Not really; the concept of a ‘Gravity Balloon’ is probably the closest to your idea- a balloon filled with atmosphere surrounded by asteroid ballast, with numerous spinning constructs inside. Alan Rominger came up with this idea a few years ago, and has developed it here.
Here’s my take on it
You couldn’t have a layer of oxygen in a normal gas giant’s atmosphere, because it would combine with the hydrogen and fall as rain into the lower levels. Uranus and Neptune both have very large water mantles, with the water in various phases of ice - but almost certainly no free oxygen. Possibly some types of waterworld would would be small enough to lose their hydrogen into space, leaving a layer of photodissociated oxygen-rich atmosphere - but no-one has seen one in enough detail yet to confirm this possibility.
Here is his episode on Shell Worlds that describe exactly what’s being asked and how you’d do it.
Thanks for the link, but I probably will never watch it. I’m a Luddite–I like (well written) text descriptions of things, have rarely watched one of the flashy personality-driven YouTube videos, and have literally never listened to a podcast.
Also, even though my Dyson lawn is the size of billions of Earths, stay off of it.
Well, the video goes into some detail about how you’d build a shell world and why you might want to do it. Boiled down, you could basically make a world with a lot more habitable area, though the cost in mass per square foot of usable space is a lot higher than if you build a rotating habitat. However, if you used a gas like, say, hydrogen then your interior mass could double as your power fuel (assuming you worked out that whole fusion thingy). You can also change the size of the world wrt it’s diameter by shifting the density of the interior and juggling the numbers to keep it at whatever gravity you were shooting for. And you could do a sort of Russian doll shell world series, with shell worlds inside of shell worlds inside of shell worlds, if you really wanted something like that. The conclusion is that you could do this, but the only real reason to build a shell world would be if your civilization was planning to be around for a long time…measured in trillions of years. It wouldn’t be worth all of the effort if you weren’t planning to do that.
Shell worlds aren’t really used that heavily in sci-fi, at least that’s my personal anecdote. Outside of Ringworld (which isn’t really a shell world but similar concept), I can only think of a few examples.
As for the video, it’s a pretty short one at least wrt his usual videos which can be quiet lengthy. If you can’t bring yourself to watch it that’s fine, but it answers some of your questions if you can. You could google shell worlds as well…there are some hits in there that have articles on the concept if you’d rather go that route.
Well exactly. Also, an almost pure oxygen atmosphere would be extremely dangerous on a base/city like that.
But this is the Universe where a moon sized base gets blown up over a planet sized moon and somehow doesn’t cause mass extinctions. And where another world has liquid water all the way through it’s core, which can somehow be traversed in a small craft.
I discussed and presented some estimates in [POST=16974132]this thread[/POST] regarding why the calculated performance that Freeman Dyson presented was incorrect (and to be clear, Dyson knew this to be the case; he was trying to promote the use of nuclear pulse propulson to get funding for Project ORION after the US Air Force passed on it as a super-ICBM or intercontinential troop transport). All of the estimates that present nuclera pulse propulsion as offering sufficient performance to get up to a couple of magnitudes of order of c assume highly idealized exhaust velocity (again, treating the initial speed of the energized bomblet as the effective exhaust velocity of the material ejected off of the pusher plate with total conversion and no thermodynamic losses) and a massive spacecraft on the order of millions of tons which would be logistically impossible to construct in space. (Dyson conceived to launch ORION spacecraft from Earth’s surface which must have seemed plausible in 1958 but the idea of setting off a string of large nuclear explosions in the atmosphere today is fantastical to say the least.)
The linked video provides no more information or detail beyond repeating frequently cited values for performance. Just applying the Tsiolkovsky rocket equation (which I do in the thread linked above in [POST=16981639]post #41[/POST]) demonstrates that even assuming an I[SUB]sp[/SUB] = 100,000 s requires ridiculous propellant to payload ratios. Short of somehow efficiently producing extremely energetic photons as a propellant, the rocket equation prevents the use of momentum transfer using an internal propellant to cross interstellar distances in anything like a human lifetime.
I think pretty much any civilization capable of building space megastructures is going to be assumed to also have a high degree of automation with the ability to control and modifiy substantes down to the atomic level, as well as command essentially unlimited energy conversion from their sun or other sources. So…basically magic. Realistically, habital megastructures make about as much sense as battleship-sized land tanks of steampunk fiction; it’s a Victorian-era solution to a problem that will look completely different by the time the technology to support it is remotely practical. But that’s science fiction and technology speculationin a nutshell; almost nothing works in detail as it is imagined decades before it comes into practicality, even if there are superficial similarities such as Vannevar Bush’s Memex and the actual World Wide Web.
Pretty much nothing you see in Star Wars is remotely physically workable, so I wouldn’t worry too much about the residents of Cloud City being able to walk out on open platforms (often with no hand railings, to boot). However, buoyant structures floating on Saturn’s atmosphere are certainly plausible, and wouldn’t even require a lot of buoyant space in Venus, although the corrosiveness and lack of water in that atmosphere might be as problematic as anything you would experience on a solid surface. However, aside from research I can’t see the appeal of such structures; in both cases, you wouldn’t have much of a view since you’d be embedded in a thick, opaque atmosphere.
Stranger
Here’s my take on the Shellworld concept.
Actually there are two different, but vaguely related, types of shellworld on that page. The first idea is the oldest one, which consists of a series of caverns excavated inside a dead world like the Moon, which then provides raw material to build a series of roofed habitats on the surface. Probably only two or three layers possible on such a world.
The second, and much larger concept includes multiple suprashells supported by orbital ring technology. This sort of object could be almost arbitrarily large.
Iain Banks’ SF novel Matter is about a shellworld, but he doesn’t really explaiin how it works; I think it is probably some variant on the second type.
The largest megastructure concept I’ve ever heard of is the Supraself concept by Paul Birch - a vast shellworld constructed from all the matter in an entire galaxy. This would be so massive that its gravity field would cause time dilation, despite never exceeding one Earth Gravity at any point on the many surfaces. Here’s my take on that concept.
As Geoff Landis has pointed out, the 50km layer in Venus’ atmosphere is just about the most Earth-like environment in the Solar System (similar temperature, pressure and gravity). In all other respects it is deadly.
I’ve done a version of this concept too, for Orion’s Arm, but I’ve posted enough links for now.
Neat. I see there is a rather significant problem with the air in the habitat coming into contact with the cylinder that is spinning.
A couple of things then I plan to drop this as it’s not really what this thread is about. First off, I agree with you that no one is talking these days about using something like this from the planets surface. Any use of any sort of nuclear rocket is for outside the atmosphere, and probably a fair distance from the planet in the case of Orion. Secondly, I read your first link, and you don’t seem to be addressing Orion at all…you seem to be discussing the specific impulse of a nuclear thermal rocket in that other thread. You are asserting that the 100k ‘requires ridiculous propellant’ (which I’d say is the definition of 1000 1KT fusion weapons tossed out the back end of a vessel using a big ass plate to absorb the shock), but then you say in the same sentence ‘frequently cited values for performance’, by which I presume you mean the range of potential specific impulse numbers in use by a wide range of people, including from my own video (it’s on his message board as well in a bunch of different threads, but I’m not going to link to them or even the board). I also cited a NASA paper from after 1958 that put the range (in the mid '60 according to what I recall of the paper) at between 8000-80,000…so not that far off of the 100k (and this was using only 800 bomblets) depending on the type used.
At any rate, as I said, I plan to drop this and return the thread to more interesting topics.
That’s a pretty cool web site. It’s along similar lines to the video I linked to, though obviously it goes into more detail. I even recognize some of the artwork from IA’s videos, so they must use similar public domain images. 
Like I said, I don’t think that shell worlds are all that likely. It’s a lot more efficient to create various megastructures in space than to build a shell world. What you COULD do that seems more likely is orbital rings like this from another of his videos. As he says, you could use this method to do what you are describing wrt the second concept.
No, Isaac Arthur uses a few of my images (with permission); we have even worked together on a page for that site.
Perhaps we could turn this into a feature. We need to circulate the air in a balloon like this, otherwise detritus and water droplets might collect in clouds or clumps that could turn mouldy (a similar problem occurs in the ISS, I believe). The rotating habitats could be used as fans to circulate the air.
I’d keep the rotation as slow as feasible- you might need gravity for some purposes, but do you really need a whole Earth gravity? Lunar or Martian gravity should suffice for most purposes.
Yes, what I am talking about is that even if you make the outside of the cylinder very smooth and properly curved, there might be a lot of waste heat buildup from the air friction.
I’m not actually sure, this was just one article talking about it. I wasn’t aware that a spinning metal cylinder, even if it’s very large, that is a smooth surface actually has any significant interaction with air around it.