Hard sci-fi question: rotational artificial gravity space station

Umbran

Mod Squad
Staff member
Supporter
I agree that a more realistic take of the rotating sections is to have at least 2 layers set up with a ceiling/wall separating the strictly residential from the other uses that take advantage of low-gravity. Can't see any practical reasons not to do that, and it's how the Babylon 5 and Deep Space Nine stations were set up IIRC.

Again - you are thinking like someone who has to use compact architecture for reasons of limitations of real estate area, and the structural strength of materials that have to support their own weight under compression. Neither of these hold for a structure Out There. The stresses on the structure resemble those on a suspension bridge more than those on a skyscraper - specifically, most of a terrestrial building's forces are "compression", while this spinning sphere or cylinder instead has lots of tension. And you don't have to worry about restricting your building to fit in a small ground footprint.

The structures we are considering were intended to maximize "normal" living area and psychological impact. The idea is to have high open spaces, because humans are designed psychologically to walk under the open sky on a regular basis. If you put in a ceiling, you negate that.

By the way, DS9 didn't have any major open areas - it was built like a starship that didn't move, and the biggest open areas we saw were large concourse hallways ("The Promenade"), at best a couple stories high. But DS9 assumed artificial gravity generation, not using spin to generate gravity.
 

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MechaPilot

Explorer
Since the image in the OP shows homes and the OP mentions a "residential" area, I'm going to have to assume that we're thinking that people will be having families there. So far as I know, there really isn't any good information about the effects of low or zero gravity exposure to the development of fetuses and children. If low or zero G exposure is potentially harmful or deleterious to the development of fetuses and children, then it's possible that the low or zero gravity sections might have warnings specifically for children and pregnant women.

Of course, it would make sense that such areas would have warning signs anyway (I'm imagining a diamond-shaped yellow and black sign, sort of like a pedestrian crossing road sign, but with a stick figure floating horizontally in zero g instead of crossing a street), and the people who live there might already be aware of any child or pregnancy issues low or no gravity might cause.


Note: I am using zero g and no gravity despite knowing that there really is no such thing as no gravity: it's just a convenient shorthand. I do know that every object with mass exerts some kind of gravitational influence on other matter, it's just usually so sleight that it's imperceptible in daily life.
 

MarkB

Legend
I agree that a more realistic take of the rotating sections is to have at least 2 layers set up with a ceiling/wall separating the strictly residential from the other uses that take advantage of low-gravity. Can't see any practical reasons not to do that, and it's how the Babylon 5 and Deep Space Nine stations were set up IIRC.

Actually, Babylon 5 had both. Its working and accommodation areas were mostly layered and enclosed, but a large portion of its interior was entirely open and landscaped, with a train running along the central spine.
 

Morrus

Well, that was fun
Staff member
Again - you are thinking like someone who has to use compact architecture for reasons of limitations of real estate area, and the structural strength of materials that have to support their own weight under compression.

More because building a Jupiter-sized space station is a lot more work than building a football field sized one. Same reason the ISS isn't the size of the moon, despite being in space. And once you have your X-sized space station, you then optimize usage of the interior of it. There might be a lot of space, but you can't live outside the thing.
 

tomBitonti

Adventurer
Since the image in the OP shows homes and the OP mentions a "residential" area, I'm going to have to assume that we're thinking that people will be having families there. So far as I know, there really isn't any good information about the effects of low or zero gravity exposure to the development of fetuses and children. If low or zero G exposure is potentially harmful or deleterious to the development of fetuses and children, then it's possible that the low or zero gravity sections might have warnings specifically for children and pregnant women.

Of course, it would make sense that such areas would have warning signs anyway (I'm imagining a diamond-shaped yellow and black sign, sort of like a pedestrian crossing road sign, but with a stick figure floating horizontally in zero g instead of crossing a street), and the people who live there might already be aware of any child or pregnancy issues low or no gravity might cause.


Note: I am using zero g and no gravity despite knowing that there really is no such thing as no gravity: it's just a convenient shorthand. I do know that every object with mass exerts some kind of gravitational influence on other matter, it's just usually so sleight that it's imperceptible in daily life.

The term "micro-gravity" is used instead of "zero gravity". Gravity still has an influence. One particular one is tidal forces.

There are probably studies on micro-gravity fetal development in small animals. Something to search for. Not something that seems advisable for people. Edit: There are a lot of matches. Not only is development to be considered, but the physical mechanics of fertilization and implantation must be considered as well.

Moments of low gravity are all around us. Any fall has a moment of no gravity. A tall drop in a roller coaster has a longish moment. So short exposures are not harmful. Long term exposure is a problem for everyone -- see my prior link. I have no idea after how much time there starts to be a problem.

Thx!
TomB
 
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Umbran

Mod Squad
Staff member
Supporter
More because building a Jupiter-sized space station is a lot more work than building a football field sized one.

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

On Earth, when you want to build a structure, one of the first constraints is the size of the plot of land you have to work on. If you want to maximize how much value and/or use you can get out of that plot of land, you need to build up or down, because your reach sideways is limited. You are driven by constraints to build layers to get the most out of a particular footprint.

In space, you are not limited in footprint.

Same reason the ISS isn't the size of the moon, despite being in space.

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!

But, consider - The ISS has 32,333 cubic feet of pressurized space. If being compact were really the driving factor, then that could be fit in a cube about 32 feet on a side. Or in a sphere of about 20 foot radius. But, instead, it's in a string of modules over 160 feel long. Compared to what it could have been, it is a sprawling structure. Having the pressurized space be compacted into minimal external dimensions wasn't driving the design. It was driven instead by weight considerations, and being able to build segments on the ground, and merely attach them to each other once in orbit. For this huge station, we can't build functional segments on the ground at all, so that's not a concern. Mass is the issue.

And once you have your X-sized space station, you then optimize usage of the interior of it.

On Earth, yes. However, when considering these structures, there's reason to consider making two cylinders, or making one twice as long, rather than make one multi-level cylinder. And it is related to what I mentioned about the forces involved - tension.

We are going to make a spinning cylinder. On Earth, where most structures of any size don't spin, a building has to support itself under it's own weight - the controlling engineering issue is whether the foundation will support the pressing weight of the building. And, with our terrestrial building materials, we can build a foundation that will support two stories for just about the same cost as a foundation that will support one story. We have the option of simply throwing more reinforced concrete at most building designs.

With the station, as we spin this cylinder, it has to hold together not against forces that are going to crush it, but against forces that are trying to fling it apart. The result is basically that, in terms of engineering, this cylinder is really like a suspension bridge - take a length of bridge, and pull the ends up until they meet - the cables become like spokes on a wheel. Spin that wheel, and the cables hold the thing together. Stack these wheels side by side, and put caps on the end, and you have a cylinder.

The controlling issue is the strength of those cables. How much tension can they support? Since you *only* lift to space the amount of materials you need, with as little waste as possible, your cables are not terribly over-engineered - they are as light as you can get them. They're only as strong as you need them to be. So, you don't get a whole new layer for free - that layer must be supported by more cable.

So, if you need to effectively build a separate "foundation" of cables to support that second layer, you don't get much cost advantage to making the layered form. If you want a low-G area, it is just about as cost effective as to build a separate cylinder of smaller size.

Which is all to point out, in the markedly different environment, what counts as "efficient" may not be the same as it is on the ground.
 

Quickleaf

Legend
Again - you are thinking like someone who has to use compact architecture for reasons of limitations of real estate area, and the structural strength of materials that have to support their own weight under compression. Neither of these hold for a structure Out There. The stresses on the structure resemble those on a suspension bridge more than those on a skyscraper - specifically, most of a terrestrial building's forces are "compression", while this spinning sphere or cylinder instead has lots of tension. And you don't have to worry about restricting your building to fit in a small ground footprint.

The structures we are considering were intended to maximize "normal" living area and psychological impact. The idea is to have high open spaces, because humans are designed psychologically to walk under the open sky on a regular basis. If you put in a ceiling, you negate that.

By the way, DS9 didn't have any major open areas - it was built like a starship that didn't move, and the biggest open areas we saw were large concourse hallways ("The Promenade"), at best a couple stories high. But DS9 assumed artificial gravity generation, not using spin to generate gravity.

Oh, I totally get what you're saying about tensive vs. "compressive" forces & psychology of "livability."

I was thinking economics. I have a station that's supposed to be one of the older models of its kind, now outclassed by newer tech with improved materials, construction techniques, and an entirely greater magnitude of size.

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.

I was assuming because of this we would maximize use of space — not out of any structural limitations / space being at a premium — but out of a need to build as economically as possible. I mean, the ISS isn't exactly roomy.

But maybe that's false?

Maybe in the future it will be as economical to build larger as it would be to build smaller in space?
 

Umbran

Mod Squad
Staff member
Supporter
But maybe that's false?

What may be false is that you can add that second layer at dramatically reduced cost (and weight), as outlined above - unless/until you have super-lightweight materials of arbitrarily high strength, making two separate modules may be more efficient than making one module be heftier.
 

tomBitonti

Adventurer
For big cylindrical O'Neal type structures, two cylinders are preferential to one because the pair can be rotated in opposite directions, giving the whole structure zero rotational momentum.

Favor drifted from cylinders to tori when the minimum size constraint was realized. That is, when it was realized how big across a cylinder needed to be to provide adequate gravity while avoiding motion sickness, a torus was looked to as more practical. 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.

If a long cylinder is being built, what prevents there being multiple layers on the surface of the cylinder? Choosing torus or cylinder seems to be independent of deciding how many floors to have.

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.

IMO, for aesthetics, a big O'Neal cylinder wins hands down over a torus.

Thx!
TomB
 
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tomBitonti

Adventurer
Side note:

The plural of Torus is Tori, not torii, which is a kind of Japanese gate:

https://en.wikipedia.org/wiki/Torii

A torii (鳥居 ?, literally bird abode, /ˈtɔəri.iː/) is a traditional Japanese gate most commonly found at the entrance of or within a Shinto shrine, where it symbolically marks the transition from the profane to the sacred (see sacred-profane dichotomy).

For some reason I had the doubled "i" stuck in my head as the pluralization, and had to fix that.

Thx!

TomB
 

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