Shell Worlds

Calliban · 2023-10-05 06:58:41

Kenneth Roy discusses shell world stability.
https://www.researchgate.net/profile/Ke … bility.pdf

For bodies some 40% more massive than Ceres, the effects of scale height are enough to provide a counteractive force that will restore a displaced shell. On these worlds, pressure containing shells could be built without the need for any physical connection to the central body. For smaller worlds, cables or towers would be needed to physically anchor the shell in place and prevent it from displacing and impacting the surface. Roy doesn't seem to have accounted for the compression that would result from a displaced shell. Given that speed of sound is only 343m/s under standard conditions, any movement of a planet sized shell will compress the gas underneath faster than it can escape. This has nothing to do with scale height and would provide an additional restoring force. So I think his shell concept could be applied to smaller bodies than he anticipates.

I think a more probable concept to shell worlds is the tunnel world. A large asteroid like Vesta could be riddled with tunnels and cavities as a result of mining activities. These could be hundreds or even thousands of metres in diameter. If these are more than about 200m beneath the surface, the overbearing weight of the rock would contain the upward force resulting from pressurisation.

Tunnel worlds could be built up incrementally as a byproduct of the mining needed to build space habitats. They aren't things that necessarily require a dedicated effort to build and can start small, growing bigger as excavation removes more material. This makes them a more probably outcome in my opinion.

The conventional shell might eventually be used to enclose outer solar system objects like KBOs. These bodies are 50% water ice by mass. A sufficienctly powerful thermonuclear heat source could be used to melt this ice. An inflatable skin would then be placed over the surface and inflated with air to low pressure. The liquid water will then be pumped from beneath the skin onto its surface, where it would freeze into solid ice. As the ice layer thickens and its weight increases, air pressure will grow to balance it, allowing net zero shell stress. Eventually, we have a mostly rocky world, with a gap of say 10km between its surface and a thick icy shell above, with the weight of the shell largely balanced by air pressure, leaving only a weak compressive stress within it. Waste heat removal would favour keeping most of the above the shell liquid. So the roof itself will need enough integrity to prevent water from draining out of tge shell onto the ground.

Last edited by Calliban (2023-10-05 07:19:21)

Void · 2023-10-05 09:27:49

I liked your post. If you can tolerate it maybe we can talk about a radiator that has a two-part cycle.

If you have a radiator of metal perhaps, and you discharge evaporation into it, then the air pressure inside can be kept low, by freezing.

If the shape of the radiator were basically a cylinder, when the level of frost was high then you could pull a sock over it as thermal insulation.

Then you could allow the air pressure to build up inside, and so the cooling output from the heat source you want to sink, could melt the ices. So, maybe a phase change cooling in this part of the cycle?

Of course, then you need a method to draw off the fluids that result from melting or evaporating the ices.

Rinse and repeat.

I just got up so maybe there is a flaw, but please let me know what you think.

Done

Last edited by Void (2023-10-05 09:30:34)

Void · 2024-02-08 13:08:07

I guess this could be a candidate for a shell world, as the sea is so young, we may not anticipate life: https://www.msn.com/en-us/news/technolo … r-BB1hYRUB Quote:

Indy 100
Hidden ocean discovered beneath the surface of moon
Story by Harry Fletcher •
4h

I would not go so far as to make a high pressure atmosphere under such a shell, just a method to reach the ocean.

For instance, if you harvested the ice shell to fill up aqua habitats, you would eventually reach the ocean, and then with robots you could mone the core.

If Calliban wishes he might do some calculations of conditions of such a terraformed world.

Done

Last edited by Void (2024-02-08 13:11:36)

Calliban · 2024-02-08 16:38:58

Void, that is a fascinating discovery. Well done for digging it up. Here is the space.com article that goes into more detail.
https://www.space.com/saturn-death-star … face-ocean

At -100°C, the thermal conductivity of ice is 3.5W/m.K. Mimas has a radius of 200km and the ice shell is expected to be 30km thick. By my estimates, the temperature difference between the sea and the surface, must be at least 150K. To keep the sea liquid, about 8GW of heat must be generated by core-ocean interactions. Maybe tidal flexing induced by the gravity of Saturn and its other moons provides this heat.

But 8GW is not a huge amount of heat on a planetary scale. It is the heat generated by two 1400MWe nuclear reactors. In the future, a human colony of a million people could generate this sort of waste heat. And a small icy world gives that colony a place to dump waste heat without huge radiators. So aquaforming is something we may be seeing a lot of.

It occurs to me that an ice shell 100km in diameter and several km thick in a gravity field of ~0.001g, has both a short radius of curvature and low compressive shell stress. It should be possible to inflate an air bubble between the ice layer and the ocean that humans can live in. Because the ice layer is curved, it should function as an arch.

Last edited by Calliban (2024-02-08 17:04:03)

Void · 2024-02-08 19:44:42

Thanks, Calliban. I have some new notions about shells. I will stay ambiguous as I want others to consider if they have input.

To get to the ocean a tunnel method is needed, I suppose that would be a first base.
Getting to the ocean, you might do the things you have suggested. Now I wonder about a simple spherical shell to spin around the moon.

A simple version is just that a sphere, that is outside of the moon and spins and has artificial gravity on its equator.

Doing this then something needs to be done about the stability of ice. and the sea.

Frankly I want the shell to be quilted sort of multi-layer, so that rupture is less dangerous. I originally thought that the interior of the shell would not be pressurized. But now I wonder if it can tolerate a certain level of O2. Maybe as high as 1/3 g???

The notion of a mega satellite for Ceres invokes magnetic bearings. So here I am supposing the moon might have magnets that point magnetic north poles outward, and the shell would point magnetic north poles at those magnets.

You have a sort of an air bearing if the distance between the shell and the moon is enough. Don't know if we can get away with it though.

If you could have a 1/3 bar or maybe less O2 atmosphere you could use air breathing aircraft to pass from the moon to the shell.

Granted, you could probably have towers at the spin poles that would allow trams between the moon and the shell.

So, the shell would have enough gravity at its "Equator" whatever sufficient gravity were.

The outer shell could have a rectenna on it, and power plants may send power to the apparatus. I know solar is not popular for Saturn, but concentrating mirrors are simple and can be rather thin, so solar is not ruled out for Saturn and company.

And in the Saturn system we have Nitrogen for making a greater atmosphere simulation.

Done

So, notions of modifications and concerns are welcome.

Done

My profile for the moon is probably not correct, but it is hard to get the correct information.

https://phys.org/news/2024-02-mimas-tin … ocean.html

OK, hard to get the information I want but just now I think that perhaps 90% of the moon is melted or rock. Not that much rock, but still if it were even 5%, then that is something.

The anti-humans don't want our germs anywhere in space. Basically they wish we were dead, I think. The want their servants to serve them and then be dead, I think.

Done

Last edited by Void (2024-02-08 20:41:15)

Void · 2024-02-09 09:08:45

I am not sure that Mimas is the best case for a spin shell. It could be a good case, but what about other worlds? The further away from the world, then the less gravitation on the shell. Spin would help hold the shell up at least near the equator. But can you have a very large spin shell around a small world? For instance Vesta.

Then if you wanted could you cook up a partial pressure atmosphere for the spin shell? Using magnetics to keep the small world centered in the spin shell, and can the air be like an air bearing?

Could you fly aircraft from the little world to the interior of the shell and land at the equator? Of course a crash might rupture the shell, so I anticipate that the shell would have many layers and some method to patch a hole.

As far as Nitrogen goes I guess you might have spaces with a higher pressure and Nitrogen.

If you have a sphere for a shell, then you have various spin gravity gradients which could accommodate various industrial processes.

You could actually have microgravity at the poles, if you had subshells that could be counter spun.

But the interior of the shell does not have to be pressurized, in some cases I simply imagine multiple shells with pressurized compartments where needed. This would be less vulnerable to accident and military actions.

Done

Last edited by Void (2024-02-09 09:15:46)

Calliban · 2025-01-31 18:22:56

Gravitational space balloons
https://gravitationalballoon.blogspot.com/

This is similar to the shell world concept, but does not necessarily include a world at the centre. Instead, we have a spherical shell of rock or ice. The shell is pressurised with atmosphere, such that internal pressure balances the inward pull of gravity that the shell exerts on itself. The result is a pressurised spherical volume with very little internal gravity.

Human habitats or buildings would hang from the inside of the shell and would rotate to produce gravity. I think there would also be hanging platforms, with microgravity environments. The advantage the a space balloon offers is sustainability. O'Neill cylinders would wear out, due to the finite stress cycle of metallic shells. This means that whatever we build in them would have a short lifespan. But a space balloon has close to zero shell stress, allowing long term stability. We would replace and recycle internal components over time, but the shell itself would remain stable practically indefinitely.

Last edited by Calliban (2025-01-31 18:31:02)

Void · 2025-01-31 21:57:47

I hesitate to respond today, but have some lets say ideas that can be entertained in the mind.

Vesta was mentioned. I wonder if while tunneling it out for mining purposes could a "Hill Shell" be built similar as to a Balloon of the sorts suggested in the materials of your post. More or less a shell on the outer boundary of the Hill Sphere of Vesta. I don't intend to see it purposely pressurized. Rather sub-Balloons inside of it might be pressurized and then sub-worlds inside of those might be given artificial gravity.

Where Vesta may spin, this Hill Shell would be sun locked to resemble a tidal locked world. So the one side would be warmer and perhaps tap solar energy. The dark side being very cold, if air were to escape from the sub-Balloons, it would tend to condense as a frost on the inside of the Hill Shell. And so could be recovered mechanically. Vesta itself might be kept centered in the Hill Shell with magnetic force perhaps.

And then from the proceeding and receding sides of the Hill Shell a ribbon platform could extend outward to encompass the orbit of the sun. This to collect energy. The energy to flow through a common grid. A sort of a Ribbon Dyson Element.

Something like this might be contemplated on a much smaller scale for the Moons of Mars.

Where Phobos is expected to break apart in a number of millions of years this structure could be better suited to endure for tidal forces. But if Electron beams are a possible method of propulsion, could a Phobos ring and a Deimos ring modify each others orbital energy? Deimos moves out due to tidal force and Phobos moves in. Perhaps we can transfer these forces to each moon-ring from the other.

But perhaps I do not understand electron propulsion well enough yet.

But I feel it is good to try these ideas to better learn in that case, or to succeed even sometimes, maybe.

I guess that is a lot for now.

Last edited by Void (2025-01-31 22:08:17)

Void · 2025-02-01 09:40:54

If I am annoying the membership, I will ask for forgiveness.

I have been thinking about removing the ice shells for worlds that have a subsurface ocean. I actually have the opinion to be protective about any world with significant signs of life.

But I will not tolerate "Royal Thinking" on the matter, where self-appointed elites have given evidence that their actual goals may simply be to keep the surfs down.

For entertainment, I would like to think of partially disassembly of Callisto and perhaps Enceladus as example possibilities.

By the time we had started on such a thing humans would have some clues as to possible life on some worlds, like Venus, Mars, Ceres, Titan, and Enceladus for instance.

If we check several worlds and many of them have alien life, and those are not from panspermia, then it could be speculated that life is all over the universe on worlds with seas. If several worlds in the solar system have genetically related life, then we can presume one case of a solar system with panspermia. If we find no life, then we can presume that the same is likely all over the universe.

In the case of Callisto, then stripping the icy top layers off might expose an ocean that could be covered in a shell.
The entire mass of the removed materials could construct many of the Balloons that are mentioned in Callibans post.

The sea, if it exists, would have been very cold and salty, perhaps not the best for life. Although geothermal might have warmed spots in that ocean. There could be some Uranium dissolved in that ocean.

Obviously, Enceladus could be checked for life and Uranium, earlier on. If it is true that these oceans have Uranium, then we might think about Pluto and Charon.

Ending Pending

Last edited by Void (2025-02-01 09:53:55)

Calliban · 2025-02-03 07:16:24

The balloon world idea is most likely to develop as a result of mining, with the interior of large asteroids hollowed out like a swiss cheese. The thing that works against it is wasteheat generation. Even though rock is not usually considered to be an insulator, a thickness of many hundreds of metres provides a lot of insulation. In the short term, the heat capacity of the rock has huge thermal inertia. But over time, as thermal gradient stabilises, any heat generated in the interior would tend to accumulate. A balloon world would need shafts containing water, that carries heat to radiators on the surface.

Last edited by Calliban (2025-02-03 07:16:52)

Void · 2025-02-03 13:02:16

Rocky asteroids mined may give Uranium and Thorium. But with mirrors solar also has value.

Icy Asteroids like Ceres, may yield dissolved Uranium if they have underground seas. Asteroids that are too wet, may need a different way to handle things.

Keep in mind that if life is discovered in a lake, sea, or ocean, it is my attitude that that is very important, and we might want to divert economic planning away from such "Wildlife Preserves". So, I don't think that I am totally immoral.

I think that eventually fusion will become actual as a energy source, but that it may not be competitive against some energy sources in some locations.

Both you and previously Antius have pointed out the importance of radiators.

In working with "Wet" worlds like Ceres and Callisto, I wonder if volumes of water could be used along with "Metals" to make free floating radiators?

Is the shape of a red blood cell a good shape for a free floating space radiator? https://en.wikipedia.org/wiki/Blood_cell

https://en.wikipedia.org/wiki/Red_blood_cell

On an icy world like Callisto or even perhaps Ceres, you could melt a lake. Cover its bottom with regolith to slow down the melt process. Have radiator domes over the lakes to hold the water vapor, and to allow the domes to radiate. Granted you might have to defrost the domes from time to time, but that could also reject waste heat as well.

Image Quote:

You could have diving bell air filled containers as habitats, and some with Vacuum, so that you could have Synthetic Gravity machines.

But the free floating radiators built from the materials of Callisto, might perhaps reduce the radiation in the radiation belts by taking the hit.

I will save other things for another time.

Ending Pending

Last edited by Void (2025-02-03 13:20:09)

Terraformer · 2025-02-22 14:21:19

(Copying from another thread)

One of the most abundant substances available for building habitats out of is ice. Certainly useful as a shield. We've discussed building shellworlds with it, relying on self gravitation IIRC; whilst its (probably...?) not strong enough in tension for anything useful, in compression very cold ice can be comparable to concrete.

Dwarf planets are good places for centrifuge towns, sunk into the ground with angled floors. Imagine an entire world tiled in such hexagons. The planet provides a very large amount of mass to anchor spinning habitats and prevent tumbling, and allows for shielded rail (and foot) transport between them.

Or even a hollow one, formed from a vast geodesic sphere used to connect centrifuge modules together and covered in ice for protection, perhaps with a layer of soil and a thin atmosphere for a microgravity ecology, definitely with a magnetosphere. The comet shellworld idea except we're incorporating the habs into the shell. If they're say 200m long 100m diameter, each hab has about six hectares of surface area, whilst taking up idk two hectares of the shell (the ends are around 0.8 Ha, I'm not trying for precise design here).

A shellworld that's 100km across will have a surface area of 31,000 km^2 approximately 100,000km^2 of habitat area whilst looking suitably planet like from the spacecraft our intrepid heroes are in tongue That is half the size of Great Britain, admittedly broken into chunks; the ideal size per tile is probably 10x bigger. Though there would be less surface area in that case if length is not proportionally increased -- tile size grows with the square of radius, internal surface growth is linear). If they are say 500m rings 1km across, thats 150 Ha per hab (a good sized small town -- city even, if we put our gardens on the room and in basements) but overall we're down to about 24,000km^2. If we increase length to 2km -- proper Onhyl cylinder time -- we're back to our space England (okay, three quarter sized Space England) with 6km^2 chunks. Alas, still not large enough for reintroducing the wolf, but I think foxes might be okay.

Calliban · 2025-02-23 11:55:38

For a pressure vessel, you pay for volume not surface area. Economically, it makes far more sense decking out a Bernal sphere such that the entire internal volume is living space. The problem with doing this in free space is that radiator area also scales with floor space. So a volumetric habitat would need a radiator many times larger than the hab itself just to lose enough heat to space to keep internal temperature tolerable.

Putting the hab on a dwarf planet or icy comet obviates this problem, because you cool the hab by pumping water through a compact heat exchanger and dumping it into the icy body. This would allow humans to build volumetric habitats of enormous size without being concerned about needing an immense radiator. So there is a significant advantage to putting rotating habs on an icy dwarf planet or comet. It is substantially cheaper than building it in free space and the hab can be more compact for the same living space. The ultimate limit to how far you can take this is given by the amount of heat the dwarf plant can radiate into space without melting.

If the dwarf planet is big and has substantial gravity, like Pluto or Eris, then waste heat will lead to volatile evaporation and the formation of a thick atmosphere. We could end up terraforming these places by accident, as waste heat from habitats and fusion power sources creates an atmosphere and melts subsurface water ice. Putting habitats on dwarf planets and moons, allows us to accumulate a human population in a way that would be difficult to achieve in free space. Assuming that fusion eventually provides cheap energy on a large scale, humans are ultimately limited by the amount of heat they can dump into the environment. Having a giant lump of cryogenically cold ice that can be used as a heat sink, is a major long term advantage.

Last edited by Calliban (2025-02-23 12:06:15)

Calliban · 2025-02-24 08:38:41

I have run the equations shown in this post to calculate the pressure at the centre of a number of asteroids, moons and cometary objects.
http://newmars.com/forums/viewtopic.php … 77#p229977

For Eros: r = 8.4km, rho = 2.67t/m3
Pressure at centre = 71.37KPa (7.137 tonnes/m2).

For Phobos: r = 11.08km, rho = 1.861t/m3
Pressure at centre = 60.327KPa (6.033tonne/m2).

For Deimos: r = 6.2km, rho = 1.465t/m3
Pressure at centre = 11.71KPa (1.17tonne/m2).

For Himalia (irregular moon of Jupiter): r = 79.8km, rho = 1.63t/m3
Pressure at centre = 1808KPa (180.8tonne/m2).

For an 'average' KBO: r = 50km, rho = 1.0t/m3
Pressure at centre = 349.26KPa (34.93tonne/m2).

Assuming a density the same as water, how wide would a body need to be to have 1 bar pressure at its centre? Answer: r = 26.75km. So KBOs, moons and icy asteroids with diameters above 53km, will have pressure in the centre greater than 1bar.

Phobos is interesting. It is just about big enough to be able to support a pressurised space with breathable atmosphere. It is also in a very useful location. It is likely to be heavily mined out to provide reaction mass for spacecraft and building materials for infrastructure in Mars orbit. If we mine out the core of Phobos, the tunnels and caves created could be pressurised with breathable air without needing to be pressure vessels.

Eros is a Mars crosser with a perihelion of 1.1334AU. If it is colonised and the core is mined out, it could have a valuable secondary use as a cycler.

There are an estimated 100,000KBOs with diameter greater than 100km. There are roughly 8x as many with diameter greater than 50km. So if humanity decided to make a home of the Kuiper belt, there is no shortage of objects to choose from.

Last edited by Calliban (2025-02-24 08:53:17)

New Mars Forums

Announcement

#26 2023-10-05 06:58:41

Re: Shell Worlds

#27 2023-10-05 09:27:49

Re: Shell Worlds

#28 2024-02-08 13:08:07

Re: Shell Worlds

#29 2024-02-08 16:38:58

Re: Shell Worlds

#30 2024-02-08 19:44:42

Re: Shell Worlds

#31 2024-02-09 09:08:45

Re: Shell Worlds

#32 2025-01-31 18:22:56

Re: Shell Worlds

#33 2025-01-31 21:57:47

Re: Shell Worlds

#34 2025-02-01 09:40:54

Re: Shell Worlds

#35 2025-02-03 07:16:24

Re: Shell Worlds

#36 2025-02-03 13:02:16

Re: Shell Worlds

#37 2025-02-22 14:21:19

Re: Shell Worlds

#38 2025-02-23 11:55:38

Re: Shell Worlds

#39 2025-02-24 08:38:41

Re: Shell Worlds

Board footer