What's the minimum number of people you should send in a generational ship to Proxima Centauri?

June 15, 2018 by Matt Williams, Universe Today
What’s the minimum number of people you should send in a generational ship to Proxima Centauri?
A concept for a multi-generation ship being designed by the TU Delft Starship Team (DSTART), with support from the ESA. Credit: Nils Faber & Angelo Vermeulen

Humanity has long dreamed about sending humans to other planets, even before crewed spaceflight became a reality. And with the discovery of thousands exoplanets in recent decades, particularly those that orbit within neighboring star systems (like Proxima b), that dream seems closer than ever to becoming a reality. But of course, a lot of technical challenges need to be overcome before we can hope to mount such a mission.

In addition, a lot of questions need to be answered. For example, what kind of ship should we send to Proxima b or other nearby exoplanets? And how many people would we need to place aboard that ship? The latter question was the subject of a recent paper written by a team of French researchers who calculated the minimal number of people that would be needed in order to ensure that a healthy multi-generational could make the journey to Proxima b.

The study, titled "Computing the minimal crew for a multi-generational space travel towards Proxima Centauri b", recently appeared online and will soon be published in the Journal of the British Interplanetary Society. It was conducted by Dr. Frederic Marin, an astrophysicist from the Astronomical Observatory of Strasbourg, and Dr. Camille Beluffi, a particle physicist working with the scientific start-up Casc4de.

Their study was the second in a series of papers that attempt to evaluate the viability of an interstellar voyage to Proxima b. The first study, titled "HERITAGE: a Monte Carlo code to evaluate the viability of interstellar travels using a multi-generational crew," was also published in the August 2017 issue of the Journal of the British Interplanetary Society.

What’s the minimum number of people you should send in a generational ship to Proxima Centauri?
The Project Orion concept for a nuclear-powered spacecraft. Credit: silodrome.co

Dr. Marin and Dr. Beluffi begin their latest study by considering the various concepts that have been proposed for making an interstellar journey – many of which were explored in a previous UT article, "How Long Would it Take to Get to the Nearest Star?". These include the more traditional approaches, like Nuclear Pulse Propulsion (i.e. the Orion Project) and fusion rockets (i.e. the Daedalus Project), and also the more modern concept of Breakthrough Starshot.

However, such missions are still a long way off and/or do not involve crewed spaceflight (which is the case with Starshot). As such, Dr. Marin and Dr. Beluffi also took into account missions that will be launching in the coming years like NASA's Parker Solar Probe. This probe will reach record-breaking orbital velocities of up to 724,205 km/h, which works out to about 200 km/s (or 0.067% the speed of light).

As Dr. Marin told Universe Today via email:

"This purely and entirely rely on the technology available at the time of the mission. 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."

What’s the minimum number of people you should send in a generational ship to Proxima Centauri?
Weighing in at 60,000 tons when fully fuelled, Daedalus would dwarf even the Saturn V rocket. Credit: Adrian Mann

With their baseline for speed and travel time established – 200 km/s and 6300 years – Dr. Marin and Dr. Beluffi then set out to determine the minimum number of people needed to ensure that a healthy crew arrived at Proxima b. To do this, the pair conducted a series of Monte Carlo simulations using a new code created by Dr. Marin himself. This mathematical technique takes into account chance events in decision making to produce distributions of possible outcomes.

"We are using a new numerical software that I have created," said Dr. Marin. "It is named HERITAGE, see the first paper of the series. It is a stochastic Monte Carlo code that accounts for all possible outcomes of space simulations by testing every randomized scenario for procreation, life and death. By looping the simulation thousands of times, we get statistical values that are representative of a real space travel for a multi-generational crew. The code accounts for as many biological factors as possible and is currently being developed to include more and more physics."

These biological factors include things like the number of women vs. men, their respective ages, life expectancy, fertility rates, birth rates, and how long the crew would have to reproduce. It also took into account some extreme possibilities, which included accidents, disasters, catastrophic events, and the number of crew members likely to be effected by them.

They then averaged the results of these simulations over 100 interstellar journeys based on these various factors and different values to determine the size of the minimum crew. In the end, Dr. Marin and Dr. Beluffi concluded that under conservative conditions, a minimum of 98 crew members would be needed to sustain a multi-generational voyage to the nearest star system with a potentially-habitable exoplanet.

Illustration of the Parker Solar Probe spacecraft approaching the sun. Credit: Johns Hopkins University Applied Physics Laboratory

Any less than that, and the likelihood of success would drop off considerably. For instance, with an initial crew of 32, their simulations indicated that the chances for success would reach 0%, largely because such a small community would make inbreeding inevitable. While this crew might eventually arrive at Proxima b, they would not be a genetically healthy crew, and therefore not a very good way to start a colony! As Dr. Marin explained:

"Our simulations allows us to predict with great precision the minimum size of the initial crew that will leave for centuries-long space travels. By allowing the crew to evolve under a list of adaptive social engineering principles (namely, yearly evaluations of the vessel population, offspring restrictions and breeding constraints), we show in this paper that it is possible to create and maintain a healthy population virtually indefinitely."

While the technology and resources needed to make an interstellar voyage is still generations away, studies of this kind could be of profound significance for those missions – if and when they occur. Knowing in advance the likelihood that such a mission will succeed, and what will increase that likelihood to the point that success is virtually guaranteed, will also increase the likelihood that such missions are mounted.

This study and the one that preceded it are also significant in that they are the first to take into account key biological factors (like procreation) and how they will affect a multi-generational crew. As Dr. Marin concluded:

Project Starshot, an initiative sponsored by the Breakthrough Foundation, is intended to be humanity’s first interstellar voyage. Credit: breakthroughinitiatives.org

"Our project aims to provide realistic simulations of multi-generational space ships in order to prepare future space exploration, in a multidisciplinary project that utilizes the expertise of physicists, astronomers, anthropologists, rocket engineers, sociologists and many others. HERITAGE is the first ever dedicated Monte Carlo code to compute the probabilistic evolution of a kin-based crew aboard an interstellar ship, which allows one to explore whether a crew of a proposed size could survive for multiple generations without any artificial stocks of additional genetic material. Determining the minimum size of the crew is an essential step in the preparation of any multi-generational mission, affecting the resources and budget required for such an endeavor but also with implications for sociological, ethical and political factors. Furthermore, these elements are essential in examining the creation of any self-sustaining colony – not only humans establishing planetary settlements, but also with more immediate impacts: for example, managing the genetic health of endangered species or resource allocation in restrictive environments."

Dr. Marin was also quoted recently in an article in The Conversation about the goals of his and Dr. Beluffi's project, which is all about determining what is needed to ensure the health and safety of future interstellar voyagers. As he said in the article:

"Of the 3757 exoplanets that have been detected, the closest Earth-like planet lies at 40 trillion kilometers from us. At 1 percent of the speed of light, which is far superior to the highest velocities achieved by state-of-the-art spacecraft, it would still take 422 years for ships to reach their destination. One of the immediate consequences of this is that interstellar voyages cannot be achieved within a human lifespan. It requires a long-duration space mission, which necessitates finding a solution whereby the crew survive hundreds of years in deep space. This is the goal of our project: to establish the minimum size of a self-sustaining, long duration space mission, in terms of both hardware and population. By doing so, we intend to obtain scientifically-accurate estimates of the requirements for multi-generational interstellar travel, unlocking the future of human space exploration, migration and habitation."

In the coming decades, next-generation telescopes are expected to discover thousands more exoplanets. But more importantly, these high-resolution instruments are also expected to reveal things about exoplanets that will allow us to characterize them. These will include spectra from their atmospheres that will let scientists know with greater certainty if they are actually habitable.

With more candidates to choose from, we will be all the more prepared for the day when interstellar voyages can be launched. When that time comes, our scientists will be armed with the necessary information for ensuring that the people that arrive will be hail, hearty, and prepared to tackle the challenges of exploring a new world!

Explore further: Tests ensure astronaut, ground crew safety before Orion launches

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5 / 5 (2) Jun 15, 2018
"By allowing the crew to evolve under a list of adaptive social engineering principles (namely, yearly evaluations of the vessel population, offspring restrictions and breeding constraints)"

Sorry, but the minimum crew proposed sounds like a population ripe for revolt. Breeding constraints means mating based on genetic diversity. Forget dating and social norms (like dating and marriage). Remember that the breeding program would have to be maintained for 20+ generations.

Increasing the minimum by a factor of 5 or 10 sounds much more plausible.
1 / 5 (2) Jun 15, 2018
Why Proxima? A crap star with a crap planet & it's receding from us. You have to launch in the direction the target system is traveling. Not at it's present location.

By then Alpha Centauri will be closer to Sol. Still to be determined if it is worth the effort.

Except MAYBE restocking volatiles & other consumed materials. Instead of wasting time bleeding off precious delta/v stopping to refuel? Send a fleet of robots ahead to collect the materials, to sling them out to rendezvous with your community ship.

Those robots can also do a preliminary. close-up recon of the system. To determine if stopping would serve any purpose that robots couldn't do better. Except of course for the all important ego boost of being videoed planting whatever flag on an alien world. Cause we've got to keep our priorities straight. For those all important bragging rights!

If a Living World should be found? For onsite recon, robots built in sterile conditions should be sent.
3.7 / 5 (3) Jun 15, 2018
1) carry a sperm/egg bank with millions of different individuals

2) the greater concern is social breakdown after the first generation grows old and loses power

What's likely to happen is a degeneration of information between the generations through a sort of "broken telephone" effect even assuming that the later generations turn out physically and mentally healthy, because all they would have ever experienced is life on a space ship. What their understanding and motivations are is anybody's guess, so they might even be starting wars about who gets to have the top bunk.

The whole thing would have to be constructed like a prison ward run by immortal robots to keep the people in line, but then what would you get? Would the AI just kill anyone who disobeys? Would that be literally everyone?
5 / 5 (3) Jun 15, 2018
Forget dating and social norms (like dating and marriage).

Only procreation itself would have to be strictly regulated for this to work. The population would still be able to date, have sex and marry.
1 / 5 (3) Jun 15, 2018
Trouble is going to be enforcing those commandments chipped in stone by earthside eunuchs.

For crying outloud! Once you are in Space and you have resolved the dual problems of irradiation and gravity? There's an entire empty universe with umpteentonnage of resources drifting around to be artificed and populated.

Think BIG! Little tincans and sparse monastic cells hewn in rock will be an unnecessary act of self-flagellation! Whom is going to set the limits for Mr & Mrs Future once they are out of your clutches?
not rated yet Jun 15, 2018
the Daedalus is what we should use to go to Mars and stay.
5 / 5 (1) Jun 16, 2018
Crew of all women, plus a load of deep frozen eggs with lots of genetic diversity.

Yer welcome.
3 / 5 (4) Jun 16, 2018
We haven't evolved enough out of the caves to be worth populating other planets. Why do we want to send such low consciousness humans to poison other environments in the galaxy? We can't even figure out how to stop fighting among ourselves on this planet, and so we want to populate others so we can, what, fight there, too? Its unlikely we could figure out how to get along long enough to survive the entire journey, anyway. Let's realize together the Oneness of Mind that's underneath separate human egos before attempting what would be a doomed endeavor.
2.7 / 5 (7) Jun 16, 2018
Well b3, I was going to warn you against expressing sensible and reasonable ideas on this forum.. A good many of the commentators just can't handle any good advice against their bloated egos.

I agree with your assessment that humans need to make a better effort for the survival of life on this world. Before we go raring off to inflict our mass stupidity and greed on the rest of the universe.

The good news is, those most eager to commit genocide on Alien Life? Are in general, the most incompetent to actually accomplish the mission.

The bad news is these incompetents are successful at exactly one task. Destroying the Earth's biosphere.

Uhh, I suppose it would be genetic improvement for Humanity. And a respite for the beleaguered Earth Life. If we shipped all those wanna-be-a-conquistadors to that deathtrap Mars.
Da Schneib
not rated yet Jun 16, 2018
Sex is one thing; mating is another. There is such a thing as birth control.

But such a small population would indeed pose problems that a larger population would not face, problems that could force draconian solutions and oppression because survival is at stake.

Then there's the argument about birth labs and artificial wombs. And genetic engineering.
3.7 / 5 (3) Jun 16, 2018
hollowed out asteroids, 1g acceleration out, reverse and 1 g deceleration to a stop ( from Stanislov Lem)
no radiation, no gravitational deprivation and, depending on asteroid composition, much resources - all this stuff may take hundreds of years to prepare, but they will definitely take hundreds of years in travel, so who cares, and lets move whole cities worth of people, something that could start a civilization any place with enough resources, anywhere in the galaxy.
not rated yet Jun 16, 2018
Then there's the argument about birth labs and artificial wombs. And genetic engineering.

It's already possible to synthesize genes, so with some R&D it should be possible to make a databank of billions of individuals, and then swap that genetic code in the eggs/sperm of the crew members, which would totally eliminate the genetic diversity issue since you can essentially re-generate the genetic variety of earth once you reach the target.

That solves the social problem as well, because you could in theory genetically engineer a bunch of human "robots" with all the undesirable and unneeded traits removed, so you could essentially have a space ship full of clones of the perfect spaceman for the transit part of the mission, and then regenerate normal humanity once you reach the destination planet.
5 / 5 (1) Jun 16, 2018
The question of what sort of "material" should be sent over is always a matter of what anyone thinks should be the "destiny" of mankind. The issue is that every kind of individual has a point - sometimes you need ruthless dictators, sometimes mellow collectivists, sometimes you need crazy people to shake things up, sometimes rigid rationalists to make things work. Evolution is about throwing everything at the wall to see what sticks, and trying to limit the process most likely ensures an extinction because it's ruling out possible ways to get out of a dead end.

If you try to engineer the perfect human being, like one wise guy once said, "I can perfectly imagine a plague of saints".

not rated yet Jun 17, 2018
unless there is a planet with a biosphere there that can support human biology, which I imagine is extremely unlikely. there's no point of going there. unless you want to live under a dome, which you can do in this solar system. no need to go that far.
not rated yet Jun 17, 2018
Going so far in space isn't going to happen soon. Going to Mars and other places we could adapt or where we could adapt ourselves would probably be easier and wiser.
Let's not forget space colonies as well. O'Neill cylinder and the such could allow our population to grow somewhere else, if our solar system feels full already.
I can imagine science evolving well enough to allow manking to find new way to travel through space waaaaay faster than it actually does and go to other solar system (and further?), but more easily with space colonies included and several centuries (millenias?) spent in our current solar system than without them.
not rated yet Jun 17, 2018
Multi-generational spacecraft to other stars are a bad idea. We need revolutionary new methods to get us there a lot faster than current technology allows.

Inbreeding, no matter how large the crew, which size is limited by the investment, will corrupt DNA to the point where all the male colonists will arrive at their new world born into their lives with a head full of hair and a business suit, not to mention an absent functioning X chromosome. Not a good prescription for establishing diplomatic relations with another world.
4 / 5 (1) Jun 17, 2018
Who would want to go on a trip like this?
1) you'll die along the way
2) your offspring might curse you for forcing them to spend their lives in a ship rather than on a nice planet
3) you'll probably be passed midway by a much faster ship with more advanced technology. Would they stop? Could they?

The only good reason might be if the entire solar system would soon be unlivable and cryosleep wasn't possible. Then the number of passengers to go per ship would be determined by whatever tech was available at the time.
not rated yet Jun 17, 2018
DNA... will corrupt DNA to the point where all the male colonists will arrive at their new world born into their lives with a head full of hair
-So how does DNA decrepitate in 2-5 gens?

Anyone see the recent Chris pratt/jen Lawrence movie Passengers?

"On a routine journey through space to a new home, two passengers, sleeping in suspended animation, are awakened 90 years too early when their ship malfunctions. As Jim and Aurora face living the rest of their lives on board..."

(Spoiler alert) he woke her up on purpose. Cold. But the ending left one with 2 questions; if the passengers were meant to sleep the whole trip why was the ship built like a huge trump casino... and why did they die without reproducing? That was the whole point of going, yes?
Da Schneib
1 / 5 (1) Jun 17, 2018
@Eikka, seems to me that a lot gets left out if you just take a bunch of genetically engineered colonists and dump them in a new environment. You won't get "humanity" as we know it. We are not just the product of our genes; culture is also required, and I invite you to examine authoritarian and religious societies for examples of a culture that is self-perpetuating and static.

And the argument about genetically engineered semi-clones is going to be religious; they're already using religious arguments and have been for going on 200 years to oppose abortion.
Da Schneib
1 / 5 (1) Jun 17, 2018
Let me give the gut punch: they'll be calling children (children!) born from artificial wombs "demon spawn" in a heartbeat and putting them in concentration camps, just like any number of authoritarians have put children in concentration camps over the centuries.
not rated yet Jun 17, 2018
I just found this article today, and was amused because last night MeTv ran the Star trek TOS episode "For the world is hollow and I have touched the sky". Some of the comments here were explored in that episode. After 10,000 years, the people seemed pretty normal, of course they appeared to have the standard Star Trek artificial gravity, but they were ruled by an AI that would punish and even kill them for saying or thinking "bad things", and only the High Priestess was allowed to choose her mate.
not rated yet Jun 17, 2018
People are imagining some sort of prison-like ship and a boring ride. I think if people do this they would have a rich VR life available for them.
not rated yet Jun 17, 2018
Multi-generational spacecraft to other stars are a bad idea. We need revolutionary new methods to get us there a lot faster than current technology allows.

Inbreeding, no matter how large the crew, which size is limited by the investment, will corrupt DNA to the point where all the male colonists will arrive at their new world born into their lives with a head full of hair and a business suit, not to mention an absent functioning X chromosome. Not a good prescription for establishing diplomatic relations with another world.

That's easily solved by bringing a few thousand frozen cells.

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