In order to successfully have 3 orbital rings around a planet how do you have to orient them?

Question

I am writing a short story about an overworked planet whose civilization has achieved space elevators and orbital rings.

The planet, which is earth-sized, has three complete orbital rings in stable orbit, each one 200 meters in width, which is about an eighth of a mile.

The rings are used for heavy construction and other industrial uses.

Where do you have to put the rings relative to each other for them not to have any issues or break, and should the rings be fixed onto the ground or allowed to orbit freely?

Answer 1

I am writing a short story about an overworked planet whose civilization has achieved space elevators and orbital rings.

Note that there is no known material strong enough to build a space elevator. People will talk about carbon nanotubes, but even with the best manufacturing capabilities imaginable small imperfections in the material will reduce its breaking length to a point too short for elevators. With orbital rings you picked the best launch assist megastructure there is, since the ring is unchangeable regarding scalability, general utility, throughput and possible take of velocity.

The planet, which is earth-sized, has three complete orbital rings in stable orbit, each one 200 meters in width, which is about an eighth of a mile.

Sounds perfectly reasonable dimension wise. Note that orbital rings have tremendous energy requirements to be started up, a skeleton ring will need half our annual energy production to get going as noted is this paper, which will give you more information on orbital rings, but the civilisations building them should have mastered fusion or off world solar or at least mass fission, so it will be fine.

The sole purpose of the rings is to allow spaceships to enter orbit.

As Algebraist already noted is his answer, rings can be used for so much more. Definitely check out the Isaac Arthur video he linked, the guy is amazing. Concerning other things to do with the ring: hyper fast on planet transport, shellworlds, supermundane planets or megaearths, chandelier (hanging) cities (or gardens), colonising ice giants, gas giants and even suns and much more.

Where do you have to put the rings relative to each other for them not to have any issues or break, and should the rings be fixed onto the ground or allowed to orbit freely?

The simple answers are wherever and whatever you like. As long as the rotor sits in an orbital path around the planet and two rings rotors do not intersect everything is possible. Maybe having one equatorial ring for transfer to the planets habitat swarm and moon, one aligned with the systems plain of the ecliptic for interplanetary launches and one polar ring for power beaming receivers (Atlas towers will do the same) on the poles and more exotic launch trajectories is an optimal three ring setup.

I would suggest anchoring them to the ground, because one would lose so much of the rings utility if they were free floating. The only times you want to use free floating rings are when you are colonizing objects with no solid surfaces like ice-giants, gas-giants and suns.

Answer 2

There is only one orbit for a space-ring consistent with space-elevators - that is an equatorial orbit at an altitude above the earth's surface of approximately 35,800 km. At that altitude the ring will be in geo-stationary orbit - i.e. the ring will rotate at the same angular velocity as the earth-s surface so tethers stretching from the earths surface to the ring (i.e. space elevators) will not stretch or bend (significantly).

If you don't want to connect your space elevators directly to the ring (i.e. you have both, but they are independent from each other) then in principle you can have the ring in any orbit. That is to say at any altitude (outside the atmosphere) and at any orientation to the earth's rotational axis. So they could be equatorial, trans-polar, or at any angle you propose.

I say in principle, as:

• any orbital ring will be in an unstable equilibrium, so would need continual correction to remain in one piece;

• no materials are known to exist that could be used to construct such a ring;

And in regards to your comment

The sole purpose of the rings is to allow spaceships to enter orbit.

A single space-elevator-tethered-geostationary space-ring has obvious benefits for getting materials into space in an energy-efficient manner (if you ignore the enormous sunk energy cost of building it in the first place). But I can see no energy, resource, or logistics benefit in multiple rings, so it is unlikely that this would be their "sole purpose".

Answer 3

Once you have a single orbital ring, your best bet is to make it wider and thicker. The places you bean stalks (space elevators) have extensions anyway for the counter weight to balance the weight of the stalk. Usually this is a small asteroid at around 100K from the earth.

For in system flights by matching speed with one of these exterior spoke (cable to a docking engine) you can save substantial amounts of fuel. Repeated encounters have to balance momentum in the long run.

See Arthur C. Clarke "The Fountains of Paradise" Charles Sheffield "The Web Between the Worlds.

Answer 4

Any way you want.

It depends on the energy you have available.

To not tether them requires that you have thrusters of some kind to enable them to maintain position (ie. not crash into the planet).

The most energy efficient way to orient them would seem to be in line with the ecliptic plane, because this will require little energy to maintain.

Another possibility is that one could be as stated above requiring low energy to maintain, another could be in an orbit (since there are three) at 60 degrees to the first, another at 120 degrees. This arrangement would potentially require no energy to sustain it's orientation either. The reason why would be gyroscopic stability, It would mean that your planet would revolve beneath these layers, and the layers would stay on their own planes, relative to the stars (ie. not relative to the planet or sun). This would mean that the latter two rings would precess around the planet once a year, but since the planet rotates once a day, it would allow you to select which ring at which time you need to land on to be closest to any destination on the surface of the planet.

However: You can have them in any orientation you wish if you have the energy to counter the forces that would prevent their precession (Which would be quite prodigious BTW).

Ultimately, the whole thing would be a trade-off between the energy required to keep them from crashing into the planet versus the energy (if tethered) to stop them from deforming because of gravitational forces caused by the planet's rotational axis being not tidally-locked to the sun, not to mention the moon's pull on their bodies. It depends on the materials, the flexibility and the energy available to make them behave.

Answer 5

Using the orbital ring itself for habitation is a poor use of its potential on a utility/unit mass basis.

To keep building up an orbital ring, you need to spin up the rotor even faster, or add mass to the rotor. Both are non-trivial requirements.

A more elegant solution would be to have a band or orbital habitats, connected together by physical supports but traveling at orbital velocity, with each habitat spinning to generate artificial gravity on the inside.

People planetside can hop on the elevators (they're not true space elevators, they don't bring you up to orbital velocity at the end), transfer to a maglev carriage on the orbital ring that accelerates them to match orbital speed with the habitat ring, then disembark unto whatever habitat they want to travel to.

You might even have a second maglev system for inter-habitat travel, which does not require the enormous rotor of the orbital ring.

Isaac Arthur did a good video on Orbital rings on YouTube: https://www.youtube.com/watch?v=LMbI6sk-62E