Shell World

Megastructure for sale! Get yer sci-fi megastructure here! Any authors that want to play with this idea welcome.

This is a write-up of an interesting idea I had back in August 2020. It’s for a particular type of sci-fi megastructure which should be stable (at least to back-of-the-envelope calculations) and would make an interesting setting/location/super-architecture-style for any authors who are interested. Not practical to build anytime soon, but interesting.
I’m not sure if this is original or not (I haven’t looked very hard.) If it is, I’m staking my claim! Publish or perish!

Shellworld Writeup

The basic idea, as described in the document, is that for a thick enough, large enough shell of matter, the force of gravity can balance internal pressure. The radius divides out, so this structure can be built without tensile stress to arbitrarily large radii, allowing the construction of massive amounts of habitable volume.

(PS: after some comments with James Cambias, it turns out this idea may not be original to me. Darn.)

Comments (2)

  1. 8:22 am, November 26, 2021Karl Hallowell  / Reply

    What is providing the internal pressure? I guess there would be two things I’d be concerned about. First, that you can’t provide enough internal pressure on the megastructure without making the internal side unusable. Second, you’re limited by the gravitational effects of what’s in the interior as well. For example, let’s suppose you want to make a 1 AU radius sphere hold up under the pressure of the interior contents, then you’re going to either need an incredible amount of mass (with the shell subject to the pressure of the atmosphere of this object at 1 AU.

    To get a pressure of 1 atmosphere, you’re going to need something like a supergiant star.

    If you want something that holds up under the light pressure of a normal star, say the Sun, then the object is going to have a variable thickness. At the equator, you can match its speed to orbital velocity and effectively have a Niven ring. At the poles, the material has to directly resist the gravity of the Sun and would be of a thickness similar to a thin Mylar film. In other words, this would be a ring structure capped with a thin film.

    If you’re thinking structures in the hundreds to thousands of kilometers, you probably could wrap a pretty big structure around 1 atmosphere pressure of Earth-mix air (with a moderately higher pressure in the center). It would be a lot of air, unless you had another shell closer in to fill much of the void.

    Come to think of it, there are ways to make an inflatable balloon that is lighter than air by creating pressured cells that form an outer shell around an inner cell that remains depressurized. The outer shells can have a high pressure and the inner cell be vacuum (say the outer cells have the cross-section crudely of a trapezoid with the small end oriented inwards). As long as the structure doesn’t buckle or leak (say due to an object running into/through it), it can hold its shape well.

  2. 3:51 am, November 27, 2021William Barton  / Reply


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