Ring (or more like Square) around a planet or moon??

[Jaedinator]

I was thinking about it lately and wanted you opinion on it.

If we managed to dock large segments of a ring/square (whatever is more comfortable to build) together in an orbit around a planet in a way we would have a ring/square around the planet, how would it react to orbital physics as its center of mass is pretty much exactly on the planetary center of mass (calling it COM from now on).

I could image due to it having no actual horizontal/vertical velocity it would try to fall towards kerbin, but if we build it stable enough it could resist that pressure (if it even exists, im really not sure how it reacts). Or we could make it rotate (very hard i guess) so it stays in its position (just an idea again).

As I am writing this, it came to my mind that it would be probably easier to build a ring the size of minmus (or maybe gilly i guess its even smaller) in kerbin orbit and then fly it over to minmus with its COM directly pointed at minmus COM and as soon as minmus is moving "through" the ring we decallerate to have their COMs aligned.

What do you think of it, i mean i dont think it would be easy to build it, and I'm not sure if i would even try to. But how do you think it would be reacting if placed around a planet/moon??

Thanks for reading, discuss

edit1: We are assuming that physics would be calculated all the way throug the ring. (thanks Richy teh space man )

Edited June 11, 2013 by Jaedinator

[Richy teh space man]

The longest you could build it is around 2.5km, after that the physics stops loading for objects outside.

[Jaedinator]

The longest you could build it is around 2.5km, after that the physics stops loading for objects outside.

ok, then its not possible in right now ksp, but what if physics would be calculate all the way through, or maybe we take the idea out of ksp and into the real world, someone must have thought about that one day.

[Cryocasm]

I've actually done the Gedankenexperiment, or thought experiment, pertaining to this question.

Considering orbital construction, it would be orbiting, hence at completion, it would still be orbiting. This is still logical.

Now lets think about stopping its orbit, making each segment stationary with a velocity of 0 m/s.

It would require lots of power, as well as engines placed symmetrically (to avoid creating torque and crashing everything into the parent body), but in complete theory, it would never collapse, given the materials are strong enough to uphold the whole torus along the whole length.

If the materials were too weak, it would be crushed, compressed, and would fall to the parent body.

Edited June 11, 2013 by Cryocasm

[Kerbface]

According to Vsauce, the gravitational forces would be near impossible to control and it would shake all over the place and rip itself apart or if it couldn't, crash into the planet. IIRC.

I guess to test this sort of situation you could get a magnetic ball and put an oppositely charged much lighter ring around it in microgravity and see what happens.

Edited June 11, 2013 by Kerbface

[Cryocasm]

According to Vsauce, the gravitational forces would be near impossible to control and it would shake all over the place and rip itself apart or if it couldn't, crash into the planet. IIRC.

I guess to test this sort of situation you could get a magnetic ball and put an oppositely charged much lighter ring around it in microgravity and see what happens.

That's a bit hard, even the slightest perturbation would repulse them away from each other.

The orbiting ring is fine, provided its a perfect trace of the equator and in equatorial orbit. The stand-still ring would need to counter compression by gravity.

[K^2]

A solid, rigid ring around a planet/star is unstable. It will end up crashing into the planet/star in question. I'm not sure about a flexible ring under tension, but without tension, it is obviously stable, as it is identical to a swarm of satellites in a circular orbit.

Note that any other shape will not work without some additional forces present. If you build a square frame around a planet, it will break apart due to tidal forces whether you make it spin or not. There is absolutely no way to avoid that. Each segment must follow a closed orbit. If you don't mind the thing stretching/shrinking, it can be an ellipse. Otherwise, you are stuck with a perfect circle. You are probably also going to be limited in inclinations you can use if you are building it near a planet. Earth is not a perfect sphere, and that will result in perturbations that will break the ring apart under any random inclination. As Cryocasm indicated, you are probably stuck with a perfect circle in equatorial orbit.

P.S. I'll try to check if the tension makes the thing unstable.

[DisarmingBaton5]

It is not possible in KSP, but irl i think it would be possible.

[RickyKSP]

It's impossible. The force of gravity on the object will collapse on either side of the planet. You would need something 20 times stronger than carbon nanotubes to make it possible.

[dharak1]

Speaking of micro-gravity tests... Would that work? I mean if they brought up a 60cm perfectly spherical ball of some dense material like iron to the ISS would they be able to orbit tiny things around it? Could they test rings on globes made of iron or filled with osmium?

[Yourself]

Speaking of micro-gravity tests... Would that work? I mean if they brought up a 60cm perfectly spherical ball of some dense material like iron to the ISS would they be able to orbit tiny things around it? Could they test rings on globes made of iron or filled with osmium?

No, the gravitational field of an object that size would be exceptionally weak and easily overpowered by electrical forces. Not only that, but the sphere of influence of a sphere that size likely wouldn't be much bigger than the sphere itself, so you couldn't have stable orbits around it anyway, even if you just had it orbiting earth.

[dharak1]

Well, that was only a theory... But if we had a larger one (much more expensive) could we make a ring if it was perfectly spherical? I mean if the problem is changes in gravity because of density and shape. It would be a neat little thing to have a huge iron ball with a ring.

[Xeldrak]

you mean like this:

[Nibb31]

No because the ISS is still in the Earth's gravity field. You can't have a perfectly stable orbit in real-life.

A solid ring is not possible, because each part of the ring will be under slightly different gravitational forces. Even if the Earth was perfectly spherical, the ring would be under the variable forces of the Moon, the Sun and the other planets. It would be ripped apart.

What would be the purpose anyway? It's easier to build lots of smaller colonies, or just to stay on the surface, than something that huge.

Edited June 12, 2013 by Nibb31

[falofonos]

http://www.alcyone.com/max/writing/essays/why-niven-rings-are-unstable.html

For a reason why orbital rings are unstable from Niven's ringworld stories.

You may be able to place a spinning ring at a lagrange point which would maintain its shape from centripetal force but it would need station keeping jets to maintain its' position.

To go tangential for a moment, unless the ring were made from non-conductive material or broken into short sections with non-conductive "fire walls" the whole thing would heat up from the planetary magnetic field inducing current and potentially melt through somewhere giving you a pretty but also pretty useless waving ribbon.

Edited June 12, 2013 by falofonos

[Acidum]

In KSP it is impossible, in RL it is plausible.

About it's stability: Take a satellite in near-perfectly circular orbit (equatorial). If it is above atmospheric influences (no drag) it is stable. Now take more satellites in same orbit with equidistant spacing until they are positioned at each 10 meters. Gravity is still ok, they are not falling down, their own SOI is still far smaller than their respective sizes. And now connect them with e.g. thin strings or cables. No gravitational well is formed, they are still playing around the Earth like children in park. Keep forming ring-like structure symetricaly until You build Niven ring, and it will still not fall down. Period.

Structure won't need to be rigid and superstrong. It will have to be elastic. Even Earth is not rigid.

As long as You don't put this ring in eccentric orbit, it will be stable.

PS. Think of whirligig (ser. ÄÂigra) in vacuum!