Open Air Space Habitats aka Bishop Rings

[someone_else]

I was looking for something cooler than Cold War designs in the space hab department, and I found Bishop Rings.
The link to the original article in Wikipedia is down, The Wayback Machine has a backup you can read.

So, does something like this make sense without handwaving?

Any peculiarty something of this size (and material) would have?

How big does it need to be to not lose significant amounts of atmosphere from the open-ended part?

[Simon_Jester]

The Wikipedia article alone shows that this isn't a practical near-future or mid-future design. They're talking about objects hundreds of kilometers across.

Basically, you need spin-gravity good enough to create the full depth of a planetary atmosphere inside the habitat- this requires an atmosphere something like 50-100 kilometers deep to reduce mass losses.

[Terralthra]

"The whole thing will be built out of carbon nanotubes!" kinda tells you everything you need to know about plausibility.

[Ahriman238]

But, I question: why would you want it open in the center? Diversity and size are cool in and of themselves, but I don't really see a practical benefit to the design over closed types.

Slightly less materials/cost? Granted, it's not like you save more than a little compared to what you're already spending on the thing. Then again, a little cost cutting percentage wise is probably going to be a lot in absolute numbers.

[Simon_Jester]

What I don't understand is... why? Why build such huge habitats and rely on spin gravity? Wouldn't it make more sense to stack 'tuna can' habitats that are 'only' a few kilometers across?

[Batman]

What I don't understand is... why? Why build such huge habitats and rely on spin gravity? Wouldn't it make more sense to stack 'tuna can' habitats that are 'only' a few kilometers across?

The moment you have that kind of technology, I think 'because you can' becomes an if not valid, then at least believable reason. Sure, lots of space habitats make tons more sense from a practical point of view, are more economic, and can actually be moved if the need arises. But I can absolutely see the 97th century equivalent of Howard Hughes going 'you don't think I can build a functioning Bishop Ring? Well let's just see about that!'
I mean why would anybody build ringworlds or Dyson spheres (I mean solid Dyson spheres, not a gazillion loosely connected solar collectors here and there enveloping a star) other than to prove they can?

[someone_else]

What I don't understand is... why?

[commercialmode]Because it is the most natural form of inhabiting space.
With the size allows you to rely much more confortably on ecosystems to do the air and waste-recycling jobs without assuming ludicrously low population densities.
I've always been skeptical that a tincan of the Cold War designs could actually make a real ecosystem that does not need a buttload of babysitting.
Say a forest fire would be dangerous in an O'neill cylinder, much less so when you have something with more than 1% of the Earth's land area.
The design in the article I linked in the OP has a surface that is around 2% of the Earth's land area.
Around 40% of land area is actually exploited as farmland/pasture, add a 10% for cities and other stuff (rivers/forests/lakes) and with 25 of those you have created an Earth in orbit.

If you assume that farms will be in separate (vastly cheaper) farm-oriented stations you need much less of those, 4-5 at most even with ludicrously "pastoral life" habitats.[/commercialmode]


I'm more interested in making a single big station with both space for crops and space for people. That was the goal of my research. Something able to bridge the gap between a swarm of tincans and the TERRAFORMING OF MARS.

To show that your civilization is badass, and potentially colonize every system in a way compatible with most pulp-ish stories. I was looking for cool factor, but still relatively more plausible than a terraforming to have the "wow" without pulling out total bullshit.

Consider that those hundreds of kilometers of side wall are just holding air. In a closed one, you only have maybe 1/10 the length of unpopulated wall. (the top of the habitat isn't waste in either case, since it is populated there. It's only the middle air sections that differ.)

Yes, and that's wildly better than having them strong enough to support a pressure-tight roof of this size (and not needing the abovementioned pressure roof), like a torus design would usually require.

The side walls make like that have the same role than the side walls of a o'neill's cylinder's walls at the top and bottom of the cylinder. They just need to keep pressure in, no need to be strong enough to keep up a ceiling. And are pointless as habitation space.

For something of this size, I think it's better to have an inherently stable shape, but nothing stops you from making huge cylinders (although then you have to make it like a chess board to leave windows without weakening its structure with full-lenght open sections like O'neill cylinders). Their mass will keep them very stable anyway.

Ships can launch from it and leave out the sides which scores some coolness points. Attacking ships could fly right in there too which is kinda cool.

Yes, it will be much more like Earth. Although there is a catch.

To reach "orbit" (cancel the speed from the cylinder's rotation on a vessel) you need around 3 km/s for the 2000 km diameter thing in the article linked in the OP. That's a joke for any kind of rocket. This also makes easy to employ dangerous kinetic stuff from the "orbit" without particular issues about losing that energy in the reentry.

But also means that you have to design your aerospace fighters to survive mach 10-ish conditions, and without the gravity pull it's gonna be hard to aerobrake something properly without using a buttload of fuel for course corrections.

Space elevators are not overtly useful in this case, since you still have the same angular velocity at any height. And unless you kill it somehow, you will slingshot anywhere at 3 km/s when you leave the beanstalk.
For planets that's actually a feature, since they give you "free" orbital speed, but a spacecraft has to do a matching-speed burn to dock to this thing.

Carbon nanotubes are only strong in the pulling direction. Other forces can break their asses a little too easily. Redundancy and self-repair can counter this (this is built into the moderate handwave).

The article I linked below the Wikipedia one (that none here seems to have read, btw) calls for making the structure of a 2000 km diameter habitat of a cloth made of nanotubes. (and describes his 2000 km wide CIRCULAR LOOM IN SPAACE!!!!!)
In theory that being a cloth, should exploit the tensile strenght of the nanotubes to do the trick.

I would like to know how to calculate the stress this thing must support to stay in one piece... so I can see how big I can make these things without needing handwaving again.
It's probably a very dumb question, but I'm just asking for an how-to, not prepacked answers.

[Simon_Jester]

I'm more interested in making a single big station with both space for crops and space for people. That was the goal of my research. Something able to bridge the gap between a swarm of tincans and the TERRAFORMING OF MARS.

I'm not sure this is significantly easier to do than terraforming Mars- mostly because of the scale of the construction and the demand for super-duper-advanced materials.

It makes a lot more sense as a large tin can habitat, if you ask me.

[Swindle1984]

So basically a Bishop ring is just an admission that Ringworld was a really cool concept.

[someone_else]

I'm not sure this is significantly easier to do than terraforming Mars- mostly because of the scale of the construction and the demand for super-duper-advanced materials.

CN aren't exactly super-advanced materials. I see us mastering their construction well before we manage to have a decent space engine (necessary for terraformning).
The issue about terraforming mars is mainly that you have to ship an extreme amount of gas to bring its atmosphere into the breathable range. And that the only way to do it is stealing it from the outer system's moons or gas giants (I'm looking at nitrogen mostly, oxygen is easily available from its rocks).

This habitat's mass is only a tiny fraction of that mass and its building materials don't need to be shipped from so huge distances.

It makes a lot more sense as a large tin can habitat, if you ask me.

Yes it does. I need some "wow factor" though.

Have you actually studied the cold war designs or are you just going with some gut feeling of "omfg grass and trees means LUDICROUSLY LOW"? The ecosystem stability is tied to average population density.

A stable ecosystem with a decent biodiversity (the only reason to waste so much space on one single habitat imho) needs much more land area than what those designs can provide with any kind of population inside. But they were meant for confortable human habitation, so that's not their fault anyway. Trees and grass are there to please/feed the Men (and Women), not to really export (parts of) Earth's ecosystem.

I don't know which is a better direction to go. If I was god, I'd do both!

I'm personally on the "people live in tincans and we create a few big things that are biodiversity pools (parks)", but I wanted something to say "mah civ roxxors and you suxxx n000bz" so my real opinion isn't really relevant anyway.

How are you imagining these forces? Keep in mind that it's all weightless.

My ass. It is spinning to simulate gravity. And gravity is simulated on the whole structure. Everything in it feels "centrifugal force" that pushes it away from the center of rotation (I know there is a centripetal force doing the opposite but it's a detail), the habitat's roofs and walls are not exempt. That's an issue for spinning toruses designs where the roof has to be strong enough to support its own weight, while in spinning cylinders you only have the endcaps that must stay in one piece under their own weight (and some tensile stress in the middle).

This gives a maximum size to the spinning toruses, depending on how strong the materials are. Open-Air habs avoid the issue by sheer size.

Meh, launching "up" is cool, but not ideal. I'd launch through the ground, even here. By launching off the outer surface, you use that as your starting velocity - there's your bonus, instead of something to be fought against.

Yup. Through airlocks in the side walls would be better though. That's 3 km/s of free boost for anything. Which means this hab can launch kinetics (with a 3 km/s booster) that reach a speed of 6 km/s before impact. Be afraid.

Or, if you launch them from 1-km poles from outside of the outer surface, you get a nice 6 km/s of free boost. It starts to look interesting as spacecraft boosting system.

Yeah, I read it, but he didn't actually show his work. My tensile strength thing was referring to the supporting cables in my idea rather than the article's specific design.

So, to get this right, you are making a tensile frame of CN and then bolt metal plates (or kevlar/vectran whatever more lightweight polymers) to them?

So basically a Bishop ring is just an admission that Ringworld was a really cool concept.

Heh, you have to content yourself with what you can. This thing would be larger than the Moon, impressive but still tiny in comparison to a full-blown Ringworld.