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I mean in the far future megascale be advanced enough to allow the construction of a ring world around Earth or around a low mass star( a red dwarf for exemple).

If yes, how big Earth would look from the ringworld?And how big and thick the ringworld would look seen from Earth?

How day and night cycles would be simulated?And how an Earth-like climate would be possible?

The ringworld would also function as an artifitial ring(however a ring-like space station would also have this feature), since earth don't have any rings unlike Saturn.The sky would be much more interesting to look at.

How the ringworld would look at night?Could the ring world have its own moon or moons?A hollow artifitial moon with little or no gravity?

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Would a Halo ring be more realistic than a ringworld around Earth?

This is a halo ring:

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    $\begingroup$ You have a lot of questions (eight !) in there which are in many cases too broad or opinion based. The images are also just clutter that add nothing to the question. $\endgroup$ – StephenG Jun 6 '18 at 0:05
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This question periodically pops up on the Physics SE: Why is Larry Nivens Ringworld Unstable.

The summary is, the whole concept of a ring world is not stable; the ring will not stay centered on the star. The concept is similar to trying to balance a pencil on its point: any disturbance will cause the pencil to topple.

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    $\begingroup$ And yet the question is whether it can be built, not whether it'll stay up for five minutes. ;-) $\endgroup$ – SRM Jun 5 '18 at 23:25
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Although it is a romantic idea, the incredible forces and shear amount of material required is tremendous.

The scale of the earth is big - really really big. An orbital ring around it, with a continuous surface on the inside, would require unfathomable amounts of material, engineering, and technical expertise.

You would need to:

  • Get the material up there
  • Expend inordinate amounts of fuel to do so
  • Keep it stable when under construction
  • Engineer it precisely (I think this is beyond the capacity of a human - perhaps AI could do it)

All of the above is quite difficult.

But is it possible? Yes - but I would suggest highly improbable. Perhaps a smaller ring (perhaps just a few hundred meters) is more possible.

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  • $\begingroup$ The first two points could be made moot by using the Moon as the raw material. The third can probably be handled by doing most of the construction with the pieces in orbit. I doubt the precision required is outside our capabilities right now. But even with all that, your underlying point remains 100% valid. $\endgroup$ – Gene Jun 6 '18 at 16:20
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The initial question, "could" it be done someday, is almost certainly going to be declared to be opinion based. The only answer is "who knows?"

So let's assume it could be done, and look at the feasibility and effects.

If the ring were around the Earth, the effect of gravity would be pretty massive. The original, Larry Niven Ringworld was in orbit around a star - still affected by gravity, but much less so. I'm not sure of the speed it'd have to be spinning to counteract that gravity, but it might result in more than one gravity of perceived force on anyone living on the interior. There's certainly no material built to take that strain, so we must assume scrith exists.

Any questions on what would it look like from Earth would require some details on how large the ring is, and how far away it is. Unless it's staggeringly wide and/or dangerously close, like a couple hundred miles wide, it'd likely not be seen as anything but a narrow ribbon in the sky. Certainly not large enough to have any effect on the planet, no permanent band of darkness anywhere. At the equator, any such band, however small, would move above and below the equator as the seasons changed.

Assuming it's orbiting above the equator, it'd be in darkness as one or the other hemisphere of the Earth is in darkness, as the planet would block the sunlight.

You could put solar collectors on the outside and generate more power than the Earth (and the ring itself) could ever use.

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  • $\begingroup$ I think "could" hinges on the amount of matter available in the solar system, and I've seen estimates that suggest the answer is "no, there's not enough 'stuff' around." But I can't find citation. $\endgroup$ – SRM Jun 5 '18 at 23:27
  • $\begingroup$ Larry's original idea was mining the entire matter in a solar system to make a planetary orbit-sized Ringworld. The OP is discussing a Ring only large enough to orbit Earth, which is quite a bit smaller. I'd bet the asteroid belt alone would hold enough matter to do that smaller task. $\endgroup$ – VBartilucci Jun 6 '18 at 0:30
  • $\begingroup$ The gravity issue depends entirely on how far out the ring is and how fast it's spinning. If it's at orbital speed, there won't be any stress on the ring whatsoever, and the occupants won't experience any apparent gravity. The problem isn't that it's hard to make a ring that holds itself together, but that it's hard to make a ring that holds itself together while spinning fast enough to produce ~1G of apparent gravity. $\endgroup$ – Gene Jun 6 '18 at 16:29
  • $\begingroup$ Which is why we have to accept the existence of scrith, the material used to build the one in the books. $\endgroup$ – VBartilucci Jun 6 '18 at 16:57
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The calculated forces, on a spin-gravity generating Ringworld, exceed the strong force that binds atomic nuclei together at the sub-atomic level Larry Niven says so in Ringworld Engineers you can't build them using any known substance. The larger the ring the faster it has to spin and the stronger it has to be.

If a material with sufficient strength can be found you could build a ringworld around anything, star or planet but only after dismantling all of it's natural satellites to prevent collisions. It would need attitude jets to stablise it's orbit. If you put around a planet it would need to be thin enough and far enough off the surface to get a good amount of sunlight to be habitable.

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  • $\begingroup$ "The smaller the ring the faster it has to spin and the stronger it has to be." That doesn't make sense. We can (now!) build a really really tiny "ring world" (i.e. a centrifuge) that can generate way in excess of 1G apparent gravity. Sure it's not the other way around? $\endgroup$ – Gene Jun 6 '18 at 16:14
  • $\begingroup$ @Gene Sorry you're quite right I inverted a sign somewhere along the way. $\endgroup$ – Ash Jun 6 '18 at 16:19
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I have no solution for the stability problem but for star-scale ringworlds there is a solution to the unobtainium problem:

In the traditional ringworld design there is no counter force to the 1g of spin gravity being generated. This means it shows up as tension on the ring--and not even the nuclear binding force is strong enough to hold up to this.

Thus the solution is "simple", provide a counter force. There are only two possibilities (engines of some kind--a very bad solution) or gravity. The latter is at least theoretically feasible. Instead of just the ringworld you have a big mass behind it just sitting there--not in orbit. The star's gravity acts on this mass. Looking at our solar system at Earth's orbit the sun's acceleration is .0059 m/s^2. Thus your backing mass must have 1661x the mass of the ring itself. The ring is really a truly huge maglev train riding on this mass.

This removes the tension on the ring but we still have the walls that require super materials. The answer here is to get rid of them, instead of a vertical wall the edges of the ringworld (and backing mass) are stair-stepped, no one vertical segment is high enough to be a problem and there is a horizontal section on the backing mass to take the load.

This stair-stepped wall would simply be too wide for use on a planetary-scale ringworld, thus this design is restricted to a star-scale ringworld. (Not that I can see a good reason for a planetary scale ringworld anyway.)

Note that if you want shadow squares to work you'll need a transparent backing mass for them.

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