spacecraft with rotational artificial gravity

[Ken Fabian]

Although I wonder if it’s possible these rotating rooms and small centrifuges problem was not the artificial G but the artificial G combined with an equally powerful earth G which confused the ear?

For a person standing the rotational direction in a room rotating on a flat disc on the ground is around a vertical axis (yaw) instead of head over heels rotation around a horizontal axis (pitch); from the point of view of the inner ear canals the sensations are very similar but from a keeping balance point of view the actual head over heels tumbling sensations of a spinning space station or ship could be worse.

But how about a large enough ring structure, let’s say 100 meter diameter with sleeping pods that insert into the structure and go round and round on rails on the inside of the ring. Like cars on a circular rollercoaster.

From the perspective of the person and their inner ear they will be in a 100m diameter structure, just with a faster spin rate. To overcome the problem it needs slower spin rates. Not sure but the mass and motions of such a rail system would defeat the purpose of reducing the engineering stresses within the structure.

Possibly we could turn to medical intervention... but losing or diminishing that balance sense would be debilitating. Or else replacing it with some kind of prosthetic vestibular organ - but that is drastic and currently beyond our abilities.

 

[billslugg]

Yes, any large "donut" shaped object would be dangerously susceptible to imbalance, bending, structural failure.
However, the forces are in tension, easily borne by a system of spokes made of carbon fiber. The strength of the cables need be no more than what would lift a spoke's share of the donut on Earth.

 

[Helio]

Fun thread. Perhaps this table will help. It shows the gravitational force (g-units) for a given radius and a given period (sec.). I lacked the time to double check it thoroughly, but I think it's correct.

ally

 

[Helio]

Yes, any large "donut" shaped object would be dangerously susceptible to imbalance, bending, structural failure.
However, the forces are in tension, easily borne by a system of spokes made of carbon fiber. The strength of the cables need be no more than what would lift a spoke's share of the donut on Earth.

Yes, but carbon fiber may not even be required.

My calculations show me that it even titanium would easily handle the job.

Take a 150m radius ring, spin it at, say, one rev in 40 sec, producing a g force that of Mars (0.38g), and if you have 6 spokes, the total cross sectional area matching the yield strength of titanium is a square with each side being 2.65 inches. Of course, the design would be much larger for the spoke, but the cross sectional area of the metal would still be the same.

Balancing shouldn't be too hard with auto controls using cables inside the spokes, or perhaps just near the center or outer edges. I haven't given this much thought, but automation is everywhere, especially in balancing systems.

 

[billslugg]

Balancing is not needed. The assembly will rotate smoothly around its center of gravity.
But, if the CG is not at the physical center, inhabitants in the ring would feel a speedup/slowdown once per cycle.

Yes, titanium could work. Lots of it on the Moon, for example. Some areas up to 10% TiO2.
Very little carbon on the Moon. Best soils contain about 0.5% carbon.

 

[billslugg]

Actually, every spot within an unbalanced donut would have its own circular orbit at its own radius. G forces would not be the same everywhere in the structure. You would be heavier in some rooms than others. Not really a big deal.

However, it woud be of great scientific importance to have an inertial platform from which to do experiments. This could only be located at the rotational center by a platform rotating opposite the donut. Adjustable spokes would be needed to keep it dead center.

 

[Helio]

Balancing is not needed. The assembly will rotate smoothly around its center of gravity.
But, if the CG is not at the physical center, inhabitants in the ring would feel a speedup/slowdown once per cycle.

Agreed. I would assume the c.g. and centroid would be very close, so very little change.

If, say, 100 people gathered in a room, shifting weight there, it would only cause a tiny shift in weight.

So, playing with an example, if we had a 6-spoke donut with:

1) radius = 100m
2) period = 30 sec.
3) ring width = 15m
4) ring height = 10m
5) wall thickness (total for more than one) = 0.5 inches
6) inner wall thickness = 0.1 inches
7) material = titanium
8) spoke load safety factor = 3
9) total weight, ignoring furniture = 2.4E6 lbsm.
10) g force at radius = 0.44g

Then the diameter of a solid round spoke would be = 2.5 inches. Note that this diameter is reduced from a 1 g load to the 0.44 g load.

Of course, the spoke would not be solid, but the cross-sectional area of the metal itself would be this equivalent.

The curvature along the ring would allow someone to look down the ring 60 feet before their level eyesight would reach the curved floor, if their eyes are at 5.5 feet.

I have set all this up in Excel should anyone want to play with other designs.

Yes, titanium could work. Lots of it on the Moon, for example. Some areas up to 10% TiO2.
Very little carbon on the Moon. Best soils contain about 0.5% carbon.

That's interesting.

 

[Helio]

However, it woud be of great scientific importance to have an inertial platform from which to do experiments. This could only be located at the rotational center by a platform rotating opposite the donut. Adjustable spokes would be needed to keep it dead center.

I'm unclear what this is. Are you saying you want to have a small room in the center where the g-force can be dialed-up or down?

 

[billslugg]

I am looking for an inertial platform, one experiencing no acceleration. We could mount telescopes on it and the images would be stable.

Moving 100 people to the other side of a 2.6 million pound donut is about one part in 170. The central point would need to move about half a meter.

The donut ring should be circular in cross section to minimize any additional stiffening structure. At 12 meters diameter, in a one atmosphere environment (15 PSI), hoop equation is: Inside pressure equals skin tension divided by radius: Skin tension = pressure x radius = 15 x 236 = 3540 pounds per inch of skin width.

Well within the capability of a 0.5" wall made of titanium.

 

[Helio]

I am looking for an inertial platform, one experiencing no acceleration. We could mount telescopes on it and the images would be stable.

Moving 100 people to the other side of a 2.6 million pound donut is about one part in 170. The central point would need to move about half a meter.

The donut ring should be circular in cross section to minimize any additional stiffening structure. At 12 meters diameter, in a one atmosphere environment (15 PSI), hoop equation is: Inside pressure equals skin tension divided by radius: Skin tension = pressure x radius = 15 x 236 = 3540 pounds per inch of skin width.

Well within the capability of a 0.5" wall made of titanium.

Ok. That makes sense. It would be a better design to include a central cylinder-like room where the loads of each spoke could connect, so each spoke could be monitored. The other benefit would provide the room you need.

The round shape for the ring would certainly be better mechanically, but I'm not sure it the psychological effects would be satisfactory, but perhaps the young would be fine with it. I'm too old. I would guess something more oval to minimize the gussets and other bracing needed for any square-like design, which would also produce less living space per wall material area.

I'm guessing there might be outer wall sections that would help prevent blowouts from meteroid penetrations. Plus, this thickness includes the ring's inner and outer walls, hence there would be four layers, so an average of 1/8" each. I think the ISS has walls that are 1/20" (1.4mm), though I've read they also use Kevlar and other material that might be as much as 5" thick, so I'm a rookie in addressing thickness for long term spaceflight.