I’m looking for two sides here, both the “practical” side (i.e. if a few wealthy billionaires were bored or a few countries wanted a joint tourist attraction) and the “if every country did it and damn the economic and environmental consequences” (a.k.a the “what WOULD it take”) side.
A sky island is basically a large chunk of land (not necessarily real, could be constructed mostly out of Disneyland-grade plastic or metal) that’s being floated well above the ground, what seperates it from a space station is that it’s open, and well enough in the atmosphere that you can breath and (presumably) get there by normal air travel. The key points would be free construction versus freeing a piece of Earth and lifting it here (I’d imagine you’d have to encase the dirt in a shell and rig the propulsion on the shell). The size isn’t too special, probably not too small, maybe the size of a particularly small village plus some outside room, but we can evaluate different sizes independently. I should also mention I don’t care how long it flies, it could be one day or an hour, ideally we’re talking indefinitely (and in the “whatever it takes” scenario, until we run out of resources), you probably should provide for a safe landing, but again, I’m not picky.
What would be the main hurdles? Obviously the fuel and materials (as well as making it not fall apart) would be tough, but personally I think the biggest deal would be making it easily controllable, as well as able to compensate for extra weight and force exerted on it since you really don’t want the thing accidentally drifting over New York City one day and you don’t want it dipping too much every time a full 747 lands on it. I’d imagine that making it maintainable (especially without allowing it to land) would also probably be somewhere between painful and impossible. We’ll ignore the “someone nukes it” pitfalls, have the tenants sign a waiver that they ain’t getting much in the way of security or something.
I think (but can’t find evidence online) that Buckminster Fuller proposed a flying city built from a gigantic enclosed geodesic structure and floated via a temperature difference between the city and ambient air that was renewed by the daily sunlight cycle; the structure is essentially a giant blimp. The surprising thing is how little it really takes; with a large enough structure only a few °C is necessary to achieve buoyancy, assuming that you can opaque the structure against radiative heat in the nighttime and insulate it well against convective loss. This probably isn’t quite so suprising to meteorologists and cloud physics researchers who are used to dealing with thousands of tons of water suspended in mid-air in the form of clouds, but for the average person (YHN included) it is quite astonishing that it can be done even using conventional high strength materials. There would certainly be significant engineering challenges in making the structure failsafe, and of course you’d need some way of propelling it out of the way of significant climate structures like hurricanes and large storm fronts, but it isn’t impossible. However, there seems to be relatively little advantage beyond the coolness factor; it would probably be easier and cheaper to build large marine floating structures at the mid-latitudes, fed from aquaculture and powered by wave action.
Update: Scooped by Squink; “Cloud Nines” Tensegrity sphere was what I was looking for.
There are a series of high mountains in Southern Arizona that form Sky Islands - this is a term used by ecologists/biologists. They rise high above the surrounding desert floors…and have conditions conductive to pine and fur forests. The species of plants and animals found on these isolated chunks of real estate were marooned there as the climate dried and warmed at the end of the last ice age.
In the summer, you can find lots of tourists and locals who have traveled to these high places, both for their own beauty and to escape the heat. In the winter, some of the Island that have roads feature skiing.
Maybe this would do to meet your requirements…or not. But they do exist.
If we’re assuming magical super-strong materials here, one could make a lighter-than-air structure of variable buoyancy by creating it with a large internal chamber. Simply pump air from the large container out into the atmosphere, creating a lighter-than-air chamber inside that would lift the whole island up. This would let you compensate for barometric changes and the addition of extra weight. You also might be able to steer just a little, by rising or falling into and out of different winds at different altitudes.
Squink, that link is in French. Did you mislink, or do you have a translation?
Weather would be a big one. As large airships have demonstrated, on a large and necessarily flimsy structure, even mild storms can create very troublesome stresses.
On something like a floating city, the problem would be dramatically worse. The difficulty of maneuvering this thing out of the path of bad weather would be related to its size, which would obviously be enormous.
I’ve heard of a similar idea on a smaller scale. The idea was to build large buckyball-type molecules with an empty chamber inside. If they were big enough and no air could leak in between the carbon atoms, the internal vacuum would make them buoyant. If this would work you could make lighter-than-air bricks out of the stuff.
Wow, I was expecting to get funny looks and hilarious Mythbusters-esque levels of “overdoing it” in a fumbling around in the dark attempt to FORCE it to work. Though it probably would have been easier if I’d been in a zepplin/buoyancy mindset. I’ll admit I sort of had steampunk on the brain and was imagining lush islands with huge slabs of dirt under them propelled by embarassingly large amounts of fuel and steam coming out of brass vents, you can imagine it being a bit hard to conceptualize getting a sky island to work with that image in your head.
That’s amazing, and thanks for the book source, Squink.
Because the Official Committee for Determining Sky Islandness (Current Members: Jragon, Current Chair: Jragon, Current Lead Analyst of Islandness: Jragon) has deemed those fake sky islands. So nyah!
Or to be serious for a second, the entire point of a Sky Island is to be free-floating (I was going to say not connected to the ground, but that’s not true, chaining them so they don’t drift wouldn’t make it not a sky island, the real mechanism is the fact that it floats of its own accord), while I’m certain a pillartop city would be an impressive feat of engineering and pretty damn cool, it’s not a Sky Island as I’ve seen them talked about/written about. Which brings us right back to… because I said so.
The inhabitants or guests of the sky island would have to be carefully screened and disciplined if they did not behave. I can envision a lot of scenarios where drunken people throw junk off of the edge of the island, which would (at best) pollute the environment and at worst land on someone below and kill him. Garbage would have to be disposed of carefully; maybe the island could periodically float over a landfill and the garbage could be dumped over it. Permanent inhabitants of the island might be driven insane by the isolation from the outside world and throw themselves off of the side; there would have to be high walls, to prevent this from happening, but if they were too high then the novelty of the floating island would be eliminated because people would feel closed off from the open air. Maybe the best solution would be huge walls of thick plexiglass, transparent, with ventilation areas but none large enough for someone to fall through.
People would have to be incredibly careful not to start fires. A fire in a house can be put out and the house can remain standing; a fire on an aircraft, and you’re really fucked. There would have to be firemen everywhere to ensure maximum safety.
That reminds me… wasn’t there a floating island in a Douglas Adams story, maybe one of the Hitchhiker books, that was in essence a party ship, sailing over the countryside, demanding food and booze from the resentful peons below?