Anchored ringworlds

Terraformer · 2025-02-22 14:40:24

I feel this requires its own topic. And since this subforum includes everything from "conventional" terraforming to shellworlds and asteroidal magnetospheres

An equatorial ringworld... now that would be something. Around a dwarf planet the shell would help to counter the centrifugal pressure. If we have 400km snowball with 1% Earth surface gravity, 1km overburden would counter 10 tonnes/m^2 of spinning ringworld. If its 10km wide, the ringworld has 12,500 square kilometres of range. Now that will serve us well. And we can go wider than 10km, and add further rings to the north and south.

Can we do this on some of the larger asteroids and comets and KBOs? If the body is 100km wide, we need to add 4x the overburden. Lets say 10km, to allow margin (and we're not using 10 tonnes/m^2 of soil, we dont need to go that far even for trees). 80km across, 5km wide, 1,250 km^2. 1g, because the whole point of doing this is to provide earthlike spaces for "wildlife". More rings bored north and south, a magnetosphere provided, human cities studded throughout. The core is still the vast majority of the mass, providing stability (I just remembered that Phobos -- or Deimos? -- in the Mars trilogy built a train centrifuge...).

Large expanses of 1g habitat that can really seem earthlike are... tricky and resource intensive. Obviously the dream is supramundane shells around Neptune and Uranus, supported by their atmospheres. But on a smaller scale, we have to build ringworlds and cylinders, and it would be nice to make big ones.

tahanson43206 · 2025-02-22 14:51:40

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Calliban · 2025-02-23 12:22:11

A ringworld in free space needs to have enough tensile strength to withstand the outward centrifugal force resulting from rotation. That is a significant structural burden that implies a lot of cost.

If the ringworld is under 1+km of ice on a world with 1% Earth-g, then it can transfer load to the ice above it. It can do this by magnetic levitation, if the ceiling of the ice-cave torus has a conducting metal strip within it. This reduces the tensile force acting on the outer skin of the ringworld. This reduces structural mass and cost. It would also allow a ring habitat to built as a compressive structure from brittle materials. There are also the benefits of having something you dump waste heat into. These are all big cost savers.

Another benefit of building a hab on an icy world is employment. The inhabitants of the hab can mine the ices for things like ammonia and nitrogen, that can be sold throughout the solar system. Ice is also a good source of reaction mass if the inhabitants want to engage in interplanetary trade. Even with fusion powered engines, a ship still needs to throw something out the back to achieve thrust. So having a load of ice nearby is important if you want ships to be able to come and go.

Last edited by Calliban (2025-02-23 12:29:19)

Terraformer · 2025-02-23 12:57:34

You calculated this before, but I can't remember the figures -- if we are using the weight of ice to counter pressure, what is the minimum size body to withstand 10 Tonnes/m^2 in a central cavern? On asteroids and comets we can dig all the way down to the centre and put a cylinder habitat from pole to pole, though the parts closest to the surface would have to either spin slower or faster with a smaller radius, to maintain the required overburden of ice to make use of compression.

Still, a 100km long cylinder... that's more like it. Especially if the interior is landscaped as a spiral valley.

Calliban · 2025-02-23 13:44:30

You can work out pressure at any radius from the centre of a body with constant density, using the formula contained in this link.
https://cseligman.com/text/planets/internalpressure.htm

Pr = (3/(8pi x G))*(gR^2)*(1-(r/R)^2)

Where R is the radius of the body, r is distance from the centre (i.e R minus depth), gR is surface gravity, G is Newtons universal gravity constant (6.67E-11).

The surface gravity of a spherical world is proportional to its radius and density. Pluto has a density of 1.853t/m3, a radius of 1188.3km and a surface gravity of 0.62m/s2. Using this as a reference, the surface gravity of any body would be given by:

gR = 0.62*(r/1188.3)*(rho/1.853)

Where r is measured in km and rho in tonnes/m3.

Lets solve the equation for a sphere of nearly pure ice, with a density 0.9t/m3 and a radius of 25km. What is the pressure in its centre?

First, we calculate surface gravity, gR. This comes to 0.006335N/kg. Which is about 1/1800 earth gravity. At the centre of the body, r=0 and the equation reduces to:

P0 = (3/(8pi x G))*(gR^2)

Solving for the body under consideration gives a core pressure of 71,829Pa, or about 0.72bar.

The link contains a graph showing how internal pressure decreases as one heads from the core to the surface. I have reproduced it below.

This illustrates that for r/R=0.2, there is virtually no reduction in pressure. This is because gravity close to the core is almost zero and the pressure gradient heading out from the core is small until one gets to r~0.4R.

Last edited by Calliban (2025-02-23 13:53:56)

Calliban · 2025-02-25 05:01:11

A geostationary ring built around a dwarf planet or asteroid, would be a useful tool for mining the object. It would allow material to be lifted out of the gravity well without need for propellant.

In fact, if we allow a tether to extend beyond geostationary, we can use the angular energy of the dwarf planet to power the tether. So lifting material out of the gravity well will not cost us any energy, until the dwarf planet's rotation starts to run down. On a fast rotating body, a tether could be a considerable source of power. We can use it to extract energy from the rotation of the body.

Void · 2025-02-25 10:03:34

A good topic. Probably the next thing after Mars. Actually, it might divert settlers from Mars after a while, as it may offer a great deal to people.

I believe that this falls into the vision of Dr. Zubrin as I have read it. If we then simply say that our Moon is a wild card, then we might get most people to converge on a popular plan, I hope. Over time our Moon may rise in value to be part of a trade pattern it gets included into, or it may only then be a sort of a scientific object for study. Allow it to become what it will.

The method looks good for many worlds, but with Mars/Phobos/Deimos as a steppingstone, the Major Asteroids may become very attractive.

https://en.wikipedia.org/wiki/List_of_e … _asteroids
Image Quote:

Ending Pending

Last edited by Void (2025-02-25 10:11:57)

Void · 2025-02-25 21:45:49

In post #6, Calliban said:

Calliban
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From: Northern England, UK
Registered: 2019-08-18
Posts: 3,921
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A geostationary ring built around a dwarf planet or asteroid, would be a useful tool for mining the object. It would allow material to be lifted out of the gravity well without need for propellant.
In fact, if we allow a tether to extend beyond geostationary, we can use the angular energy of the dwarf planet to power the tether. So lifting material out of the gravity well will not cost us any energy, until the dwarf planet's rotation starts to run down. On a fast rotating body, a tether could be a considerable source of power. We can use it to extract energy from the rotation of the body.

A very nice idea. But now consider the "Relativistic Electron Beam".
I may not understand this technology, but I hope it can be used internal to our solar system. https://en.wikipedia.org/wiki/Relativis … ctron_beam
Quote:

Relativistic electron beams are streams of electrons moving at relativistic speeds. They are the lasing medium in free electron lasers to be used in atmospheric research conducted at entities such as the Pan-oceanic Environmental and Atmospheric Research Laboratory (PEARL) at the University of Hawaii and NASA. It has been suggested that relativistic electron beams could be used to heat and accelerate the reaction mass in electrical rocket engines that Dr. Robert W. Bussard called quiet electric-discharge engines (QEDs).[1]

So, after you fling a payload, can you beam heat and inertia to it? Could you do it in such a way that you not only assist propulsion to the payload released but could spin up the Anchored ringworlds spin by using the recoil. Then could you give modification to the path and speed of an incoming payload, and also use the recoil to spin up the Anchored ringworld?

I understand that unlike Photons which only carry inertia, Electrons do have mass.

Last edited by Void (2025-02-25 21:53:03)

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#1 2025-02-22 14:40:24

Anchored ringworlds

#2 2025-02-22 14:51:40

Re: Anchored ringworlds

#3 2025-02-23 12:22:11

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#4 2025-02-23 12:57:34

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