Hard sci-fi question: rotational artificial gravity space station

[Eltab]

My understanding of the costs of building in space is that, besides human labor, the main cost would mostly be for fuel required to get the building materials into space.

Older book you may find helpful: Space Resources, Breaking the Bonds of Earth.

If a society has the industrial capability to build a 1 km radius cylinder, it will have some industrial capacity already in space / in orbit. Use THAT as your primary source of parts. Bring in a metallic asteroid for raw materials.

 

[Eltab]

whereas if you have two linked, counter-rotating cylinders there will inevitably be friction at the point of connection

Use magnets to avoid physical friction. (I'm thinking something that looks like a ball-and-cup joint).
Maybe you can generate electricity from them, too - or maybe you get a nasty short circuit. Comments from electricians welcome.
You still would need a motor to keep up spin in case the counter-rotating magnetic fields cause resistance against each other.

 

[Eltab]

If you want to put an "upper story" inside your rotating habitat, you could locate residences for the elderly there. Old people are prone to falls and recover poorly from one, so being in lower-gravity would be a boon to them.

 

[Quickleaf]

A sphere would be strange in many ways, for instance not only would things be "pulled downwards" but they would also be pulled towards the "equator". I am not wording that correctly but basically, the further something is from the "equator" the less aligned the "gravity" would be with the "floor". There are also some air circulation things that would happen.

Rendezvous with Rama is not a terrible read, if your into that sort of thing.

I thought the cylindrical sea along the equator was interesting in that book. While Arthur C. Clarke's science was probably more accurate, as far as narrative goes I am more a fan Robert Heinlein.

Older book you may find helpful: Space Resources, Breaking the Bonds of Earth.

If a society has the industrial capability to build a 1 km radius cylinder, it will have some industrial capacity already in space / in orbit. Use THAT as your primary source of parts. Bring in a metallic asteroid for raw materials.

Very interesting premise. It makes sense of course, but making that connection between being able to build a 1 km radius cylinder and industrial capacity in space is a great insight. I wouldn't have assumed that.

If you want to put an "upper story" inside your rotating habitat, you could locate residences for the elderly there. Old people are prone to falls and recover poorly from one, so being in lower-gravity would be a boon to them.

I was actually thinking of the upper story being more light industrial. Long-term low-G dwelling apparently could contribute to bone brittleness, so that's probably contraindicated for elderly at increased risk of osteoporosis.

 

[Shayuri]

Just remember, if you have an 'open architecture' cylinder or torus, then the air pressure is going to drop towards the axis. Any habitable volume up there is going to need life support. I suspect it'd be fun to 'parachute' from the axis to the ground, but you'd better bring some oxygen up there when you do.

 

[tomBitonti]

A sphere doesn't seem that bad, and would naturally provide a set of terraces with good views / access to the central open space. The outermost section could be scaffolded to provide a big flat band near the equator (with lots of space beneath for offices, storage, industry, or whatever. Having different gravity levels might be an advantage. The design is one of the three top designs, and is called a Bernal Sphere.

Something I recently read: A problem with rotating cylinders is that they want to convert the rotation from along the long axis to along a short axis. I'm sure there is a statistical / kinematic reason why that happens. The tendency means that active spin management is needed, independent of hub friction problems.

Thx!
TomB

 

[Shayuri]

I don't know the exact physics, but I wonder if, with a sphere, there might be problems with different bands of air rotation being in contact with one another. The air rotating at the equator of the sphere would be moving faster than the air rotating along north and south of the equator.

That happens on Earth too, and makes for a lot of entertaining weather patterns you probably wouldn't want to duplicate on a space station, even on a smaller scale.

 

[Quickleaf]

Just remember, if you have an 'open architecture' cylinder or torus, then the air pressure is going to drop towards the axis. Any habitable volume up there is going to need life support. I suspect it'd be fun to 'parachute' from the axis to the ground, but you'd better bring some oxygen up there when you do.

Totally. There was actually an episode of Babylon5 (maybe in season 4?) where Captain Sheridan had to leap out of the train running the axis due to a bomb threat. The way the emergency door blew off made it seem like there was a difference in air pressure between the interior of the train and the environment of the central axis of the cylindrical station. Of course, then he started falling, and IIRC there was something about him hitting the ground at 60mph once he landed.

A sphere doesn't seem that bad, and would naturally provide a set of terraces with good views / access to the central open space. The outermost section could be scaffolded to provide a big flat band near the equator (with lots of space beneath for offices, storage, industry, or whatever. Having different gravity levels might be an advantage. The design is one of the three top designs, and is called a Bernal Sphere.

Something I recently read: A problem with rotating cylinders is that they want to convert the rotation from along the long axis to along a short axis. I'm sure there is a statistical / kinematic reason why that happens. The tendency means that active spin management is needed, independent of hub friction problems.

Does "convert the rotation from along the long axis to along a short axis" mean that the cylinder would tend to wobble over time? (without active intervention)

I don't know the exact physics, but I wonder if, with a sphere, there might be problems with different bands of air rotation being in contact with one another. The air rotating at the equator of the sphere would be moving faster than the air rotating along north and south of the equator.

That happens on Earth too, and makes for a lot of entertaining weather patterns you probably wouldn't want to duplicate on a space station, even on a smaller scale.

I think at the scale these projects were imagined for that's very likely. On the one hand, there could be psychological benefits to changing weather and benefits to creating a rain system to support your agriculture. Then again, thunder and lightning are probably things you don't want on a space station.

 

[tomBitonti]

Does "convert the rotation from along the long axis to along a short axis" mean that the cylinder would tend to wobble over time? (without active intervention)

Yes.

Here is an example:

https://en.m.wikipedia.org/wiki/Explorer_1

Explorer 1 changed rotation axis after launch. The elongated body of the spacecraft had been designed to spin about its long (least-inertia) axis but refused to do so, and instead started precessing due to energy dissipation from flexible structural elements. Later it was understood that on general grounds, the body ends up in the spin state that minimizes the kinetic rotational energy for a fixed angular momentum (this being the maximal-inertia axis). This motivated the first further development of the Eulerian theory of rigid body dynamics after nearly 200 years—to address this kind of momentum-preserving energy dissipation.[18][19]

Lecture notes:

Lecture L27 - 3D Rigid Body Dynamics: Kinetic Energy; Instability; Equations of Motion

http://ocw.mit.edu/courses/aeronaut...fall-2009/lecture-notes/MIT16_07F09_Lec27.pdf

Thx!
TomB

 

[Eltab]

Long-term low-G dwelling apparently could contribute to bone brittleness, so that's probably contraindicated for elderly at increased risk of osteoporosis.

Your point is well-taken.

Near-Zero-G is known from experience to cause problems. I haven't heard of any experiments in say Half-G or 1/3-G or 2/3-G. (Where would such experiments be held ?!)

If a sphere is built, a doctor could balance the health factors for each fragile elderly person, and place them in the gravity zone where they would be most comfortable / safe.