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Comment by sigstoat | Hacker News Reader

> the ability to design large stable systems is relevant for when thinking about the question "How many O'Neil cylinders can we build in the habitable zone?".

pretty sure the answer is "as many as we can figure out how to get the mass for".

absent dismantling the gas giants themselves, you're not going to do anything very interesting do the dynamics of the solar system, regardless of what you take apart, or how you reconstitute it.

and the man-made structures can include mechanisms for closed-loop control of their position. which they'd need anyways, as they'd accumulate positional error from vehicles coming and going.

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I think the point of building habitats is that spherical planets are a very inefficient use of matter from a surface-area-to-mass ratio point of view. We could create a lot more surface area (i.e. usable land) with less material if it were arranged in a more useful configuration.

However, spherical masses are much more stable gravitationally because the total gravitational potential energy of all mass is the minimum.

those are all completely true things. i assume something i said has been misinterpreted, but i can't imagine what or how.

Probably this line:

> absent dismantling the gas giants themselves, you're not going to do anything very interesting do the dynamics of the solar system, regardless of what you take apart, or how you reconstitute it.

I would consider reconfiguring available materials to achieve more usable surface area to be interesting (not to mention potentially useful if we manage to accomplish it someday).

However, what's "interesting" is highly subjective and dependent on context. Perhaps you meant something different by "you're not going to do anything very interesting" than the way some of us are interpreting it?

"you're not going to do anything very interesting..." to the dynamics of the solar system.

the orbital dynamics of the solar system. (the thing you'd be worried about if you thought you needed to learn how to make 416-body systems stable.)

certainly packing the habitable zone full of new places to live is interesting, on all sorts of social and technological levels. it just doesn't raise any questions about the stability/dynamics of the n-body system that is the solar system (until you maybe start taking apart the gas giants).

hopefully that clears that up?

Yeah, thanks.

And I agree; it turns out that planets are really heavy and have an incredible amount of inertia; moving some asteroids around isn't going to cause the Earth to slip on a banana peel and fall into the sun.

The original article about placing 416 Earth-sized planets in a stable orbit does involve a quantity of mass greater than Jupiter (at 317.8 Earth masses), but building habitats out of what we have available in and inside the asteroid belt is a much more modest scope.

I love how turning the entirety of the asteroid belt, and maybe Mercury, into livable space stations "is a much more modest scope". :-D

Not that I disagree! We also have the Hilda, Trojan, and Greek asteroids (in Jupiter's Lagrange points) to work with. The Jovian and Saturnian moons too. It'll be a long, long time before we need to worry about dismantling the gas giants themselves.

On our path towards maximizing the livable land area in the Solar System, I wonder what we will run out of first. It looks like water, iron, carbon, etc. are all pretty abundant. We'll run out of* some rarer element (like Phosphorous or something) before we ever approach maximum constructed land area.

*And by "run out of", I mean even with perfect recycling, the spot market demand for the material maintains a price level where it's uneconomical to develop further, barring discovery of new supplies or more efficient usage.

This assumes that we don't create such elements as a by-product of fusion or other processes that we develop in parallel with the technology advances required to bring significant industry outside earth's gravity well.

Habitats don't need to be solid rock. It's possible to make many large habitats using the materials from a single large body.

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