Plausible dyson shell...?

[Imperial528]

Okay, so, I was reading a topic in Pure Trek, and someone mentioned Dyson shells and how they're so inefficient. So I thought, what if you really needed to harness all of the energy coming from a star, would preferably want to live on the construct, but you didn't want to make a massive sphere of metal that takes more energy to make then it gives back.

And then I thought of this:



You could harness all of the energy without a solid sphere, just by making a Niven ring and using it to join two half-spheres of a thin carbon nano-tube fiber mesh with the interior covered with solar panels and threaded with cables leading back to the ring, with a few thinner arches supporting the fabric and carrying the primary conduits.

Gray is the ring, blue is the mesh, and white is the support arches. The relative sizes aren't exact, only to show the concept.

Thoughts on this concept?

[GrandMasterTerwynn]

Okay, so, I was reading a topic in Pure Trek, and someone mentioned Dyson shells and how they're so inefficient. So I thought, what if you really needed to harness all of the energy coming from a star, would preferably want to live on the construct, but you didn't want to make a massive sphere of metal that takes more energy to make then it gives back.

And then I thought of this:



You could harness all of the energy without a solid sphere, just by making a Niven ring and using it to join two half-spheres of a thin carbon nano-tube fiber mesh with the interior covered with solar panels and threaded with cables leading back to the ring, with a few thinner arches supporting the fabric and carrying the primary conduits.

Gray is the ring, blue is the mesh, and white is the support arches. The relative sizes aren't exact, only to show the concept.

Thoughts on this concept?

Niven rings are made up of unobtanium, so no. You're better off building a free-flying swarm of smaller collectors.

[Imperial528]

Which won't be able to capture every last photon, unfortunately. There's a reason why I said shell, not swarm, since if I wanted some of the energy I would just use a swarm and be done with it.

However, another way to do this that just occurred to me is to remove the ring and make the mesh essentially one giant statite, but the density of it would have to be very low.

I'll run some numbers on it, just to see how it comes out.

[RecklessPrudence]

You mean kinda like a Buuthandi? (Definition expanded on in this footnote[/url]) It's basically a Dyson's Helium Balloon, with the majority of the structure being a contiguous solar sail/collector, and then habitat upon habitat upon habitat 'hanging' from the 'inside' of the balloon. You have to be able to compensate for the mood swings of the star, of course.

[keen320]

Why do you need to capture every last photon, exactly? Really, trying to capture every last photon just sounds like hubris.

Kinda off topic, but has there ever been a story where someone built a starship around a star that could supposedly move? I doubt it would be remotely plausible, but surely it would be one of the most ridiculously overpowered soft sci-fi vehicles ever concocted.

[Eleventh Century Remnant]

The story awaits to be written as far as I know, unless the short and msytically silly passage in Stapledon's The Star Maker counts, but the hardware has already been imagined, and it is not unrelated to this; what you're looking for may be a Shkadov Thruster. http://www.daviddarling.info/encycloped ... kadov.html- essentially, a dyson swarm of statites with mirrored interior surfaces, gravitically balanced and anchored to the star, reflecting their share of the radiation- basically, so much of the starlight goes one way that the overall system picks up momentum from it.

Very, very sublight speeds, of course, but possibly the ultimate form of sublight interstellar travel; bringing the star with you.

[Imperial528]

Why do you need to capture every last photon, exactly? Really, trying to capture every last photon just sounds like hubris.

Who knows? Maybe you need just that extra few percents' worth of power in that system, maybe you're studying stars over their lifetime and don't want to miss out on anything. Maybe you're that guy who has to fit each Kardashev rank exactly.

[Simon_Jester]

Niven rings are made out of unobtanium because they are spun for gravity. That creates huge stresses on the ring and requires impossibly strong materials to hold them together.

A saner version of the Niven ring, not spun for gravity, with habitat modules anchored to the ring Buuthandi-style, will not require such enormous structural strength because it's in equilibrium. The ring rotates around the star at the appropriate orbital velocity for an orbit radius equal to the radius of the ring, and a man standing on the surface of the ring will feel as though they are in microgravity.



That said, Imp, there's really no reason to try and build a quasi-solid structure. It makes the design much more awkward, because while you can put a Niven ring around the equator of a star and spin it at orbital velocity to keep it in place without structural strain, you can't do the same for a solid sphere. The parts of the sphere 'over' the poles of the star feel gravity pulling them into the star, and aren't in orbit so they can't cancel that out with centrifugal force.

To beat this you design the solar panels to 'hover' at an altitude above the star where light pressure alone cancels out gravity... which results in a very small, uninhabitably hot, Dyson sphere of the traditional proper swarm variety.

[Imperial528]

In my original idea the sphere was just two fabric half-spheres anchored to the ring, with the arches for support. The sphere itself is not self-supporting, and unless it were very lightweight (read: low density), radiation pressure wouldn't hold it up, either. So I placed the arches to hold up the fabric through tension forces. Of course, the arches would also have to resist shear forces from the orbital spin of the ring, and the gravity of the star at the poles. So the sphere itself isn't anything resembling solid, and would likely crumple and fall in should the arches fail.

[Simon_Jester]

In my original idea the sphere was just two fabric half-spheres anchored to the ring, with the arches for support. The sphere itself is not self-supporting, and unless it were very lightweight (read: low density), radiation pressure wouldn't hold it up, either. So I placed the arches to hold up the fabric through tension forces. Of course, the arches would also have to resist shear forces from the orbital spin of the ring, and the gravity of the star at the poles. So the sphere itself isn't anything resembling solid, and would likely crumple and fall in should the arches fail.

Thing is, the arches have to be ridiculously strong for this to work, and you need a lot more of them than you drew in on the diagram.

To hold a Dyson sphere in place using radiation pressure, you just move the solar collectors closer to the star. You still need very light collectors, but frankly, given the sheer size of the masses you need to throw around to make this work, they need to be pretty light anyway unless you're talking about dismantling planets to make it work.

[Rabid]

Kinda off topic, but has there ever been a story where someone built a starship around a star that could supposedly move? I doubt it would be remotely plausible, but surely it would be one of the most ridiculously overpowered soft sci-fi vehicles ever concocted.

The Therians in the (now deceased) game franchise AT-43. Basically, they have, in roughly half a million years of existence, converted several galaxies worth of stars systems into Dyson sphere that they can move around like starships.

Their long term goal is to prevent the heat death of the universe.

I think this makes them one of the most powerful sci-fi factions.

[Lord of the Abyss]

Kinda off topic, but has there ever been a story where someone built a starship around a star that could supposedly move? I doubt it would be remotely plausible, but surely it would be one of the most ridiculously overpowered soft sci-fi vehicles ever concocted.

The Ringworld itself was supposed to be theoretically capable of that, even before it had hyperdrive added. It could manipulate the star into emitting a jet that would move it, dragging the Ringworld along, while gathering more hydrogen fuel as it went. A very large version of a Bussard ramjet.

John Brunner's Catch a Falling Star had a solar system that was used as a slow starship; they moved the star, which carried their planet along.

For the really large scale, there's the core generator in Schlock Mercenary which can move the entire galaxy ("Ramming speed!")

[Skgoa]

So what about a set of rings that orbit in all inclinations? This would also be a way to get day/night cycles and different climates.

[Beowulf]

To beat this you design the solar panels to 'hover' at an altitude above the star where light pressure alone cancels out gravity... which results in a very small, uninhabitably hot, Dyson sphere of the traditional proper swarm variety.

I'm fairly certain the math shakes out such that any altitude above the star, the light pressure and gravity cancel out, so you can build it at whatever altitude you have materials for.