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Images of O'Neil cylinders captivated me as a child, and they still do now. So familiar and yet so weird. Something similar is depicted in the film 'Elysium'.

Images of O'Neil cylinders captivated me as a child, and they still do now. So familiar and yet so weird. Something similar is depicted in the film 'Elysium'. But it is a open torus, rather than a closed cylinder and they never explain how they keep the atmosphere in.

jazzyjackson 5y ago
> they never explain how they keep the atmosphere in. not familiar with the design, is there gravity? that’s why our atmosphere sticks around, right?
- adwn 5y ago
  There's no gravity on Elysium's habitats, but there's a centrifugal force caused by the rotation of the torus. However, that wouldn't be nearly enough to keep the atmosphere in, because the walls are only a couple 10s of meters high. For comparison, Earth's atmosphere stretches out for several 10s of kilometers. And even if their atmosphere wasn't lost, the inhabitants would quickly suffocate and die due to low air pressure. On Earth, there's 10 tonnes of atmosphere pushing down on every square meter at sea level, compressing the air to 1 bar. Reduce that ~100 km column of air to ~100 m, and the pressure would be very much lower.
  - rm999 5y ago
    This doesn't seem right to me, why don't astronauts suffocate on the International Space Station? You can pressurize air in a spacecraft, I believe the ISS is kept at ~1 atm.
    - numpad0 5y ago
      The habitat in Elysium is quite bizarre. The entire donut is built Cabriolet style flying LEO and protagonists just lowers commandeered space helicopters through inner perimeter. It could be said the Chekhov's gun principle applied beautifully but quite bizarre.
      - f00zz 5y ago
        Also there's a scene at the beginning where the main character looks up and it's just hanging up there, seemingly stationary. At LEO it should be zapping across the sky (the ISS orbits the Earth every 90 minutes).
    - rtkwe 5y ago
      The Elysium habitat in the movie is open topped with walls on a spinning torus not a sealed container like the ISS. On Earth this works because of the combination of gravity and the size of the atmosphere pressing on itself. https://image-engine.com/case-studies/elysium/ https://image-engine.com/case-studies/elysium/
    - vimacs2 5y ago
      OP is referencing an open air habitat so a comparison with the ISS doesn't make sense. Open air designs do actually work once you scale up the size of the habitat enough. This is where we get the idea of Bishop rings which use a wall a hundred or so km in height to keep the air in. Mckendree cylinders (which are a supersized version of O'Neil cylinders) can also have end caps that are open provided you have a high enough wall. The main advantage of open air designs is it allows you to use aerobreaking when approaching the habitat which could be a significant save in fuel.
      - hermitcrab 5y ago
        The Elysium habitat in the film has (from memory) walls only hundreds of metres high. So there is no way that would contain an atmosphere for any length of time. I guess their could be some sort of high tech field that kept it in, but it would have to be something that doesn't stop a shuttle entering (as they do in the film).
        vimacs2 5y ago
        Yeah, that wouldn't work at all but then again, inaccurate science was far from the only problem that movie had imo. One possible solution is to ionise the air near the walls and then use a magnetic field to contain it. This would not really prevent all air leakage but you don't really have to as long as it's substantially reduced since even the relatively diminutive size of the Elysium habitat would contain a fairly formidable volume of air. There can also be outside magnets that can arrest the momentum of the escaped ionised air enough so it falls back down to Earth. Then all you need is a tether extending down to the atmosphere with an internal air pump and you have a self contained cycle.
    - BBC-vs-neolibs 5y ago
      There is no apparent roof in Elysium, that's the difference.
  - fallingfrog 5y ago
    I haven’t done the math, but I suspect that for habitats where gravity comes from rotation, having a wall without a top to hold in the atmosphere wouldn’t work no matter how high the wall is. That’s because when you move in an antispinward direction your apparent gravity decreases and if you go antispinward at the speed of rotation your apparent gravity is zero. Fast moving particles that are bouncing every which way are going to randomly have zero gravity a significant fraction of the time and just drift away. Liquids don’t do this because they are bound together through surface tension and other mutual dipole attraction forces and solid objects of course have all the atoms bound together, but gasses I’m pretty sure would just float away.
genedan 5y ago
O'Neill cylinders are also frequently depicted in the various Gundam series.
- TomAbel 5y ago
  Off Topic but I finished my last exam today and I wanted to start watching Gundam. I wanted to know if you have any recommendations for which Gundam series I should start with first as someones who likes anime but has never watched Gundam.
  - dta5003 5y ago
    Gundam Wing! It's not a huge commitment either - 50 episodes plus a couple movies.
    - deleted 5y ago
      [deleted]
    - TomAbel 5y ago
      Thank you for the recommendation.
      - Apocryphon 5y ago
        It's definitely one of the more kiddie Gundam series, but it touches upon the themes of the original 1979 show, and is one of the few to depict the Stanford torus rather than O'Neill cylinders.
  - kuraudoOishii 5y ago
    I recommend the universal century, one year war movies to get you started: The mobile suit gundam movie trilogy followed by 0080: war in the pocket (a masterpiece of both storytelling and animation). In fact, starting with 0080 war in the pocket isn't a bad idea given the self contained story. From there, I'd check out 0083: Stardust memory and move on to the Zeta Gundam tv show. Then, for a completely different experience, you can check out the alternate universe shows like Mobile Fighter G Gundam or After War Report Gundam X
Kaibeezy 5y ago
Ringworlds, Culture Orbitals and Halo Arrays are also open-faced. Centripedal force? How tall do atmosphere retaining walls on rotating space habitats need to be? https://worldbuilding.stackexchange.com/questions/119739/how-tall-do-atmosphere-retaining-walls-on-rotating-space-habitats-need-to-be https://worldbuilding.stackexchange.com/questions/119739/how...
- ncmncm 5y ago
  Short answer: really tall. 100 km is not enough.
- marcosdumay 5y ago
  I doubt it's possible. It doesn't matter what frictionless calculations say, the air will climb through any wall you create until it gets out of the station.
  - hermitcrab 5y ago
    The atmosphere falls off exponentially (IIRC). No matter how high the wall is there will be some loss as energetic molecules reach the top of the wall and fall out of the side. But the loss would be very small for a wall that is 100km+ high as very few air molecules will be energetic enough to get that high. According to the stackoverflow entry above, a 10km high wall on a ringworld would leak about half the atmosphere every century. Obviously the wall would have to be airtight.
    - jandrese 5y ago
      Half of the atmosphere from a Ringworld is a stupendous amount of gas. 100 years is basically nothing on the timescales you need to think about when building a Ringworld. You might be able to slow down the loss of gas by putting lips on the tops of the walls and maybe even air jets blowing downward though. Or leave it mostly closed except for a few openings for spacecraft to enter or leave. Also, working out the practical considerations for a Ringworld is an exercise in futility anyway. You are already well beyond practical when you start building one.

jazzyjackson 5y ago

> they never explain how they keep the atmosphere in. not familiar with the design, is there gravity? that’s why our atmosphere sticks around, right?

adwn 5y ago
There's no gravity on Elysium's habitats, but there's a centrifugal force caused by the rotation of the torus. However, that wouldn't be nearly enough to keep the atmosphere in, because the walls are only a couple 10s of meters high. For comparison, Earth's atmosphere stretches out for several 10s of kilometers. And even if their atmosphere wasn't lost, the inhabitants would quickly suffocate and die due to low air pressure. On Earth, there's 10 tonnes of atmosphere pushing down on every square meter at sea level, compressing the air to 1 bar. Reduce that ~100 km column of air to ~100 m, and the pressure would be very much lower.
- rm999 5y ago
  This doesn't seem right to me, why don't astronauts suffocate on the International Space Station? You can pressurize air in a spacecraft, I believe the ISS is kept at ~1 atm.
  - numpad0 5y ago
    The habitat in Elysium is quite bizarre. The entire donut is built Cabriolet style flying LEO and protagonists just lowers commandeered space helicopters through inner perimeter. It could be said the Chekhov's gun principle applied beautifully but quite bizarre.
    - f00zz 5y ago
      Also there's a scene at the beginning where the main character looks up and it's just hanging up there, seemingly stationary. At LEO it should be zapping across the sky (the ISS orbits the Earth every 90 minutes).
  - rtkwe 5y ago
    The Elysium habitat in the movie is open topped with walls on a spinning torus not a sealed container like the ISS. On Earth this works because of the combination of gravity and the size of the atmosphere pressing on itself. https://image-engine.com/case-studies/elysium/ https://image-engine.com/case-studies/elysium/
  - vimacs2 5y ago
    OP is referencing an open air habitat so a comparison with the ISS doesn't make sense. Open air designs do actually work once you scale up the size of the habitat enough. This is where we get the idea of Bishop rings which use a wall a hundred or so km in height to keep the air in. Mckendree cylinders (which are a supersized version of O'Neil cylinders) can also have end caps that are open provided you have a high enough wall. The main advantage of open air designs is it allows you to use aerobreaking when approaching the habitat which could be a significant save in fuel.
    - hermitcrab 5y ago
      The Elysium habitat in the film has (from memory) walls only hundreds of metres high. So there is no way that would contain an atmosphere for any length of time. I guess their could be some sort of high tech field that kept it in, but it would have to be something that doesn't stop a shuttle entering (as they do in the film).
      - vimacs2 5y ago
        Yeah, that wouldn't work at all but then again, inaccurate science was far from the only problem that movie had imo. One possible solution is to ionise the air near the walls and then use a magnetic field to contain it. This would not really prevent all air leakage but you don't really have to as long as it's substantially reduced since even the relatively diminutive size of the Elysium habitat would contain a fairly formidable volume of air. There can also be outside magnets that can arrest the momentum of the escaped ionised air enough so it falls back down to Earth. Then all you need is a tether extending down to the atmosphere with an internal air pump and you have a self contained cycle.
  - BBC-vs-neolibs 5y ago
    There is no apparent roof in Elysium, that's the difference.
- fallingfrog 5y ago
  I haven’t done the math, but I suspect that for habitats where gravity comes from rotation, having a wall without a top to hold in the atmosphere wouldn’t work no matter how high the wall is. That’s because when you move in an antispinward direction your apparent gravity decreases and if you go antispinward at the speed of rotation your apparent gravity is zero. Fast moving particles that are bouncing every which way are going to randomly have zero gravity a significant fraction of the time and just drift away. Liquids don’t do this because they are bound together through surface tension and other mutual dipole attraction forces and solid objects of course have all the atoms bound together, but gasses I’m pretty sure would just float away.

genedan 5y ago

O'Neill cylinders are also frequently depicted in the various Gundam series.

TomAbel 5y ago
Off Topic but I finished my last exam today and I wanted to start watching Gundam. I wanted to know if you have any recommendations for which Gundam series I should start with first as someones who likes anime but has never watched Gundam.
- dta5003 5y ago
  Gundam Wing! It's not a huge commitment either - 50 episodes plus a couple movies.
  - deleted 5y ago
    [deleted]
  - TomAbel 5y ago
    Thank you for the recommendation.
    - Apocryphon 5y ago
      It's definitely one of the more kiddie Gundam series, but it touches upon the themes of the original 1979 show, and is one of the few to depict the Stanford torus rather than O'Neill cylinders.
- kuraudoOishii 5y ago
  I recommend the universal century, one year war movies to get you started: The mobile suit gundam movie trilogy followed by 0080: war in the pocket (a masterpiece of both storytelling and animation). In fact, starting with 0080 war in the pocket isn't a bad idea given the self contained story. From there, I'd check out 0083: Stardust memory and move on to the Zeta Gundam tv show. Then, for a completely different experience, you can check out the alternate universe shows like Mobile Fighter G Gundam or After War Report Gundam X

Kaibeezy 5y ago

Ringworlds, Culture Orbitals and Halo Arrays are also open-faced. Centripedal force? How tall do atmosphere retaining walls on rotating space habitats need to be? https://worldbuilding.stackexchange.com/questions/119739/how-tall-do-atmosphere-retaining-walls-on-rotating-space-habitats-need-to-be https://worldbuilding.stackexchange.com/questions/119739/how...

ncmncm 5y ago
Short answer: really tall. 100 km is not enough.
marcosdumay 5y ago
I doubt it's possible. It doesn't matter what frictionless calculations say, the air will climb through any wall you create until it gets out of the station.
- hermitcrab 5y ago
  The atmosphere falls off exponentially (IIRC). No matter how high the wall is there will be some loss as energetic molecules reach the top of the wall and fall out of the side. But the loss would be very small for a wall that is 100km+ high as very few air molecules will be energetic enough to get that high. According to the stackoverflow entry above, a 10km high wall on a ringworld would leak about half the atmosphere every century. Obviously the wall would have to be airtight.
  - jandrese 5y ago
    Half of the atmosphere from a Ringworld is a stupendous amount of gas. 100 years is basically nothing on the timescales you need to think about when building a Ringworld. You might be able to slow down the loss of gas by putting lips on the tops of the walls and maybe even air jets blowing downward though. Or leave it mostly closed except for a few openings for spacecraft to enter or leave. Also, working out the practical considerations for a Ringworld is an exercise in futility anyway. You are already well beyond practical when you start building one.