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I need a spaceship habitat for a million humans, comfortably, for indefinite time.

I have read many questions around here, perfectly answered, about the size a spaceship should be to store enough technology to feed a million people indefinitely. I read about a spaceship which would be a cylinder half a mile wide and a mile long which will include entertainment for roughly 500 people, but not including creating new food.

I would like to expand this further.

By comfortably, I mean with enough space and variety to avoid psychological problems for a lifetime, not locked up in a prison with 20m^2 rooms.

I want a place where enough veggies could be farmed to not only sustain humans but also feed animals to be used as livestock. A place where people can actually "take a walk".

Basically I need a spaceship which could make these people not to regret leaving Earth, even in the hypothesis of never ever finding a suitable planet to land upon.

Making my personal computations, which are very childish, I came upon a sphere (best shape to prevent heat dispersion and to move in space) with around 4 miles radius. Rotating, obviously, to create artificial gravity.

But I will welcome completely different results.

If you think a sphere is not the best shape to move in space and prevent heat dispersion, or to place the thrusters, notify me. If you think no material, ever, not even in 5 centuries, will be able to prevent a structure such size from collapsing while accelerating or to resist minor debris impact, notify me. If you think my numbers are stupid, notify me. If you know there's no way getting enough oxygen, notify me. If you think there's no way getting enough energy for supports and thrusters, tell me.

Basically, as the very beginning of my question, I want a spaceship habitat (so not a human cargo) for a million humans for indefinite time.

Just hard science, given 500 years of human development.

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    $\begingroup$ The question is a bit long and doesn't really get to the point. Could you edit it down to the essentials of what the problem you're trying to solve is? If it's just down to the heat-loss factor, then energy is a problem in your world? What will hard-science look like in 500 years in your world? (You can add the hard-science tag, but be sure to include your hard-science question - at present there doesn't seem to be one.) $\endgroup$ Commented Feb 6, 2023 at 7:19
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    $\begingroup$ I understand the desire to get livestock for meat, but food from animals is incredibly inefficient. Each organism uses energy before it's eaten, and the process of digestion is also energy heavy. Technology to create artificial meats or things like milk goes with leaps and bounds, so you're more likely to have no or little livestock. Any livestock would be multipurpose, like giving companionship, mixing soil, fertilising, meat and eggs. This can make the size of spaceship much more feasible. $\endgroup$
    – Trioxidane
    Commented Feb 6, 2023 at 7:54
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    $\begingroup$ Have you thought about how spin-simulated gravity will work with a sphere? Are you wanting different gravities at different lattitudes in the sphere and/or for all ground to be increasingly sloped as you move further from the "equator" (without terracing)? There's a reason most spun habitats are shaped as cylinders - which you could do by keeping the inhabitable portion a cylinder and then nesting it inside a sphere - but why? $\endgroup$ Commented Feb 6, 2023 at 11:19
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    $\begingroup$ What exactly is your question? Do you want us to design a whole space ship for you? Which aspects of the design would be interesting to you? What design problems do you see which you can't solve yourself? $\endgroup$
    – Philipp
    Commented Feb 6, 2023 at 11:42
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    $\begingroup$ Currently any such experiments ran into a collapse due to oxygen level failure, see Biosphere 2. There appeared to be a runaway bacterial infection that caused atmospheric oxygen to run low, and cause asphyxia in humans and livestock, while bacteria could still proliferate with that low oxygen levels. So, "if there's no way to get enough oxygen" looks true. Also re 20 m^2 - you're speaking about 20 m^**3** as it's volume that matters in space, not square. $\endgroup$
    – Vesper
    Commented Feb 6, 2023 at 14:28

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Let's start with food requirements. Based on this article in Primal Survivor, it takes roughly 5 acres of crops for food self-sufficience. Multiply that by a million, and you get 8,000 square miles. This number will dwarf all other living space requirements combined. In fact, if you had a surface this big, you would have copious living, working, etc. space under the floor of said surface.

I think your optimal configuration for this kind of ship would be an O'Neill cylinder. The default 5-mile diameter, 20-mile long cylinder has an interior surface area of 314 mi2, and is reported to be able to support 50,000 people, so you'd need a fleet of 20 of these.

How much can you compress this? You could stack that in grow spaces, but you said you wanted space to walk around in, so just stack the vegetables (roughly half of the space) and have most of the surface be a big orchard.

On the list of technical challenges to get to this point, I could write a book, and that's not appropriate for this site. I suggest you start by reading the Wikipedia article on generation ships.

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  • $\begingroup$ Thank you. For my worldbuilding purpose I need one single big ship because the overall feeling I want the passengers to feel is the idea that if something goes bad there's no plan B. Surely it would be easier to create a fleet but I'll come with something like the fear of the Govs for frictions between factions, I don't know. One big ship. Can I just make math formulas or we would be crossing some limits I do not foresee like "add joules and you'll have 200C water", no you would get steam for we crossed the 100C degress change of state in normal pressure. $\endgroup$ Commented Feb 6, 2023 at 18:42
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    $\begingroup$ The limit for the diameter is the tensile strength of steel, which gives out around 4 miles. You can get creative by using carbon nanotubes, or running cables across the inside of the cylinder, but this is up to your imagination. $\endgroup$ Commented Feb 6, 2023 at 19:59
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    $\begingroup$ The limit for length is the amount of twisting that it'll do when you try to accelerate it. You could make it 400 miles long, but that would be like pushing a rope. Alternately, you can just pull it, but then the length of the rope would be washed by exhaust. $\endgroup$ Commented Feb 6, 2023 at 20:01
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    $\begingroup$ You can compact the people more, but that's TOTALLY up to your willingness to be creative. O'Neill didn't have stacked farms to work from, so it presumes that the entire inner surface is farming. $\endgroup$ Commented Feb 6, 2023 at 20:02
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    $\begingroup$ @FringesExplorer What you could do is have one engine frame with three or four repeated bundles of six 0'Neil cylinders wrapped around the core/frame. so you can have the habitats that Robert suggests and have the one ship like you are after. $\endgroup$ Commented Feb 7, 2023 at 0:17
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You can feed people on 20m² each using high-yield techniques

  • Takao Furuno fed 100 families on six acres. They ate an omnivorous diet of ducks, eggs, 15+ kinds of vegetables, rice and more, delivered to their door. Instead of chemical fertilizer, he used ducks. Instead of insecticide: ducks. Instead of herbicide: ducks. Six acres is 24,000m². Making the overly conservative assumption that each of the 100 families had an average of three people, that is 80m² per person.
  • "SH garden produces 2 kilos of vegetables a day per 20m2 space" (calling 2kg/day one person's food is more than fair)
  • https:www.youtube.com/watch?v=_BRfvnCDOvE&t=1h03m35s – a guy who designed food production systems for NASA says 20m²
  • https://www.youtube.com/watch?v=ILzWmw53Wwo&t=4m09s – Getjan Meuuws of PlantLab, who develop mathematical models for growing plants: grows 200g of vegetables in a day in 1m², so 2kg in 20m²
  • Another way to think of this: a vegetable (a head of broccoli or whatever) might take 50 days to mature, so each hole grows 0.02 vegetables/day. (I'm also making the pretty reasonable assumption than a head of broccoli is enough veg for a man for a day.) So you need a grow-system with 50 holes, maybe twice that for redundancy. You could stack them four-high while allowing easy hand-harvesting, and indefinitely high with a robot harvester.

Vegetables don't take much room. Meat and grain can. One option is to leave grain out or replace it with potatos, yams, sweet potatoes, etc.

Meat can't feasibly be replaced under current technologies, but could with the technologies of spacemen. You could grow rabbits (eating them vegetables) on a fairly small footprint, and Black Soldier Fly larvae and tilapia.

More futuristically, some sort of precision fermentation (aka protein yeast) could replace meat. Or of course, vatgrown flesh.

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