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#1 2015-09-10 05:57:53

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

Asteroids & Shells

As a result of our collective work on this board, I have increasingly come to the opinion that Earth crossing asteroids will be the first worlds subject to large scale human colonisation.  This may occur before large scale habitation of low earth orbit and is almost certain to occur before large-scale settlement of Mars.

Many of these bodies can be reached at an energy cost comparable to that required to reach lunar orbit, when orbital injection burn is included.  Most significantly, all of the propulsive work required to reach these bodies can be accomplished using low thrust electric propulsion, with virtually no chemical rocketry required beyond low earth orbit delivery.  The Delta V required to reach the asteroid surface from asteroid orbit, is typically less than 100m/s, which implies negligible propellant mass required for landing.

On the surface, the asteroid provides most of the advantages provided by a larger planet.
1. Its bulk shields out at least 50% of cosmic ray dose;
2. Its thermal mass provides a large heat sink, allowing a surface settlement to regulate temperature and even generate power by exploiting day/night temperature differences.
3. A ready source of materials for manufacture.
4. A day/night cycle for plant growth.
5. As a fixed body, both cosmic ray and solar flare shielding can be provided by magnetic fields, using magnets crafted from native iron, cobalt and aluminium, with mass being essentially irrelevant.
6. A stable mass against which rotating items can be clamped.

Other advantages that would not be provided by a larger planet:

1. Constant solar power is easily provided, either by placing panels and cables around the equator, or by placing a solar power plant at the end of a tether, therefore remaining outside of the asteroid shaddow for 90% of the time.
2. With negligible gravity, surface transport is easy - simply place an object on a sub-orbital trajectory.
3. Launch and landing are simple for the same reason.
4. Terraforming the smallest of bodies is comparatively easy, as it is possible to completely enclose asteroids <100m in diameter with polymer pressure vessels without excessive mass budgets.  These could be launched by existing or soon to exist heavy lift rockets from Earth.  This would dramatically simply mining the body, as it can then be accomplished in shirt-sleeve conditions.
5. Asteroids benefit from relatively high enrichment of rare metals.

Near earth asteroids suffer from a number of disadvantages:
1. Transit times will typically be much longer than those required to reach the moon, though comparable to those required to reach Mars.
2. Low gravity complicates many problems, such as grounding equipment and people to the surface.  Unless a colony is built very deep on a large asteroid (see later) it will not be possible to balance internal pressure against gravitational force.  On Mars, we can build pressurised brick structures and simply bury then a few metres underground to balance the required internal pressure.  On asteroids, most pressurised spaces will need to be built within tensile pressure a vessel, which increases cost and required technological sophistication.
3. Gravity is necessary for many industrial and physical processes and is obviously essential for human health.  Colonisation of as asteroid requires as a prerequisite that human habitats be capable of rotation to simulate gravity.  The human vestibular system places limits on the minimum possible radius, although there is evidence to suggest that human beings are capable of adapting to higher rotation rates than typically assumed.  Really, the practically of asteroid colonisation hinges on the ability of human beings to adapt to high rotation rates.

Hollow asteroids:

As part of the shell world discussion, I was interested in exploring the practical size limits of gravitational shells.  By this I mean hollow spherical shells of rock or ice that are pressurised within, for which the self-gravity of the shell balances the internal pressure.  In this condition, the net shell stress would be zero.

My early attempts were limited to relatively large diameter shells, as my spreadsheet was based upon the thin walled pressure vessel equation.  One interesting result is that for large shells the required thickness does not increase as diameter increases.  Provided the gravitational effects of any internals are neglected, a 1000km diameter shell world would have the same required shell thickness for the same internal pressure, as a 50km diameter shell world.  This is because mass is proportional to surface area and gravitational field strength also follows the inverse square law.

I have since updated my spreadsheet to account for situations where the shell is thick compared to its diameter.  This is especially significant for smaller bodies as it allows the shell thickness to decline as a result of the difference in radius of curvature between the inner and outer surfaces of the shell.

I used the spreadsheet to work out the maximum possible diameter of an internal pressurised central cavity with various bodies.  I took the internal pressure to be 34KPa, this is a 5PSI pressure comparable to Skylab.

Here are some of the results for spherical bodies with a bulk density of 2000kg/m3 (i.e. S-type asteroids).  The first number refers to the asteroid diameter; the second the maximum possible cavity diameter at 34KPa:

100m     = 0.7m
500m    = 17.5m
1000m    = 70m
1500m    = 156m
2000m    = 278m
2500m    = 430m
3000m    = 616m
5000m    = 1640m

For stony asteroids with diameters greater than 1500m, one could carve out internal pressurised voids large enough for a small city.  The process could be carried out incrementally.  An initial team of astronauts would drill down into the centre of the asteroid to create an initial base.  As more equipment and people arrived from Earth, the cavity would gradually expand.  Large asteroids like Eros, could house literally millions of people in this way as the internal cavity could approach several km in diameter.  Humans would live in rotating buildings within the pressurised cavity, suspended from the interior surfaces.  The interior could be landscaped in three dimensions, to include plants, trees and animals.  Food could be grown in small pressure domes on the asteroid surface.

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#2 2015-09-10 09:01:05

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

Re: Asteroids & Shells

One of the things that an asteroid could be made into is this:
worldshipSF3.jpg
I believe this counts as a shell world, just look at the size of this thing! Its shell in this case happens to be cylindrical and rotates to simulate gravity, More that half of its volume is propellent, and inbetween is a "Pulse Unit' factory, the pulse units are basically thermo-nuclear bombs given the size of this space ship. Certain types of asteroids contain Uranium, what this ship needs is a breeder reactor, which in the process of producing electricity also breeds plutonium, the plutonium then goes into the cores of hydrogen bombs, which are euphemistically called "pulse units" in this diagram, each hydrogen bomb is created as needed in an automated factory onboard the ship, a certain amount of fuel is apportioned for each bomb and some reaction mass, mainly hydrogen is laid out around each bomb, each bomb is arranged to explode in the gigantic reaction nozzle to the right, the fuel and propellant tanks are to the left. Such a starship would reach the Alpha Centauri System in over a century, so it would have to be a generation or ark ship, one type is specialized to deliver human inhabitants, and the other type to deliver ocean in a smaller cylinder due to water's greater mass. But it is also something which could be produced out of an asteroid, and can also relocate itself to any place in the Solar System as well.

This type of generation ship is most similar to an O'Neill Cylinder.
15475681072_fe7b7bb228_z.jpg
This is a model of an O'Neill Cylinder. You can modify the above design, to make it into an O'Neill Cylinder, by cutting out half of its real estate and devoting that area with large floor windows and giant mirrors that unfold like the pedals of a flower.

The Giant Ship would orient its reaction nozzle towards the Sun, or whatever star it happens to be orbiting giving its interstellar capability, and it would open its giant mirrors and reflect the sunlight into its interior for day and night, during interstellar transits it would use artificial light sources powered by its breeder reactor. The mirror panels would have LED displays on the opposite sides, when fully extended the mirror panels can rotate 180 degrees and close inward with LEDs facing the opposite valleys of each habitation cylinder, the LEDs are powered by the breeder reactors which take in Uranium as fuel and produce Plutonium for the bombs that are produced to propel the ship.

When the ship arrives at Alpha Centauri, it orbits Star A at the habitable zone, extends its LED panels rotates them 180 degrees so that the mirror surfaces face inward and then close to the 45 degree position to reflect light from Alpha Centauri A into the interior opposite valleys.

I would relocate the agricultural ring shown in the model to around the pulse unit factory, there it is still shielded by the erosion shields and propellant tank from interstellar particles, and it is also further away from the exploding nuclear bombs in the reaction nozzle.

Last edited by Tom Kalbfus (2015-09-10 09:24:37)

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#3 2015-09-11 05:48:46

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

Re: Asteroids & Shells

Tom Kalbfus wrote:

One of the things that an asteroid could be made into is this:
http://www.bis-space.com/wp-content/upl … hipSF3.jpg
I believe this counts as a shell world, just look at the size of this thing! Its shell in this case happens to be cylindrical and rotates to simulate gravity, More that half of its volume is propellent, and inbetween is a "Pulse Unit' factory, the pulse units are basically thermo-nuclear bombs given the size of this space ship. Certain types of asteroids contain Uranium, what this ship needs is a breeder reactor, which in the process of producing electricity also breeds plutonium, the plutonium then goes into the cores of hydrogen bombs, which are euphemistically called "pulse units" in this diagram, each hydrogen bomb is created as needed in an automated factory onboard the ship, a certain amount of fuel is apportioned for each bomb and some reaction mass, mainly hydrogen is laid out around each bomb, each bomb is arranged to explode in the gigantic reaction nozzle to the right, the fuel and propellant tanks are to the left. Such a starship would reach the Alpha Centauri System in over a century, so it would have to be a generation or ark ship, one type is specialized to deliver human inhabitants, and the other type to deliver ocean in a smaller cylinder due to water's greater mass. But it is also something which could be produced out of an asteroid, and can also relocate itself to any place in the Solar System as well.

This type of generation ship is most similar to an O'Neill Cylinder.
https://farm4.staticflickr.com/3937/154 … b228_z.jpg
This is a model of an O'Neill Cylinder. You can modify the above design, to make it into an O'Neill Cylinder, by cutting out half of its real estate and devoting that area with large floor windows and giant mirrors that unfold like the pedals of a flower.

The Giant Ship would orient its reaction nozzle towards the Sun, or whatever star it happens to be orbiting giving its interstellar capability, and it would open its giant mirrors and reflect the sunlight into its interior for day and night, during interstellar transits it would use artificial light sources powered by its breeder reactor. The mirror panels would have LED displays on the opposite sides, when fully extended the mirror panels can rotate 180 degrees and close inward with LEDs facing the opposite valleys of each habitation cylinder, the LEDs are powered by the breeder reactors which take in Uranium as fuel and produce Plutonium for the bombs that are produced to propel the ship.

When the ship arrives at Alpha Centauri, it orbits Star A at the habitable zone, extends its LED panels rotates them 180 degrees so that the mirror surfaces face inward and then close to the 45 degree position to reflect light from Alpha Centauri A into the interior opposite valleys.

I would relocate the agricultural ring shown in the model to around the pulse unit factory, there it is still shielded by the erosion shields and propellant tank from interstellar particles, and it is also further away from the exploding nuclear bombs in the reaction nozzle.

Interesting concept.  I wonder why the ship has to be so enormous?  Cost is proportional to size at the end of the day.  The bigger and heavier the ship, the more bombs you need and the more powerful those bombs need to be.  I would guess that the size is partly a result of the need to achieve reasonable propulsive efficiency using almost pure fusion bombs, which are neccesarily large.  The size of the pulse units therefore drives the need for a bigger ship.

For very large ships, magnetically confined fusion engines would be technically much easier to achieve, as confinement times naturally increase and the required plasma density and magnetic field pressures decline.  For smaller ships, a staged fission fragment rocket would allow good propulsive efficiency even for relatively small ships.  A hybrid reactor approach would eliminate the need to carry large stocks of fissile material.  The propellant could be thorium or natural/depleted uranium.

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#4 2015-09-11 07:23:56

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

Re: Asteroids & Shells

the other reason is because the trip would take over a century even with fusion pulse units, also the lack of planets they could live on at the destination is most likely the case. The starship would also be their home once they got there.

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#5 2015-09-15 13:50:33

Void
Member
Registered: 2011-12-29
Posts: 5,032

Re: Asteroids & Shells

Ok, so I looked it up on the web, and it indicated 13,000 NEO's.  I suppose those are significant objects.

https://en.wikipedia.org/wiki/Near-Earth_object

Near-Earth object


From Wikipedia, the free encyclopedia


Near-Earth asteroid 433 Eros visited by the space probe NEAR Shoemaker (December 2000)
A near-Earth object (NEO) is a small Solar System body whose orbit brings it into proximity with Earth. All NEOs have a closest approach to the Sun (perihelion) of less than 1.3 astronomical unit (AU).[2] They include about thirteen thousand near-Earth asteroids (NEAs), more than one hundred near-Earth comets (NECs), and a number of solar-orbiting spacecraft and meteoroids, large enough to be tracked in space before striking the Earth. It is now widely accepted that collisions in the past have had a significant role in shaping the geological and biological history of the planet.[3] NEOs have become of increased interest since the 1980s because of increased awareness of the potential danger some of the asteroids or comets pose to Earth, and active mitigations are being researched.[4]

NEAs have orbits that lie partly between 0.983 and 1.3 AU away from the Sun.[5] When an NEA is detected it is submitted to the IAU's Minor Planet Center for cataloging. Some NEAs ' orbits intersect that of Earth's so they pose a collision danger.[6] The United States, European Union, and other nations are currently scanning for NEOs[7] in an effort called Spaceguard.

In the United States, NASA has a congressional mandate to catalogue all NEOs that are at least 1 kilometer wide, as the impact of such an object would be catastrophic. As of June 2015, there have been 872 NEAs larger than 1 km discovered, of which 153 are potentially hazardous.[8] It was estimated in 2006 that 20% of the mandated objects have not yet been found.[7] As a result of NEOWISE in 2011, it is estimated that 93% of the NEAs larger than 1 km have been found and that only about 70 remain to be discovered.[9] Our inventory is much less complete for smaller objects, which still have potential for large scale damage.

Mining
http://www.space.com/19368-asteroid-min … tries.html

"They can be like the Iron Range of Minnesota was for the Detroit car industry last century

smile

So, I see that this is appearing to get ready to happen relatively soon.  Some stories have it 10 years off for automated retrieval of water from small objects.

So, that could be the start of the game.

But what I see above, is that as an insurance policy to protect the property of Earth, and beyond the value of the materials of the 872 NEAs, there should be a possibility to talk sense into many Earth bound powerful persons, pointing out that a NEA that can be made to have navigation (To avoid the Earth), and which has a population which does not wish to die by crashing into the Earth, is an advantage, because not only would it protect the assets of Earth, which make life more comfortable for common and rich people, but the objects can provide many things, such as riches, and cultural diversity.  In some cases providing havens for cultures which would be harassed by other populations on Earth, and also allowing new cultures to develop.

So an economic case both for material expansion, and for an insurance protection could be made.  Obviously the smaller objects matter as well, but the big few, are quite an assortment of opportunities in themselves.

I am wondering about a "Construction assembly" which could be propelled by a pulsed method, maybe the one mentioned by Tom, so as to allow it to visit each object in turn, and "Light" it's fire, that is establish an infrastructure sufficient to allow them all to develop as you have suggested.

That would be a lot of "Worlds".

Last edited by Void (2015-09-15 14:07:55)


Done.

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#6 2015-09-15 20:20:51

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

Re: Asteroids & Shells

We'd have to build them, this would probably be true of Alpha Centauri as well, so you need a giant ship to act as a home for humanity in that system once it gets there. I figure we start with 250,000 people on the ship and through natural births we end up with 1,000,000 to 10,000,000 when it gets there, and from there people will build more O'Neill cylinders and expand throughout that system, maybe even find a planet to terraform.

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#7 2015-09-16 05:02:36

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

Re: Asteroids & Shells

I ran the shell world spreadsheet for an icy body 50km in diameter with an assumed density of 1000kg/m3 (as per Void's original suggestion).  This is a typical Kuiper belt object.

The internal shell diameter for a 34KPa pressure is 38.8km.  The internal void volume is 30,584 cubic kilometres.  If decked out accordingly, such a body could house a population of hundreds of millions, i.e. an entire civilisation.  Humans would need to spend the majority of their time in rotating buildings, but the ecosystem could be allowed to evolve to function in micro-gravity, in this case ~0.001g.

This raises the question as to whether a future civilisation would bother trying to colonise planets at all, when there exists such a huge number of cometary bodies and small icy moons capable of sustaining them.

Last edited by Antius (2015-09-16 05:08:56)

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#8 2015-09-16 10:03:41

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

Re: Asteroids & Shells

Its true, its much cheaper to colonize our own Solar System than some other star system. It is expensive to get the travel time down to 133 years, but each star system has plenty of resources for such a mission. It might not be wise to wait for our Solar System to be "bursting at the seems" before we start colonizing other stars. Also isolating one group of humans or post-humans might be of benefit, because then we don't all have to get along. Case in point, suppose we captured a bunch of religious zealots intent on waging a Jihad against the rest and humanity and forcibly converting everyone to their religion or killing them, such people cannot get along with the rest of us, and se we pack them on a starship and send them to a star system that is conveniently far away from us, so we don't have to worry about them again.

Call this a Botany Bay type of colony if you like. The Universe is vast! Once we send a Generation ship on its way, it will only have enough fuel to slow down upon arrival, it won't have enough to slow down turn around and come back, that would take much more fuel! Send it on its way toward Alpha Centauri, and they won't be able to turn around and come back until they get there and find some resources to fuel their ship for the return voyage back to the Solar System.

Also some people will choose isolation, such as they are afraid of runaway nanotechnology or something like that, and they just want to get out of the Solar System before it is consumed.

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#9 2015-09-17 18:41:46

Void
Member
Registered: 2011-12-29
Posts: 5,032

Re: Asteroids & Shells

With information about the likelihood of Mars visit capability/settlement by people as sponsored by government entities around the planet, on the Planet Mars, I suppose we should be in despair.

However Asteroids & Shells, which humble starts, might actually offer significant hope, that of economic interests that might expand over time, and yes I suppose in a very distant future, the very outer solar system, and if existing, the small objects of adjacent solar systems.

By this method, it is inevitable that eventually Mars would be settled.

So, really, unless someone like Musk comes through for Mars, I would say this thread is the "Last Best Hope".

Human motivations are human motivations.  Governing entities always will have greater priorities than to expend wealth to create a new domain that they cannot extract wealth from.  Since the governments on Earth cannot own/control settlements on Mars, no linkage exists that would impart to the governing individuals and groups special favors, so psychologically there are no primitive drives acting on them for the most part, drives such as gaining position/power/social satisfactions.  It is hard to buy votes by promising to help some very fringe personalities to achieve such a dream.  Fringe people for the most part, are going to be the ones who will invent a new reality, for their own motivations.

So, it looks like the business model, and a lot of patience are all that might work.

The present generation is very materialistic, needing and wanting materials.  It is as it is scheduled to be.  It is normal apparently that they should be this way.  So the political game is to get wealth for them.  Governments can get it for them from those who have some, and who are small enough to take it from.  Even if a new baby boom generation were to come, (With spiritual values), they have not even been born yet, are not even in the cribs.  So, find a way to get people rich from space, or really, other than a few (And most likely fewer) automated space probes, not much happening I think.  Anyway, the baby boomers (Which I am one), kind of got spiritual in the wrong way, for the most part.  Didn't really, or couldn't really make the big lifts in the end.  Too bad.

Last edited by Void (2015-09-17 18:49:53)


Done.

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#10 2015-09-18 04:07:56

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

Re: Asteroids & Shells

China wants to claim the South China Sea even though that is International Waters, so in the future some Nation Might want to tear up the UN Space treaty and lay claim on the Moon or Mars. China and Russia certainly have set the precedent for that for claiming the South China Sea and the North Pole respectively! Why can't the United States claim the Moon?, It has already planted six US flags into its soil!

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#11 2015-09-18 09:59:34

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

Re: Asteroids & Shells

Void wrote:

With information about the likelihood of Mars visit capability/settlement by people as sponsored by government entities around the planet, on the Planet Mars, I suppose we should be in despair.

However Asteroids & Shells, which humble starts, might actually offer significant hope, that of economic interests that might expand over time, and yes I suppose in a very distant future, the very outer solar system, and if existing, the small objects of adjacent solar systems.

By this method, it is inevitable that eventually Mars would be settled.

So, really, unless someone like Musk comes through for Mars, I would say this thread is the "Last Best Hope".

Human motivations are human motivations.  Governing entities always will have greater priorities than to expend wealth to create a new domain that they cannot extract wealth from.  Since the governments on Earth cannot own/control settlements on Mars, no linkage exists that would impart to the governing individuals and groups special favors, so psychologically there are no primitive drives acting on them for the most part, drives such as gaining position/power/social satisfactions.  It is hard to buy votes by promising to help some very fringe personalities to achieve such a dream.  Fringe people for the most part, are going to be the ones who will invent a new reality, for their own motivations.

So, it looks like the business model, and a lot of patience are all that might work.

The present generation is very materialistic, needing and wanting materials.  It is as it is scheduled to be.  It is normal apparently that they should be this way.  So the political game is to get wealth for them.  Governments can get it for them from those who have some, and who are small enough to take it from.  Even if a new baby boom generation were to come, (With spiritual values), they have not even been born yet, are not even in the cribs.  So, find a way to get people rich from space, or really, other than a few (And most likely fewer) automated space probes, not much happening I think.  Anyway, the baby boomers (Which I am one), kind of got spiritual in the wrong way, for the most part.  Didn't really, or couldn't really make the big lifts in the end.  Too bad.

Some sort of 'foot in the door' strategy would appear to be appropriate.  Establish the colony with a single heavy lift and a crew that are prepared to stay long-term.  The transfer vessel can be a light-weight reusable ion/reaction driven solar powered vessel and could be reused time and time again, rather like an ISS with engines.  The crew would mine the asteroid with a boring machine that would be ballasted with local rock and would literally drill down into its centre.  At that point, the crew would put in an airlock pressurise the deepest part of the tunnel and begin expanding the cavity.

What is needed is a minimalist mission concept, developed with off the shelf hardware and shown to be profitable on paper at least.  A mission with a starting mass in LEO of no more than 100te and from then on much smaller annual launches to sustain the base.

As the habitable internal cavity expands through mining, no doubt governments will be interested in buying or renting the space.  Agriculture on the surface of the asteroid could be expanded to support the growing base by reeling out poly tunnels.

Last edited by Antius (2015-09-18 12:01:54)

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#12 2015-09-18 12:03:27

Void
Member
Registered: 2011-12-29
Posts: 5,032

Re: Asteroids & Shells

http://www.space.com/30582-asteroid-min … lsion.html
APIS_ASTEROID.jpg?1442544639

I think a humble start.  (Actually this is quite ambitious).  Hope they pull it off!


Done.

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#13 2015-09-20 12:23:57

Void
Member
Registered: 2011-12-29
Posts: 5,032

Re: Asteroids & Shells

Just saying, that if you can graft your plans into the plans of others for asteroid mining, you very likely have something.  It is going to be very hard for social entities on Earth who for various reasons I will not explain want to put roadblocks in the way of human expansion into space, for them to put those roadblocks there on the basis of the potential existence of life.


Done.

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#14 2015-09-21 06:46:25

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

Re: Asteroids & Shells

Void wrote:

http://www.space.com/30582-asteroid-min … lsion.html
http://i.space.com/images/i/000/050/309 … 1442544639

I think a humble start.  (Actually this is quite ambitious).  Hope they pull it off!

I have an idea from this picture. What if you inflated a balloon half a kilometer in diameter around a small asteroid, then you got a giant mirror and focused sunlight on the asteroid to vaporize a part of it at a time, the asteroid being something like 50 meters in diameter in the center of this balloon. the asteroid material vaporizes and recondense on the inner surface of the balloon. as it expands outward from the asteroid it cools and it cools and solidifies on the surface of the balloon to build something like this:
External_view_of_a_Bernal_sphere.jpg
Or at least the sphere portion of it, we can cut holes in it as needed.

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#15 2015-09-27 21:58:41

Void
Member
Registered: 2011-12-29
Posts: 5,032

Re: Asteroids & Shells

I choose to stay in terraforming, noting that this post would be benefited by an efficient method to transport mined materials, especially one that uses throw mass potentially consisting of metal waste from space junk, or indeed metals from small worlds.  No need then, if this actually works, to bring Neon up from the surface of the Earth, (or Mars for that matter).

As for the Moon of Earth lots of Magnesium there I do believe.  (I am thinking advanced interplanetary shipping, in the more future view).


http://zeenews.india.com/news/net-news/ … 02935.html
http://techxplore.com/news/2015-09-ion- … iency.html

Ion space drive is said to break fuel efficiency record

Making note also that among those worlds could be small asteroids, and phobos and demos.

While Ion drive is slow, being efficient, can't be without value.

Anyway shell worlds, sending payloads out, using a metal based propulsion method.  This has to be something to keep an eye on.

And of course it would be valuable to have an efficient and convenient method to transport such a heavy object in the manner indicated previously:



http://zeenews.india.com/news/net-news/ … 02935.html
http://techxplore.com/news/2015-09-ion- … iency.html

Ion space drive is said to break fuel efficiency record

I would anticipate that local to the dome would be an artificial gravity machine as well.

Then having all that it could occur that as profits from mining accumulated, and speculation occurred, then indeed shell worlds, and the value of habitable real estate in the orbit of Mars, could be a real value added item.

Giant Machines!

Last edited by Void (2015-09-27 22:20:32)


Done.

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#16 2015-09-28 02:02:39

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

Re: Asteroids & Shells

The following are shell worlds:
Bernal_Sphere.png
alien2basteroid2bspaceship2bmars.jpg
6df3f9a7a6250a64492ab848ff52206c.jpg
space-colonies-collage.jpg
0.jpg

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#17 2016-02-03 06:28:43

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

Re: Asteroids & Shells

I revisited the shell world concept yesterday using my old spreadsheet programme.

Cometary bodies with a diameter of 10km and density close to that of water are hugely abundant in the Kuiper belt.  My question is: how deep down into such a body would one need to dig before the weight of the ice and rock overhead is equal to 10tonnes/m2 (i.e. 1 bar)?  The answer is about 4km. 

My spreadsheet suggests that a body the size of Halley’s comet could support an internal pressurised cavity 2km in diameter if pressure were 1bar.  For a cavity of this size, internal pressure would precisely match the force of gravity holding the hollow shell together.  If this interior void were decked out such that ceiling heights were 30m (100ft), then a low-gee habitable space of 140km2 could be created.

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#18 2017-10-30 06:01:51

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

Re: Asteroids & Shells

I solved the equation embedded in this document...
http://www.asterism.org/tutorials/tut38 … iation.pdf

...to calculated the pressure at the centre of Phobos.
https://en.wikipedia.org/wiki/Phobos_(moon)

It works out to be 59.5KPa, which is 0.58 atmospheres.  Therefore I would suggest that Phobos may be a useful potential shell world.  A shaft could be dug to the gravitational centre of the moon and an internal cavity could be mined out, which could then be lined and pressurised.  The excavated material could initially be used as reaction mass in mass driver impulse engines ferrying cargo between Earth and Mars.  With a breathable internal atmosphere, mining of the moon will be substantially simplified.

As mining excavates larger proportions of the moon, pre-stressing cables could be laid across its surface to ensure it remains intact against internal pressure.  These could also be made from excavated material.

A tower could be built to the L1 point some 3km above Stickney.  Mass driver tugs could dock here to take on reaction mass and offload people and payload.

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