Super Massive "Station" In Orbit

[Greenfire32]

So everyone here (or at least the overwhelming majority) knows that an object in orbit isn't "floating" above the planet, but rather traveling around the planet at the same rate that it's falling toward the it.

This is a fairly easy concept to visualize when the object is (relatively) small like a shuttle or a space station. Heck, even the rings of Saturn aren't made of a single object, but many many tiny ones.

What if there was a massive ring-shaped "station" in orbit? Would the planet's gravity pull on the ring equally from all sides, keeping it stationary in "orbit" (fig. A)? Would this mean that the "station" wouldn't need any rotation since it's size alone would mean that the planet's gravity just keeps it in place (fig. ? Or would the "station" be so massive that it just rolls over the surface, causing stupid amounts of destruction on the surface (fig. C)?

Now the goal here is to avoid massive support beams to hold the ring up (fig. E) and to just have a free-floating ring if possible. Would adding thrusters to generate spin keep it in orbit (fig. D)? Is this even possible?

This is just something I thought of while on lunch break. I've got a small rubber band ball and a ring made out of twist-ties on my desk in the office that kind of made me visualize all this. It just kinda sparked my thought process and I figured since I don't really know how this would work, I'd throw it at all of you and see what you say.

For the sake of the argument, please assume that mankind has a material strong enough to hold this super-structure together and the resources required to build it in the first place.

[-Velocity-]

It need not rotate; in fact, rotation does not help you any to keep it suspended, assuming it's rigid. The main problem with this idea is that such a ring is not stable. Any disturbance from the perfect balancing point will result in a net force that leads to a larger disturbance, and so on. You could potentially add thrusters that thrust the ring back to the equilibrium point when there is a disturbance. This is a control system which acts to create a net restoring force when there is a disturbance from equilibrium. Such a system would require fuel and energy, of course.

If you are willing to accept tethers, however, you can tether a ring around Earth with a radius larger than geostationary orbit, and it will be held up there by centrifugal force. It would be nothing but a ring of space elevators.

Edit- an alternative to a thruster control system would be a if you had a ring that WASN'T rigid, but could be actuated. Say that one side of the ring started to drift away from the central gravitating body (which correspondingly makes the other side drift closer). Normally, this slight imbalance would be amplified till the closer side of the ring crashed into the central body. However, if you could actuate the ring- deform it at will- then you could move portions of it closer to the cental body to create a force imbalance in one direction, which you could use to keep the ring suspended. Again though, this would require energy.

Another alternative control system I just thought of would be to spin the ring, and wind or unwind weights to various lengths on long tethers. As the rotation speed is fixed, unwinding the weights further out would cause them to exert more centrifugal force on part of the ring they were attached to. In this way, you could apply restoring forces to the ring to keep it suspended.

Edited April 13, 2015 by |Velocity|

[HoloYolo]

B is the thing that will happen. Saturn's Rings do the same thing, they are around the planet and the rocks in them orbit as the ISS does with Earth and this ring structure.

[BlueCosmology]

So everyone here (or at least the overwhelming majority) knows that an object in orbit isn't "floating" above the planet, but rather traveling around the planet at the same rate that it's falling toward the it.

This is a fairly easy concept to visualize when the object is (relatively) small like a shuttle or a space station. Heck, even the rings of Saturn aren't made of a single object, but many many tiny ones.

What if there was a massive ring-shaped "station" in orbit? Would the planet's gravity pull on the ring equally from all sides, keeping it stationary in "orbit" (fig. A)? Would this mean that the "station" wouldn't need any rotation since it's size alone would mean that the planet's gravity just keeps it in place (fig. ? Or would the "station" be so massive that it just rolls over the surface, causing stupid amounts of destruction on the surface (fig. C)?

Now the goal here is to avoid massive support beams to hold the ring up (fig. E) and to just have a free-floating ring if possible. Would adding thrusters to generate spin keep it in orbit (fig. D)? Is this even possible?

http://i67.photobucket.com/albums/h289/Greenfire31/Fig%20A.jpg

http://i67.photobucket.com/albums/h289/Greenfire31/Fig%20B.jpg

http://i67.photobucket.com/albums/h289/Greenfire31/Fig%20C.jpg

http://i67.photobucket.com/albums/h289/Greenfire31/Fig%20D.jpg

http://i67.photobucket.com/albums/h289/Greenfire31/Fig%20E.jpg

This is just something I thought of while on lunch break. I've got a small rubber band ball and a ring made out of twist-ties on my desk in the office that kind of made me visualize all this. It just kinda sparked my thought process and I figured since I don't really know how this would work, I'd throw it at all of you and see what you say.

For the sake of the argument, please assume that mankind has a material strong enough to hold this super-structure together and the resources required to build it in the first place.

For a perfectly spherical mass, with a material strong enough enough to hold together, then yes it's pretty trivial to show that a ring would be able to just float above the planet with its axis of symmetry going through the axis of symmetry of the mass. Consider the force of gravity on any point of it, there will always be a point on the opposite side of the ring with exactly the same force on it but with the opposite direction, cancelling it out.

However, this would clearly be incredibly unstable. The smallest difference in gravitational force on one point from another would cause it to no longer cancel out, and a runaway collapse would occur. If one point was the tineist bit closer to earth, it would have a higher gravitational pull and hence be pulled closer, gaining an even high one and so forth. The smallest difference from equilibrium would instantly collapse it.

Since we have things such as a moon. Or the fact that the earth isn't perfectly spherical. Or dust. Or the CMB not being perfectly isotropic, this setup is not possible to maintain.

[Nibb31]

Orbital rings have been theorized for ages. I think Tesla was the first to suggest the idea. Since then, they have been proven to be unstable. A theoretical orbital ring would either break up under gravitational forces or fall to the ground like a hula-hoop.

[Greenfire32]

It need not rotate; in fact, rotation does not help you any to keep it suspended, assuming it's rigid. The main problem with this idea is that such a ring is not stable. Any disturbance from the perfect balancing point will result in a net force that leads to a larger disturbance, and so on. You could potentially add thrusters that thrust the ring back to the equilibrium point when there is a disturbance. This is a control system which acts to create a net restoring force when there is a disturbance from equilibrium. Such a system would require fuel and energy, of course.

So as long as there is some kind of "correcting force," this could hypothetically be possible then?

If you are willing to accept tethers, however, you can tether a ring around Earth with a radius larger than geostationary orbit, and it will be held up there by centrifugal force. It would be nothing but a ring of space elevators.

An interesting thought about this. If the station were to become tethered to the Earth (like in fig. E), would that cause the Earth's natural rotation to slow down? Similar to how a figure skater extends her arms to slow her rotation down and brings her arms in to speed it back up?

Could a station like this, being tethered to the Earth, cause more harm this way?

B is the thing that will happen. Saturn's Rings do the same thing, they are around the planet and the rocks in them orbit as the ISS does with Earth and this ring structure.

But the difference is that Saturn's Rings and the ISS are relatively small objects that orbit the planet, where as this station would be a single solid object. The basic thought here is whether or not a single object big enough to encompass a planet would even have the possibility of orbiting said planet.

Since we have things such as a moon. Or the fact that the earth isn't perfectly spherical. Or dust. Or the CMB not being perfectly isotropic, this setup is not possible to maintain.

Oh I didn't even think of the moon screwing everything up!

[HoloYolo]

For a perfectly spherical mass, with a material strong enough enough to hold together, then yes it's pretty trivial to show that a ring would be able to just float above the planet with its axis of symmetry going through the axis of symmetry of the mass. Consider the force of gravity on any point of it, there will always be a point on the opposite side of the ring with exactly the same force on it but with the opposite direction, cancelling it out.

However, this would clearly be incredibly unstable. The smallest difference in gravitational force on one point from another would cause it to no longer cancel out, and a runaway collapse would occur. If one point was the tineist bit closer to earth, it would have a higher gravitational pull and hence be pulled closer, gaining an even high one and so forth. The smallest difference from equilibrium would instantly collapse it.

Since we have things such as a moon. Or the fact that the earth isn't perfectly spherical. Or dust. Or the CMB not being perfectly isotropic, this setup is not possible to maintain.

Saturn isn't spherical, and it had rings for over 100 million years.

[Ralathon]

Saturn isn't spherical, and it had rings for over 100 million years.

Ah, but Saturn's rings aren't rigid. They're just the result of millions of small rocks, each in their own orbit.

[Greenfire32]

Saturn isn't spherical, and it had rings for over 100 million years.

Correct, but the rings of Saturn are made of up millions of tiny objects, where as we're more concerned with a theoretical single object.

Edit: Ninja'd

[-Velocity-]

So as long as there is some kind of "correcting force," this could hypothetically be possible then?

Yea. An example from fiction is Larry Niven's Ringworld series. It's about a gigantic ring around a star that is habitable. I've only read the first book in the series, and it was merely OK. But supposedly, after readers pointed out that the ring was unstable, Niven wrote a sequel to Ringworld that deals with this. (I think he introduces a control system for the Ringworld to keep it stable, and so the plot might center around the system breaking down or malfunctioning.)

An interesting thought about this. If the station were to become tethered to the Earth (like in fig. E), would that cause the Earth's natural rotation to slow down? Similar to how a figure skater extends her arms to slow her rotation down and brings her arms in to speed it back up?

Could a station like this, being tethered to the Earth, cause more harm this way?

It depends on how you build the ring. If you first create individual space elevators and then send the rest of the stuff on those elevators, then yes, it would slow down Earth's rotation. But the slowdown would not be significant enough to affect anything. In an extreme case, you might add an extra few milliseconds in a year (defined as 365 days), or something like that. Big deal. You'd have to send up a huge fraction of Earth's mass before it would have significant consequences for life... and by that point, just by the mining required to send up that much of Earth's mass (you'd have to strip the entire crust and work your way into the mantle a large distance), life would be long extinct anyway.

The bigger environmental impact could be caused by the ring brightly illuminating the nighttime sky, disrupting all sorts of biological balances. Circadian rhythms of wild creatures, the navigation of moths, etc. Predators would find it much easier to hunt at night. You could cause many species to go extinct.

Edited April 13, 2015 by |Velocity|

[Bill Phil]

Density isn't uniform, so gravity isn't equal around the planet. It'll collapse. Now, if you had one big station that was Moon-sized... In a very large orbit...

[-Velocity-]

Hmm... of course, if the ring were solid, and stiff enough, and supported by multiple tethers, then I suppose you could put it in low Earth orbit; it doesn't HAVE TO BE at geostationary orbit. However, in LEO, now the tethers have to support almost 100% of the weight of the ring, whereas, in geostationary orbit, most of the weight that the tethers would have to support is just the weight of the tether itself. It's hard to conceive why you would want an LEO ring as compared to geostationary ring. Strong enough materials almost certainly do not exist in this universe for an LEO ring, whereas a geostationary ring is possible if space elevators are possible.

[Greenfire32]

The bigger environmental impact could be caused by the ring brightly illuminating the nighttime sky, disrupting all sorts of biological balances. Circadian rhythms of wild creatures, the navigation of moths, etc. Predators would find it much easier to hunt at night. You could cause many species to go extinct.

Wow....more things I didn't think of. And as someone who has DSPD (Delayed Sleep Phase Disorder) I know all about circadian rhythms not being wired correctly XD

Density isn't uniform, so gravity isn't equal around the planet. It'll collapse. Now, if you had one big station that was Moon-sized... In a very large orbit...

That's no moon

[itstimaifool]

There's not much I can add scientifically to this discussion, but I just want to say, I love your "stupid amounts of destruction" diagram.

[Bill Phil]

Yea. An example from fiction is Larry Niven's Ringworld series. It's about a gigantic ring around a star that is habitable. I've only read the first book in the series, and it was merely OK. But supposedly, after readers pointed out that the ring was unstable, Niven wrote a sequel to Ringworld that deals with this. (I think he introduces a control system for the Ringworld to keep it stable, and so the plot might center around the system breaking down or

I believe it was large thrusters. The people there cannibalized them to make ships, and Ringworld began to lose stability.

[YNM]

Problems would be from non-uniform gravitational pull. Earth does have sites where there's more mass locally, hence different gravitational pull, so the ring can't be very stable. Even if it's uniform it's got to be very stiff, no flexing, no expansion, and also, umiform density (if the density isn't umiform something akin of non-uniform gravitational pull would occur)

Also, as others pointed out, a geostationary ring with tethers should fare better - superficially there'd almost be no acceleration on the object. Don't know about at the surface (should be some serious tidal force).

[K^2]

The main problem with this idea is that such a ring is not stable.

That's what the thrusters on the rim wall are for.

[AngelLestat]

Yes. this remind me ring world too from Niven.

First the option A is not possible no matter if you make all the ring from perfect graphene. Is like have a 1000km bridge without any support, at that height the ring curvature does not help you in nothing to support its own weight.

If you make the ring spin to orbit velocity then it will be unstable and crash anyway (not sure, hard physsics).

But there is an option X which may work:

You need a series of magnets orbiting in ring shape (not connected between them and faster than its orbit velocity), those would act as your bridge support for a superconductor ring which is not rotating.

You can adjust the speed of each individual magnets from the ring it self.

[KSK]

Reminds me of Star City from Arthur C. Clarke's 3001: Final Odyssey. That resembled option E if I remember rightly with four very large space elevators tethering the ring.

[crazyewok]

As others have said it would be a very very bad idea.

One miscalculation and the station comes crashing down destroying everything underneath like a giant asteroid.

It would likely end up a ELE for everything expect a few microbes.

Edited April 20, 2015 by crazyewok

[magnemoe]

I believe it was large thrusters. The people there cannibalized them to make ships, and Ringworld began to lose stability.

More accurate bussard ramjets using the solar wind, this would have the benefit of not require fuel. This worked well until they got an large solar flare.

[linkxsc]

Well even if rotating didnt help, it would probably have to orbit earth (seeing as the various parts would have had to be in orbit before being assembled)

[sgt_flyer]

the 'tether' version should keep steady enough - if you find something structurally resistant enough - and that regardless of the orbital speed / altitude.

if the 'station' starts to fall from one side, the tether on the other side of the station would then be extending and prevent the station from going further in that direction. - no need for heavy support structures - but you'll need darn resistant cables as tethers. (though they might be useful for carrying your elevators)

now, for a thing like this to keep useful, you'll still need to build it at geostationnary orbit - so your spacecrafts would be already at orbital speeds when they take off from the station.

well, of course, no current material / metamaterial currently known would be up to the task for building such huge thing

[AngelLestat]

Somebody read my solution to the ring problem?

http://forum.kerbalspaceprogram.com/threads/115522-Super-Massive-Station-In-Orbit?p=1836871&viewfull=1#post1836871

I can make a draw if is not clear enoght.

[FlyingPete]

In 3001: The Final Odyssey, humans have constructed such a ring at geostationary orbit. It's supported by four towers equally spaced around the equator, which also serve as space elevators. In the narrative, it's fairly well described how weight gradually reduces as you ascend, reaching zero at GEO. The towers would be under tension at the top (hanging from the ring) and compression at the bottom (standing from the ground) with a 'swing' point somewhere with nominally zero forces on it.

The advantage of building such a thing would be that there would be no need to launch a spacecraft from the ground again- you'd just transport the components to GEO and assemble it there. In fact, if you extended the towers to a higher altitude, they'd be going faster than orbital speed and so you'd get further savings in delta-V by simply letting go at the right moment.