Keeping a crew of 500 alive for the journey to another star

Keeping a crew of 500 alive for the journey to another star
Weighing in at 60,000 tons when fully fueled, Daedalus would dwarf even the Saturn V rocket. Credit: Adrian Mann

There's no two-ways about it, the Universe is an extremely big place! And thanks to the limitations placed upon us by Special Relativity, traveling to even the closest star systems could take millennia. As we addressed in a previous article, the estimated travel time to the nearest star system (Alpha Centauri) could take anywhere from 19,000 to 81,000 years using conventional methods.

For this reason, many theorists have recommended that humanity rely on generation ships to spread the seed of humanity among the stars. Naturally, such a project presents many challenges, not the least of which is how large a spacecraft would need to be to sustain a multi-generational crew. In a new study, of international scientists addressed this very question and determined that a lot of interior space would be needed!

The study, which recently appeared online, was led by Dr. Frederic Marin of the Astronomical Observatory of Strasbourg and Camille Beluffi, a particle physicist with the scientific start-up Casc4de. They were joined by Rhys Taylor of the Astronomical Institute of the Czech Academy of Science, and Loic Grau of the structural engineering firm Morphosense.

Their study is the latest in a series conducted by Dr. Marin and Beluffi that address the challenges of sending a multi-generational spacecraft to another star system. In a previous study, they addressed how large a generation ship's crew would need to be in order to make it to their destination in good health.

They did this using custom-made numerical code software developed by Dr. Marin himself known as HERITAGE. In a previous interview with Dr. Marin, he described HERITAGE as "a stochastic Monte Carlo code that accounts for all possible outcomes of space simulations by testing every randomized scenario for procreation, life and death."

From their analysis, they determined that a minimum of 98 people would be needed to accomplish a multi-generational mission to another star system, without risks of genetic disorders and other negative effects associated with inter-marrying. For this study, the team addressed the equally important question of how to feed the crew.

Credit: Universe Today

Given that dried food stocks would not be a viable option, since they would deteriorate and decay during the centuries that the ship was in transit, the ship and crew would have to be equipped to grow their own food. This raises the question, how much space would be needed to produce enough crops to keep a sizeable crew fed?

When it comes to space travel, the size of the spacecraft is a major issue. As Dr. Marin explained to Universe Today via email:

"The heavier the satellite, the more expensive it is to launch it into space. Then, the larger/heavier the spaceship, the more complicated and resource-expensive will be the propulsion system. In fact, the size of the spaceship will constrain many parameters. In the case of a generation ship, the amount of food we can produce is directly related to the surface area inside the ship. This area is, in turn, related with the size of the population aboard. Size, food production and population are in fact intrinsically connected."

To address this important question – "how big does the ship need to be?" – the team relied on an updated version of the HERITAGE software. As they state in their study, this version "accounts for age-dependent biological characteristics such as height and weight, and features related to the varying number of colonists, such as infertility, pregnancy and miscarriage rates."

Beyond this, the team also took into account the caloric needs of the crew in order to calculate how much food would need to be produced per year. To accomplish this, the team included anthropomorphic data in their simulations to determine how much calories would be consumed based on a passenger's age, weight, height, activity levels, and other medical data.

"Using the Harris-Benedict equation to estimate an individual's basal metabolic rate, we evaluated how many kilo-calories must be eaten per day per person in order to maintain ideal body weight. We took care to include weight and height variations to account for a realistic population, including heavy/light corpulence and tall/small people. Once the caloric requirement was estimated, we computed how much food geoponics, hydroponics and aeroponics farming techniques could produce per year per kilometer square."

Keeping a crew of 500 alive for the journey to another star
The Project Orion concept for a nuclear-powered spacecraft. Credit: silodrome.co

By comparing these numbers with conventional and modern farming techniques, they we are able to predict the amount of artificial land that would have to be allocated to farming inside the vessel. They then based their overall calculations on a relatively large screw (500 people) and derived an overall figure. As Dr. Marin explained:

"We found that, for an heterogeneous crew of, e.g., 500 people living on an omnivorous, balanced diet, 0.45 km² [0.17 mi²]of artificial land would suffice in order to grow all the necessary food using a combination of aeroponics (for fruits, vegetables, starch, sugar, and oil) and conventional farming (for meat, fish, dairy, and honey)."

These values also provide some architectural constraints for the minimum size of the generation ship itself. Assuming the ship were designed to generate artificial gravity by centripetal force (i.e. a rotating cylinder) the would need be a minimum of about 224 meters (735 feet) in radius and 320 meters (1050 feet) in length.

"Of course, other facilities besides farming are necessary – human habitation, control rooms, power generation, reaction mass and engines, which make the spaceship at least twice larger," Dr. Marin added. "Interestingly, even if we double the length of the spaceship, we find a structure that is still smaller than the tallest building in the world – Burj Khalifa (828 m; 2716.5 ft)."

For aficionados of interstellar space exploration, and mission planners, this latest study (and others in the series) are highly significant, in that they are providing an increasingly clear picture of what the mission architecture of a generation ship would look like. Beyond merely theoretical propositions of what would be involved, these studies provide actual numbers that scientists may be able work with someday.

And as Dr. Marin explained, it also makes such a grandiose project (which seems daunting on its face) appear that much more feasible:

Keeping a crew of 500 alive for the journey to another star
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

"This work gives us an insight on the real possibility to create generation ships. We are already capable to build such large structures on Earth. We have now quantified with precision how large should be the surface dedicated to farming in generation ships so that the population can feed during centuries-long trips."

According to Marin, the only remaining issue that needs to be explored is water. Any mission involving a large crew spending upwards of a few centuries in interstellar space is going to need plenty of water for drinking, irrigation, and sanitation. And it is not enough to simply rely on recycling methods to ensure a steady supply.

This, Marin indicates, will be the subject of their next study. "In deep-space (far away from planets, moons or large asteroids), water might be very difficult to collect," he said. "Then the resources on-board might suffer from the lack of water. We must dedicate our future investigations to solve this issue."

As with most things pertaining to deep space exploration or the colonization of other worlds, the answer to the invariable question ("can it be done?") is almost always the same – "How much are you willing to spend?" There is no doubt that an interstellar mission, regardless of what form it might take, would require a massive commitment in terms of time, energy, and resources.

It would also require that people be willing to risk their lives, so only adventurous people would apply. But perhaps most of all, it would need the will to see it through. Barring urgency or extreme necessity (i.e. planet Earth is doomed), it's hard to imagine all of these factors coming together.

However, knowing exactly how much it will cost us in terms of money, resources and time to mount such a project is a very good first step. Only then can humanity decide if they are willing to make the commitment.


Explore further

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

More information: Numerical constraints on the size of generation ships from total energy expenditure on board, annual food production and space farming techniques. arxiv.org/abs/1901.09542
Citation: Keeping a crew of 500 alive for the journey to another star (2019, February 6) retrieved 20 August 2019 from https://phys.org/news/2019-02-crew-alive-journey-star.html
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Feb 06, 2019
"How do you keep them down on the farm? Once they've seen Gay Polaris?"

Feb 07, 2019
The biggest problem is one of choice: only the first generation will choose to be on the ship. All future generations will be trapped by a choice someone else made for them. That's dangerously close to slavery, is it not? How do you deal with those who resent being born in space? You can brainwash them from birth, but when has that ever been a 100% effective solution?

So what happens when a bunch of depressed, hormonal teens decide they aren't okay with everything and they're going to mutiny, take over the ship, kill any dissenters, and head back to Earth? Is someone seriously thinking that some dystopian scenario like constant brainwashing and executing all dissenters is going to work? Or keeping everyone in a coma and having robots handle inseminations, births, and corpse disposal?

There's a very good reason that submarine service is 100% volunteer, and that is that people have to choose to put themselves in harm's way to be even partially reliable. Wake up, folks.

Feb 07, 2019
Very smart commentary, Doc.

In previous articles of unfettered optimism? When I attempted tp point out the short-comings of such sloppy planning? Other readers became incensed that any one would throw cold water on their dreams of ravishing green Orion slavegirls.

People. whom I usually respect for cogent comments about other issues? Were frothing at the mouth at my suggesting they learn from successful mass colonization efforts such as the Mormons.

No. they wanted to emulate Cortez & the Pizarro brothers. I warned that all they'll accomplish is cannibalizing crew as at the Jamestown & Plymouth colonies!

I had suggested they talk to Naval submariners & commercial deep-sea divers. Most important they needed to learn about logistics.

But the twits whined that their comicbooks promised them when they got into trouble a hundred million Km from Earth? Mighty Mouse will show up to save the day! Then they start babbling favorite Sfx & CGI from TV & movies.

Feb 07, 2019
Death by radiation-induced genetic malfunction will be rampant. Spontaneous abortion and stillbirths will limit or eliminate crew replacement. A graveyard vessel filled with corpses will arrive at the destination.

Feb 07, 2019
Not that I think a generation ship would work Doc and rrwillsj, but aren't those technical problems rather than conceptual flaws? The way I see it your arguments are an issue of scale. I was born on this planet of parents who did not consult me about whether or not I thought this was a good idea, and due to my limited resources I can not leave Earth. I happen to be on a much larger space ship some number of magnitudes larger than any proposed ship.

Is there no size of ship that could offer enough varied experience to keep new generations occupied with what they perceive as a full life? Not to mention the whole concept of children leaving their family to make their "own" way is a novel concept no more than a few hundred years old at best. For the majority of human history people were born on a farm, never traveled more than a few towns over, and died on said farms after continuing the cycle by having their own offspring.

Build a bigger ship, no?

Feb 07, 2019
Rhugh, I hope they would consider radiation exposure before launching into interplanetary space let alone interstellar.

I think the biological Island effect would be what would get them. Viruses and bacteria mutate much faster than larger more complex organisms. They would have a hell of a time keeping crops, and I don't know if my answer in the previous comment would work. I have no idea how large a ship it would take to effectively mimic Earths very rich and deep biosphere to the extent that a population (all life including bacteria, and whatever plants and animals are brought along) could maintain homeostasis.

Kim Stanley Robinson's book Aurora was very illuminating in regards to the many many possible things that could go wrong with such an endeavor. rrwillsj I know i know its science fiction but they the author essentially agreed with you so its gotta be worth something no!?

Feb 08, 2019
In my opinion, there are two major hosts of problems. The first host will be tactical, technical issues.
if we can't prevent or at least resolve these technical failures here on Earth?
It'd be a bloody damn miracle to change a flat-tire in Outer Space!

The greatest problem, the most intractable? Is the issue of Gravity.
It must be proven, before Human lengthy space travel will be practical, that biological organisms can thrive, reproduce & sustain over multiple generations in micro-to-zero gravity.

Not looking good so far.
If eventually, there is incontrovertible evidence Biology is an Earth function & has no place in Space? Will people be mature enough to accept the reality? That space travel will have to be experienced vicariously? Through drones & robots?

Yeah? Well, I didn't think so either.

Artificial gravity is one of those bad ideas that will have to be proven & re-proven. Over & again, at great expense. As a futile endeavor.

- cont'd -

Feb 08, 2019
- cont'd -

The second host of problems will be social & psychological. That our society suffers from the delusion that "conquest" is a sustainable form of "progress". No matter how many times Humanity's nose has been rubbed in the self-destructiveness of such an evil addiction.

Then there are the perpetual adolescents who think repeating failures, endlessly, will some how create something they can pretend is success.

"Technical Problems" are not a fault of the workers or their dependents. Replacing workers with robots, will not resolve the problems of productivity or maintenance.

In actuality,. "technical problems" are a Management issue.
As a failure of Management to manage the all too predictable failures.

As a society we refuse to consider "Why". "Faje it till you make it" is the new American slogan. No matter gow dusastorous the consequences.

Why waste resources & lavishly spend with liberal abandon our wealth to accomplish so damn little?

Feb 09, 2019
Salute from behind the iron curtain.
In fact, as You're able to prevent air leakage? Only robots, not humans being! Robots must reproduce themselves. The biggest problem is the source of energy. Nuclear fuel will break down during the flight. The thermonuclear reactor is not built yet.

Feb 09, 2019
I do not see producing energy as a major problem.
If we are sensible enough to use robots? Why waste energy on speed? We are not talking NASCAR here.
Efficient & methodical will be the keys to success.

Aside from the multiple issues of habitat atmosphere & environments.
Biology & machinery produce heat as waste. In the vacuum of Space, disposing of the excess heat is a serious problem.
For safety reasons, a multiple series of methods will need to be developed.

Producing energy will be the simple beginning to the complicated process of how to collect, control, store regionally, distribute regionally, store locally, distribute locally, restore unused excess & salvaged waste energy & dispose of unsafe levels of excess.
All this, safely, efficiently & with built in extra in case of disaster or other unpredictable events.

It is not enough to build a better mouse trap. You have to be thinking ahead when the better mice catch up too you.

Feb 09, 2019
Artificial gravity is one of those bad ideas that will have to be proven & re-proven. Over & again, at great expense. As a futile endeavor.


No, artificial gravity is simple, just rotate the ship. Plenty of problems with long term space travel, artificial gravity aint one of them.

Scaling up the ship would help a lot with both radiation protection and also long term sustainability. Interstellar travel is hard as it is, especially with crew. We are not going to do it with a small ship. A city-sized one will be required.

Feb 10, 2019
SM, if you have invented some miracle material that can withstand the stress & torque of the usage you are describing?

Run! Do not dawdle, your way to the US Patent Office. Before somebody beats you too it. Don't forget to include testable samples!

As for dealing with internal Coriolis forces & inertia? One word "turbulence", If you have those minor details figured out? Please publish the results of successful tests.

A scaled up habitat-ship is a large target for cosmic & other hard radiation. Expecting the structure to protect the contents is just trapping the cascading radiation inside the vessel, with you.

There are two viable options.
Well three, if you are willing to pay for the hermit crab strategy of using a disposable outer shell?
The best existing method?
Is gold-foil, draped over the outside of your vessel. It may reflect or capture a lot of the varieties of Space radiation.

Or invent a shielding energy-capture mechanism. Thrifty.

Feb 12, 2019
The 3 acre Biosphere was not large enough for 8 people for more than 2 years without pumping in extra oxygen, something you can't do past the Oort cloud.
The idea of containing humans for centuries like lab rats is a fools errand.
This is not a journey intended for biological humans.

Feb 12, 2019
The 3 acre Biosphere was not large enough for 8 people for more than 2 years without pumping in extra oxygen, something you can't do past the Oort cloud.
The idea of containing humans for centuries like lab rats is a fools errand.
This is not a journey intended for biological humans.


Wasn't the problem with biosphere (2?) something to do with CO2 from the concrete?

Feb 12, 2019
"As we addressed in a previous article, the estimated travel time to the nearest star system (Alpha Centauri) could take anywhere from 19,000 to 81,000 years using conventional methods."

After arriving at AC, then what? There are no habitable planets there......I guess on to the next star is that it? Another 80k lyrs worth of travel time?

The New Horizons presently travels at 36,5k mph. One light-year is 5,878,499,810,000 miles. it would take New Horizons 18,500 years to travel one light year, 75k to AC.

Feb 12, 2019
I think I'll stay home.

Feb 12, 2019
travel time to . . . Alpha Centauri . . . could take anywhere from 19,000 to 81,000 years


Anything longer than 28,000 years would miss the closest approach of Alpha Centauri to our solar system. After than, Alpha Centauri gets further away.

https://en.wikipe...n_dwarfs

Feb 12, 2019
Minimum velocity to reach Alpha Centauri is very roughly 50,000 mph. Slower than than and Alpha Centauri will simply pass you by.

Feb 12, 2019
Reminds me of the great book

"Footfall is a 1985 science fiction novel by American writers Larry Niven and Jerry Pournelle. The book depicts the arrival of members of an alien species called the Fithp that have traveled to our solar system from Alpha Centauri in a large spacecraft driven by a Bussard ramjet. Their intent is conquest of the planet Earth"

-Earthers collect earths nukes in secret and build a daedalus class ship out of shuttles and ICBMs and battleship gun turrets and misc parts and kick their elephantine asses. Glorious.

Spoiler alert (oop too late)
biggest problem is one of choice: only the first generation will choose to be on the ship. All future generations will be trapped
If you think about this old meme instead of just repeating it you might realize that everybody is trapped right where they are with limited choices and options.
I think I'll stay home
-and wait for the quakes. What a trooper.

George doesnt like anything nuke-powered.

Feb 12, 2019
So what happens when a bunch of depressed, hormonal teens decide they aren't okay with everything and they're going to mutiny
You mean like normal? Theyll have virtual liberal arts colleges onboard you know. Chances are they cant wait to get to their own planet where they can do whatever they want. No draft, no laws, make babies out the ass...
take over the ship, kill any dissenters, and head back to Earth?
Hey why dont you write a novella? Add it to the extensive list. First explain how you turn such a ship around in mid flight.

Feb 12, 2019
Minimum velocity to reach Alpha Centauri is very roughly 50,000 mph

Musk space tesla - 75,560 mph

"Daedalus was to have obtained an eventual cruise velocity of 36,000 km/s or 12% of light speed from over 700 kN of thrust, burning at a specific impulse of 1 million seconds. Travel time to flyby at destination would be approximately 50 years"

-Internet- good for looking shit up and shaming the lazy

Feb 13, 2019
Minimum velocity to reach Alpha Centauri is very roughly 50,000 mph. Slower than than and Alpha Centauri will simply pass you by.


Math is not Otto's strong suit, but try to run the numbers and see what you come up with. AC is going to pass us by in about 28,000 years at a distance of about 3.2 light years. If you don't get there by then, you will have to intercept AC at a greater distance while it is receding. To meet AC at its closest approach you would have to be traveling about 77,000 mph. However, I seem to recall it is possible to intercept AC at down to around 50-some thousand miles per hour as it is receeding. Any slower than that and you will simply miss the encounter.

Similarly, this is kind of like walking 2 miles to catch a train departing at 8 am sharp. If you have 2 hours to get there, you cannot walk slower than 1 mph or you will simply miss the train's departure.

Feb 13, 2019
Musk space tesla - 75,560 mph


What does that even mean with regard to reaching Alpha Centauri? "Musk space tesla" is not leaving the solar system so it is not at all clear how that is related to traveling to Alpha Centauri. How about a link instead of your weak insults?

Feb 13, 2019
SM, if you have invented some miracle material that can withstand the stress & torque of the usage you are describing?
As for dealing with internal Coriolis forces & inertia?
Is gold-foil, draped over the outside of your vessel. It may reflect or capture a lot of the varieties of Space radiation.


You do not need a miracle material. Dealing with Coriolis is trivial, make your radius of rotation at least few hundred meters, and Coriolis is insignificant. Considering that any realistic design is city-sized, this condition is trivially true. As for radiation, you are once again off the mark. You need a several meters thick layer composed of light atoms on the outside. Water, fuel or plastic. That is enough to mitigate the danger of cosmic rays.

Feb 15, 2019
SM, lookup turbulence & pipelines. When you invest that kind of money? There are no trivial forces to blithely disregard.

U don't know if you are old enough to have lived in an building with steam heated radiators.? If not, search through old movie databases & I'm sure you can find several comedy flicks loudly banging away at the subject.

As for petty Coriolis? There is no such critter as "artificial gravity. There is Gravity as a Constant of Mass or there is not mass & therefore, no gravity. Being in a big, rotating pipe you experience Acceleration. DO NOT confuse with Momentum.

Even in an rotating airless pipe, the forces of Momentum caused by Acceleration will apply some harsh lessons.

A real "Come to jeebus moment!"

Acceleration moves you along, Momentum keeps you moving. Then Inertia is what smashes you into whatever is in the path of your trajectory, Just like a bug splattering on a windshield!

- cont'd -

Feb 15, 2019
- cont'd -
I don't give a flaming fart what fabulisms the comicbooks, CGI & Sf/x promise you.

Off Earth is as harsh a place for survival as the very worst, most deadly environments to be found in. on or under the Earth.

Back to the rotating pipe. You have accelerated the pipe to spinning. Pretend the stresses are not ripping it apart. Fill it with air. Remember, no art-g. What is the ring velocity? That air will not remain unmoving. Now you get to experience the Coriolis turbulence.

& for fun, please to explain how you are getting around? As the floor goes one way & you want to go that away?

Back to Gravity. You can shut off, reverse, &/or direct all forms of energy. Except Gravitational Attractant Force. It does not wear out, use-up, shut-down, reverse or direct. It never runs out of fuel. It does not go quietly into the eternal dark night. Gravity in the dark dead universe will be what is left after everything else, all the other Forces are long extinct.

Feb 15, 2019
It is getting stronger . I can tell. It started sapping the spring out of my step, and now has slowed me down going upstairs.

Proof.

Feb 16, 2019
Math is not Otto's strong suit
-And yet I know the relative difference between 50,000 miles per HOUR and 36,000 km per SECOND. Do you?

And re the tesla, we are already propelling things faster than 50kmph.

Feb 18, 2019
Otto, I wrote "Minimum velocity to reach Alpha Centauri is very roughly 50,000 mph." What part don't you get?

Feb 27, 2019
Artificial gravity is one of those bad ideas that will have to be proven & re-proven. Over & again, at great expense. As a futile endeavor.


No, artificial gravity is simple, just rotate the ship. Plenty of problems with long term space travel, artificial gravity aint one of them.

Scaling up the ship would help a lot with both radiation protection and also long term sustainability. Interstellar travel is hard as it is, especially with crew. We are not going to do it with a small ship. A city-sized one will be required.
says shotman maslo

I agree with the size that you're suggesting. City-sized might give 500 Souls aboard a bit more room and not feel enclosed as though in a tin can or a submarine. That would go a long way toward preserving their mental health.

Feb 27, 2019
Sailing the Stars

81,000 years using conventional methods
in space vehicles
for 81,000 years
is problematic
because
of survival of the species
as from a child being born
that child in 30 years, has a family
so
every 30 years
every 30 years each new born child has a family
so
if we dived 81,000/30
equates to 2,700 family's
that as populations compound
2,700 family's is 3,000, 4,000 families and increasing
The Desolate Reality
these families have never know Planet Earth
these families have never felt the sun on their backs, the wind in their hair
and most Desolate
these families have never experienced gravity
so
my friend these families are not coming home
they are too far away
they have evolved in zero gravity
and
finally
because
my friends
they are already home, in the only home these people know
Their home is their Space Vehicle

Feb 27, 2019
When all you know, SEU

As what you know is your home
Your home is your planet, your earth
as
when all you know is your home, your Space Craft
you do not become insane
because
you know no different
but
what you do become
is insular
cut of from the world
no longer exposed to variety, history, culture
and
you pass this devolution on to your offspring
your language suffers
your mannerisms suffer
your whole demeanour suffers
when that day
eventually materialises
when your come face to face with your ancestors
Earthlings, unable to stand our gravitational attraction

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