
What's the Minimum Number of People for a Generational Ship to Proxima Centauri? - ohjeez
https://www.universetoday.com/139456/whats-the-minimum-number-of-people-you-should-send-in-a-generational-ship-to-proxima-centauri/
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yawz
_> If we would create a spacecraft right now, we could only reach about 200
km/s, which translates into 6300 years of travel. Of course technology is
getting better with time and by the time a real interstellar project will be
created, we can expect to have improved the duration by one order of
magnitude, i.e. 630 years. This is speculative as technology as yet to be
invented._

This is the dilemma that should make us really consider and possibly wait for
the right technology. Otherwise it is quite possible to arrive to destination
and find it populated for millennia.

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ohjeez
There have been at least a few SF stories built on that premise. It's driving
me nuts that I can't recall which they were.

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jgroszko
Alistair Reynold's Revelation Space universe explores this, often times with
sub-light travelers arriving at what they thought would be one of the largest
cities in known space only to find it devastated by a plague. More relevantly,
the book Chasm City, set in this universe, explores a set of generation ships
competing to arrive first at an uninhabited planet.

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RodgerTheGreat
Assuming you can cryogenically preserve sperm indefinitely, it seems like you
could simply stock the ship with a large supply of frozen sperm gathered from
distinct males and use this stockpile exclusively for reproductive purposes.
As long as you have enough sperm samples there is no risk of inbreeding.
Frozen sperm should, at any rate, consume far fewer resources than male
colonists for an equivalent supply of genetic variety.

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wonderwonder
While a logically sound solution, the issue with this is that the second /
third generation would not have committed to the trip and would want to
produce their own offspring as opposed to those of someone else.

I have to imagine being born on a ship and being told that your grandparents
signed you up to live and die on it for a science experiment would potentially
cause a psychological aversion to wanting to follow the rules set down a
generation before regarding sex and procreation.

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seanalltogether
My first thoughts while reading this article was this exact issue. Are there
any good sci-fi books or movies that explore this concept of what it might be
like to be a middle generation on the way to a new solar system? You have
little attachment to the original mission that your great-grandparents signed
up for, and you'll never live long enough to see your destination.

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perl4ever
Seems plausible to me that after the society and its people had adapted to
living in deep space, they might end up simply never landing anywhere. Or
finding a rogue planet and burrowing in because stars are too volatile and
dangerous.

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natch
The idea that the travelers need to be people as we know them today is a huge
assumption that should be jettisoned.

As we improve medicine and merge with AI, we should expect other changes to be
possible, not just brain interface changes, but also body changes. Essentially
we are still a version 1.0 and the iterations to new versions haven't even
started yet... but these should be well underway in the timeframe of starting
voyages to other stars.

Even for Mars, much closer obviously, we should think about whether it's
easier to change body types in the medium term than it would be to terraform
Mars to a desirable level.

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stephengillie
> _...we should think about whether it 's easier to change body types in the
> medium term than it would be to terraform Mars to a desirable level._

This could be called _bioforming_ [0][1] and here's an abstract for a paper
that suggests modifying humans, alongside modifying Mars, to speed
colonization.[2]

[0] [http://memory-alpha.wikia.com/wiki/Bioforming](http://memory-
alpha.wikia.com/wiki/Bioforming)

[1]
[http://terraforming.wikia.com/wiki/Bioforming](http://terraforming.wikia.com/wiki/Bioforming)

[2]
[https://www.researchgate.net/publication/289486325_Bioformin...](https://www.researchgate.net/publication/289486325_Bioforming_and_terraforming_A_balance_of_methods_for_feasible_space_colonization)

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mevile
Having a child that is bound to live their entire life on such a ship strikes
me as tragic and depressing. I don't think I could personally be responsible
for creating a life in that kind of environment. I'd hope we'd get the quality
of life possible in space very high before we ever attempt any kind of thing
like this.

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crooked-v
It seems to me like the only reasonably ethical way to do it would be to have
a small city's worth of people (a small city's worth of living space) and thus
"society" rather than "crew".

But that runs into the organizational problem that a society that's lived in
space for two or three generations may not want to deal with this messy,
disease-ridden, gravity-encumbering planet business again.

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reificator
Which brings up a much overlooked issue regarding colonization efforts:
antibodies and the human immune system in general being exposed to an alien
environment after generations of sterile space travel.

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majewsky
Colonizable planets will either:

1\. be sterile, meaning that this is not a concern. (The only germs that
settlers will run into are those they brought with themselves on the ship.)

2\. contain alien germs, in which case no humans would have antibodies for
them regardless of origin or travel speed.

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reificator
Sure, but I know people who are just allergic to metals in jewelry. Maybe it's
germs on it, but if it's not...

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bmcusick
Interesting discussion, but not very forward-thinking on the biology side. As
a simple critique, they claim that 32 crew would result in too much
inbreeding, but what about IVF? There's no reason all the children have to be
the full children of the crew. They could put sperm and egg cells from
thousands of donors into deep freeze before leaving.

There's also no discussion of life extension, which seems more near term than
interstellar starcraft.

Anyway, we will probably have good data on the optimal size of asteroid
colonies long before interstellar colonization is a live issue.

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drb91
> There's also no discussion of life extension, which seems more near term
> than interstellar starcraft.

So long as we’re comparing unknown unknowns, we might as well throw fusion and
GAI in there.

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Comevius
The worst thing about spaceships is that they are easy to destroy.

Hard times create strong men. Strong men create good times. Good times create
weak men. Weak men create hard time.

This social dynamics would not go well on a generational ship.

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squirrelicus
Can't wait to see perspectives on this one. I looked into this years ago and
remember finding the number to be around 150-300 if you centrally plan
reproduction (and no, you don't want an unequal gender distribution). Also
that cheetahs experienced a population bottleneck of this magnitude and so we
have some data on what it looks like.

Take that with a grain of salt, memory and amateur research are finicky.

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IpV8
0\. Just have a robot incubate some clones once it gets there.

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crooked-v
This gets you a bunch of feral children who die after unintentionally breaking
something essential for life support.

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IpV8
Good point. We'll need to send some robot mothers too.

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crooked-v
That gives you step -1 of "invent general-purpose AI that can completely
replace a human". If you've got that, why not just send the robots by
themselves?

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TooBrokeToBeg
Why not just send rocks? The concept is the migration of the species, ie the
fulfillment of genetic imperative. If you aren't interested in that, the rocks
will be fine without us.

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paulpauper
yeah instead of taking rocks from space, send rocks into space lol

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paulpauper
it's pretty fascinating how just 98 can sustain a colony for 6000+ years

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coldacid
Actually it sounds like they're targeting the 600-700 year journey.

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stevecalifornia
TLDR: "Moore concluded that a 200 year-long mission should have an initial
crew of 150 – 180 people. (...) Among other results, it was found that an
initial crew of 14000 – 44000 members is well-optimized to ensure healthy
offspring, even in the case of a sudden disaster occurring once during the
mission. According to his study, a crew of 150 people would always be on the
verge of extinction in the case of a large-scale catastrophe."

[https://arxiv.org/ftp/arxiv/papers/1708/1708.08649.pdf](https://arxiv.org/ftp/arxiv/papers/1708/1708.08649.pdf)

I had to go to the linked study to get the answer. If an article posits a
question in the title...it should answer it in the body. Hopefully in the
first paragraph.

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true_tuna
Cold sleep?

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ninetyEight
Answer: 98

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rurban
That's not even a multiple of 42

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BrandoElFollito
TL;DR: 98 people.

With 32 the chances of success drop to 0%

I thought the number would be 10-50 times larger.

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joeblow9999
2

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Analemma_
No. Contrary to the sci-fi trope you occasionally see crop up, you could not
make a sustainable human population starting from two people. The inbreeding
would render everyone sterile (and probably severely physically and
intellectually disabled) after just a couple generations.

The actual number in the paper is 98, and even that probably wouldn't be a
very healthy population of humans. Around 600, with significant initial
diversity, is the number I've seen tossed around as the minimum number for a
genetically healthy population.

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cfadvan
This is asking the wrong question. We don’t know how to create a robust
artificial biosphere, we don’t know how to shield such a large ship from
radiation efficiently, we don’t know how to maintain or create the human
microbiome, because we’re nowhere near understanding it. We’re so far from
being able to survive off of Earth that we don’t even know all of the
challenges that exist.

Even if we had the propulsion, which we don’t, we’d still be screwed.

