[Spaceships] SM+35 Toroid Station?

[Anthony]

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.

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).