Is it possible for there to be a generation ship that was completely self-sufficient? An airtight vessel that used plants to create food and oxygen, and reused everything with a tight hold on population control and other such factors. Maybe even taking apart molecules to create other molecules to get things like trace nutrients. Could it be done? Or would everything end up being soil (because of the plant waste turning into compost)?

  • $\begingroup$ This is probably a question for Space Exploration SE. $\endgroup$ – StephenG Oct 25 '17 at 1:17
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    $\begingroup$ @StephenG I'm willing to accept a sufficiently large generation ship as a "world" ... ;D and as such we can sneak it in. $\endgroup$ – akaioi Oct 25 '17 at 1:54
  • $\begingroup$ So...life with only recycling bins? No trash at all? Some things are hard to recycle, like computers and batteries and pets and medical waste. $\endgroup$ – user535733 Oct 25 '17 at 1:55
  • $\begingroup$ Welcome to Worldbuilding! :) There are a couple of incongruent parts to your question, making it unclear. "Is it possible...?" I guess so. But some of the details suggest you may want to narrow down to just a specific part of the question. Is it about self-sustainability? Organic farming vs molecular transmogrification? Lastly I doubt the plastics in the ship will break down into compost if they have molecular control. Do they give up? Get lost? Forget? What you have posted is sort of a zen poem, a thought experiment. But we can't pitch answers when we don't understand what the problem is. $\endgroup$ – wetcircuit Oct 25 '17 at 2:09
  • $\begingroup$ If you think long and hard about this one, you will realize that the earth itself is one very large self-contained generation ship. $\endgroup$ – Justin Thyme Oct 25 '17 at 2:50

TL/DR -- Yep, you sure can!

How do I know? Because we have tiny versions of same, available at amazon.com: https://www.amazon.com/dp/B005J0V33E/

Basically, it's a sealed glass jar with plants and little shrimp inside, like so:

World's smallest generation ship

Update -- some of the reviews claim that they have had this or similar ecosystems live for 9-10 years! That's pretty metal, and relevant to our purpose here.

Now, the bigger the population and the more you actually care about its survival -- shrimp are pretty expendable, right? -- the harder it is. You'll have "slippage", where some compounds accumulate which are hard to reprocess. These can be jettisoned, or used as extra ammunition for your mass-driver weapon. I can imagine your generation ship also needing a big warehouse full of "extras"; extra nitrogen perhaps, extra marshmallows, and so on.

Why all the extras? Well ... mistakes happen. Your calculations may be slightly off. You need margins. You also need extensive testing before you send the ship off; see the sad fate of Biosphere 2: https://en.wikipedia.org/wiki/Biosphere_2

Biosphere 2

Looks pretty, but it was like Mad Max inside. Privately, I think they tried to be too cute about it and model too many ecosystems inside, instead of optimizing for survival, but hey. I wasn't invited to the design meetings...

Update: Hey, what about a light source?

Thanks to Justin Thyme for pointing this out. We'll be a tolerable far way from the Sun for most of our journey, so we'll need to do something. Again, our own primitive technology is edging toward the answer. Check here: https://www.spectrumkingled.com/whats-different-about-spectrum-king-led-grow-lights/ . Specifically:

Spectrum King LED full spectrum LED grow lights consistently emit wavelengths in the range of 380 to 779nm. This includes those wavelengths visible to the human eye (what we perceive as color) and the invisible wavelengths, like ultraviolet and infrared. Our 400+ and SK600 LED grow lights truly mimic natural sunlight while matching intensities of traditional HPS lamps with over 100,000 Lux.

Now this product is aimed toward, um ... mitigating the scourge of glaucoma, but clearly these hobbyists are highly motivated to grow plants away from sunlight, low-flying DEA aircraft, and satellite photography. So, now that you have these lamps, any source of electricity will keep your farms in action!

Anyway -- the technology is there. What's missing is the art and the practicum.

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    $\begingroup$ Your generation ship still needs light from the outside. $\endgroup$ – Justin Thyme Oct 25 '17 at 2:48
  • $\begingroup$ @JustinThyme thanks for pointing that out! I've dropped some ideas about that into the main answer for you. $\endgroup$ – akaioi Oct 25 '17 at 2:56
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    $\begingroup$ I did the math on creating a ship using numbers pulled from Biosphere 2. It wasn't terribly promising: 2000 square meters of biosphere per human and weighing in at 10,000 tonnes of material. $\endgroup$ – Draco18s no longer trusts SE Oct 25 '17 at 3:12
  • $\begingroup$ @Draco18s the mass is going to be tough. The space maybe less so ... 2000 sq meters is just as square 44m on a side. Plus see above for my dark thoughts about Biosphere 2; I think they were showboating a little trying to fit in as many different ecologies as possible. But the mass ... yikes. The shipbuilders had better be really motivated. $\endgroup$ – akaioi Oct 25 '17 at 3:18
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    $\begingroup$ Make it bigger, not smaller. There are reasons we don't build generation ships yet and you will want to have a stable system for more than 10 years and not only in "some of the cases". And something a bit more complicated than a shrimp / plant / bacteria system. the idea with bs2 is if one of your ecosystem has a problem the others act as buffer. So you might want to have more ecosystems and more space, at least up to a decent minimum size. Aurora might be too pessimistic but explains some of the problems of complex systems. $\endgroup$ – Henning M. Oct 25 '17 at 22:07

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