiation itself isn’t especially harmful–it is traveling so fast that its interaction with organic materials would be slight–but its interaction with dense materials like aluminum and titanium will result in frequent spallation into exotic particles with much lower energies which then decay into more dangerous ionizing radiation that is very harmful, especially for long term exposure. A shielding of water–whether in ice or liquid form–is about the best radiation blocking material that is readily available and easy to work with, e.g. it flows under pressure, forms a relatively hard solid, has high latent heat, et cetera, and most importantly, is made of two of the most readily available elements in the cosmos which are frequently found already together. However, the shielding has to be all the way around the habitat as cosmic radiation comes in from all directions, so just a ring on the outside only provides a limited benefit, and not having it as part of, or at least intimate contact with, the habitat structure limits its utility as a thermal sink and moderator.
Yeah, so I read elsewhere 30 feet, but I believe that Stranger is correct. My proposed design, imagine a Cambell’s soup can, complete with the ribbing in the side of the can. Now, imagine a smaller can, 30 meters smaller on all sides, inside the larger outer can. Finally, imagine a bicycle inner tube riding on a maglev track - shaped just like the one at Disney World - that goes all the way around the inside of the can.
That’s all I am proposing. Oh, and there’s actually a minimum of 5 of these inner tube shaped rings. 2 of them are habitable, one is between the 2 habitable rings and contains hatches on both sides and in the roof and acceleration chairs and gas and liquid tanks. Finally, 2 more rings just contain metal weights and their spin speed varies to keep the whole thing balanced.
There are not “bearings” like you might be used to thinking of - there doesn’t even need to be complete rings. Maglev cars riding on the rails is all that is needed. It’s not a monorail, each car rides on several rails, and there is enough redundancy to support the structure in the event of rail failure.
I still don’t get the purpose of the maglev system - is it to keep the two halves rotating at the same (opposite) speed? What’s the big deal if they don’t?
I think a single rotating structure makes more sense. There’s no need to ever stop the rotation. We have plenty of experience and technology to perform structural maintenance under 1g acceleration. Also, a single rotating structure would be inherently stable in its attitude (like a gyro), as long as it’s rotating around the largest moment of inertia (i.e. a ring, not a long slender cylinder). Whereas counter-rotating sections would not be.
Consider also, if you design the habitat so its rotation can be stopped, it introduces a lot of other problems. Namely, everything inside needs to be bolted to the “ground” or floor, or it will float away when the rotation is stopped. You can’t have open containers of water; every toilet, every pond, every swimming pool, every chemical/fuel storage tank - they all need sealed covers. Same issue with any loose aggregate material, like soil - it needs to be covered and contained. You can’t even hang a picture on the wall with a nail, you’d have to glue it or use Velcro.
Make the radiation shielding which weighs tons per square meter not place stress on the structure
Make the structure itself not place stress on the structure. The structure only has to support the apparent “weight” of the actual habitable stuff - the rooms and paintings and so forth. Not it’s own “weight”.
Instead the “cars” “ride” on the maglev tracks.
It makes it very easy to keep rotating and non-rotating sections. If the non-rotating section ever begins to rotate (from bleed over due to friction), increase current to the maglev track set going in the opposite direction from that direction of rotation. Conservation of angular momentum means that rotation must stop.
You don’t have to decelerate very quickly, you can do it slowly, 2 rings gives you the option of doing so without paying a cost in real propellant. I can imagine that even a civilization that is capable of building something like this won’t want to burn up propellant if they don’t have to.
We’re talking about a couple of huge spinning cylinders, surrounded by a non-spinning ice shield, right? Is the “maglev” a magnetic bearing system to keep them aligned, so the habitat cylinders don’t come in contact with the shield (or each other)?
My understanding is that having counterrotating parts on something like an O’Neill cylinder would be specifically to allow the attitude to be changed as the structure orbits the sun (to keep the parts that are supposed to be lit up, lit up, and keep the shady parts shady) without using rockets.
My concern with any of the traditional “spinning structure, non-rotating center” is how a sealed bearing would hold 1 atmosphere (14.7psi) and yet be at least 10 feet in diameter to allow shirtsleeve transition between the spinning and non-spinning sections.
I would suggest the simplest structure has either zero or one of these seals.
Zero - the transition is by a shuttle box or elevator that connects solidly to the stationary side, people get in, it disconnects, then spins up to match the rotating side. Or - the entire core rotates too, no non-rotating part, and spacecraft rotate to sync and dock … to the accompaniment of a Strauss waltz.
One seal - there is a tube coming out of the center structure on one side, connecting to the non-rotating component. The seal is on the circumference of this tube.
I worry about the seals because their integrity is crucial to maintaining an atmosphere. A complex design that means air leaks at an excessive rate is not a good design, especially since this air probably has to be brought from a long ways away to replenish the system. Minimizing leaks is your biggest goal.
I suspect the OP design is excessively complex. The obvious solution is to build the rotating section, soup can or 2001 bicycle wheel, so that the structure can support the weight. If we can build Burj Dubia-sized buildings, we can build a structure able to suspend the weight of 30 feet of ice from a central core.
My design has zero seals. You cannot transfer to the other section via shirt sleeve tunnel. You have to get into the “transfer ring” - mentioned in my OP and followup posts. This is just a maglev car or complete ring (it doesn’t have to be a complete ring, a single car can do it) that is speeding around the maglev track at the same speed as the main habitat module it is synced with. Very easy to do with modern electronics and sensors, basically trivial. There’s an extendable airlock tunnel that connects to the side of the ring it is synced with. You board the transfer ring and sit down in accleration couches. Once all are aboard and seated, the hatches close and the airlock tunnel retracts. The transfer ring track motors slow the ring down to zero and then speed it up so it rotates in the other direction. Once it matches perfectly with the other ring (you can easily tell with optical sensors that look at markings on the other ring) you extend the airlock tunnels on the other side and dock them. Open the hatches.
You can also bring this ring to zero and open hatches in the ceiling. This lets you go into the zero G hub.
I was thinking of the same design, essentially, between the rotating and non-rotating parts at the hub. Enter rotating room, close the hatches, the room stops spinning, slides over to non-rotating part, connects, and you open hatch to step into the non-rotating part.
In both my design and yours, the smaller the space between the hatches for the transfer unit and the station, the less air needs to be pumped out (recovered) for each cycle.
I just see your design as overly complicated. Offsetting counter-spinning cylinders are unnecessary as far as I can see. The whole unit should not need significant maneuvering (that would be disruptive), so a series of jets to occasionally correct drift should be sufficient. Computer control of rim-mounted rockets could probably have the same effect as flywheels.
The key point here is you don’t seem to think a spinning habitat could handle the weight (centrifugal force and mass) of the water shield. I suggest this is not extreme engineering. Plus, for added stability, the majority of the water would be ice. Recall the WWII concept for a frozen wood pulp (iceberg) aircraft carrier, almost impervious to submarine attack - the same would apply to our spinning ring. The ice would spin, and would have a large number of fine strong fiber reinforcements frozen embedded into the ice for structural stability. The engineering challenge would be the suspension mechanism to carry the weight of spinning ice.
I just see the design as a ring rather than a can, because I agree a long axis for a spinning habitat would complicate the structural needs. (there’d be pillars or suspension cables at regular intervals) If necessary, build a container can that does not spin around a cylinder that does, like your design, but just one spinner, no need for fancy maglevs or bearings, there would be no need for contact between the units outside of the axle. If you must have multiple separated habitats in this can, transfer is more simply done by an elevator that spins to match each habitat while travelling along the axle.
Thinking about it more - if the circular skin structure can carry its own weight - basically a circular suspension bridge with no need for internal pillars or wires - then the cylinder axis can be any length.