Hard sci-fi question: rotational artificial gravity space station

Quickleaf · Apr 20, 2016

[MENTION=13107]tomBitonti[/MENTION] Are you talking about two separate but connected O'Neal Cylinders like this?

Umbran · Apr 20, 2016

tomBitonti said:
F A torus is, after all, a section of a cylinder: Building a torus is the same as building a small part of a big cylinder. Then, it's not hard to see that putting a ceiling on a torus is less material than two big flat walls reaching to the center. To create more living space in a torus, multiple floors seem practical.

But, then, why not multiple tori? That gets you back to them being counter-rotating, so that the overall structure doesn't have angular momentum to worry about.

If a long cylinder is being built, what prevents there being multiple layers on the surface of the cylinder?

Not much prevents it. I'm merely pointing out that it isn't necessarily cheaper or easier to build, that the ground-bound intuition on how to build things may not always apply.

Choosing torus or cylinder seems to be independent of deciding how many floors to have.

I'd largely agree with you. The difference is mostly a question of scale (and thus cost in lifting mass).

That tori can be more easily divided into sections seems to be a big advantage: Safer (decompression is limited to one section), and easier to build and put into use a section at a time.[/.quote]

Well, opposing pairs of sections, at least. If it is lopsided, and you try to spin it up, I believe it will start to tumble, and that's *bad*.

tomBitonti · Apr 20, 2016

Quickleaf said:
[MENTION=13107]tomBitonti[/MENTION] Are you talking about two separate but connected O'Neal Cylinders like this?

Hi,

Yes, exactly. Just one rotating cylinder by itself is a big gyroscope -- hard to turn. With two cylinders:

https://en.wikipedia.org/wiki/O'Neill_cylinder

The cylinders would rotate in opposite directions in order to cancel out any gyroscopic effects that would otherwise make it difficult to keep them aimed toward the Sun.

Two cylinders also give direction control which does not require rockets. From the same article:

Attitude control

The habitat and its mirrors must be perpetually aimed at the Sun to collect solar energy and light the habitat's interior. O'Neill and his students carefully worked out a method of continuously turning the colony 360 degrees per orbit without using rockets (which would shed reaction mass).[1] First, the pair of habitats can be rolled by operating the cylinders as momentum wheels. If one habitat's rotation is slightly off, the two cylinders will rotate about each other. Once the plane formed by the two axes of rotation is perpendicular in the roll axis to the orbit, then the pair of cylinders can be yawed to aim at the Sun by exerting a force between the two sunward bearings. Pushing the cylinders away from each other will cause both cylinders to gyroscopically precess, and the system will yaw in one direction, while pushing them towards each other will cause yaw in the other direction. The counter-rotating habitats have no net gyroscopic effect, and so this slight precession can continue throughout the habitat's orbit, keeping it aimed at the Sun.

Thx!

Thx!
TomB

Morrus · Apr 20, 2016

Umbran said:
You're being hyperbolic, and that obscures the point.

Does my use of the word "Jupiter" really obscure my point to you, Umbran? I don't think it does.

No. The ISS is the physical size it is because of limits of *mass* (specifically, the cost of lifting that mass), not limits of available space to put it in. The ISS isn't the size of the moon because we can't lift that much stuff into orbit!

Yes. That's my point. Building small things is easier than building big things. This is one of the main reasons.

Honestly, did my use of the word "Jupiter" really obscure that? Replace it with "Empire State Building" (or any other word of your choosing) if the word's really causing that much of a blockage. Hyperbole is a valid debating tactic, y'know! It's usage doesn't diminish the underlying point.

Umbran · Apr 20, 2016

Morrus said:
Does my use of the word "Jupiter" really obscure my point to you, Umbran? I don't think it does.

It attempted t obscured the point, by way of bait-and-switch. By blowing it way out of proportion, you blew past the fact that "size" actually has a few different meanings here. We were really talking about one, when you brought in another under the same name.

That's the point of talking about volumes. The ISS can be compact, or spread out, for the same useful volume. They chose a spread out design - for the same useful volume it was built with a larger effective "size".

Morrus · Apr 20, 2016

Umbran said:
It attempted t obscured the point, by way of bait-and-switch. By blowing it way out of proportion, you blew past the fact that "size" actually has a few different meanings here. We were really talking about one, when you brought in another under the same name.

That's the point of talking about volumes. The ISS can be compact, or spread out, for the same useful volume. They chose a spread out design - for the same useful volume it was built with a larger effective "size".

But we're talking about spheres. A larger volume sphere is a larger mass by definition. There's no getting around that. A big space station like described is harder to build than a small space station like described.

MarkB · Apr 20, 2016

Morrus said:
But we're talking about spheres. A larger volume sphere is a larger mass by definition. There's no getting around that.

A larger-volume single-layered sphere is not necessarily more massive than a smaller-volume multi-layered sphere. And aren't we mostly talking about cylinders?

Morrus · Apr 20, 2016

MarkB said:
A larger-volume single-layered sphere is not necessarily more massive than a smaller-volume multi-layered sphere. And aren't we mostly talking about cylinders?

Sphere/cylinder makes no difference to this particular point of discussion.

OK, let me try to explain what I mean. You build your sphere (or cylinder). It has X mass and Y interior surface area. It's lovely, but the population grows. You can then increase the interior surface area by (a) replacing the entire thing with another, larger spherical space station or (b) putting an interior floor in. Which do you do?

MarkB · Apr 20, 2016

Morrus said:
Sphere/cylinder makes no difference to this particular point of discussion.

OK, let me try to explain what I mean. You build your sphere (or cylinder). It has X mass and Y interior surface area. It's lovely, but the population grows. You can then increase the interior surface area by (a) replacing the entire thing with another, larger spherical space station or (b) putting an interior floor in. Which do you do?

(c) Build a second station of equal size. That way, I don't have to mess with the existing, populated station, and I'm building a tried-and-tested design. Also, I now have multiple redundancy.

And that's the whole point, really. If you're going to build a second floor, it doesn't cost much more in materials to build that second floor adjacent to your existing station instead of inside it.

Morrus · Apr 20, 2016

MarkB said:
(c) Build a second station of equal size. That way, I don't have to mess with the existing, populated station, and I'm building a tried-and-tested design. Also, I now have multiple redundancy.

And that's the whole point, really. If you're going to build a second floor, it doesn't cost much more in materials to build that second floor adjacent to your existing station instead of inside it.

Sure it does. You have to provide air and power and stuff to your second station. You have to replicate the entire infrastructure, rather than just building a new floor. There's no way that building an entire new station is easier than adding a floor to an existing one.