Rotating circumplanetary ring structure. Math heavy.

[SunJumper]

What I'm thinking of here, is a ring structure that goes around the Earth, above the Geostationary orbit altitude. Not only does the ring rotate with orbital velocity, but there is additional velocity that creates a ficticious centrifugal force that works as artificial gravity.

If we assume a ring at twice Kerbin's geostationary orbit altitude (2869km), then if it orbits normally, the acceleration due to gravity is 0.088m/s/s. The velocity of this ring if it were forced to be keostationary would be 1843.6m/s. The acceleration toward the centre would be 0.54m/s/s (and the acceleration felt would probably be 0.45m/s/s.

If we use the Earth as an example, then at 180,000km (one half of the Moon's perigee), acceleration due to gravity would be 0.012m/s/s. If this ring were forced to be geostationary, its velocity would be about 13.09km/s. Centripetal acceleration would be 0.95m/s/s.

If instead we want centripetal acceleration to be one gee (9.81m/s/s), then the velocity required would be 42.02km/s.

If we want the acceleration to be 0.5 gee, then the required velocity would be 29.71km/s/s. This is only 70m/s less than Earth's orbital velocity.

Now, these values of accelerations are quite small, requiring ridiculous velocities to work. For example, to dock with this ring, such a spacecraft would need at least 52km/s delta-v. If the ship fails to dock, it will be flung out of Earth's SOI at up to 42km/s, escaping the sun with initial velocity of up to 71.8km/s. This is 19.33km/s less than the velocity required to escape the Milky Way.

Now, if this ring orbited the Sun (preferably inside Mercury's orbit), then with a radius of 23,000,000,000 metres, the required velocity for one gee is 475km/s. This shows me that the slowest ring would be at the lowest possible altitude (as we would not want people accidentally whizzing out of the milky way). Should've been obvious, really, but oh well.

At 7000km altitude (well above the messy atmospheric drag - hopefully), the required velocity for one gee is 11.2km/s

Could this work at all, or am I simply a madman ?

[LewisTherin]

So you mean build a ring at a given radius and then spin it faster, right?

Given that the radius of the orbit is intrinsically linked to the velocity, I would have thought that would lead to immense forces acting on the ring trying to push it out to a higher orbit (stretching the ring outwards in that radial plane in all directions at once), tearing it apart in the process, but it would be interesting to check what sort of material strengths you'd require for that not to happen.

[Awaras]

Have you read the 'ringworld' novels by Larry Niven?

[phoenix_ca]

You're definitely a madman, but where there's a will, there's a way. The thing is...you'd probably need to smash a lot of asteroids and maybe even a planet to build such a thing...

The concept reminds me of the Earth Torus from X3:TC. (Which I know is based of the previous theoretical discussions positing such a torus, but the one in X3 is a splendid visual. Shame it went boom.)

[pwnedbyscope]

So you mean build a ring at a given radius and then spin it faster, right?

Given that the radius of the orbit is intrinsically linked to the velocity, I would have thought that would lead to immense forces acting on the ring trying to push it out to a higher orbit (stretching the ring outwards in that radial plane in all directions at once), tearing it apart in the process, but it would be interesting to check what sort of material strengths you'd require for that not to happen.

But since gravity is universal it would be pulling on the ring from all directions down or in or however you think of it, with this in mind you would just need to do some math to find at what altitude the centripetal velocity matches the gravitational pull the two cancel each other out equaling a non-explody ship, the only problem we are left with is if this altitudeis in the moons SOI that could create some problems, think tides but in space

[maltesh]

Have you read the 'ringworld' novels by Larry Niven?

Aye, James Clark Maxwell proved that solid rings around a planet are unstable back in 1859. If you don't have some sort of thruster system to push them back into place (Which Niven retroactively added in The Ringworld Engineers), any disturbance that pushes your ring off-center results in it accelerating off-center until it comes into contact with the planet.

[SunJumper]

Which is why you have the ring rotating, so that every atom of the ring is in ORBIT around the planet, rather than hanging stationary. If you poke a satellite, it won't deorbit, will it?

[Vanamonde]

Rotation alone wouldn't prevent the issue Maltesh is talking about, and if you made the ring half of the moon's orbital radius, the moon would be tugging on it rather signficantly. Stability would be a problem.

What kind of materials would you use to hold this thing together against the magnitude of forces involved?

But a more important question is, what would be the point? What benefits would outweigh the costs it would require?

[SunJumper]

The materials would be a type of matter which is incredibly strong, like magmatter from Orion's Arm. The point is communications and a place to put people when the planet can handle no more...

[Thiel]

Communication can be handled much cheaper by geostationary rockets.

If you're going to build hugely big space colonies why not just build one of those hollow spinning tubes? Much easier to design and build (For a given value of easy) and if you run out of space you can just build another one.

[LewisTherin]

Alternatively if you want space / resources etc, you can go down a similar route to that in Peter F. Hamilton's Night's Dawn Trilogy, tow asteroids into orbit, set them rotating and mine the minerals present, once that's done hollow out habitation space and convert it to low gravity manufacturing or some other (currently sci-fi) use.

[HarvesteR]

With anything built at those scales, I'd think regardless of the materials you choose to build the ring, as a whole it would have the consistency of overcooked spaghetti. It would probably be very difficult to manage spinning it up evenly in a way that doesn't end up with the thing flinging bits of itself off to visit the far reaches of the solar system.

Maybe an easier solution would be to just have a geostationary ring, which can act as several vessels in orbit, strung together (where each section does its own orbital corrections to reduce stresses on the structure), and then mount many independent gravity wheels, that rotate along the axis of the main ring. That way, the center core sections would be a microgravity environment (which does have many uses), and the wheels would be your 1G living spaces and long-term habitable areas. Each wheel would essentially be something akin to a city block, and the core axis like the roadways connecting them.

Just my take on it... I figure just because we can build a planet-sized structure, it doesn't mean we shouldn't be practical about it.

Cheers