Quote:
Originally Posted by AlexanderHowl
On a more serious note, do we need a hollow object that is 95% trace atmosphere? If you constructed multiple levels, you could have g's ranging from .1 to 1.0 without difficulty.
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Yes, but it's unclear what benefit you get out of it, since your primary limit is that you can saturate your available energy and heat dissipation with a very small number of layers.
If you don't care about horizons, though, you can save a lot of weight by making the outer shell have a low ceiling. With no ceiling, that 2 bar surface pressure corresponds to an atmospheric mass of 100 tons per square meter, or 10^17 kg for the entire million square kilometers of habitat. Put a 1 km ceiling on the world and you reduce that to 2.4 tons.
Note that this requires a much different design than previously suggested, because the natural shape of an inflated torus is
round, and with a 250 kilometer width, that's ridiculous. Fortunately, we already know how to make a flat inflated object: it's called an air mattress. Somewhat counter-intuitively, this also saves us on structural mass, because most of the atmospheric pressure is supported by internal struts (support length 1 km) instead of the belt of the torus (support length 650 km); the only stuff that has to be supported by the belt is now the static mass, which at 10 tons per square meter (plenty for a dirt belt) is still only around a tenth of the atmosphere.
The drawback is that you have considerably shortened sight lines and a bunch of pillars limiting line of sight (using the same sorts of materials as you'd need for the general case, you need something like a 3 meter pillar every kilometer).