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Message: <blockquote data-quote="tomBitonti" data-source="post: 6880162" data-attributes="member: 13107">I'd think that whether an existing structure could be extended would depend a lot on how the initial structure was build.  If the initial structure wasn't built to be extended, adding to it might be very hard.  I'm considering, for example, adding a whole new layer of roads to an existing bridge.  I'm thinking that for most bridges, that would be very hard, because the bridge design was done as a whole, with the design fit very carefully to having just one roadbed.  Similarly a space station might be hard to extend.  But it would really depend on the initial engineering.This seems to be a bit of a quibble.  There seems to be no reason a-priori that you couldn't have multiple layers, or not have multiple layers.  I would prefer a structure with several layers, if not a dozen or more, if the material physics allows it, simply because the structure seems more robust, and you get a lot more living space that way.In any case, any modifications would need to preserve the mass distribution so the entire structure didn't wobble or have undue stress in any area.  But that's no different in principle than adjusting weights in a plane or on a boat to adjust the center of gravity of the vehicle, and can mostly go unstated.I don't know if three or four element structures would work out better or worse than two.  I just know that one by itself has problems.  I can imagine that the physics that applies to two cylinders could be applied to an ensemble of three or more, except I don't know how well balancing the rotations would work with an odd number of cylinders.To keep this straightforward: Both a cylinder and a torus can be made to work, with the caveat that there is a minimum size which means the cylinder might have to be very big, and that a single spinning structure is hard to turn.  (I wonder how that is fixed for a single torus, or if these would be designed to have two parallel parts spinning in opposite directions.)  And there are a lot of options for the particulars of the structure, including how many layers and whether there is a corridor running down the middle, or if there are round or flat end caps, or if a torus is built with multiple parallel rings, some smaller and with lesser gravity and others larger and with more gravity.A problem which we have not discussed is protection from radiation.  That either limits where the structure is put (inside the magnetic belt of the earth) or requires quite a bit of shielding on the outside to provide protection (I've read that a structure could be built from material sent from the moon via linear accelerator, with unused/waste material put on the outside as a protective layer.)What I've read as a way to bootstrap all of this is to build a base on the moon which would be a combination mine/solar power array/linear accelerator, to send materials to one of the Lagrange points, then build big O'Neal cylinders there as habitats and factories, with the eventual goal, in part, to manufacture power satellites which would transmit sunlight converted to microwaves to the surface.Anyways,TomB</blockquote>

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