# Thread: A Generation Ship - How big would it be?

1. ## A Generation Ship - How big would it be?

Thinking ahead and making a few very large assumptions - how big would a generation ship have to be to be successful? (First assumption - Success would be establishing a viable colony)

Other Assumptions:

• An earth like planet is found around a sun in our local group.
• A propulsion system is found which will accelerate a ship to some percentage of light speed (10-15%?)
• A way is found around the friction and radiation problems discussed in : http://www.bautforum.com/showthread....would-be-fatal
• The ship would carry a complete ecology
• A way is found to design the ship to protect against all forms of radiation

Of course the biggest assumption is that there would be a will to go, and that there would be a commitment to a project which would take several hundred years to complete.

But how big would this ship have to be? How many people would it have to carry? What resources would it also have to carry? What animals, and seed stocks would be a minimum?

2. The idea of a Stanford Torus seems like a great start, with regard to creating artificial gravity within a fairly large area, while still being able to utilise nearby stars to create the 24 hour day/night cycle. The problem is what you could do to simulate a star when travelling between stars.

The Stanford Torus, if it could be adapted, would carry approx. 10,000 people.

IsaacKuo has some fantastic ideas about space ships, so he might be able to point out all the problems with such a design. I imagine there are a lot of problems with this, since it's really an artifical habitat design intended for use orbiting a star, if I understand correctly.

Wonderful question though!

3. Originally Posted by Spoons
The idea of a Stanford Torus seems like a great start, with regard to creating artificial gravity within a fairly large area, while still being able to utilise nearby stars to create the 24 hour day/night cycle. The problem is what you could do to simulate a star when travelling between stars.

The Stanford Torus, if it could be adapted, would carry approx. 10,000 people.

IsaacKuo has some fantastic ideas about space ships, so he might be able to point out all the problems with such a design. I imagine there are a lot of problems with this, since it's really an artifical habitat design intended for use orbiting a star, if I understand correctly.

Wonderful question though!
Thanks Spoons. Would be great to get some feedback from IssacKuo too.

The Stanford Torus would have some draw backs in protecting the inhabitants from radiation, but certainly the artificial gravity would be required and a torus would seem to be the logical solution. Would 10,000 inhabitants be enough? It would have to last several generations to make it between stars. Would that provide enough genetic diversity?

I did see an idea that you can increase diversity with a stock of frozen embryos, and frozen eggs and sperm - but you still need mothers for these, unless we figure out how to do that artificially.

4. I saw IsaacKuo post recently, I think he was saying that basically, one of the key concepts was to design around the basis of building a ring-like structure, with the key element being to create a magnetic shield, and then to attach pods to the internal side of the ring structure.

The magnetic shielding sorts out the radiation problem (don't quote me, this is from memory, and my memory is worse than old rock revivals), and then you need some form of physical shielding for protection from asteroid-like objects.

I'll see if I can find the post I'm thinking of, because he's much better with words, concepts and all that jazz than little ol' me.

If you'd like his input, you could wait for him to find the thread, or you might like to try PM him to prompt some input. I'm not sure how kosher that is... who knows?

Would 10,000 people provide enough genetic diversity? Not sure, but we still have the Royal family alive and kicking. *ducks for cover after a supremely ign'ant comment*

5. Here is the post I was thinking of. You could try searching for other posts of his if you like.

6. A community needs on the order of 100 people to work, so it should hold that many (of course, that assumes controlled growth). A decent size (couple miles in diameter) asteroid could be hollowed out for the purpose. That would be space for a small town, with some left over for agriculture and wildlife. Of course, since the only closed community we have even tested is as big as the Earth (those biodomes required supplies to be brought in, the ISS needs supplies taken to it), we can't be totally sure. So some steps along the way include building an undersea or an Antarctica base that maintains its own food and oxygen.

7. Originally Posted by tdvance
A community needs on the order of 100 people to work, so it should hold that many (of course, that assumes controlled growth). A decent size (couple miles in diameter) asteroid could be hollowed out for the purpose. That would be space for a small town, with some left over for agriculture and wildlife. Of course, since the only closed community we have even tested is as big as the Earth (those biodomes required supplies to be brought in, the ISS needs supplies taken to it), we can't be totally sure. So some steps along the way include building an undersea or an Antarctica base that maintains its own food and oxygen.
I imagine the design of the ship will depend a lot on the propulsion, and shielding requirements - But yes I was imagining a tube or torus, a mile or more in diameter - and several miles long...

The human component is one consideration - and now we have ranges from 100 to 10,000. (With the example of the royal family..)

But a whole ecology would be required, wouldn't it? The ship would need everything from fungi and moss to trees and cows. How much would be the minimum? How big does the ship get to support this population?

8. I love the idea of these ships, I want to design one, one day.

Apparently there is a formal concept of minimum viable population in biology. I suspect that getting the ecology right would be the most complex part of the whole process. It might also set the lower limit to the size of your ship.

9. Here is a brilliant post, and a very good subsequent discussion on this topic:

Designing society for posterity

It concentrates on "human factor" -- it is relatively easy to design a ship which takes only 100 well-trained people to run, but how can you be sure next generation will be equally well-trained AND willing to keep births at just the right level?

If you can crank yourself up to 1% of light-speed, alpha centauri is more than four and a half centuries away at cruising speed. To put it in perspective, that's the same span of time that separates us from the Conquistadores and the Reformation; it's twice the lifespan of the United States of America.
We humans are really bad at designing institutions that outlast the life expectancy of a single human being. The average democratically elected administration lasts 3-8 years; public corporations last 30 years; the Leninist project lasted 70 years (and went off the rails after a decade). The Catholic Church, the Japanese monarchy, and a few other institutions have lasted more than a millennium, but they're all almost unrecognizably different.

Consumer capitalism along our current model simply won't work as a way of running a long-duration generation ship (the failure modes are lethal and non-recoverable). Communism (or rather, Leninism) has a slightly better prospect, but is still a long way from optimal. Monarchism is just a pretty word for "hereditary dictatorship supported by military caste". What are the alternatives? And what do we need to consider when designing a society that can survive for a 500-1000 year voyage in a bottle without exploding?

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Originally Posted by Atraveller
The Stanford Torus would have some draw backs in protecting the inhabitants from radiation, but certainly the artificial gravity would be required and a torus would seem to be the logical solution. Would 10,000 inhabitants be enough? It would have to last several generations to make it between stars. Would that provide enough genetic diversity?

I did see an idea that you can increase diversity with a stock of frozen embryos, and frozen eggs and sperm - but you still need mothers for these, unless we figure out how to do that artificially.
In short term circumstances (i.e. a couple generations,) it'll only take about 100 people to maintain genetic diversity. For long term (i.e. making an entire civilization just off those genes,) it only takes 300 people to create enough diversity to have no negative effects ever.

I think that for a Generation Ship-type interstellar ship, the best bet would be to take an asteroid, break it out of the Sun's orbit, and send it through interstellar space. Using some sort of lower power fusion reactor (not the ramjet design, though if the flaws were worked out with that, it'd work,) to power everything that the resident humans and their Earth life friends would need.
So for that kind of action, perhaps take a mid-sized asteroid and use pre-learned paraterraforming and asteroid colonizing techniques to create an entire self-sustaining system out of it. Have enough room for a couple thousand humans and then some, room for every single plant and animal on Earth, and make sure it can be self sustainable so the colonists will have as much time as they want to finally get down to whatever planet they want in the system (or there might not even be one, though we'd probably make sure.)

11. Originally Posted by Ilya
Here is a brilliant post, and a very good subsequent discussion on this topic:

Designing society for posterity
Good post on your part, but I don't like his ideas. Apparently hard work, efficiency, and capitalism are bad things that would cause us to be at each others throats before too long. And if we somehow survived that, the ship would explode.

Having said that, I'm all in favour of a Naval approach, including lashes of rum and, well, lashes. A huge brig is the first thing that should be built.
Last edited by PraedSt; 2010-Apr-09 at 11:05 PM.

12. Originally Posted by Spoons
The Stanford Torus, if it could be adapted, would carry approx. 10,000 people.

IsaacKuo has some fantastic ideas about space ships, so he might be able to point out all the problems with such a design.
I actually like the idea of a torus shaped starship. My preference is for a magnetic loop with 2-3 spherical modules strung along it like necklace beads. However, this does not provide a lot of living space, overall. A torus would provide maximum usable volume, since the zone protected by the magloop's magnetic field is indeed torus shaped.

Instead of a single magloop running through the center of the torus habitat, you'd use several external magloops around the outside.

13. That said, the idea of using a torus shaped magnetic field for protection only really applies to relativistic starships--the sort that only need a decade or two to reach the destination.

For a "generation ship", or space colonies in general, I tend to prefer spheres. Partly, this is because of the elegance of a sphere. Partly, it's because it's so easy to calculate the volume and usable area of a sphere. Partly, it's because a sphere is the most efficient shape in terms of air pressure structure and radiation shielding requirements. It's actually quite shocking how much heavier an almost sphere-like cylinder with rounded endcaps needs to be compared to a sphere.

The problem is that if the entire structure is spun up for artificial gravity, this places a pretty hard limit on your overall radius. Depending on the specifics, this radius may be a just a few kilometers. One idea I came up with to get around this problem is to not spin most of the colony. Instead, the colony has numerous internal "gravity drums". These may be 500m in diameter and they provide places high levels of artificial gravity.

Things depend a lot on your personal preferences. I like dense cities, like New York. At a living density similar to New York, you can have a spherical habitat only 20km in diameter with a population similar to that of Earth, today. Imagine an entire world full of people, and it only takes minutes to travel from one end to the other! But other people like the idea of expansive living spaces. Obviously, this reduces the potential population for a given volume...

14. Originally Posted by PraedSt
Good post on your part, but I don't like his ideas. Apparently hard work, efficiency, and capitalism are bad things that would cause us to be at each others throats before too long. And if we somehow survived that, the ship would explode.

Having said that, I'm all in favour of a Naval approach, including lashes of rum and, well, lashes. A huge brig is the first thing that should built.
As Mr Stross mentioned, humanity hasn't had great success in creating institutions that last more than a couple of generations, and none of them have had to contend with the fact that there's no outside. See, for example, Jared Diamond's book Collapse, where the people of Rapa Nui, probably the most isolated human society since the invention of agriculture, pretty much killed themselves off. See this article.

Hopefully, by the time we can launch a generation ship, we'll have had some experience with self-sustaining off-planet habitats, because some of may developed a successful long-term isolationist culture.

15. Originally Posted by swampyankee
As Mr Stross mentioned, humanity hasn't had great success in creating institutions that last more than a couple of generations, and none of them have had to contend with the fact that there's no outside.
Conversely, all of them have had to contend with the fact that there is an outside. It's hard to maintain your cultural identity if you have to deal with the influence of the superpower du jour. Even if they aren't physically invading your town, they're trading goods and enticing the young to venture out of town to where the economic opportunities are.

16. Originally Posted by PraedSt
I love the idea of these ships, I want to design one, one day.

Apparently there is a formal concept of minimum viable population in biology. I suspect that getting the ecology right would be the most complex part of the whole process. It might also set the lower limit to the size of your ship.
Wiki seems to think minimum viable population - with a 95%+ survivability for between 100 and 1000 years would be 4169 individuals. Sort of half way in the middle of the 100 - 10,000 we were tossing about before.

The other question is population growth - in near terms we are looking at a doubling of human population every 20 or so years. This would make the population of our generation ship more than 100,000 in 100 years - obviously some population growth controls would have to be part of the society.

But what about the chickens, cows, pigs, goats, etc that would be needed to feed this population - do we need 4169 of each of them too? Or will they all be kept freeze dried until the destination is reached?

Either way the ship is becoming increasingly large... More like a small moon than an asteroid...

17. Originally Posted by Atraveller
But what about the chickens, cows, pigs, goats, etc that would be needed to feed this population - do we need 4169 of each of them too? Or will they all be kept freeze dried until the destination is reached?

Either way the ship is becoming increasingly large... More like a small moon than an asteroid...
Well you did want a complete ecology. That's complicated

18. Originally Posted by swampyankee
As Mr Stross mentioned, humanity hasn't had great success in creating institutions that last more than a couple of generations, and none of them have had to contend with the fact that there's no outside. See, for example, Jared Diamond's book Collapse, where the people of Rapa Nui, probably the most isolated human society since the invention of agriculture, pretty much killed themselves off. See this article.

Hopefully, by the time we can launch a generation ship, we'll have had some experience with self-sustaining off-planet habitats, because some of may developed a successful long-term isolationist culture.
That's why we need the lash and brig!

My main grouse (see above) is that he advocates a slovenly crew, but I'm also sure he's got his societies, institutions and individual entities all mixed up. Individual entities do have short life spans, but the underlying institutions have much, much longer life spans. Societies, which are one step higher than institutions, last even longer. He also seems has a problem with institutions evolving through time, and I can't understand why.

Having said that, we do have to find a way of stopping intra-ship war. But that brings us back to the lash...

19. Originally Posted by Atraveller
Either way the ship is becoming increasingly large... More like a small moon than an asteroid...
Well, let's suppose you want a starship with a ground area and population similar to Great Britain--219,000 square kilometers and a population of 60 million. If you can get the floor spacing down to 10m, then you need 2190 cubic kilometers, or the equivalent of a sphere with radius of only 7.2km. That would be about the size of Deimos.

If we scale things down to a population of only 100,000, then the required size goes down to a radius of only 860m. Bear in mind that this is assuming a population density similar to Great Britain--including all of the farmland and back country, etc.

20. Originally Posted by IsaacKuo
Well, let's suppose you want a starship with a ground area and population similar to Great Britain--219,000 square kilometers and a population of 60 million. If you can get the floor spacing down to 10m, then you need 2190 cubic kilometers, or the equivalent of a sphere with radius of only 7.2km. That would be about the size of Deimos.

If we scale things down to a population of only 100,000, then the required size goes down to a radius of only 860m. Bear in mind that this is assuming a population density similar to Great Britain--including all of the farmland and back country, etc.
That is quite surprising, and I had to go through your calculations twice before I was satisfied you were quite correct. Amazing to think the population density of GB is 1 person per 4m^2.

But - You are assuming the use of the entire interior surface... Won't the poles be unuseable? The sphere is going to have to rotate to simulate gravity, and only the equator will have full gravity. Wouldn't an elongated spheroid be better? Stretch the useable area at the equator?

21. Originally Posted by Atraveller
That is quite surprising, and I had to go through your calculations twice before I was satisfied you were quite correct. Amazing to think the population density of GB is 1 person per 4m^2.
You mean 1 person per 4,000m2. A square kilometer is equal to a million square meters, not a thousand square meters.
But - You are assuming the use of the entire interior surface... Won't the poles be unuseable? The sphere is going to have to rotate to simulate gravity, and only the equator will have full gravity. Wouldn't an elongated spheroid be better? Stretch the useable area at the equator?
Assuming simple spin gravity, you would have practically zero gravity along the centerline, gradually increasing to maximum gravity at the equator. But I figure that the central areas can be used for zero/low gravity "farmland", power systems, general storage, and other things which don't mind (or even benefit) from low gravity. Keep in mind that even though the usable area is similar to Great Britain, the transport distances are much less--only 7km to get from a central water processing system all the way to the outer rim.

The amazing potential of deeply "shelled" space colonies is why I disdain the idea of "hollow" colonies which emulate terrestrial suburbia. When your habitat has 700 floors, you can fit so much more in!

22. Originally Posted by Atraveller
But - You are assuming the use of the entire interior surface... Won't the poles be unuseable? The sphere is going to have to rotate to simulate gravity, and only the equator will have full gravity.
To help visualize things, the "surface" isn't really what's being used. The bulk of the colony consists of self-supporting concentric cylindrical floors, with numerous bulkheads and/or columns between them to maintain proper spacing. The cylindrical floors support themselves against artificial spin gravity via hoop tension.

It's like a sphere carved out of a tree trunk...the tree rings are the floors, nested within each other.
Wouldn't an elongated spheroid be better? Stretch the useable area at the equator?
I used to favor a "stubby" cylinder shape, with rounded caps. But then I found out that a sphere is about half the mass as a cylinder for a given volume and pressure. As such, it makes more sense to put a "stubby cylinder" within an even larger sphere...simply wasting the extra volume between them. The bounding sphere has a bit more surface area, but much less mass because it's only about half as thick.

Of course, it seems a shame to simply waste that extra volume...it might as well be filled in with floors also, even though the artificial gravity level will be a bit high.

A slightly flattened spheroid would be ideal, because it minimizes the mass of the outer pressure shell.

23. Originally Posted by IsaacKuo
You mean 1 person per 4,000m2. A square kilometer is equal to a million square meters, not a thousand square meters.

Assuming simple spin gravity, you would have practically zero gravity along the centerline, gradually increasing to maximum gravity at the equator. But I figure that the central areas can be used for zero/low gravity "farmland", power systems, general storage, and other things which don't mind (or even benefit) from low gravity. Keep in mind that even though the usable area is similar to Great Britain, the transport distances are much less--only 7km to get from a central water processing system all the way to the outer rim.

The amazing potential of deeply "shelled" space colonies is why I disdain the idea of "hollow" colonies which emulate terrestrial suburbia. When your habitat has 700 floors, you can fit so much more in!
Pesky thing a "k" - miss one and the result looks completely different...

The concentric decks make perfect sense - and using the poles to store water (and other supplies and resources) might be an idea - they then become naturaul shields to augment your magnetic field.

But wouldn't some open space be required? Otherwise the generation that get to the new planet will be agorophobic...

24. Originally Posted by Atraveller
Thanks Spoons. Would be great to get some feedback from IssacKuo too.

The Stanford Torus would have some draw backs in protecting the inhabitants from radiation, but certainly the artificial gravity would be required and a torus would seem to be the logical solution. Would 10,000 inhabitants be enough? It would have to last several generations to make it between stars. Would that provide enough genetic diversity?
I use a torus in my starship design

These are the mass catchers. They ride on top of the ship during the acceleration phase. During the coasting part, they move ahead of the ship. They're equipped with sensors and laser cannons to ionize oncoming debris.

Riding behind the mass catchers is this star ship:

The top part is a spinning toroidal hab (you will notice that, like the mass catchers, this also has sensors and laser cannons on its roof. Redundancy is a sensible policy.)

Just below the spin hab is a garage that contains landers, probe vehicles and other stuff.

Then a long rod to put some distance between vulnerable humans and the engine.

Then radiator fins to dump waste heat from engines.

Then the propellent tank. Most of the initial mass of the space ship is propellent.

Then at the bottom is a fusion reactor and rocket engine. Fusion is one of the schemes to achieve the necessary propellent exhaust velocity.

25. Originally Posted by Atraveller
But wouldn't some open space be required? Otherwise the generation that get to the new planet will be agorophobic...
Personally, I think it would be awesome if no one ever colonizes a planet. I personally would rather live in one of these space colonies than on a planet. I'm imagining an entire world full of interesting niches and "back alleys" and cultures and it only takes a few minutes to travel anywhere to visit or enjoy a meal.

So according to my vision, the colonists would be moving into more space colonies--constructed using materials from the destination star system.

But, if anyone wants to try and colonize a planet, they can take a shot at it.

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Originally Posted by Spoons
The idea of a Stanford Torus seems like a great start, with regard to creating artificial gravity within a fairly large area, while still being able to utilise nearby stars to create the 24 hour day/night cycle. The problem is what you could do to simulate a star when travelling between stars.

The Stanford Torus, if it could be adapted, would carry approx. 10,000 people.
Studies done in the 70s show that 1 rpm at 1 G is best for humans, so whatever diameter is required for that would be ideal. But it's unbelievably large. Thus, 3 rpm at .8 G provides for the smallest acceptable design which, combined with weight/resistance training, would allow generations of humans to retain their 1 G physiology.

My concern is one of disease. A lot of people talk about simply screening well, but I see two problems with this idea:

1. You can't screen for the thousands of organisms we naturally harbour, and sooner or later one of those in someone will mutate into something a bit more problematic.

2. If you try to insulate against everything, by the time the nth generation arrives, their immune systems will be very weak, perhaps far too weak to survive landfall.

The other issue is one of quarantine. Thus, I propose three independant rings, one spinning counter to the other two. All three would share the same axis, and the propulsion would be slight, perhaps 1/10th of a G, along that axis. Basic fixtures including floors, tables, countertops, and beds should be adjustible to counter the slight difference between rotational gravity and that induced by thrust.

I think there should be quaranteen zones between the rings, perhaps 2 weeks, maybe a month, which would allow people to mix things up while protecting the rings from one another. Naturally, each ring should have a fully viable flora and fauna, but varied i.e. you might find aardvarks in Ring 1, but only Ring 1, while Ring 2 would be the primary for, say, antelope. Then again, perhaps each species should be kept in 2 of three rings, but not the third.

27. Originally Posted by mugaliens
Studies done in the 70s show that 1 rpm at 1 G is best for humans, so whatever diameter is required for that would be ideal. But it's unbelievably large.
Not really--that's a radius of only 900m, or a diameter of less than 2km.

This matches well with my example 100,000 person colony with a radius of 860m. I'm thinking that a much lower level of artificial gravity should be doable, though.
My concern is one of disease.
I don't think we have sufficient experience to make a good robust plan against disease on these time scales.

My preference is to err on the side of bigger-is-better for a baseline idea, with an understanding that the actual minimum practical size should be much smaller. That's why I give the example of a Great Britain scale colony--7.2km radius for a population of 60 million.

The plan against disease? Let the residents deal with it...hopefully they'll figure out how to deal with it effectively. If not, then a country the scale of Great Britain should be able to "absorb" losses to disease, with enough survivors to repopulate the colony.
The other issue is one of quarantine. Thus, I propose three independant rings, one spinning counter to the other two.
Why independent rings, with counter-rotation? It would be simpler and more efficient to just partition the colony into quadrants--thick slabs of structural steel (the same sort of steel as the outer hull) will be enough of an obstacle.

I'm wary of the idea of setting up such isolated environments, though. One of the causes for nasty diseases is isolation--one population builds up immunity to the local diseases, but then inter-population travelers bring these diseases to populations with no immunity.

28. Originally Posted by IsaacKuo
Not really--that's a radius of only 900m, or a diameter of less than 2km.

This matches well with my example 100,000 person colony with a radius of 860m. I'm thinking that a much lower level of artificial gravity should be doable, though.
That all seems to work out quite nicely - A 860m (r) Sphere rotating at about 1 RPM will give us about 1 G. If there are concentric decks filling the outer half of that - we would get 80 - 100 decks... The inner deck would still have about 1/3 G (some one want to check my math? I've already proven that is a weak point...:~) And there could still be some open area to "fly" (ie. play) in, and to help avoid agoraphobia.

Fusion might well end up being the power source as Hop_David suggested - but I would hope a better system could be developed. Is some form of a Bussard ram jet possible, using the centre core of the sphere, and providing magnetic shielding at the same time?

I wouldn't be terribly worried about disease "developing". The number of species and individuals, although intended to give genetic diversity, and a full ecology, would not be large enough to provide the kinds of numbers required to develop a new strain of disease...

And, although it might be interesting to live in a ship of this type, I do think the human race needs to think about long term survival - and it ain't going to happen if with stick to just this rock... ( If we do not succeed, then we run the risk of failure. - Dan Quayle )

29. Originally Posted by mugaliens
Studies done in the 70s show that 1 rpm
Later studies indicate that the humans can grow accustomed to higher rpms

http://chamberland.blogspot.com/2006...l-gravity.html

http://www.graybiel.brandeis.edu/his...lthamnews.html

http://www.graybiel.brandeis.edu/his...lfrontier.html

http://www.ncbi.nlm.nih.gov/pubmed/14501105

http://jn.physiology.org/cgi/reprint/80/2/546.pdf

Originally Posted by mugaliens
at 1 G is best for humans,
Actually, this is not known. Can Martian gravity keep healthy? Lunar gravity? This is one reason why LEO spin gravity labs should be a top priority. We should determine if humans can do long term stays in those places before we try to establish permanent bases.

This could also save us a lot of money when designing spin habs for minimum gravity to keep us healthy.

If we can endure 4 rpms and lunar gravity, adequate spin habs could be made with vastly smaller radius and vastly less expense than the behemoth Stanford tori the antiquated 70's studies seemed to mandate.

Getting back to star ships, If various fractions of gravity all work equally well to keep humans healthy, the spinning torus in the star ship could be multi level. The levels closer to the center would have fractional G, but they'd still serve to house humans.

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Aside: Given the fact that a simple ESC hit reduces all that I spent half an hour typing, this will be brief. And, arg - can the Admin of this system kindly turn off this function? Thank you.

In the meantime, it's back to typing in notepad before copying and pasting here. Arg.

Originally Posted by IsaacKuo
Not really--that's a radius of only 900m, or a diameter of less than 2km.

This matches well with my example 100,000 person colony with a radius of 860m. I'm thinking that a much lower level of artificial gravity should be doable, though.
Given the fact that this would be roughly 20,000 times the volume of the ISS, I'll stand by my original description of it being "unbelievably large."

Onto the executive summary:

The radius of a 1G, 1 rpm torus is 894.56 m, and has a circumference of 5,620.72 m.

However, on further research, it appears nearly everyone quickly gets used to a 2 rpm spin. However, "nearly everyone" isn't everyone, so let's compromise and call it a 1-1/3 rpm, in membrance of our old 33-1/3 vinyl records, for a radius of 503.2 m, and a circumference of 3,161.7 m.

Assuming a width 20% of the radius, that's 100 meters, for a net cross-sectional deck width of 785 ft, which, interesting, happens to be the roughly 800 square feet per person I was shooting for, so, given the roughly 10,000 foot radius, that's about 10,000 people per ring. Times three rings, that's a population of 30,000 people.

I don't think we have sufficient experience to make a good robust plan against disease on these time scales.
I don't think we do, either, which is the justification behind my separating this into three rings, each fully functional without any input from the other two, but with routine crossflow of personnel, but buffered by quaranteen (isolation) chambers.

My preference is to err on the side of bigger-is-better for a baseline idea, with an understanding that the actual minimum practical size should be much smaller. That's why I give the example of a Great Britain scale colony--7.2km radius for a population of 60 million.
I think planning for something which would hold three times the population of the mean of the world's three largest cities is rather extraordinary. And it's too many eggs in the basket, so to speak. We must remember than between 500 and 300 years ago, colonies set forth here on this Earth, for which we were supremely adapted, and yet many of the colonists did not survive. Indeed, entire colonies did not survive. We must plan for the contingency that these first peoples will indeed be colonists, who must be taught from the get-go the most advanced survival skills, even if it's learning how to survive by diving 30 feet beneath the waves to munch on the worst-tasting, but life-supporting scum growing on the rocks below the first 20 feet, which happen to be poisonous. No doubt if they do survive they'll figure out a way to turn it into an English muffin, scones, and tea, but in the meantime, we have to prepare them for the worst - for survival in the harshest of conditions.

From a survival standpoint (not the tv show, counfound it) the failure of Jamestown was a disgrace given the abundance of four-season food sources along the Eastern seaboard and the originally friendly natives.

The plan against disease? Let the residents deal with it...hopefully they'll figure out how to deal with it effectively. If not, then a country the scale of Great Britain should be able to "absorb" losses to disease, with enough survivors to repopulate the colony.
Not if it takes 200 years to reach their destination. Again, that's why I proposed the three-ring system. Let's add a system of government similar to our own tricameral system, whereby no one ring would ever be able to harm another, and whereby any vote of two rings would be able to "pull the teeth" on a third ring bent on destruction, but even then, never be able to harm it. Thus, at worse, you'd have all three rings arriving intact at destination, even though they've be fuming.

That's possibly a worse scenario, but I know I and half a dozen guys here could figure out grassroots ways of disabling another ring in a hurry, so it's pretty much a pipe dream...

...hence the cross-cultural flow between the rings I was talking about. It's very important to keep this alive. In fact, it might be best to enforce it every couple of months, save for marriage, but with full and unfettered communication between the rings.

Why independent rings, with counter-rotation? It would be simpler and more efficient to just partition the colony into quadrants--thick slabs of structural steel (the same sort of steel as the outer hull) will be enough of an obstacle.
That's doable, as well, with quaranteen buffer zones between them, where the people can continue their work, their research. I'm thinking, though, it may be best to simply separate the population between three rings with some significant distance between them, as well as various protcols, not unlike the system of passports and entry/exit control systems we have today.

Some might decry these systems. Some may raise holy hell against these systems. Keep in mind, though, that they're not designed to hamper progress, but rather, to protect it against the very few who, gone berserk, would seek to either destroy the system, or at least undermine it?

Seriously! We're talking a multigenerational design, here. A mother and father could pass all psychological, interrelational, and observed interactions tests, with flying colors while their offspring may prove to be a pain in the arse!

Perhaps it would be best to select for compliance, whereby in one's family history, if there's any uprising against authority of any kind, it's a key for non-selection.

Sadly, this proves to be an interesting, but delicate balance for survival. There are some, but only some, who can survive all extremes while maintaining the utmost of human civility i.e. no cannabalism, extortion, coercion, threats, manipulations, etc.

That percentage of the human population, people, is less than 1%.

Furthermore, most people, is that really the caliber of person which is required?

Er, no. It's a different mindset altogether which can be thrust into an unfamiliar land and make do with anything and everything possible, including diving 30, if not 100 ft just to scrape food from rocks.

I'm wary of the idea of setting up such isolated environments, though. One of the causes for nasty diseases is isolation--one population builds up immunity to the local diseases, but then inter-population travelers bring these diseases to populations with no immunity.
Hence my controlled interoperational cycle. Quaranteen wouldn't eradicate disease, but would allow it to progress through the colonies in a controlled fashion, allowing most members to build up immunity, and yes, for some to die.

I know that's a hard thing. Trust me when I say that I know this when a commanding officer once looked at the bunch of us, asked us to look left and right, then said, "one of the three of you will die in the next three years."