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Comment by naasking | Hacker News Reader

> A Dyson sphere is technically possible without any new physics with a few decades of work

Not a chance. I disagree 100%. The materials science and orbital mechanics for coordination alone are way beyond our capabilities.

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Dyson sphere as conceived by Dyson himself is a swarm of orbiting objects, not a literal sphere around a star (that's Star Trek interpretation). We could start sending out solar panels to orbit the Sun today, and start adding space stations later this/next decade.

It doesn't count as a Dyson swarm until it captures a large percentage of the sun's output. As I said, that science and the computational power needed to coordinate those kinds of orbital mechanics are beyond us.

It doesn't all have to be at a single distance from the Sun. Some objects can be as far as Earth is and other objects can be at Mars level, at Merkur level or wherever else. There's plenty of space for this to be too hard.

That doesn't matter if we're talking about scenarios where a significant fraction of the sun's surface area is covered. That requires enough mass for each fragment to make such a loose "shell" that they would influence each other gravitationally and perturb each other's orbits.

Not significantly. Do the math: a thickness of 100 microns with existing silicon solar panels, or perhaps as little as 0.1 microns, out of, say, 1 AU (1.5e11 m). We're talking about filling 2e-15 of a 1-AU sphere with solid orbiters, totaling roughly the mass of Earth's moon, if we're using current silicon solar cells, and potentially a few orders of magnitude less than that.

You could use a smaller or larger radius, resulting in higher or lower irradiance and higher or lower orbiter density, but we have a lot of experience with different kinds of solar panels at 1 AU, so we know it will work.

No, there's no problem with orbital dynamics, control, computation, communication, or any of that nonsense. 50 years ago those were potentially challenging problems, but not now. Today the only remaining obstacles for a Dyson sphere are manufacturing and politics.

Not to mention that that much surface area would catch a lot of solar wind, causing all sorts of rotational moments that will need constant correction. The control theory needed for this sort of thing is complicated and N body problems are undecidable in general.

It would catch approximately all the solar wind. "All sorts of rotational moments that will need constant correction" means that, if your orbiters are thin enough, they don't need reaction wheels or thrusters to change course to avoid an imminent collision — just solar-sail louvers. An occasional collision is unimportant to the viability of the system, like dust settling on solar panels, or dermis cells dying in a follicle to grow hair.

N-body problem instances are never undecidable in the automata-theory sense; you can answer any question about the future trajectory from given initial conditions straightforwardly, if slowly, with interval arithmetic. The question of whether initial conditions exist that evolve to a given result is undecidable, but as with undecidability results in general, we do not need to decide it in order to build a working system, only to prove the optimality of a given program.

You seem to be making up reasons to justify a preselected conclusion without bothering to think about whether they are true or relevant or not, and I wish you would not do that.

You'll see.

It's just a bunch of automated drones flying in formation. Trying to calculate their orbits ahead of time in any kind of detail would be a fool's errand, instead we'd just use solar light pressure to steer them as needed (they would be very thin, there's no point to making them thick).

With really thin sails (0.78 g/m^2) they don't even need to orbit, as they can use light pressure to compensate for gravity (what Robert Forward termed a 'statite'). The light they reflect hits other sails on the other side, but this isn't a problem if they are distributed uniformly.

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