Could You Build a "Non-Orbital" Ring?

[Spike Spiegel]

A thought popped into my head and I thought I'd ask some of you more knowledgeable folks about it.

Let's say you build an artificial ring around a planet or a moon, like a truss or a tensile structure, something like that. As you build this ring, you of course put the sections up by launching them into orbit. You build thrusters at intervals along this ring, all the way around. You keep doing this until you've ringed the entire planet, joining the ends together.

Now, what if you fire the thrusters retrograde until the rotation of the ring stops? Does the structure stay "up", or does it collapse and fall to the planet?

I have a feeling I know what the answer is, but I want to see if I'm right or not.

 

[SiberianTiger]

If the structure is absolutely rigid and there are no gravity/tidal disturbances, it will stay hanging "on itself".

 

[Warped]

The centrifugal force, holding the ring outward, would come to a stop. So unless the ring is strong and rigid, I think that it could buckle and fall down.

As for the ring not rotating, you might start to get into some frame-dragging issues, but i'm not an expert on that.

 

[T.Neo]

Well, assuming the ring is made out of unobtanium- I doubt any real substance would be able to withstand the forces involved.

AFAIK it wouldn't be any better than a ring spinning at orbital velocity. It would be unstable (RINGWORLD IS UNSTABLE) like a ball balancing on a pin.

But tidal forces would have a large effect as well, I'd imagine.

 

[jedidia]

Now, what if you fire the thrusters retrograde until the rotation of the ring stops? Does the structure stay "up", or does it collapse and fall to the planet?

If you want to do this to get some gravity, it might actually be better to speed it up. most materials can handle tension much better. But it wouldn't be a very practical arrangement either way. Such a contraption would be a nightmare to dock with! (hmmm... maybe a "falling" docking port on a theather, that can be retracted together with the ship once docking is complete...)

 

[Izack]

Such a contraption would be a nightmare to dock with!

My sentiments exactly. As a concept, it looks feasible, there is absolutely no practical application of it that I can see. Waste of fuel to despin, and nearly impossible to dock with.
If you wanted to build it at geostationary orbit, that's a little different. It would appear stationary relative to the Earth and would not be so much of a problem to dock with. You're still looking at a nigh-infinite cost to build, fictional materials and little practical application, but you have one hell of a cool space station. :thumbup:

 

[Spike Spiegel]

Okay, that's close to what I was thinking. I actually expected the ring to collapse under gravity, thinking that the rotation would give it some force to hold it up... stop that and it had better be made of something unrealistically strong to stay up and in one piece. Actually, it would probably need to be made of unobtanium either way.

As far as traveling to the thing, I was thinking (if you could even build such a construct in the first place) you could not slow it down completely, but decelerate it to a geostationary speed, then have space elevators to reach it. As a couple of you mentioned, if it was in low Earth orbit that would still create the problem of actually docking with the thing to do anything at all useful with it. Spacecraft wouldn't be able to reach a geostationary object in low Earth orbit unless those ships had some Star Trek physics going on.

But yeah, it would LOOK pretty cool.

 

[dgatsoulis]

That was a great question Spike Spiegel!:thumbup:
I'm a little confused with the answers i've seen.
Wouldn't you need to apply constant thrust (after assembling the thing in orbit) to keep it "still"?

And another question, (which might be stupid), "still" relative to what?
We should take inclanation into consideration, no?

But even if we thought of 0 degrees inclanation, wouldn't the Moon mess up our (non)orbit? (Another reason for constant thrust).

Those where just a couple of things that came to mind...

 

[docabn]

space elevators to reach it.

It seems to me and I'm probably wrong but multiple space elevators also built of unobtanium, would make the structure infinitely more stable as they would cause the ring to effectively become an extention of the earth rather than a freely orbiting object. Working like spokes on a wheel. The stresses that such a structure would be subject to seem to me to be a bit extreme.

 

[Izack]

It seems to me and I'm probably wrong but multiple space elevators also built of unobtanium, would make the structure infinitely more stable as they would cause the ring to effectively become an extention of the earth rather than a freely orbiting object. Working like spokes on a wheel. The stresses that such a structure would be subject to seem to me to be a bit extreme.

Yeah, an enormous amount of cables attaching it to Earth's equator would keep it stable.
Dgatsoulis brought up a valid concern though: What would the Moon do to it?
A constant unbalanced outward force slowly rotating about the thing at an unequal inclination would play hell with it. Even if it remained stable, it would develop an axial wobble, which would spell probable doom to the elevators and exert torque on the ringworld.

 

[vonneuman]

What about the combined effect of the sun and moon? Both the sun and moon cause tides on the earth. Now imagine what would happen during a full moon. With the sun and moon at right angles pulling on the ring. Or what happens when the sun and moon are pulling in the same direction? The sun and moon could pull it in one direction, lowering its altitude on one side of the planet and raising it on the other rendering the ring unstable. Now the ring will behave more like a hula hoop, getting worse the more the sun and moon pull on the ring