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

  1. #91
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    A Generation Ship - How big would it be?

    Hi Matt and welcome to the forum. Just so you know, Issac hasn't posted on Cosmoquest for more than two years so there is a fair chance that he may not see your question in this thread that was started more than eight years ago.
    Last edited by schlaugh; 2018-Nov-05 at 10:41 AM.

  2. #92
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    About 100 is the minimal number
    https://arxiv.org/abs/1806.03856

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    Quote Originally Posted by PraedSt View Post
    I phrased my question wrong. Where did you think I suggested to "keep them ignorant"? I suggested hard discipline. I fail to see the connection.
    Most of the anti-authoritarian revolutions of the 19th Century involved a) groups subject to “hard discipline” and b) educated groups without power.

    Or one can look at something like the Spithead Mutinies, peasant revolts, and urban riots caused by harsh policing.
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  4. #94
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    A genship size and crew mix depends on the length of the journey and the speed it goes. It will need to be as close to a fully self-supporting, closed system as physically possible, ecologically and industrially. That would require enormous mass.

    One factor that will not be an issue, is that there will be no "return trip" for a crew born en route, strangers to Earth. Likewise, it is not going to be a pure-science mission; they are going to live wherever the destination is, for better or worse. At the very worst, they will just stay on the ship and mine the destination system for resources.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

  5. #95
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    Quote Originally Posted by Matt456 View Post
    hi Isaac I like the idea of dense living also but when you say you could have a population similar to earths living in a 20km diameter what size population do you mean
    You might try to contact him through Skype or the other contact references shown in his posts, but let's see what you could do with a 20 km diameter sphere: That's a 10,000 meter radius sphere, so solving for volume, or about 4.19 trillion cubic meters. Divide by 7.5 billion people, and if I did all my math right, that's about 559 cubic meters per person. That sounds a bit tight to me per person when you figure in things like food, water and air recycling, structure, dealing with waste heat and various other issues (I assume power would be supplied from the outside), but technically you could apparently fit the world's population into something of that volume.

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  6. #96
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    Quote Originally Posted by Van Rijn View Post
    about 559 cubic meters per person. That sounds a bit tight to me per person when you figure in things like food, water and air recycling, structure, dealing with waste heat and various other issues (I assume power would be supplied from the outside), but technically you could apparently fit the world's population into something of that volume.
    So, a single cubicle with all the resources for a single person for an indefinite period would be about 8.25m on a side.
    Yeah. That seems pretty small.

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    Quote Originally Posted by DaveC426913 View Post
    So, a single cubicle with all the resources for a single person for an indefinite period would be about 8.25m on a side.
    Yeah. That seems pretty small.
    Downright cozy. It makes me think of Robert Silverberg's The World Inside. (People live in giant towers on Earth, with essentially no privacy) Off hand, I'd think a population of 7.5 million might make more sense - depends on how much volume is needed for food/air/etc. production and recycling, maintenance. Then too, sections could be spun for artificial gravity - without a bit of genetic engineering, I doubt regular humans will do well in permanent microgee environment. Spin gravity sections would also reduce usable volume.

    Though most of the recycling and food production spaces may be kept separate from where the human population would be, and there might be ways to make, for instance, volumes for plants very space efficient.

    Still and all, it's interesting to see what you get when running the numbers.

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    Kids raised on a genship will never want to stand on a planet, with open space all around and a floor that curves the wrong way.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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    thanks for the info I am interested in the science of generation ships there design etc most sci fi designs are aerodynamic when they don't need to be and do things like completely ignore the law of thermodynamics

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    I'm interested in the hard science of generation ship design and construction most people have genships that are sleek and aerodynamic when they don't need to be but ignore things like creating an artificial gravity for the passengers or the law of thermodynamics I welcome any input

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    Quote Originally Posted by Matt456 View Post
    I'm interested in the hard science of generation ship design and construction most people have genships that are sleek and aerodynamic when they don't need to be but ignore things like creating an artificial gravity for the passengers or the law of thermodynamics I welcome any input
    Unfortunately, at this point we can discuss some of the things that would be necessary, but we have a long way to go to get there. Right now, environmental support systems have limited closure (in the 60% or so range) and there has been little attempt to produce food for spacecraft. Realistically, a generation ship would need extremely high closure if it's not to carry a ridiculous amount "make up" mass, and it would need to be stable - something like a crop failure could be deadly. We would need most of the same technology for interplanetary colonization, so I'd expect we'd get some experience before anyone ever tried to build an actual interstellar generation ship.

    And then, of course, the crew would need to be able to keep the hardware running and be able to build habitats or more generations ships at the end of the journey. It's unlikely there will be any true earth twins, so for there to be a point to a generation ship, they would need very flexible and capable manufacturing capability. That's another thing I expect we would first learn if we expand into the solar system.

    A fission reactor could supply long term power, but there would be design issues for something that would run for centuries. I could imagine something like an advanced breeder reactor using structural materials that don't easily become radioactive. Fusion reactors are also a possibility, but that gets into even more future technology issues.

    And then there's the propulsion issue. Unless we're willing to settle for travel times between stars of tens of thousands of years, we'll need significantly better propulsion. Getting up to a few percent of the speed of light, especially for a massive generation ship, is hard. Mass ratios for rocket systems can become ridiculous, especially considering it would need to slow down again at the destination.

    I think it's safe to say we aren't going to see generation ships any time soon. It isn't even just the technology - assuming the basic technological issues are resolved, you'd probably want to test for decades (at least) while still in the solar system to see if long term problems would come up. There would also need to be some interesting social experimentation to try to find how an on-board population could have a long term stable society.

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  12. #102
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    Quote Originally Posted by PraedSt View Post
    That's why we need the lash and brig!
    And thus presumably an autocratic leadership.

    My main grouse (see above) is that he advocates a slovenly crew,
    He was advocating having a safety margin. That is why many things are designed to be much stronger than what they might seem to need to be. Are you advocating having barely enough crewpeople to do the work that needs to be done to maintain the ship?

    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.
    The problem with evolving over time is that a generation-ship society may go off-mission, as one might say. Its members may end up using up the ship's consumables too fast or lose interest in living on planet surfaces.

    Some societies have indeed been very long-lived, but they have gone through a lot of changes over their history.

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    Quote Originally Posted by PraedSt View Post
    Good post on your part, but I don't like his ideas. Apparently hard work, efficiency, and capitalism are bad things ...
    So easy work is a sin? Also, if work for the sake of work is good, then one ought to dig holes and then fill them up again.

    As to keeping the crewpeople ignorant, it would be keeping them ignorant of their mission, and maybe even ignorant of their being aboard a generation ship. Something like Star Trek TOS "For the World is Hollow and I have Touched the Sky".

    An extension of this approach is some outright falsehood, something like Plato's Noble Lie. It is from Plato's Republic, written about 2400 years ago, and likely the oldest surviving utopian tract, a description of an ideal society. This Republic was to have an official religion that Plato called a "noble lie" (gennaion pseudos). It was designed to "demonstrate" the legitimacy of its political and social system. According to it, the philosopher-ruler guardians are made of gold, the soldiers of silver, and the common people of brass and iron, and the hierarchy of value of these metals shows what the social hierarchy is to be. The stories of Plato's society's religion were to be banned as full of bad examples like heroes lamenting and gods laughing. Theater was to be banned because virtuous male actors would have to play villains and women. Movies and TV shows were over two millennia in the future, but they are essentially high-tech forms of theater. People are to be brought together to be married by lot, but what seems like random drawing will be rigged behind the scenes by the guardians on eugenic principles. Like what one does with farm animals.

  14. #104
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    Quote Originally Posted by Matt456 View Post
    I'm interested in the hard science of generation ship design and construction most people have genships that are sleek and aerodynamic when they don't need to be but ignore things like creating an artificial gravity for the passengers or the law of thermodynamics I welcome any input
    I have not seem any such examples, except the fictional genship used in ads for the Ascension miniseries. Most proposed designs by engineers and scientists are basically mobile space stations with spin gravity, and modular design based on the necessities of the propulsion system.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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    I think that a serious and underappreciated problem is maintaining the technical expertise necessary for maintaining the ship and for colonizing some suitable destination planet.

    Only a small fraction of people ever seem to get very good at advanced technical sorts of things, and for a small total number of people, the number of technically skilled people is like to get dangerously small, if it stays nonzero. If only 1% of the population gets very technically skilled, then one needs much more than 100 people to have a good community of technical experts, at least 1,000 or 10,000 people. Those numbers give 10 to 100 technical experts.

    I think that we need a community of such people, and that means at least 10 and likely 100. So that means 10,000 people.


    Ten Thousand Years of Solitude | DiscoverMagazine.com
    The curious case of the people who forgot how to fish - Filthy Monkey Men
    Why did the Tasmanians Stop Eating Fish? | ScienceBlogs

    They were some 5,000 people who lived in isolation from the rest of humanity from when their mainland connection was drowned by melting Ice-Age glaciers to when Europeans arrived. Along the way, they lost fishing and bone tools, despite their obvious utility and despite these people not having improvements on them. But they nevertheless survived until European settlers arrived, and they still used fire and stone tools and animal skins.

    To the north of Tasmania is Flinders Island, inhabited by some 400 people until around 4,500 years ago, when they all died out.

    So that's actually happened.

  16. #106
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    Quote Originally Posted by lpetrich View Post
    I think that a serious and underappreciated problem is maintaining the technical expertise necessary for maintaining the ship and for colonizing some suitable destination planet.

    Only a small fraction of people ever seem to get very good at advanced technical sorts of things, and for a small total number of people, the number of technically skilled people is like to get dangerously small, if it stays nonzero.
    I doubt generation ships will be feasible without automation that can handle most of the detailed technical issues. I'd expect humans to take more of a high level managerial role, with the machines handling most of the work.

    In fact, I suspect that probably faster and smaller scout robot ships would first visit a new star system, then people back around Sol would decide where to put a habitat (perhaps on a planet, perhaps in orbit around some world) and would then send a more sophisticated robot mission to build it. Generation ships could then be sent after it was already established that a habitat was available in the system.

    "The problem with quotes on the Internet is that it is hard to verify their authenticity." — Abraham Lincoln

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  17. #107
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    Quote Originally Posted by Van Rijn View Post
    I doubt generation ships will be feasible without automation that can handle most of the detailed technical issues. I'd expect humans to take more of a high level managerial role, with the machines handling most of the work.
    I suspect that that's the most successful possible solution. I also suspect that that will be very feasible if generation ships ever become feasible.

    A generation ship will also have something that the Tasmanians never had -- a huge library, complete with lots of video. So the people of such a ship will not be starting from scratch when they reach their destination.

  18. #108
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    Quote Originally Posted by lpetrich View Post
    I think that a serious and underappreciated problem is maintaining the technical expertise necessary for maintaining the ship and for colonizing some suitable destination planet.

    Only a small fraction of people ever seem to get very good at advanced technical sorts of things, and for a small total number of people, the number of technically skilled people is like to get dangerously small, if it stays nonzero. If only 1% of the population gets very technically skilled, then one needs much more than 100 people to have a good community of technical experts, at least 1,000 or 10,000 people. Those numbers give 10 to 100 technical experts.

    I think that we need a community of such people, and that means at least 10 and likely 100. So that means 10,000 people.
    That's assuming a random selection of people and no social planning. A Navy crew would be a better comparison, train people to perform the necessary tasks. For instance, everyone aboard a submarine has a Qual-card, to let them cross train on repairing and maintaining every piece of equipment for Damage Control.
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    Quote Originally Posted by Noclevername View Post
    That's assuming a random selection of people and no social planning. A Navy crew would be a better comparison, train people to perform the necessary tasks. For instance, everyone aboard a submarine has a Qual-card, to let them cross train on repairing and maintaining every piece of equipment for Damage Control.
    That works for the original crew. What about the great-great grandchildren?
    Information about American English usage here and here. Floating point issues? Please read this before posting.

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    Actually they can't: "Heavier-than-air flying machines are impossible." - Lord Kelvin, president, Royal Society, 1895.



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    Quote Originally Posted by swampyankee View Post
    That works for the original crew. What about the great-great grandchildren?
    ...Same answer. Raise and train them to perform all the necessary tasks. Don't let random chance determine what gets done.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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    I'd recommend a generation ship consist of multiple population groups or modular "cities", each capable of existing independent of the others. And each module should carry a large surplus of organics and volatiles to support a failed neighbor if necessary.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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    Quote Originally Posted by Noclevername View Post
    ... A Navy crew would be a better comparison, train people to perform the necessary tasks. ...
    Quote Originally Posted by swampyankee View Post
    That works for the original crew. What about the great-great grandchildren?
    Quote Originally Posted by Noclevername View Post
    ...Same answer. Raise and train them to perform all the necessary tasks. Don't let random chance determine what gets done.
    But some things may be difficult for many people to learn, like higher mathematics. Even algebra seems to be very difficult for many people. I recall that some people trying to learn computer programming cannot understand what a variable is. So in a small population, something could drop out if only a small fraction of the population can easily learn it.

    That's where a big library can come in handy, because it can fill in gaps in our memory. Like show how to do things that one may not have to do very often, and show how to colonize a destination world.


    I must note that some people claim that the Tasmanians did not really lose anything, because we have lost a lot of technologies over our history. But that is a very bad analogy, because most of those losses were the result of having something better in some ways. Our Paleolithic and Neolithic ancestors made knives and similar tools by knapping, hitting some suitable rocks with other rocks to knock off pieces of them. Only a few kinds of rock are suitable for that, kinds like flint and obsidian. But when we learned how to make hard-enough metals, like bronze, that technology was abandoned by everybody who could get metal knives. Bronze itself fell on the wayside when iron smelting was invented. In another example, hornbooks got their name from being covered with thin layers of animal horn. Nowadays, we can use plastic for that purpose. I have some examples of that on my desk, some paper bus tickets enclosed in sheets of clear plastic.

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    If people are arguing that a small isolated population can maintain a high tech environment indefinitely, the only answer is that we will have to wait and see, because we have zero examples of any population with industrial level technology under those conditions yet. Personally I doubt it, but just because it's unlikely or difficult doesn't mean it's impossible.

    There's a wide distance between a single crossgen trip and a thousand year journey. How far, how long, how many and how much all matter greatly.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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