This is an issue that has been bothering me for some time. For those who are unfamiliar, an O'neill cylinder is a space habitat in the middle of space, with an atmosphere filled interior where people live, and is rotated so that the centrifugal force approximates gravity on the inner surface. Mirrors reflect sunlight through large windows into the habitat, and day and night are simulated by adjusting the mirror's angle.
My problem is that the mirrors are also rotated with the same rpm as the cylinder itself, so it will experience a much higher G-force at the edges, up to 10g or more, so obviously your everyday mirror isn't going to hold up under the strain, especially considering just how large this has to be (at least around 10km). Why does no one ever bring up this seemingly obvious problem? Even if you can find a sufficiently strong mirror material, how are you going to adjust the mirrors without the hinges holding the mirror (and presumed by everyone to be the mechanism doing the adjusting) from breaking apart due to the massive force on it?
Also a side observation, has it ever bothered any of you guys familiar with the O'neill cylinder how everyone only knows this from Gundam? Many of my friends, after watching Interstellar, simply referred to the O'neill cylinder featured at the end as "Gundams".
>>7720943
Why the need for the mirror anyway? If we are advanced enough to build massive structures in space I would hope that our led technology has reached a point where we can accurately simulate sunlight.
Also material science is booming right now so I'd imagine the material for said mirror isn't too far off.
>>7720943
>how are you going to adjust the mirrors without the hinges holding the mirror (and presumed by everyone to be the mechanism doing the adjusting) from breaking apart due to the massive force on it?
....I think the best way to design such a mirror is to construct said mirror from an ultrastrong and ultralightweight alloy. And it would be concentric (and probably slightly concaved, albeit shallow).
Just my thoughts
>>7720985
>I would hope that our led technology has reached a point where we can accurately simulate sunlight.
Because we want to use a nuclear reactor expending rare and costly fuel replicating a task that could be accomplished by a shiny piece of metal or mylar, amirite?
>>7720943
Why not just have the mirrors on a wheel that rotate in the opposite direction at the same speed?
>>7720985
What you are saying is I assume a McKendree cylinder, which I agree is a much better idea than O'neill cylinder. Although taking in energy from solar panels, or via some other form of energy generation, and then basically creating an artifical internal sun somehow feels surprisingly inelegant when you have a natural sun already, which is why I like stanford torus and similar designs. Have you read ringworld?
>>7720992
The thing is it needs to be reflective as well, so many of the materials we currently have or can develop anytime soon (e.g. Fibers, various nanotubes,etc) won't work since they aren't reflective (I assume).
Why giant mirrors?
use smaller mirrors and tether them along the length of the cylinder. It would be far easier to manage and they could be adjusted individually rather than as giant sheet
>>7721020
They are if you coat them with a thin layer of aluminum
>>7721159
Hmm. Still, I'm not sure that would work too well in practice compared to mirrors.
>>7721207
This is a troll right?
Just what do you think a mirror is?
>>7721228
I meant no one has ever tried to coat the toughest fibers and nanotubes in existence with aluminum.
>>7721000
>rare and costly fuel
>uranium/thorium
wat
>>7720943
According to wiki the O'neill cylinder is actually two cylinders rotating in opposite directions to:
"cancel out any gyroscopic effects that would otherwise make it difficult to keep them aimed toward the Sun"
So a set of fixed mirrors will not be in rotational sync with at least one of the two sections.
Could it be assumed that the mirrors might not rotate relative to the main inertial
reference and would not experience G forces in excess of those generated for the habitats ?
>>7720943
Why wouldn't an ordinary mirror and cable hold up to ten g? It's only ten times Earth gravity.
Imagine hanging a flat stack of ten mirrors, does that seem like it would be hard to do with say, steel cables?
>>7721207
>I'm not sure that would work too well in practice compared to mirrors
You can make just about any type of mirror out of just about every type of material.
All you need is a way to coat and polish the surface with a reflective substance.
Theoretically you could make a reflective material that is several nanometers thick.
The idea was proposed by a brilliant (and albeit somewhat eccentric) writer/engineer Robert L Forward. He was the brainchild behind the design of the ISS Venture Star in James Cameron's movie Avatar.
The irony is you don't see the 25 kilometer wide, ultrathin reflective parabolic photon sail deployed in the movie.
And while I realize we are talking about apples and oranges here, keep in mind the surface coating on the photon sail is still reflective (and mirror like).
You can see the r2 attenuation parabolic mirror that sits at the stern of the ship as it approaches Pandora in the movie....it is designed to protect the ship as a high energy photon laser is directed towards the aforementioned photon sail during Earth departure.
Sorry to get off track a little, but hope this helps :D
>>7722208
>>7722208
...as a reference to what I was talking about in the above post.
>>7721937
If the mirrors didn't rotate you would need them to be a full cone to provide constant sun
>>7722009
But its a mirror that's at least ten kilometer long and you want to hang it at on average at least 5g gravity
>>7722208
One factor about most materials strong enough to hold under such conditions, while it is conceivable you can make them smooth enough that they can act well enough as a mirror, they only have high tensile strength. Imagine say kevlar. You can't pull it apart under the conditions, but basically anyone can twist it so it no longer holds straight, so you'll need lots of harness and various reinforcement methods to prevent this kevlar mirror from warping into an arc. It probably won't be a catastrophic event as the mirror won't break but it will cease to function as a mirror to reflect sunlight in. If you use kevlar harnesses to hold it in place you'll need lots of it at very regular points, maybe every hundred meters, also have to deploy engines for each of these harnesses to adjust for the shifting position of the mirror (for day and night cycle), and if you use some type of reinforcement material that can prevent the mirror from curving it will probably lower the tensile strength of the mirror. It could still be done, just that the mirrors will be a much greater pain in the ass than anyone currently imagines.
>>7723157
In this case you'll need to deploy a separate engine on the mirrors fro station-keeping so it doesn't collide catastrophically with the main habitat. Also this seems like quite a waste of sunlight since you aren't using most of the reflected sunlight, so this would probably cause some legal troubles in the future from those whose space habitat is behind such non-rotating mirrors, accusing o'neill cylinder inhabitants of "unnecessarily occupying sunlight" or something
>>7723323
I still think reflectivity can be achieved with parts that mimic mirrors.
Case in point, the photon sail in >>7722208. If I recall Robert Forward came up with the original concept behind large photon light sails (in one such novel, although I can't remember which one off the top of my head) that uses ceramic "coils" that interlock with each other. They fold on molecular hinges for easy storage--something Robert envisioned with the ISS Venture Star (the Photon Sail would collapse to something the size of a suitcase).
Your idea of a kevlar based mirror is a good idea, but I think nanotechnology will miniaturize the components of the mirror to something much lighter and more durable than kevlar based mirrors.
>>7723157
> If the mirrors didn't rotate you would need them to be a full cone
Why is that ?
The two habitat sections are rotating relative to the mirrors, the mirrors are not rotating relative to the sun.
The problem would be a stroboscopic effect if the habitat windows were not most of the main hull.
>>7720943
>so obviously your everyday mirror isn't going to hold up under the strain, especially considering just how large this has to be (at least around 10km). Why does no one ever bring up this seemingly obvious problem?
OP If you assume the mirrors will be rotating relative to the sun, and thus experiencing centripetal forces on the order of 10 G's, then you can attribute this perhaps to the artist conception as trying to show the station features in a simple way.
You're right - they show paper thin mirrors that would need extraordinarily strong materials. However, the mirrors could actually be constructed out of thick latticework and be even larger than the main cylindrical habitat(s).
>>7723516
The thing is solar sails has nothing to do with this. Basically solar sails need zero structural strength, while here you need high tensile, compressional and shear strength. Obviously we can have stronger than kevlar material, but currently all very strong materials are fiber/nanotube, which all have low compressional strength. It just seems like high tensile strength and high compressional strength don't like each other (low compressional strength means it will just turn into a curved useless mirror)
>>7723572
Yes. It is doable but with all the optimism that comes whenever everyone discusses this design, I'm afraid people will be in for a hard surprise when they realize just how much harder than envisioned this will be. I'm all for space habitats, but I don't want to get anyone's hopes up, which is why I like the stanford torus and in fact all torus based designs (bishop's ring, orbitals, ringworlds, etc) more. As for the other Bernal sphere design, I think it is indeed quite efficient but unfortunately no one would want to live there, the gravity is just to variable, the only place people would want to live is very close to the equator where the land is still relatively flat.
>>7723312
You don't have to make it out of one huge mirror. Doy.
>>7723880
>The thing is solar sails has nothing to do with this
Yes I know, but I was talking in relation to material construction rather than the ultimate end product.
OP wanted to construct a light weight mirror that wouldn't warp, deform, fly apart, etc. I was only providing unique options to his idea.
>>7723899
Checked
Such monolithic designs may never come to pass, simply due to the cost of constructing such a behemoth. Furthermore we may NEVER get the chance to build such a spacecraft, even if our total world GDP allows for it.
Me thinks the future of space exploration will involve ships that will much smaller, much longer, much much MUCH more cost effective than building Bernal spheres, Stanford Torus', etc.
Then again, I'm a hopeless romantic who thinks our future chocked full of starships zipping to and fro via some sort of Alcubierre star drive system......
