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Optimal Worldship Populations

Although we tend to focus on propulsion as the major obstacle to reaching another star, the biological problems that go along with journeys lasting decades or even centuries are equally daunting. If we could devise methods that would get us to Alpha Centauri within a century, we’d still face the need to keep a crew alive within a sustainable closed ecosystem for that amount of time. If we’re talking humans in starships, then, we need a lot more data about how people interact in isolated communities, stay healthy, and manage critical self-sustaining systems.


Image: A habitat for humans over generations, a worldship poses critical questions about survivability and genetic diversity. Credit: Adrian Mann.

Centauri Dreams readers will recall Cameron Smith’s interest in these matters, as reflected in his article Biological Evolution in Interstellar Human Migration, published here last March. The author of Emigrating Beyond Earth: Human Adaptation and Space Colonization (Springer, 2012), Dr. Smith (Portland State University) looks at these issues over the course of generations. How large does a starship crew have to be in order to keep the population healthy? This article in Popular Mechanics gives a nice overview of Smith’s findings, which were published in Acta Astronautica and flesh out his earlier essay in these pages. The work was performed as a contribution to Icarus Interstellar and its Project Hyperion.

Working with William Gardner-O’Kearney, Smith constructed simulations to create scenarios for interstellar travel with the help of MATLAB, a widely used tool for numerical computation. One immediate result was to draw into question earlier calculations by John Moore (University of Florida), who had found that a 2000 year voyage aboard a generation ship would require an initial crew of no more than 150. In sharp contrast, Smith found that a minimum of 10,000 was necessary, while 40,000 would be a safer number still given the perils of the journey. Starting population size, which the duo calculated over 30 generations, is a crucial matter.

A key issue, as you would expect, is genetic diversity. Small groups like the Amish and Ashkenazi Jews suffer higher rates of diseases like cystic fibrosis and Tay Sachs largely because of intermarriage between relatives. I’ll send you to the article for the bulk of the researchers’ graphs, but I’ll show one below, illustrating what happens within groups of different sizes over time. A ship starting out with a crew of 150 loses 80 percent of its genetic diversity after thirty generations. Even 500 is too small a number, for it does not represent a wide enough swath of the human population. Somewhere between 10,000 and 40,000 is where we find a starting population that can maintain 100 percent of its original genetic variation.


Image: The decline in genetic diversity among smaller populations over time is evident here. Note the 150 line in red at the bottom of the chart, with the most robust, in purple and representing a starting crew of 40,000, shown at the very top. This number maintains 100 percent diversity. Credit: Cameron Smith/Gardner O’Kearney.

Just as we preserve a healthy gene pool with a larger population, we also safeguard against external risks, the kind of catastrophe that could snuff out the entire population of a small ship. This work makes the case that housing tens of thousands of colonists in a single generation ship would be a mistake. Far better, when launching our expedition, to use multiple ships, traveling perhaps close enough together for trade and other human interactions, but separated so that a single disaster wouldn’t mean the end of the entire venture. I’m invariably reminded of the expedition led by Sky Haussmann in Alastair Reynolds’ novel Chasm City (2001), a fleet of starships that confronts a human-caused calamity.

10,000 seems to be the minimum number for success. Says Smith: “With 10,000, you can set off with good amount of human genetic diversity, survive even a bad disease sweep, and arrive in numbers, perhaps, and diversity sufficient to make a good go at Humanity 2.0.” That’s a large crew, but history has shown us that there are always pioneers, adventurers, misfits and any number of other psychological types willing to give up everything they have known to chance their future in unknown lands. The guess here is that if a fleet of five generation ships needing crews of 2000 each is ever built, it will not lack for volunteers.

The paper is Smith, “Estimation of a genetically viable population for multigenerational interstellar voyaging: Review and data for project Hyperion,” Acta Astronautica, Vol. 97 (2014), pp. 16-29 (abstract).


Comments on this entry are closed.

  • Jim Early April 8, 2014, 10:41

    The number of generations depends on the assumptions about voyage distance and speed. We all probably have different favorite values for these parameters, but the real requirements will be set by the much longer duration of the colony. Stored genetic material (frozen sperm, etc.) will be required for the colony and should also be available for the crew. The crew size will be determined by social stability and equipment operation requirements.

  • William Blight April 8, 2014, 10:48

    Resource wise, it would be far better to carry a smaller population with a lot of frozen embryos.

  • RobFlores April 8, 2014, 11:32

    First as paramount Assumption: There something in Alpha Centauri that
    makes it an attractive colonial site. This is not a given.

    Second, The 2000 year trip: For that amount of time, maybe coax better
    performance from your propulsion system would bring in systems that are
    within 25 Light Years.

    Third: We can test long duration Hibernation here in the Solar System.
    It would not even have to be that good, just safe. Being able to sleep
    20 days for every 10 days of activity would bring the cost a substantial
    amount. While also protecting against a plague somewhat.

    Fourth: I totally disagree on breaking up the voyage into several Smaller
    vessels. We are not machines, there would be conflicts, leading possibly
    to armed conflict, especially in such a long journey. I agree that it is risky
    to send one ship, but I would rather face an unknown risk that may happen, rather than a man made risk all of human history has shown to be true. Anyhow if you design your ship and flight cleverly , you can bring those risks down to serious but manageable events.

    Regarding volunteers: I think it’s a tougher sell that we think. Pioneering
    spirit wont cut it. You are stuck on a ship, just a gene carrier and there isn’t
    enough of a challenge there. My guess is that this pioneering type of personality would make/seek out drugs to relieve boredom. What kind
    of personality would be needed in a general sense, is the big question.

  • Ron S April 8, 2014, 11:39

    Without having read the paper I’ll go out on a limb and criticize anyway. You do not need the entire genetic population base in the form of walking, talking, living humans. You can get by with far less, plus an egg and sperm bank.

    On another note, mentioning MATLAB* is a red flag to me. It’s nice to have some tools, but this says nothing of the technique and skill required to create an effective model. For example, my criticism above. Not everyone who owns a hammer can build a house.

    * Disclaimer: I don’t much like MATLAB in comparison to alternatives, based on my commercial experience.

  • Eric Hughes April 8, 2014, 11:57

    Are the authors of that study making the case that chromosome pairing is done traditionally, that is, randomly? It seems so, given the graph included. The better conclusion to draw is either that large number of people must be present or else that procreation requires some kind of technical intervention.

  • Randy Chung April 8, 2014, 11:58

    Certainly, a larger population and a larger number of vessels increases the probability of delivering a functioning society at the end of a trip of many generations. But another certainty is that the cost goes up — sending five ships will likely cost five times more than one ship, and sending 10,000 people will likely cost 100 times more than sending 100 people. But let’s try looking at the other end of the boundary, how small can the population be, or what startups call the minimum viable product.

    The absolute minimum would be one woman of child bearing age reaching the destination with the frozen sperm and ova from 40,000 people. The probability of growing a population would be low, because there’s no one to help. The next step up in probability of success would be two women of child bearing age. So in the long term, a minimum size crew for multi-generation trip might be around ten women, each one bearing a child about eight years apart. Since their health is the most important thing, the initial crew should all have attended medical school, with some specialization like OB/GYN, psychiatry, oncology, surgery, pediatrics, etc. They would teach their skills to each other and to each new generation.
    This approach would lead to many interesting and controversial subjects, and reminds me of the novel Cetaganda by Lois McMaster Bujold.

  • neutrino78x April 8, 2014, 12:02

    There are so many logistical issues with generation ships. Personally I would not send humans on an interstellar journey until we can travel at a significant fraction of the speed of light and put them in hibernation for longer journeys. :)

  • Tomas April 8, 2014, 12:08

    Why is it that people with such lofty ambition in one area of technology cannot see the progress already underway in other areas? Biotechnology is moving ahead very rapidly (remarkably so in comparison to the glacial pace of space exploration). It’s probably much easier to make people non-aging than it is to travel to another star. Both are foreseeable objectives which require substantial research effort, but the requisite engineering resources are much less demanding for the biological immortality project.

    Other relevant technologies include cryogenic preservation of gametes (already demonstrated to some extent — much easier than for macroscopic tissues or whole individuals), creation of artificial wombs through tissue engineering, germ-line and somatic gene therapy and the potential for synthetic biology and genetic engineering to simplify nutritional requirements and therefore the necessary life-support systems by creation of novel anabolic pathways.

    On a more philosophical note, I should hope that any pioneers setting out for the stars would have higher aspirations than “Humanity 2.0.” A brief review of the past and present of Humanity 1.0 reveals a plethora of irrational blunders, abominable cruelties and catastrophic wastefulness. From an evolutionary perspective, there is no reason to believe that humanity is anything other than barely adequate as a civilized species. We should really hope to do a lot better by breaking from past trends of human history and improving ourselves through the means available to us.

  • Paul Gilster April 8, 2014, 12:46

    Rob Flores writes:

    First as paramount Assumption: There something in Alpha Centauri that
    makes it an attractive colonial site. This is not a given.

    The Alpha Centauri mission was my insertion, just used as an example of an interstellar mission.

  • James D. Stilwell April 8, 2014, 12:49

    Bookmarked this post.
    Five armed armored ships ready to leave about AD 3,000 sounds good…
    Add 5,000 artilects amongst their own five ships and we’re good to go…
    All ten ships ought to survive the journey…
    But surely the course won’t be a straight line…
    Gently weaving amidst rogue planets and such…
    Even misfits will want to interview the navigators…

  • DCM April 8, 2014, 12:52

    The banks of frozen sperm and eggs are the way to preserve genetic diversity that even 40,000 people might lack.
    People seem to forget that a way of making life more bearable is to include domestic animals like cats and small dogs, maybe parakeets, plus egg and sperm banks for them.
    But what do the colonists do when after centuries in space the star they approach has no useful planets? Or the planets are inhabited already?

  • RobFlores April 8, 2014, 14:48

    I am not a bio-ethicist therefore I cant just coldly declare that we can
    use genetic materials however the hell we want. If you tell someone that
    their parents are not related to them and that they were sent to live and die on a spaceship their reaction might not be so tame.
    About the only way I might approve of the frozen embryo approach
    is if we had a compelling reason to send a lifeboat out of the solar system.
    I would not call this a dilemma as question of the status of an embryo. That is not relevant here since the ultimate objective of such embryos is full maturation. The same would apply if a molecular machine assembled
    such an embryo from some genetic database. Obcourse I you don’t believe
    it is somehow different when two beings deliberately decide to reproduce
    then I can see how someone might have little objection to it.
    The modern trends in pair bonding and reproduction unfortunately
    do not point to successful propagation of the human species on a long journey through space. In my opinion it might become necessary to send
    of the younger members of your spaceship on retreats to places on the
    ship where contraceptives are not found

    Does this seem as unethical embryo importation? No because there
    will be an extended family related to any newborns who will instinctively
    want to protect and care for them the large majority of the time.
    I welcome another view.

  • ljk April 8, 2014, 15:55

    Crew members taking drugs to ease the boredom and other psychological issues? Why not just plug into a virtual world? In fact have the whole crew think they are on Earth. When the last generation just before mission end is a mere few weeks away from the target system, tell them that an FTL drive has been invented and they can reach Alpha Centauri in just a few weeks or so. They virtually hop aboard the FTL vessel and wallah – Alpha Centauri for real!

    This way every generation thinks it is spending its life on Earth, where most humans feel comfortable anyway, and when they Worldship finally does approach the new world, they can take a virtual space journey that seems so very short. No boredom and slim chance of reverting to barbarism ala Heinlein’s Orphans of the Sky (the trick there is to put windows in the damn ship).

    Again, humans cause quite a few complications for interstellar voyages when Artilects and other machines will be so much more efficient. We should only be sending humans if absolutely necessary and even then if there is some kind of impending disaster it may not be possible to build a Worldship in time. Plus we really need to keep in mind that humans a few centuries hence will be much different than us thanks to biotech and other advances – assuming we do not revert along the way.

  • steven rappolee April 8, 2014, 18:22

    Alpha Centaurus may have a sizable asteroid belt and perhaps comets and another thought, both stars may have kicked out early planets into very large elliptical orbits around both ( we need to model this?)
    perhaps such a planet might be much like this one described in http://crowlspace.com/ (A helium deuterium world) that would with the asteroids provide plenty of opportunity for our colonists

  • Rob Henry April 8, 2014, 18:29

    Alpha Centauri can not be the destination here! My reasoning is simple. It may be hard to get to those velocities we want for startravel such as 0.2c, but here we are looking at 0.002c which is ten thousand times easier. There are just too many ways to get such a speed, as to barely be a challenge even with today’s technology. This must be for a scenario where the only viable habitation is circa 25 light years away.

  • Rob Henry April 8, 2014, 18:38

    For Alpha Centauri in 400 years, think of Pit island. That ‘experiment’ implies that if we carefully pick the initial inhabitants, we only need around 50 people if genetic health is our only consideration.

  • FrankH April 8, 2014, 19:01

    If we’re going to talk about “filling up the space ship with frozen embryos or eggs and sperm” and just grown them when they get to their destination, then we’ll also need human caretakers who’ll be little more than life long slaves to a huge creche of noisy, demanding babies and children… or advanced AI that is the equivalent of a human, capable of birthing, nurturing, protecting and educating a gaggle of ankle biters.
    The concept of Space Slaves isn’t very appealing and if you’re going to have AI that advanced why not send them instead and forget the wetware?

  • Geoff April 8, 2014, 21:26

    Maintaining human genetic diversity is not the issue. As other commenters have pointed out, that can easily be done in a population of any size, by storing frozen gametes so that no genes are lost. The worldshippers should be able to manage that, even if they have only 21st-century level technology.

    The more difficult problem – the one that might actually require a worldship – is exporting an entire ecosystem to another star. Ecosystems, with all their species interactions, are not so easy to reduce to pure genetic information. It might be that the worldship, with its fully-functioning on-board ecosystem, would ideally have a human population of… zero.

  • Alex Tolley April 8, 2014, 21:56

    It is perhaps not surprising that different researchers come up with widely varying estimates for the needed size of founder populations. I’m a little surprised at how rarely historical founder populations are used to anchor these estimates to reality. I’m also not sure why the genetic drift of small populations is seen as such a problem unless the aim to to replicate the diversity of Earth. As other shave stated, technology offers a way out – frozen embryos being one option.

  • djlactin April 8, 2014, 22:01

    I messed with this idea a while ago; the problem of supplying the population became increasingly difficult as the number increased. I present only two (obvious) complications of ecosystem management that I identified:
    1) Feeding the crew. A human requires ~10 MJ of energy per day (plus adequate supplies of essential nutrients like vitamins); how is this to be accomplished? Farming takes land and careful husbandry to maintain its fertility. Hydroponics is heavy.
    2) Maintaining the atmosphere. Oxygen and carbon dioxide levels must be optimized (while scrubbing pollutants like methane).
    Slightly off-topic: maneuvering on arrival would be a problem for a ship that is spun-up to simulate gravity, owing to the gyroscope effect.

  • djlactin April 8, 2014, 22:15

    A second set of problems arises on arrival: Establishing a viable ecosystem. This challenge entails two steps:
    1) Establishing.
    A lifeless planet would have negligible free oxygen, and perhaps a reducing atmosphere. This problem might be solved by seeding the atmosphere with anaerobic oxygen-producing microbes, but the process would require a very long time.
    A planet with life also might not have free oxygen. If it does not, the same solution may be possible; if it does there is the additional problem that it would be better adapted to local conditions than the immigrants, so it would have a great competitive advantage over any introduced species. (along with ethical questions.) If it does have free oxygen, the second problem still arises.
    2) What is a ‘viable ecosystem’? The terran system is very complex, and requires (among numerous other factors) microbes in appropriate balance. But we don’t know what these microbes are, or what the balance is.

    I think ‘getting there’ will be only the first problem.

  • steven rappolee April 8, 2014, 22:20

    I remember Hogans, “voyage to yesteryear” this is a fiction novel based on the embryo robot idea,
    it leads to a fully automated “gift economy”
    libertarians love this novel,
    as for me?
    I will stick to the rotating star ship that does take 450 years to travel 4.5 light years and does have inside its hull the equivalent of a University of California of living people, people with a living culture, people who as living beings can talk to the rest of us back home!
    Frozen Embryos?
    back up
    the slow speed of our journey will insure low collision speeds
    the slow speed of our journey will give us the possibility of slowing down with economics of scale
    given the resources this idea does not preclude the others
    send those first………………
    or send those with this world ship,a world ship with a flotilla of smaller vessels might make sense, a modification of the original article, a large world ship with 20,000 to 30,000 with the smaller vessels with 5,000 to 10,000 people ahead and behind by thousands of AU’s
    this allows for better astrometrics and navigation

    on this blog from time to time you see ideas as to what economics or energy levels a future society would need to pull this type of project
    I like to think about how do we get there?
    I think a future society a century from now would need to be free of distractions from having poor people or people in need or want or people suffering from environmental degradation, degradation caused by CO2
    I have a humble idea that could bridge this gap between us and those who will dream of this project a century from now,


    carbon tax the CO2 and invest it for 70 years in the worlds capital markets,build nuclear power plants and the investment is left untouched in till the children born 70 years before and after become pensioners
    $250 Billion per year in carbon taxes yields in 70 years at 4% $88 Trillion in 2012 dollars!
    during this 70 years you could build a $1 to 2 trillion space based solar power sat constellation,use lunar and asteroid resources to build it.
    if this $ 2 Trillion out of $88 trillion proved to be a revenue neutral investment then perhaps this is not such a great loss to the fund.
    A $ 88 trillion fund that pays out a small percentage of its assets to retirees who where born 70 years before yields a society with no elderly poor and they have income to generate employment for the young of that future age.
    the huge nuclear power plant build that my blog suggests also creates full employment.
    $ 88 trillion over 70 years cannot possibly invested in the united states! it must be invested in the world, and its the world that will need to be able to go to the stars a century from now or shortly there after

    there is grandeur in this view of economics,tax carbon,invest the proceeds over decades, do so in trust to future unborn children, invest the proceed in nuclear power that replaces CO2,free the people of the future from taxes to free the poor from this bondage,free the people in the next century from choices that are distractions from a grand journey to the stars.

    A generation starship is a social contract with those of a century from now with those yet unborn centuries later on-board the great journey, the people of a century from now will not be able to make this choice unless we of the present can see the economic and ethical grandeur of making the Intergenerational equity equity choice of taxing our carbon emissions now and building the future with those funds in order to free the future of the threat of not having the choice.

  • steven rappolee April 8, 2014, 22:42

    it should be pointed out that I do have a fondness for the Hogan post scarcity society,

    not sure how this would work in practice in our pre singularity world

  • Tomas April 8, 2014, 22:55

    With indefinite lifespans, there would be no rush to reanimate the frozen embryos. If passengers had their brains enhanced by intimate connection to digital memory and processing capabilities their psychology might be quite different from human psychology. For instance, they might be very interested in things that seem to us highly abstruse. Even the pastimes and amusements of such beings might be all but incomprehensible to the human mind. Science Fiction needs characters that we can relate to, but reality has no such constraint.

  • Zanstel April 9, 2014, 7:40

    There is two ways. The fast way, fast ship, small crew, a good fraction of speed of light, a journey shorter than a human life, and the slow way… worldships that could travel as a selfcontained world.

    Although I could prefer the fast way, the slow way could have some benefits.
    First, the ship is, at the same time, a colony. A colony that it could exists some generations before start the travel, checks all the systems, establish a good community, etc.
    Once the destination is reached, the settlement is instantaneous.

    Selfcontained space colonies don’t need planets. It could replicate as is, only with help of asteroids and comets. Probably all star systems have it.
    A world with artificial light (not redirected) don’t need even a stable star or stay near the star. And a worldship capable of interstellar travels need it.

    I think that it is a good idea, using this way of travel, to move a group of ships. In terms of energy or mass is not too much different. It’s safer (a not fatal failure allow an evacuation). Allow more diversity of communities, social organizations, so diversity allow to people adapt better.
    It is like to move from one city or country to another. Some times you need a change, and multiple ships with limited movility allows it.
    The ships could establish cycles of “acceleration”, times of “no acceleration”, bring near the ships, exchange people and resources, move away and repeat the cycle.

    In respect to DNA, i don’t see a problem. Not only you could send embryos. Probably before had the capability of interstellar travel, we could digitalize DNA and “print” it again.
    It’s the best way to replicate a entire biosphere if a terraformable planet is found.
    From a small group of species, we could replace DNA to near species digitalized and different individuals to allow diversity, and replicate the whole Earth if we want.

  • Gerald Cecil April 9, 2014, 7:40

    By the time these concerns are relevant as opposed to pointless academic exercises, epigenetics through tailored environmental exposures will probably let a smaller population maintain genetic diversity.

  • Scott Gordon April 9, 2014, 8:17

    I think the whole idea of needing a minimum population size for genetic diversity is already getting close to being technologically obsolete. In principle the minimum needed size is ZERO.

    Within a matter of years it will be possible to reliably obtain the genetic sequences of an arbitrary number of people; and store them in the ship’s computer systems for as long as you like.

    When you add the ability to produce DNA from nothing but a computer file, a good DNA synthesis machine and a set of precursor chemicals, all you need to produce a child with whatever genetic sequence you like is the means to turn replace the DNA in a human cell; turn it into an embryo; and grow it to maturity.

    None of this is very hypothetical (probably all technology available in the next few decades through research into DNA sequencing and synthesis, stem cell therapy and cloning) and it allows you to create arbitrary genetic diversity on your arrival without even using DNA which is physically from a real human.

    For that matter in principle you can use the same method to introduce pretty much any species you like to your worldship or the destination planet without needing to carry any individuals of that species. The challenge being the ‘how to’ in terms of finding suitable surrogate parents or host cells etc.

    Of course you need confidence in your technology and your supplies.

  • James D. Stilwell April 9, 2014, 10:34

    Frank H said…
    The concept of Space Slaves isn’t very appealing and if you’re going to have AI that advanced why not send them instead and forget the wetware?

    Of course this man is on target…but it will be hell developing artilects with IQs approaching 200…the artilect effort will proceed despite great resistance…yet they are the ones who will chart the heavens for humanity…building an atlas of navigational routes centuries before the wetware follows…sorry…

    But we can look forward to an occasional Buck Rogers who goes forth…

  • DCM April 9, 2014, 12:40

    As for reaching inhabited worlds I don’t like the notion of colonizing them. Contacting intelligent inhabitants and studying the biology of others is okay but I don’t like taking their home away from them.
    World ships are better simply for dispersing life. With sufficiently advanced technology planets could be assembled.
    I wonder if there might be some way to create a small object that functions like a star that would orbit a planet and be similar to the sun….

  • Marc Millis April 9, 2014, 13:39

    Technology gains for sustainable living would be really useful on Earth, even if never leading to a colony ship.

    Sociologically, if we humans ever figure out how to live peacefully and meaningfully (with all our shortcomings), that would be a HUGE gain for life on Earth, too.

    I like the situation of a ‘clean-slate’ for designing the ‘culture’ for a colony ship – without legacy biases. Historically, arguments about governance models and cultural differences have led to war and destruction. When happening in real-time, it affects us personally. In contrast, a far-future colony ship is not threatening to our lives now. Studies of colony ship life have the luxury of being an impartial crucible to scientifically assess various cultural and governance norms.

    For a starter, it is my opinion that we must first come to terms with the real nature of our humanity. In addition to all the things we boast about, we are also prone to a variety of cognitive dysfunctions (where reality and impressions are not aligned), easily scared and angered (flight or fight), prone to corruption of power, and often horny beyond reason.

    If research into the culture of a colony ship can provide insights for living peacefully and meaningfully …forever… then that lesson would save humanity from itself.

    That is a big deal.


  • JoeP April 9, 2014, 13:51

    This article almost convinces me that suffering such a seemingly everlasting journey in a city sized can is almost certain to fail. Do we think the inhabitants of the can are going to live and die, generation after generation, without causing some major disruption that would doom the mission to failure and death?

    I don’t think we are build to handle this without some significant modification. Somewhere along that chain a link will break.

    Unfortunately, it seems the kind of voyages we are currently able to withstand are similar in time to what we have seen successfully here on Earth in naval exploration. A handful of years at most.

    Thus, without any exotic breakthrough propulsion technology, my bet is on AIs taking us there (as preserved embryos or DNA) and re-establishing earth life, and humans, on some world that has been pre-terraformed for us by them in advance.

  • andy April 9, 2014, 15:43

    Such discussions tread on an ethical knife-edge! I have to admit, the first thing that came to mind on reading this was the film Dr. Strangelove. In particular, this scene has some uncomfortable resonances.

  • william April 10, 2014, 3:13

    This entire train of thought that has been going on in the last 32 comments has got me thinking about something that I’ve long wondered about but have never seen on this page. Namely, if any of the learned contributors to Centauri dreams has ever considered the following two scenarios. These are quite serious questions that I’m asking of you Mr. Gilster.

    The first question concerns that of some Earth threatening cataclysm should befall our planet, has there been any scholarly research that’s been undertaken to find out if there’s some type of Worldship that might be constructed in a pinch for at least some portion of mankind to head out into space ? I know all about the ideas that the rest of the world would be in a utter state of panic and all the possible scenarios about why certain individuals should be able to leave and not me.

    My question really has nothing to do with that even though that would be a use one topic by itself. Rather, has there been any thought as to whether or not a dedicated group could pull together the needed resources to accomplish that in today’s technology. If they have, what are the results of their studies ?

    My second question is more general and is not connected necessarily with any type of dire situation requiring immediate abandonment of Earth. Namely if a Worldship should undertake a voyage to what they considered to be a star with possibly habitable planets and upon arriving they should find that the Haven planet they had hoped would be their salvation is less than amenable for the new settlers -has anyone given any thought to that and possibly drawn up some type of contingency plans in that case? I hope that you Mr. Gilster would be able to address these kind issues in some future pages of Centauri-dreams installment.

  • Paul Gilster April 10, 2014, 8:10

    William, there are a lot of things here to write about in future posts! But the short answer is that to my knowledge, no one has seriously investigated how to build a worldship using present-day technologies. The closest thing I could mention would be the Icarus fusion starship design, but even that does not presume using today’s technologies, and it’s an unmanned vehicle, nothing remotely as complex as a worldship. All the worldship studies I am aware of presume serious advances in all the areas needed, from propulsion to closed loop life support.

    As to the second question, I know of no such contingency plans — I’m sure the question of arriving at a destination system and finding no habitable worlds there has been dealt with many times in science fiction, but in terms of hard science, the situation is still so theoretical that I don’t think anyone has tackled it head on.

  • JoeP April 10, 2014, 14:53

    William…IIRC, as far as closed loop life support systems with present day technology goes, some work was done during the Biosphere projects. I don’t remember the details, but I believe the objectives weren’t quite met and the team had to do things like exchange some atmosphere, run CO2 scrubbers, and add oxygen to maintain proper levels. And they had plenty of other challenges arise. There is no doubt plenty of info on Wikipedia on these experiments.

    Anyway, if a “dire” situation were to occur, we will still need some parameters on that to know what the best course could be. Example: A large enough asteroid impact at the same level of the Chicxulub impact would kill off most humans. But I think a “shelter-in-place” idea is far easier an achievement than building any sort of worldship. What I mean is that with, say, a decade of notice in advance, a stronghold could be built on the surface (or under) that could let a certain number of survivors live safely for a number of years until the immediate effects of the impact wear off. That technology is certainly there. The inhabitants will still have access to key Earth materials and resources such as oxygen and aquifers, for example — it doesn’t have to be closed loop. Other supplies such as food, machines, fuel, and generators do not need to be lifted out of the gravity well; they can be stored, stockpiled, and protected prior to the event.

    If the disaster will completely resurface the Earth, then a voyage to Mars or even the Moon and trying to live there would be at least an order of magnitude easier than attempting any kind of interstellar voyage. :) And that is currently beyond present technology in my opinion, especially when you consider that you will need thousands of people and all the rest of the kind of plants and animals with appropriate numbers to support the genetic diversity level requirements that Paul’s article covers.

  • Christopher Phoenix April 10, 2014, 18:47

    @William & Paul Glister- You certainly have some interesting topics to discuss in later posts. Regarding the first question, I have not heard of anyone seriously investigating how to build a worldship using current technology either. The closest design I can think of is the Super-Orion interstellar mission discussed by physicist Freeman Dyson in his paper “Interstellar Transport” (Physics Today, October 1968), but he assumes 200 years of economic growth before we are capable of building such a beast.

    The sobering fact is that we just are not capable of launching even a “low tech” generation starship using our present level of technology. We need numerous serious advances in all necessary areas ranging from propulsion systems and life support to space medicine and genetics, not to mention the necessary space infrastructure to construct and fuel the ship. There are also many unanswered questions about how many people to send to maintain genetic variation, the effect of cosmic radiation on the crew, and the social effects of sealing a society in an enclosed worldship for multiple generations. NASA would probably point out at this point that we don’t yet have the space launch technology to support such an effort, let alone the technology to build a starship one we got up there.

    This is why modern day starship studies tend to point toward what areas of research we need to focus on to lay the foundation for star travel rather than announcing plans to immediately begin laying a starship’s keel!!

    On the second question, some researchers have in fact discussed contingency plans for starships that arrive to find their destination planet unsuitable. In his book Flight to the Stars (1965), author James Strong stated that interstellar crews could not rely on finding a readily habitable “shirt-sleeve” planet at their destination system and must have the means to survive even on an inhospitable destination- by building habitats like those planned for Mars, for example.

    Robert M. Powers, in his nontechnical book The Coattails of God (1982) suggested that a generation ship could refuel from local planets and continue to another hopeful star if they did not find any interesting planets at their first destination, perhaps having chosen their first destination based partly on its proximity to other promising stars. A return to Earth would also be possible but somewhat pointless in Powers’ opinion.

    Edward S. Gilfillan took a somewhat grimmer outlook in his book Migration to the Stars: Never Again Enough People. The crews of his diminutive generation ships would have to hold out hope until they were close enough to their destination to make observations of the planets found there. If none were suitable, they would simply die after arrival. Mr. Gilfillan shrugs off this hazard, saying that as unpopular a stance it might be, human life is our one truly renewable resource. (!)

    Raymond Halyard, author of The Quest for Water Planets, has a similar contingency plan. If the crew of his starship arrive to find that their destination is unsuitable, they will simply “cease to have children” and radio back their findings so mission planners on Earth can have extra data to try to avoid such situations in the future.

    Some have suggested we might choose to live in space instead of landing on another planet. I believe that the Enzmann starship’s modules can be converted to orbiting space colonies, perhaps obviating the need for a planetary landing (or perhaps not, if long term life in space can’t be sustained forever independent of planets). I suspect that this may not work over very long timespans- once the environment begins to run down, or the crew loses the ability to maintain their environment, the delicate environmental balance of their habitats will fall apart.

    Perhaps the best plan is to remote-sense possible destination with telescopes in near-Earth space first, then send probes to take a closer look at promising candidate planets- perhaps even verify the existence of Earth 2. In this way the colonists can have a much better idea what to expect and what hazards they might encounter.

    We have already begun this process with missions like Kepler and plans for probes like Daedalus. After all, the Apollo missions did not land on the Moon until we had already mapped the near side with Earth based telescopes, sent a series of probes to take a closer look and scout out potential landing sites, and flown crewed flybys. Could the lunar astronauts have hoped to navigate past the mascons and deal with the public’s fear of lunar dust pits without this preparation?

  • intercoastal April 11, 2014, 2:40

    I’m skeptical such large populations are needed. Pacific island populations were viable with starting populations under 100, though some genetic problems cropped up (Pingelap, from 20 people, had widespread colorblindness). I’ve heard all Native Americans may come from a > Do we think the inhabitants of the can are going to live and die, generation after generation, without causing some major disruption that would doom the mission to failure and death?

    Most people through most of human history lived out their lives in a very, very small portion of the Earth.

    Also, this is an artificial ecosystem, and it’s not like we’re launching this tomorrow. I’m convinced you could make one, with the right experiments to learn exactly how to do it and the right genetic engineering of your crops and such, that was way more robust than Earth’s ecosystem.

    Plus, again, we don’t have to care about wiping out species as such — this is a purely artificial environment, we only care about the ecosystem’s ability to support human life. We don’t need to bring easily-endangered species.

    Biosphere II had problems, but it was not all that well designed, and we can learn from its mistakes. I think a Biosphere III made without the errors of Biosphere II would work very well… and scaled up to a worldship scale, even more so. I don’t think closed-loop will prove to be nearly as hard as people now think if you do it ecologically (as opposed to the ISS way).

    If we were willing to accept really long travel times, and spend massive money (IE make this a major project of humanity as a whole), and use nukes, I bet we could get an Orion worldship going in 50-80 years.

  • DCM April 11, 2014, 12:42

    I’d like to see a Biosphere III built.

  • ljk April 11, 2014, 14:20

    Biosphere II happened because the guy running the operation was essentially a cult leader with a group of followers. Those are the kind of people who will probably be among the first to establish colonies in our Sol system and beyond, or at least try. If they had the money and resources to live on Mars they would have done so. The American desert had to suffice.

    A tightly controlled group with a single mindset can get things done. Whether anyone else wants to live or deal with them is another matter, but space is much vaster than even a wilderness North America, so there are plenty of room for experiments.

    On the other hand, I do not like sounding as callous as those guys Gilfillan and Halyard mentioned above. Let’s head out to another star system and HOPE there is a habitable planet there to disembark on. If not, oh well, so much for the crew after all that effort. What kind of reasoning is that??

    THIS is why I am so wary when I see any such project, be it a Worldship or SETI, being conducted by a limited group of people who only come from the same or similar disciplines. We need a broad spectrum of experts when it involved living, intelligent beings, be they from this planet or elsewhere. Otherwise we get people being treated like just another cog in the system.

  • DCM April 11, 2014, 18:55

    That’s true. Much as I detest it, the government would be a more “diverse” entity to take on such a task — unless there’s a financial payback. I don’t see a fast payback for interstellar flight unless the fabled warpdrive is developed.

  • Christopher Phoenix April 11, 2014, 19:04

    @ljk I absolutely agree- Edward S. Gilfillan’s callousness towards the crew is rather off-putting, and the less said about his attitude towards the rights of his space crews and space construction workers the better. He probably thought himself beyond reproach for all this, though, since he was a believer in imminent and unavoidable Xrisk that called for immediate plans to send offshoots of humanity to space.

    Nuclear war, environmental degradation, overpopulation, pandemics, out of control science experiments- he discussed them all and concluded that the goal of our space program had to be to escape our impending doom. In his schemes, the starship crews were indeed only one cog in the wheels of a massive program to ensure human life continues, just not necessarily THEIR lives. Each ship was a one-off, disposable shot at colonizing a potential planet but it was assumed most would not make it.

    And while his design for interstellar ships did have some intriguing engineering about it, he willfully ignored all biological and social wrinkles in his schemes. The crew was to live and reproduce in microgravity. Yet their space-bred descendants were expected to stand and start farms upon landing on another planet centuries later. The inevitable effects of inbreeding on the twenty person crew was not even mentioned. Only the captain was to have access to higher education, as the crew would undoubtedly follow his commands if they understood he knew things far beyond them (and where in history have less educated mutineers respected the knowledge of their officers enough to call off the mutiny?). Oh, and the starship has no windows. Because Mr. Gilfillan assumes there is nothing to see.*

    This colonization effort would clearly never work. Even if the crew could somehow reproduce successfully and avoid dying off due to accident or disease, by the time they reached another plant they would be unhealthily inbred and incapable of supporting their own weight in a gravitational field- let alone starting Space Plymouth Colony on an untamed planet. Assuming they didn’t go bonkers staring at the same windowless section of wall day after day for their whole lives.

    This is the danger of leaving a broad project like starships in the hands of people specializing in similar disciplines. A biologist, a NASA doctor specializing in space medicine, an anthropologist, historian, or ethicist would all find a dozen points of failure in Mr. Gilfillan’s ideas. Without their input, such plans would never fly- or even find popular support from the general public.

    *Any amateur astronomer could tell you otherwise. The stars and nebula, Milky Way, and distant galaxies have been washed out by light pollution in urban areas, but from dark rural locations they are spectacular viewed with the naked eye. These same views would be even better seen from the porthole of a starship in deep space- we cannot even imagine the crystalline beauty of the stars free from the distorting effects of our atmosphere. Viewing this would be an excellent way of passing on the knowledge that the crew lives on a starship. A recreational observatory with large windows so the crew can see the light of the stars with their own eyes, not on a screen, as well as some small telescopes should be included in any starship blueprints.

  • intercoastal April 11, 2014, 20:03

    I don’t think it would be a “oops, no habitable planet, they’ll die” thing. I would imagine worldships would be built by a culture that has already industrialized space in our solar system, exploited asteroidal, etc. resources and built O’Neill colonies. So a worldship might not be directed to a planet at all but another system’s asteroid belt, where the inhabitants would eventually build more O’Neill colonies (and maybe settle the planets too, but it wouldn’t be a necessity for life).

    In SF worldships tend to get solipsistic. I don’t think this is really that likely, I think the fact of being on a worldship would be pretty hard to forget even over centuries or a millennium, but just in case, it might help to send a flotilla of smaller (still huge obviously) worldships, in communication, rather than one big one. This would also allow more cultural diversity. If they were traveling at the same velocity people could even travel between them.

    One reason I’m a fan of worldships is that I think hitting interstellar dust etc. will be inevitable on a journey that long, and I’m skeptical of small or flimsy craft being able to be sufficiently protected against those incredibly high-speed impacts. A solar sail might shred quite quickly (compared to the length of a thousand-year interstellar voyage). Something like an Orion would probably be more sturdy, being that it’s designed to stand up to being nuked at close range ;)

  • Brett Bellmore April 12, 2014, 14:41

    I tend to think that, by the time we’re capable of launching world ships, they won’t need planets at the other end, an asteroid belt would be just fine, or even a cometary swarm. A planet capable of being terraformed would just be gravy.

  • Peter Chapin April 12, 2014, 19:19

    The problem of a world ship not finding a habitable planet at the other end of the journey doesn’t concern me at all. By the time we have the technology to build a star ship of any kind our telescope technology will be so good that we’ll have a complete, detailed inventory of all planets in nearby star systems. The colonists will likely have their first campsites picked out based on images taken from Earth.

    In some ways the most amazing thing about the recent developments in exoplanet research is the realization that we don’t actually need to travel to remote star systems to explore the planets there; we can much more easily build super telescopes and observe those planets from here.

  • william April 12, 2014, 19:47

    Earlier about a day or so ago I was (in my mind anyway) seemingly brought up short by others that if a catastrophe should happen to our planet that it would be magnitudes of order easier to flee to some body within the solar system rather than try to do a interstellar voyage. My point was not to make the exercise simple but rather to emphasize if we have any kind of readiness to take a voyage based upon today’s extrapolated technology.

    This got me to thinking about the issue and there is a scenario realistic in which a ‘white dwarf’ (a body about the size of the asteroid Ceres but with the mass of a bit more than that of our Sun) would be able to impact our Sun and in doing so would actually cause it to disintegrate. I should emphasize that this was based upon an article that appeared in Scientific American a few years ago.

    Such a disintegration would result in our solar system flying apart and I can’t imagine with even sufficient preparatory time the bodies of the solar system could be somehow prepped to make them suitable for humanity. This would almost of necessity require that some of humanity flee within a Worldship.

    With this as he established baseline, my question then became simply that rather than plunge into a fast Manhattan style project where the crash program of some type would be initiated, there could be a another thought here.

    Is there anything that that would prevent us to have some type of low-level program in place in which we would say for the price of 5 billion or so a year every year perform some degree of study of these programs and problems on a low-level basis. Simultaneously the outline of a worldship could in fact be started physical construction say in orbit around the moon. This would be a slow building effort such that a crew of dedicated construction workers would gradually build this vessel at such a pace that be possible to make modifications as new ideas and facts were uncovered. Thus in effect we could lay the Keel even though we were not necessarily ready to do everything to completion.

  • Brett Bellmore April 13, 2014, 19:57

    “and I can’t imagine with even sufficient preparatory time the bodies of the solar system could be somehow prepped to make them suitable for humanity.”

    I can’t imagine fleeing Earth in such a scenario, unless it was destined to be destroyed in fairly short order. Geothermal heat assures that you can get all the warmth you need at moderate depth, ore bodies already located, nuclear power available, and no need to travel; An Earth ejected from the solar system, but otherwise intact, would be the ideal generation ship.

  • ljk April 14, 2014, 8:52

    It is a good idea, william, but I can see short-sighted governments and the general public refusing to spend the money on such a project. NASA has to scrape and beg for $17-18 billion a year – chicken feed for most other government agencies.

    Has anyone done the math on how often a star is given a direct hit by a white dwarf or just another star in general? I would say the odds are pretty slim and if it did happen, unless we had plenty of warning time there would be little we could do.

    Nice to know that most others here think Gilfillan and his type are off their rockers when it comes to Worldship plans. Clearly he is another ivory tower type with little relation or concern for real world scenarios or human beings. And he is exactly the kind of person that would make our interstellar plans fail before they even got off the laptop (aka the classical drawing board).

  • Michael April 14, 2014, 13:35

    @william April 12, 2014 at 19:47

    ‘This got me to thinking about the issue and there is a scenario realistic in which a ‘white dwarf’ (a body about the size of the asteroid Ceres but with the mass of a bit more than that of our Sun)’

    White dwarfs with the mass of the sun are around 5000km in diameter.

    ‘would be able to impact our Sun and in doing so would actually cause it to disintegrate. I should emphasize that this was based upon an article that appeared in Scientific American a few years ago.’

    It would not ‘disintegrate’ as such but draw hydrogen onto its surface and ‘fuse’ it increasing in brightness enormously. It would then continue fusion until its has used all the fuel available, it might even reach the white dwarf mass limit and go ‘bang’ totalling throwing the solar system apart.

    ‘This would almost of necessity require that some of humanity flee within a Worldship.’

    I doubt we would out run the supernova event though, but if they combined their masses the habitual zone would expand out to around Jupiters distance. Jupiter’s moons would most likely thaw out.

  • coolstar April 14, 2014, 16:22

    The ethical considerations on carrying sperm and eggs to increase the genetic diversity are not different than that of humans aboard having kids the “natural” way: most all of the generations are doomed to life on the ship. 10,000 people as a minimum sounds fairly silly given that there are several examples of colonies on earth that thrived with many fewer people. (it’s possible that the entire human population (current species) per continent was once less than that). The other option is just to pick people from very diverse populations, which will surely lower the number to much less than 10,000.

  • John Frazer April 15, 2014, 3:47

    Find the book “Interstellar Migrations and the Human Experience”

    AFAIC, everything else being said on the topic is building on/adding to what’s in there.
    Truly a large-scale work.
    Written about here
    Into the Oort Cloud: A Cometary Civilization?
    by Paul Gilster on March 26, 2013

    Brings up Jones and Finney and Nomadic interstellar colonies.
    I’ll say in addition to it, that if we have ships which are poor for interstellar travel; a pathetic .15C Δv makes for a fine ship for crossing the Oort cloud and supplying such colonies with marriage prospects as well as tools and parts (3 things that make the prospect of a multi-generation ship look bleak)

    This also pretty much eliminates the question of finding suitable planets. First, you won’t find anything more habitable than Mars or Titan perhaps. But you don’t need them.
    The O’Neill studies established that planets aren’t the best places to live.
    Proto planetary clouds and other stars’ kuiper belt or small moons make anything possible. Build up to another human K=2 civilization in a few hundred years.
    Leads to Dyson’s “Greening of the Galaxy”. No deliberate mutations or rubber science “treknology” needed.