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#1 2012-12-15 09:04:17

Antius
Member
From: Cumbria, UK
Registered: 2007-05-22
Posts: 1,003

Shell Worlds

Thought you might like this article, the idea has been kicking around for a long time, but these authors have breathed fresh life into it.

The basic idea is that in the far future, habitable, open sky, breathable atmospheres could be created on practically any solid planet, large asteroid, or moon in the solar system, by using a layer of rock or ice to balance the force of air pressure against gravity.  On a small scale this would take the form of pressurised caves beneath the surface of the planet/moon, with air pressure inside balanced by the weight of the rock above.  Obviously, the lower the gravity, the thicker the layer of rock would need to be.  These caves could ultimately be extended to the point where the walls would be kilometres apart and the roof hundreds of metres or more high, such that the environment could be tailored to look Earth-like, with perhaps a simulated blue sky.  This would seem to work better on smaller, lower gravity worlds where the wall stresses on the caves would be lower.

The authors take the idea to its logical conclusion and postulate that in the far future, such caves would be extended across entire planets, moons or asteroids, to create ‘shell worlds’ in which planets or moons are completely surrounded by free floating shells of rock, held in place by balancing the internal air pressure against their weight.  From the surface, such a place might be indistinguishable from the Earth’s surface, although gravity would in most cases be a lot lower.  The world could be divided between land masses and oceans, much as the Earth is.  Ultimately this would allow human beings to form Earth-like environments practically anywhere; Mars, the Moon, beneath the baked surface of Mercury or the frozen wastes of Pluto.

Obviously, this would be civil engineering on an almost unimaginable scale – essentially constructing a masonry roof over an entire planet.  It would require a huge amount of robotics, a lot of time, money, patience in equal measures.  The authors also appear to skip over the obvious problem that such a construction would be vulnerable to falling meteorites, tidal forces or a rogue nut case armed with an atomic bomb.  Once the shell were punctured and air began leaking into the vacuum of space, the remainder of the shell would collapse under gravity, as there would be no internal air pressure to hold it up.  This leads one to suspect that a more stable arrangement over geological timescales would be provided by a network of structurally independent caves, linked by tunnels that could be rapidly closed by airlock doors under gravity.  This would also lend itself to being constructed incrementally, starting with just a few caves and gradually extending them across the entire planet until a global biosphere were formed.

The stability of the shell world concept could be improved and the concept largely preserved, by making the shell thicker than required to balance air pressure and supporting it underneath using compressive columns.  This would tend to suppress oscilations and would ensure structural stability if part of the shell were punctured by a meteorite.  Interesting thoughts.

http://www.ultimax.com/whitepapers/Shel … -final.pdf

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#2 2012-12-18 07:04:07

karov
Member
From: Bulgaria
Registered: 2004-06-03
Posts: 953

Re: Shell Worlds

Antius,

Thank you for the superb topic.
I'll "intefere" in the next several days.

GK

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#3 2012-12-20 11:02:35

karov
Member
From: Bulgaria
Registered: 2004-06-03
Posts: 953

Re: Shell Worlds

I checked out what's new on www.paulbirch.net , the site of Paul Birch , it was down and checking wiki I found out that the Grand Master of the shell worlds have passed beyond in July this year! RIP.
He was REAL genius. I'm sorry I haven't downloaded all his website content, there were really wise articles.

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#4 2012-12-21 10:08:09

Antius
Member
From: Cumbria, UK
Registered: 2007-05-22
Posts: 1,003

Re: Shell Worlds

The Shell Problem:

I carried out some research yesterday that has helped me to better understand the practicalities and limitations of the Shell World concept.  Some calculations will be needed to confirm these thought experiments.  The Centauri-Dreams website featured some interesting critique, which raised questions over the stability of a shell world:

http://www.centauri-dreams.org/?p=20856

Basically, tidal forces and internal wind loadings would disturb the equilibrium of the shell, such that it would be displaced slightly from the central body.  The original authors made the assumption that gravity would act as a restoring force if a rigid shell of equal thickness where displaced in a certain direction.  In spite of the critique provided by Centauri-dreams, this would appear to be correct.  For a rigid shell, zero net force would occur when the centre of mass of the shell lined up precisely with the centre of gravity of the central body.  If the shell were displaced slightly, then its centre of mass would be displaced relative to the gravitational centre of the central body.  Hence gravity would attempt to restore the shell position back to equilibrium.  This action would exert compressive forces within the shell.  Hence it would require a certain amount of rigidity and compressive strength to survive such disturbances.

In the absence of an atmosphere, a disturbed shell would oscillate about the central body indefinitely.  However, the atmosphere would dampen oscillations with air resistance, returning the shell to zero net motion.
The atmospheric and atmospheric gradient provides two additional restorative mechanisms that would help to balance any disturbances.

As part of the shell is pushed towards the surface, it would enter denser air and would be subject to an increase in static lifting force due to buoyancy.  The far side of the shell would be pushed away from the surface and would experience a decrease in static lift.

The third force results from the compression of the atmosphere.  For a shell hundreds or more kilometres in diameter, the air itself would take considerable time to redistribute if the shell were subject to a displacement.  On the basis that the speed of sound in a solid if an order of magnitude greater than in air, shell displacements would tend to compress the air beneath them, resulting in a powerful restorative force.

It is of interest to note that for any point displaced towards the surface, the atmospheric restoring forces would exert tensile stresses.  This would partially be partially cancelled out by the compressive stress within the shell.   The side displaced away from the central body would be subject to compressive stresses due to gravity.  Hence, the shell must possess a certain degree of tensile and compressive strength.

One obvious way to improve the shell stability, would be to anchor it to the surface with supporting columns.  These would function as tensile or compressive members depending upon where the disturbing force occurs and would limit the stresses on the shell.  These could be modelled as natural features such as mountains.

Over Christmas, I will attempt to derive some simple mathematical models for shell stress.

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#5 2012-12-21 14:50:17

Antius
Member
From: Cumbria, UK
Registered: 2007-05-22
Posts: 1,003

Re: Shell Worlds

Unfortunately, there is no easy way of posting images into these threads, and equations are poorly presented.  So what follows may be hard to follow.

I made a few calculations for a shell around Ceres for clarification.  In order for the shell to stand up to decompression events, it must be capable of supporting its own weight against gravity with all atmosphere absent.  In the pure shell world concept, a hollow, free-floating shell surrounds a body and contains the atmosphere.  For this shell to support its own weight without atmospheric pressure, it must have sufficient compressive strength to avoid crushing.

In order for the shell to remain stable under gravity, the weight of each element must be balanced precisely by the compressive sine of the compressive stress acting on each element, such that:

ΣF=0

Weight of an element = pi×a^2×t×ρ×g

Opposing force= 2pi×a×t×σ×sinθ

As both forces must equal:

2pi×a×t×σ×sinθ= pi×a^2×t×ρ×g

2σ×sinθ=a× ρ×g

σ=(a×ρ×g)/2sinθ

Let a = 1m.  The value of θ can be calculated from the known circumference of Ceres:

θ=1/(2π×500,000)×360=1.15×10^(-4)

The value of ‘g’ on Ceres is 0.147m/s2.  For cast basalt, ρ is ~2500kg/m3.  On this basis, the shell stress can be calculated.

σ=(1× 2500×0.147)/(2×sin⁡(1.15×〖10〗^(-4)))=92MPa

This is approaching 50% of the yield strength for cast basalt.  If steel were used instead of basalt, the compressive stress would be 300MPa.

The conclusion would appear to be that for a small world like Ceres a stable shell is possible using ordinary structural materials, although the safety factors are not good.  On this basis, internal structural support would be valuable in reducing compressive stresses, especially if the shell is subject to tidal loadings.  On larger worlds such as Mars or Luna, it is probably essential as the required compressive strength would require unrealistically strong shells.

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#6 2012-12-26 23:51:58

Void
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Registered: 2011-12-29
Posts: 4,676

Re: Shell Worlds

I will offer what I have.  These deviate from your original query to the others and yourself.

The only way I would ever think of a shell world surrounding a gravitational mass and supported against gravity by atmospheric pressure, would be if a collapse could be survived by the population, and if they could quickly rebuild it at a reasonable cost.  I suppose if they had safety measures such as early warning and deep bunkers where they could survive the crash, or a means to depart to an orbital shelter, and if they had a vast army of robot servants to do the rebuilding, then it might be considered for small bodies as you have yourself restricted the idea to.

It is obvious that vacuum floats above air in a gravitational field, and that air floats above water, and that water floats above soil and rock.  So far, we can only violate that using stiff tensile and/or compressive structures.  We fill a tire with air, but from time to time we get a flat tire and in that case we can replace or patch it and refil it.

I would think that Vesta would be fun to try the idea on, it turns out that it's soil is impregnated with Hydrogen, and it is smaller than Ceres.  I would make the "Supports" as verticle closed cylinders shaped like an elongated soup cans filled with air.
I would link each cylinder with pressurized passageway ducts running horizontally.  Then I would cover the whole thing with a common enclosure, a roof to catch gasses leaking from the ducts, and cylinders and their airlocks.  Artificial gravitation would be from a torroid spinning structure inside of the bottom (perhaps) of each cylinder, supported with magnatism or air pressure as in a hover craft like the method suggested in the saucer section of the imaginary starship enterprise of the sci-fi "Star Trek".

Deviating even further;
-Cover Ceres with a worldwide ocean protected by mechanical means, with ice sheets as floats and solar domes enclosing "Windows".  In some cases the "Lakes" under the windows could be ice water, and in some cases with extra means they could be tropical.  Ceres is close enough to the sun where this could be worthwhile.  Going further out in the solar system, I suppose you would not bother with windows, but would rely on some unspecified energy source.

-Make a shell without a gravitational body.  I think it would be quite worthwhile to have a hollow shell world built to orbit Ceres or some other such body.  It may be only slightly pressurized (Near vacuum) to catch the leakage gasses from the artificial worlds it would enclose.  Those artifical worlds could be like the clasic torroids that early on were suggested.   They could be moved about within the parent body, repositioned, docked to a network of ducts.  Smaller non spinning worlds could also be present, sufficient to hold a group of working persons for a period of weeks or months.  I suppose I see this as each small world working with others to construct something, with robotic manipulator arms with hands.  I suppose they would work with material objects, to provide goods.  I think that this could be quite a good method for the Jupiter system.  The outer shell could be a radiation barrier.  Raw materials from Callisto, and later the other moons could be brought in.  But this is quite deviated from your original query about shell worlds.

As for energy, such shell worlds might be able to capture energy from the solar wind, perhaps quite far out.  Or in the case of the Jupiter system by entering a harmonic orbit with one of the moons and essentially converting the spin of Jupiter into energy.  They would use the magnetic field of Jupiter to generate power, and the momentum of the moon they have a harmonic orbit with to maintain orbital position.  The tides of Jupiter would replace the momentum taken from the moon with spin energy taken from Jupiter.

Such a scheme would work for otherwise uninhabitable star systems, such as small red dwarfs, brown dwarfs, and yellow stars without a reasonable "Earth", but with a significant planet with a significant moon.

So, by this method at least you could consider that solar systems inhabited would not have to be ideal ones.  So this could be a method to achive what was desired.

Good for the imagination, but I do believe it will be a long time, if ever comming.

Last edited by Void (2012-12-27 00:14:18)


Done.

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#7 2012-12-27 12:05:02

Terraformer
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From: Ceres
Registered: 2007-08-27
Posts: 3,531
Website

Re: Shell Worlds

Sort of like Virga? A massive shell containing an atmosphere, with a multitude of smaller worlds within it? One can easily imagine what sort of worlds you'd get - small (several hundred meters) asteroids surrounded by rings which spin to provide the inhabitants with acceleration and plants which grow on the asteroid itself... perhaps all illuminated by distributed fusion suns. Or even, possibly, by suns powered by beamed energy from the shell itself, which would have quite a sizeable gathering area for solar power. Pressurise the whole thing to a 100mb or so or CO2 and Nitrogen...

Around Ceres, it might be possible to have an appreciable atmosphere at ground level and need only to provide a few dozen millibars of counter-pressure at the roof, if it is high enough. That pressure could be provided by several meters of ice. Although around Ceres, I'd prefer to use multiple layers of balloons, bound together...


"I'm gonna die surrounded by the biggest idiots in the galaxy." - If this forum was a Mars Colony

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#8 2012-12-27 15:21:12

Void
Member
Registered: 2011-12-29
Posts: 4,676

Re: Shell Worlds

Well why not.  Lots of raw materials and energy, come up with a set of tools that benefits your productive process, and a means to not become dead from the space environment, and you are then the new Homo Galacticus.

Who am I to say what tools are the best.  I can simply try to provide some.

Last edited by Void (2012-12-27 15:37:47)


Done.

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#9 2012-12-28 03:31:03

Void
Member
Registered: 2011-12-29
Posts: 4,676

Re: Shell Worlds

A good place to try to develop at least part of the skills necessary, with a potential payoff might be Titan.

I suggest a bottom and a top shell.  A torus around the equator.  A flatened torus, and within the atmosphere, at a level where the air pressure would be 1 bar ideally.

http://en.wikipedia.org/wiki/Torus

Floating?  If possible, anchored.  Tensile or compressive anchors?  Whatever could work.

once established, in terms of population saftey, I am thinking that continuing safety should be possible.

Further this method would allow the limitation of the alteration of the native environment, but I suppose the presence would alter the native form, but a stable post native form should be possible.

No danger of explosive decompression,  A giant heat sink to spill heat into (The cold atmosphere),  Light materials in abundance, possible meteor heavy materials in the crust.

But likely defficient in heavy materials accessible on the surface.  A defficient power source.

Still in a solar space based trade network it might be a important place.  Heavy materials once imported are not too likely to be lost and could be recycled, and energy gathering technology does keep advancing. 

For energy the usual space solar and presumed fusion sources can be speculated on.  In addition, Saturns spin can be exploited using magnetic tether systems linked to Saturn by tides.  Curious, if Titan does not have a magnetic field, perhaps those tethers could be down on the surface.  Maybe even superconductive materials?  I am not sure if that would be very important though.

But imagining that the human race were to become interstellar, then Neo-Earths and Neo-Titans might be their best finds.


Done.

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#10 2013-01-01 13:40:35

karov
Member
From: Bulgaria
Registered: 2004-06-03
Posts: 953

Re: Shell Worlds

Yes, exactly continuous spectrum between virga-like centre-body-less world up to Birch-ean Supra-self.

The shells are of three varieties: floor-shells , ceiling-shells or both.

In fact note the very important fact that indeed we are living on a shell world. The Earth's "geosphere"* - which is A rock shell with some water spilled over - floats on thicker "toposphere"** of molten rock, magma, hot iron. The "atmosphere"*** is held via deep enough ceiling-less gravity well, which beng economically too mass-requiring solution won't be very widespread among the habitable worlds. The "luminosphere"**** is the simplest possible - using the planetary self-shading and distance to the primary source of light for "regulation".

*,**,***,**** - these terms are borrowed from the Grand Master Paul Birch ( RIP ).

1. geosphere = the habitable SURFACE. We humans can only inhabit solid surfaces - i.e. land ( accompanied with water ( liquid ) surfaces which we can cover with solid surfaces - ships, platforms, rafts ). In the extremely low-gee worlds the Geosphere is not a global phenomenon ( layer ) but bespoke feature of local environment: Atmosphere is global, and within that atmosphere the human-tolerable lands / geospheres are installed on demand - centrifuges.

2. toposphere = this what gives the world shape and provides for structural integrity - for the Earth's case this is the undercrustal mantle and core, for Virga is the ceiling-shell ( no floor-shell there, but archipelago of centrifuges providing floors / lands ). In a rotating toroidal world the toroid is the toposphere AND the ceiling for the atmosphere and eventually the luminosphere.

3. ... Smaller worlds with shallower gravity wells need ceiling-shells to hold down their atmospheres. This ceiling-shell could be regarded as inverted "toposphere" as with the rotating for pseudo-gravity worlds...  If the core body ( underbody ) is too small it won't qualify for true geosphere, but rather as solids mining site and anchorage. The ceiling shells could be solid or could be "magnetic" / plasmoid bubbles or both. ( as per the case of Ceres or other miniml size planemos -- if the ceiling is high enough so its weight to be balanced out by only few mili- or micro-bars then solar powered ( EM or particle influx capture ) global plasma window would suffice. In fact Ceres could have both - solid high shell AND plasmoid blanket / MHD generator...

One very interesting feature of the under-gees shelled worlds would be not only the arms-powered flight but also the free-fall terminal velocity. If it is 200km/h on Earth, it would be quite survivable dozens of km/h on Moon or smaller underbody, hence it won't be letal for s.o. to fall from one of the hanging from the ceiling-shell gardens to the 20-30km down surface.

===

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#11 2013-10-12 10:00:30

Void
Member
Registered: 2011-12-29
Posts: 4,676

Re: Shell Worlds

I was stimulated by posting in the topic "Supra-Polar "Continents" on Earth.  But, since I am going to make a deviation from both that and the typical shell worlds so far described (To my knowledge), I will place a post here.

Venus is my target for this, and worlds like Venus, if any elsewhere.

I am thinking of floating shells actually, but many layers. None of them will have vacuum above them.  Each shell could have open ports to allow aircraft through.

I am not thinking of altering the atmosphere beyond getting rid of the Acid vapors and aerosols.

To float each shell would have a Nitrogen/Oxygen atmosphere inside of it (Each "Shell" being at least a double shell).

So if the temperatures of the Venus atmosphere were kept constant as they are (Although that is not a mandate), the portion of atmospheric column suitable for habitation, (Where the pressure inside the double shell was quite close to the pressure outside of the double shell), would be from about 12 feet of water to 200 feet?
1/3 bar to about 6 bar with a Nitrogen/Oxygen mix. 

Deeper shells would be possible using Helium/Oxygen, but I don't know how suitable that is for humans long term. Not very I would think.

Making the shells float might actually require a Helium/Oxygen mix on the upper end, towards 1/3 bar also due to need for more buoyancy from a thinner atmosphere.

The top shell would have natural lighting, but the others would mostly require artificial lighting like normal shell worlds.

I think this would possibly evolve from small floating habitats anyway if they ever are established in the first place.  But it is an interesting supplement to the notion of creating multiple layers of "Land" on one world.  It is also convenient that Venus has a significant gravitational field not too different from Earths.


Done.

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#12 2013-10-12 11:04:24

Terraformer
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From: Ceres
Registered: 2007-08-27
Posts: 3,531
Website

Re: Shell Worlds

You start to get Nitrogen narcosis at 1.2bar partial pressure, and most people will have trouble by 2.4 bar, if I remember correctly from one of Midoshi's(?) posts. But you wouldn't want to go that deep on Venus anyway, the temperature will be too high. Much better to stay in the 1 bar, 0-50 deg. c. environment.


"I'm gonna die surrounded by the biggest idiots in the galaxy." - If this forum was a Mars Colony

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#13 2013-10-12 12:57:14

karov
Member
From: Bulgaria
Registered: 2004-06-03
Posts: 953

Re: Shell Worlds

Void,

Multi-storey shell-worlds is good when natural insolation is higher then Earth average. Indeed Earth normal radiation constant is excessive.

BECAUSE using orbital rings with maglev suspended mass-streams in vacuum will operate without friction and with negligible loss, I guess the "geo_thermal" energy present around and in Venus will be enough for billions of years to keep the multi-shells afloat above surface.

Shortcuttin' the 700+ K temperature of the 5x10exp20 kg atmosphere of Venus to a 3k univresal background radiator will give us tremendous energy - more then enough to build the shells from atmospheric and solid surface materials AND to keep them afloat forever.

Carnot cycle efficiency from 800K to 3K is 99.60%
Internal energy harvestable for CO2 at 800k and 92 Bars from 700K to 3K is about 10exp7 J/kg.
There are 10exp21 kg approx. including the solid surface layers to certain debth.
I.e. the total useful energy from shortcutting the whole of the Venusian atmosphere to a ( background universal ) 3K radiator is in the order of magnitude of 10exp28 Joules.

10exp28         3.8×10exp28 J    kinetic energy of the Moon in its orbit around the Earth (counting only its velocity relative to the Earth)

As a side effect of this heat energy harvesting all the atmosphere will settle frozen down on the pitch dark cryonic cold-ed surface.

10 shells spaced 100km from eachother will give us more then 10 times Earths habitable area with heavenly climate, illumination, etc.

Indeed:

Shell#1 - 100km above Venusian solid surface = 475 792 165 sq.km.
Shell#2 - 491 385 765 sq.km.
Shell#3 - 507 230 793 sq.km.
Shell#4 - 523 327 250 sq.km.
Shell#5 - 539 675 136 sq.km.
Shell#6 - 556 274 450 sq.km.
Shell#7 - 573 125 193 sq.km.
Shell#8 - 590 227 364 sq.km.
Shell#9 - 607 580 965 sq.km.
Shell#10 - 625 185 993 sq.km.

Total: 5 489 805 074 sq.km.
or
10.79 Earths
or
500+ times USA

IF illumination per sq.km. needing adjustment - simply another arbitrary high and surface area outer solar capture and distro shell shall be erected.

The surface gravity will gradually fall upwards until on the upmost Shell#10 will be 0.67 gees or 2/3rd Earth normal. Completely livable and safe, atmospheric retention will be guaranteed by the top-shell + unlimited supply for replenishment even export from the frozen atmosphere beneath.

In fact once tamed the real surface could be terraformed too, but with this plenty of 10+ Earths above, why not to keep it as cryo-vacuumed "basement" so interesting for industrial purposes.

Last edited by karov (2013-10-13 07:05:07)

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#14 2013-10-13 07:33:22

Void
Member
Registered: 2011-12-29
Posts: 4,676

Re: Shell Worlds

Well Terraformer, you got me smile

My coarse adjustment is off to a dangerous limit, so to respond to human limitations, the band of atmospheric column usable is constricted with the hardware I suggested, on the issue of pressure.

On the issue of temperature, it is less constricted over time, if you allow for a cooling process (I originally said no atmospheric change except the acid characteristic).

The heat of Venus is solar and internal heat.  I do not expect that the internal core generated heat can keep Venus hot.  The shells would both shade and insulate the hot atmosphere below.  But I did suggest openings where aircraft could pass through, and they could also provide ventilation. 

Further if there were ventilation ports, some where cold air poured down, and some where hot air displaced by the sinking cold air could pass upward, then turbines could harness this air flow.

A changing temperature profile for the atmospheric column, however would also change the buoyancy at a altitude, so the Floating Shells would require adjustment for that.  Either flexible hinges built in, or special compensations like ballast adjustments.

Karov, has bypassed and modified my suggestion with a counter suggestion, which as usual is much more ambitious, and also very interesting.

I guess the obvious common point is where typically Venus terraformation plans abhor the thick atmosphere and try to get rid of it, or in the case of floating cities try to live with it, in these plans, harmonization with it provides a greater potential yield of dwelling surface area.

By the way, in the future, if I do not respond in a timely manner to posts, and that seems rude, it can be because quite often when I try to access this site I get a warning of a malicious content.  (It appears to be some type of identity probe).

Karov,

So, how would your method work for Saturn, Uranus, and Neptune?  (Roughly 1 + some value g)

Last edited by Void (2013-10-13 07:38:07)


Done.

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#15 2013-10-13 13:01:10

karov
Member
From: Bulgaria
Registered: 2004-06-03
Posts: 953

Re: Shell Worlds

Void,

Everything about shell worlds and kinetic structures from the very source:

http://www.orionsarm.com/fm_store/Paul%20Birch's%20Page.htm

For Saturn, Uranus, Neptune ... for every underbody be it brown dwarf, a star, black hole ... etc. the surface area of habitat @1 gee is exactly equal to the mass of the underbody in times Earth masses.

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#16 2013-10-15 13:13:10

Void
Member
Registered: 2011-12-29
Posts: 4,676

Re: Shell Worlds

I speculate that if you did manage to put a shell around a world like Saturn, Neptune, and Uranus, that by insulating it, the core heat of those worlds would more dominate the atmospheres, causing them to expand.  Perhaps then the expanded atmosphere then being over the original shell, then allowing a second shell above the first, and that continuing until the outer shell is at a gravitation favoring the extraction of a portion of the atmospheres as raw materials.

I also wonder if so insulated, eventually the planets would shine at shorter wavelengths.  Perhaps even in visible light. 

Just speculation, not particularly useful in this age we live in, but perhaps far in the future.

Further, if that were done, maybe even boiling off all the excess of gasses and liquids, and eventually leaving behind a core as an "Earth" or Super Earth".
(Way out there).  I wouldn't feel good about that however, if all the expelled gasses were wasted.

Last edited by Void (2013-10-15 13:19:50)


Done.

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#17 2013-10-17 23:47:39

karov
Member
From: Bulgaria
Registered: 2004-06-03
Posts: 953

Re: Shell Worlds

Void,

Well, internal heat dominates anyway, but - how much is the geothermal energy flux per sq.m.?

The inner heat exploitation will shrink the planets indeed.

Puffier and hotter will blend better and will be more suitable for mining, but once the bark/s set over these planets comprise 10s of Earth masses of temperature of 1000s of K. Shotcutted to 3K universum background temp. radiator the Carnot efficiency would be 99.95%, i.e. more or less extractable on "face value".

For how long this can provide, say, 300W of power per sq.m. of circum-(say)-Neptune habitat?

If for millions or billions of years then even interstellar ( rogue ) neptunes will live well in the dark...: two shells - very thin "ceiling" one + more solid floor one.

---

Well, well, weeeellll, ...

Neptune's mantle and core are approx. 15 Earth masses or about 10exp26 kg
Mostly water-amonia, so we could approx. it to water specific heat.
Which is about 4KJ/kgK.
Amonia specific heat is 6-ish.
Iron ~ 0.4 KJ/kgK
Specific heat of water under hundreds of thousands to millions of bars and thousands of K temperature, I dunno, but ... lets say this total mass has average temperature of 3000K and the mass above and specific heat of 4KJ/kg.

10exp26 kg multiplied by 4KJ miltuplied by 3000K = 12x10exp29 J

5.5×10exp24 J is the total energy from the Sun that strikes the face of the Earth each year.

Neptune's 1gee shell-world would have 17 times bigger area then Earth

Lets assume better IR isolation and needed 10 times lower "solar" constant of 150-170-ish W/m2. ( to round the figures )

Thus the habitat could be powered for 10 000 years only by internal heat reservoir before sinking moons and external captured bodies to become necessary.

Last edited by karov (2013-10-18 15:11:07)

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#18 2013-10-21 12:43:37

Void
Member
Registered: 2011-12-29
Posts: 4,676

Re: Shell Worlds

Well thanks for doing that.  You might have noticed I am some levels below you in that regaurd.

Maybe some super advanced civilizations could manage that.

I myself think that perhaps we might consider the Asteroid Vesta or the moon Enceladus to cut baby teeth on.  Just maybe in many numbers of years our inheritors might do that.


Done.

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#19 2013-10-22 08:08:31

Void
Member
Registered: 2011-12-29
Posts: 4,676

Re: Shell Worlds

Just for fun, I have been considering Vesta.

I quickly and with little concern for precision have calculated a few things:

0.025 g for gravitation.

0.36 km/s for escape velocity.

To hold down a full 1 bar atmosphere, you would need 1280 feet of water (More if it is ice), but that is for reference, I do not propose to use water.
But if you had building materials 4 times as heavy as water, you might need 320 feet.

That shell could be a honecomb type structure, with many cells, and of course with that much better safety factor against leaking.  I suppose some of the cells could simply be filled with stony materials as balast.  Some could have centrifuges in them to generate synthetic gravity.

I would think though that as it was built and made more heavy, a progression of atmosphere imposed over Vesta could be done.

10 MB, 50 MB, 250 MB, 330 MB, 500 MB and then perhaps 1 Bar.

That world is so small that perhaps support structures from the surface to the shell could be used.

So the builders would end up with a expansive living space in a honeycomb shell, a tiny world with a biosphere on it's surface, and an extensive mining operation subsurface, which might even reach to the core.  The mining spaces when they were done with them could also provide living spaces as well.


Done.

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#20 2013-10-22 10:21:14

Terraformer
Member
From: Ceres
Registered: 2007-08-27
Posts: 3,531
Website

Re: Shell Worlds

Of course, you could use concentric shells. Have a thin layer providing Vesta with 1-2mb of atmosphere, another providing it will 10-20, then another bringing it to levels high enough for plants, then pressurised buildings for people and animals.


"I'm gonna die surrounded by the biggest idiots in the galaxy." - If this forum was a Mars Colony

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#21 2013-10-22 12:03:43

Void
Member
Registered: 2011-12-29
Posts: 4,676

Re: Shell Worlds

There would be a lot of room for variation.

If doing as you suggest, then I would also have a chatchment shell attached to and supported by the outer shell.  That shell could catch air leaking out or the outer shell propper, and keep the pressure between the double outer shell below that of molecular flow for air, and the catched leaked air could then be pumped back into the system.

That shell, and the shells you have suggested, and then below that I would eventually want built the honeycomb shell, which could hold a pressure by it's weight of at least 300 mb.  It would be really cool to have a dirt surface of an asteroid with a savanna vegitation on it.

Since I have invensted nothing but imagination so far, I can afford a savanna.  Keep the lions though.  Don't want lions leeping at me from 1000 feet away. smile


Done.

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#22 2013-10-22 14:15:01

Terraformer
Member
From: Ceres
Registered: 2007-08-27
Posts: 3,531
Website

Re: Shell Worlds

Populate it with super-elephants. At 10 tonnes, they should have a similar weight on Vesta as humans do on Terra, so it'll be difficult for them to bounce around too much.


"I'm gonna die surrounded by the biggest idiots in the galaxy." - If this forum was a Mars Colony

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#23 2013-11-01 09:01:02

Tom Kalbfus
Banned
Registered: 2006-08-16
Posts: 4,401

Re: Shell Worlds

Hello again, its been a while. I think shelling worlds is a very useful terraforming techniques. The worlds of the Solar System which might be shelled would include the following: Mercury, Venus, the Moon, Mars. Saturn, Uranus, Neptune and Pluto (Though Pluto has recently been reclassified as a dwarf planet, it still maybe shelled.

There are two possible reasons for shelling a planet (In these cases the shell is supported by atmospheric pressure underneath
1) to provide a surface for inhabitants to stand on Venus, Saturn, Uranus, Neptune
2) to prevent the gases in the atmosphere from escaping into space Mercury, Moon, Pluto
also 2a) to conserve gases required to produce a 1 bar habitable atmosphere on the World's surface (Mars)

One exception would be Jupiter, it presents a special problem, is gravity at the top of the atmosphere is significantly greater than the gravity at Earth's surface. If you take the square root of Jupiter's mass in Earth masses, you get the radius of the shell around jupiter in Earth radii that would be required to have a surface with 1 Earth gravity, the problem is this radius is greater that the actual radius of Jupiter, so atmospheric pressure could not support this shell, some other mechanism would be required to support it, a dynamic compression mechanism most likely which transfers the weight of the shell onto the atmosphere of the Planet Jupiter below. The surface area of this shell would equal 318 times the surface area of Earth, since Jupiter has 318 times the mass of Earth, this is more difficult that Saturn where the shell would simply rest on top of its atmosphere, it would also be easier to obtain the atmospheric components of a breathable atmosphere on top of a Saturn shell than a Jupiter shell, since the Saturn shell rests on top of Saturn's atmosphere, and one can simply mine out all the nitrogen, oxygen, carbon, and water from deep in Saturn's atmosphere. Since Saturn condensed out of the original solar nebula, then all those gases found in Earth's atmosphere are available in sufficient quantities in Saturn's atmosphere. Since the planet holds onto hydrogen, it would also hold onto all the gases that are heavier than hydrogen. Convection would keep the gases mixed despite the heavier components of the atmosphere, so what one would do is extract the nitrogen from the 0.01% ammonia in Saturn's atmosphere, the carbon dioxide would exist at a lower level in Saturn's atmosphere where it could exist as a gas instead of as dry ice, oxygen would come from water clouds deep below as would the water as well. Since Saturn has 95 the mass of Earth and most of it is in gases, that means even if a gas exists only in trace amounts as a percentage of Saturn's atmosphere, there is enough atmosphere there that we can obtain as much of those gases as we need. A shelled terraformed Saturn would require 95 times the breathable atmospheric mass of Earth's atmosphere since its surface area is also 95 times that of Earth and an atmosphere under an Earth's gravity would stack just the same as it would on Earth.

The next problem is providing adequate sunlight Saturn's diameter is 120,536 km. One could build a solletta ring around Saturn that concentrates sunlight around Saturn to warm it up. If the Solletta ring was 3,900,000 km in radius and 1,280,000 km wide it could gather enough sunlight and concentrate it on Saturn enough to warm up Saturn's artificial surface so it warms up Eventually the planet would absorb enough heat so that its atmosphere would expand outward, so hopefully the shell would be made of stretchable material. I imagined a similar solletta ring around Venus, but in this case it would be only 39,000 km in diameter and 12,800 km wide, the main task for that solletta would be to shield Venus from too much sunlight and give the planet a 24-hour day/night cycle by reflecting sunlight around the planet and illuminating the right hemisphere with reflected sunlight on the inside of the Solletta.

We could also shell rogue planets, the problem with rogue planets is they are very cold, and so would hold on to their hydrogen when they formed, an Earth mass rogue planet for example would be a sub-gas giant, a mini-neptune for example, its mass would equal Earth but a large portion of that mass would be in the form of the gases hydrogen and helium as they make up the primary components of interstellar gas clouds and there would be no nearby stellar radiation to blow those gases away. If we were to remove the light gases from an rogue planet, what we'd have left from an originally Earth massed planet would be something with less mass that the Earth, the radius of an Earth mass rogue planet would be greater than Earth due to its lower density and would thus have less than an Earth gravity at the top of its atmosphere. A rogue planet could be a planet like Saturn or a planet like Neptune, so the same methods we'd use to shell those would would apply to a rogue planet, the only difference would be that there would be no nearby star to focus radiation on the planet to make it habitable. One possibility is to build a double shell around a rogue planet, the bottom shell would be the surface in which you stand on, the top shell would contain the breathable gases between the two shells. On tip of the top shell would be a layer of hydrogen and helium plus fusion reactors. The hydrogen and helium would feed into the fusion reactors and the fusion reactors would provide power for the artificial illumination between the two shells.

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