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I have a work-in-progress scenario where an interstellar generation/ark/cryogenic ship has reached its destination, but there are no habitable planets. There's no turning back, and so now the colonists have to try and eke out a living in space and/or airless planetoids. At least initially, there is no suitable habitat to have farms, and not sustainable for the given population.

Given there is plenty of energy available, a small amount of existing organic material to be recycled, and carbon, hydrogen, nitrogen, oxygen, phosphorus, sulfur and possibly other chemicals available to be gathered/extracted/mined, is it technically/realistically feasible to be able synthesise a constant life-sustaining completely nutritional (if not appetising) food/substance? I'm looking for something more Haber process rather than Star Trek replicator.

The precise details of how this would work aren't too important; I just want to avoid a possible plot hole.

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Isn't this what plants do? – iAdjunct Feb 16 at 13:12
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I think I see a bigger plot hole: Why did the ship set out with a destination of an uninhabitable region of space? – Frostfyre Feb 16 at 13:17
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@Frostfyre you can't be 100% sure what's there until you get there? – Nick Feb 16 at 13:22
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What did they eat during the trip out? – JDługosz Feb 16 at 13:32
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This question of "how could they NOT know it was uninhabitle" digresses from the original question, but it's a fun question in itself. If you want to be really dramatic: Everything the telescopes told us showed that the planet is either habitable or at least doable, but of course any image of a planet 200 LY away is 200 years old. When the colonists get there, they discovered that a comet had struck the planet in the intervening decades, and the dust cloud had killed off most of the life forms. (The good news is, there may still be organic material left in some form) – Shawn V. Wilson Feb 16 at 17:04
up vote 10 down vote accepted

Yes, molecules can be made from scratch using primitive chemistry. Your plot will not be the general principal but in trying to identify and learn to synthesize every last vitamin needed.

To make the set-up for your plot more believable, you can have an in-flight disaster destroy the planned capability and stores. They are left with primitive chemistry that they need to bootstrap from 19th century technology.

Their redundancy and general salvage might come up with some nutritional algae and fungi if not a few herbs, but they find it is not a diverse enough diet to survive on. They need to synthesize things like vitamin C and who knows what else.

Whether they've arrived at another star system or are still aboard the ship doesn't matter much but affects the details.

I think such a story could be an interesting problem-solving SF if written by a chemist. It could have been an Asimov novel, had he not been taken from us prematurely.

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Things are starting to look bad for our colonists. :) – Nick Feb 16 at 14:24
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+1 because I'm now imaging a generation ship having to synthesize Vitamin C within a few months, or slowly die of scurvy. – Xantix Feb 17 at 1:20
    
Scurvy is interesting plot-wise, because of the connection to voyages of the past. There are actually different diseases for each culture, based on what their food store was and what was lacking. In Destiny's Road by Larry Nivin, it was a particular element missing in the planet's biome that came as a surprise to the colonists. – JDługosz Feb 17 at 3:28
    
Check out the Vikings. They didn't have anything convenient that was wrong, so missed the whole scurvy thing. They shipped out with dried leeks and fish as their primary staples. – The Nate Feb 17 at 7:13

How were the settlers anticipating feeding themselves? I would assume that seeds and farm animals would come along for the ride; even if the planets were habitable, there is no way to know what plants and animals live there, or if they are even edible; however, without the anticipated crop and ranch land, the animals and seeds have to be kept in cryo-storage until habitable domes are set up.

That said, synthesizing food is possible, though not easy, and it's not a good long-term plan. The human body needs a lot of different nutrients to survive, and synthetic sources aren't always as good for you as natural ones.

Water

Without water, there's no point in synthesizing anything, because no one will live long enough to see it. Hopefully, the population has enough water to survive, and a way to recycle waste; there may occasionally be water to find in space, but there is no guarantee. If there's no water, then the population is dead.

Micronutrients

Micronutrients are required in small amounts; the inorganic nutrients would be easy to either find or synthesize: Boron, Cobalt, Chromium, Copper, Fluoride, Iodine, Iron, Manganese, Molybdenum, Selenium, and Zinc. Any of those not found locally could be even be pulled from parts of the ship; with requirements in the microgram to milligram range, supplies would last quite a while, and generally could be extracted from waste. Organic nutrients (vitamins A, B complex, C, D, E, K, and Carotenoids) are harder to make, but not impossible, especially if you have some basic building blocks and the right equipment. Certain vitamins (especially vitamin D) are created naturally in the body; other vitamins like C are quite easy to synthesize. Many of the B complex vitamins, however, would be fairly difficult to synthesize, and unfortunately are required for healthy living. Difficult, but not impossible. Luckily, the human body can go without many micronutrients for months, even years, with only minimal health impact. Small amounts of micronutrients, far below the recommended values, would be enough to sustain a population of adults for quite a while. Children, of course, should get as much as possible, as their developing bodies need more nutrients than adults.

Macronutrients

Macronutrients are needed in much greater amounts: carbohydrates, proteins, fats, fibers, and alcohols, the basic sources of calories, as well as essential structures like fatty acids. Of those, carbohydrates and alcohols are very easy to synthesize; both have simple structures that can be created in a lab, though it is much, much easier to distill them from organic sources like plants. Synthetic fiber is fairly easy to create as well, and only needed in low amounts, especially with a synthesized diet designed for minimal waste. Synthetic fats have fairly simple molecular chains and could be synthesized. Synthetic protein, however, has yet to be created in a lab, except by cloning - which, frankly, might be the best option. Cloned meat would be much easier to create than chemically-produced food, and the cloning process would use much, much less material. Assuming there are farm animals, samples could be taken from still-frozen creatures for cloning.

Bacteria

While bacteria isn't technically a nutrient, it is required to break down food into a digestible form. On Earth, helpful bacteria is easy to come by, but in space, in a sterile environment with no access to other living beings, it's possible for the bacteria in your gut to go extinct - especially if everyone takes any medication that kills off bacteria. I expect one of the biologists will be a "bacteria rancher", keeping a healthy population of gut bacteria in a maintainable way. Otherwise, all it takes is one round antibacterials to wreck your digestion process forever.

Short term

Many nutrients can be ignored for quite a while; not taking any vitamins for a week (or a month) won't kill you, though going for months on end will make you sick. Most people can go without food for a month without dying, and living on reduced calories for several months would have no lasting side effects apart from weight loss. Synthesized nutrients can replace "real" food for even longer, but be aware that synthetic sources of food often have reduced impacts - that is, eating natural vitamins from a plant will have more impact than synthetic vitamins. Frequent, mandatory checkups can help lessen any nutrient deficiencies.

The best case is that the worldship anticipated a "ramp-up" period before the first crops came in, and kept a large stock of pill-form micronutrients and desiccated macronutrients to tide the settlers over. In that case, there would be enough to time clone protein and synthesize the other nutrients, and hopefully get some plants growing. Even basic fungus would be an enormous help towards synthesizing many nutrients.

Long term

While it may be possible to sustain a population indefinitely on cloned meat and synthetic vitamins, the population will begin to develop various diseases and disorders over time. They will need to focus on building a suitable long-term habitat; assuming they can find a planet with suitable gravity, they should be able to set up habitation domes within a few weeks, have viable gardens within a year. With enough room, in a few years they should have enough herd animals to start eating real meat. Life will still be tough, but at least they won't starve.

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Yes it is theoretically possible to re-re-recycle the elements over and over again till infinity, provided that you have sufficient energy to invest in the process. However the process might take a long time to finish and may involve very complex procedures.

The determining factors are these:

  • The extent of chemical labs available to the crew.

  • The amount of time available before the cycle of usage and production stabilizes.

  • The amount of chemicals available for initial consumption.

  • The amount of energy available for spending and the form in which they are available. Generally you want to have a limitless supply of electrical, thermal and light energy available.

  • The number of crew available for carrying out the synthesis. The more, the better.


Edit to add:

1- How automated do you think this process could be made?

With our current technology, semi-automatic. It also depends on which ingredients are readily available from the environments and which have to be recycled. For example, consider a scenario where you get all the vital organic elements from the planet except oxygen. Here you will have to always wear a helmet (when out on the planet) and only breathe inside it. The coating of sodium peroxide on the inner sides of the helmets reacts with carbon dioxide and releases oxygen (while also turning sodium peroxide into sodium carbonate). You can never let even a tiny breathe waste away in the atmosphere of the planet as you can never get it back.

You also have to consider the difficulties in collecting the products you want to recycle. For example, in the above scenario, since there is no oxygen on the planet, there is also no water. Which means that you have to have special types of urinals, which collect the urine and slowly evaporate them (only pure water evaporates, leaving salts as residue). Special condensers inside the mothership then condense water vapor back into drinkable water.

All in all, how much automatic the process could be made, depends solely on the level of technology available and the type of elements/compounds you want to recycle.

2- Would it require a big factory, or would you think it could be reasonably portable (this is the "future")?

We do not know what level of tech would be available in "the future" so I can only answer the question as per my knowledge of the current technology. If you decide to make a big leap of technology in your work, feel free to do so. As a general rule in science fiction works, never go on in too much detail to make things look real and practical. Just state the general idea and a few hints on how things are done. Leave the rest on readers/viewers to imagine.

Also, once again this depends on which compounds do you want to manufacture. For example, if you don't have freely available oxygen on the planet but have large bodies of water, you do not need to "recycle" your breaths (no need of those precarious helmets presented in the first answer). You can simply produce breathable oxygen by electrolyzing the water found on the planet (and surprisingly for most of us, water is surprisingly common on planets) which can be done comfortably and easily within a single room and can even be integrated inside the mothership's infrastructure. However if you want to produce nutritious food by recycling human digestive waste, this is going to take a really complex process which would probably require a small factory sized installation.

3- Or is this stretching the idea too far?

Read above. I suggest, you place most elements on the planet and only keep few as scarce. These could be calcium and phosphorous. For these you only have to recycle the dead bodies of the deceased people/animals and extract all these elements in their bodies. This would also make the plot somewhat catchy.

4- It'd be pretty bleak if everyone had to work on a production line.

Not really. Everybody could be on a production line for ... lets say ... 1 hour everyday. Make it a routine duty for everyone. Or ... you can divide the procedure so that some people have to work on recycling as their main duty, while others have to only work one hour per day and wear special suits which absorbs their sweat so as not to let any moisture go wasted (again, for oxygen depleted planets).

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p.s. notice (very carefully) that those people must live in a seme-open system. As in, they have to live in a place where they are free to bring in objects, but must not let any wastage of a precious/scarce element. For example, if the planet does not have any oxygen (not even in compound state), the people must never breath out in the open atmosphere because it would be impossible to then catch that lost carbon dioxide and recycle it for extracting oxygen. – Youstay Igo Feb 16 at 13:46
    
Many good points to think about, thanks. How automated do you think this process could be made? Would it require a big factory, or would you think it could be reasonably portable (this is the "future")? Or is this stretching the idea too far? It'd be pretty bleak if everyone had to work on a production line. – Nick Feb 16 at 14:22
    
Read my update answer below the line. This answers your question in some detail. The place in comments is too short for the reply. – Youstay Igo Feb 16 at 16:18
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This makes me think of Arrakis from Frank Herbert's Dune. Water was such a precious resource that everyone in the desert wore suits to preserve every droplet and the dead were processed to maintain the tribe's water supply. – Kys Feb 16 at 18:27
    
No oxygen -> No glucose -> No energy -> No living. The chemical reaction(s) that allow respiration convert glucose + oxygen -> water + carbon dioxide + usable energy. There is oxygen in sugar... – wizzwizz4 Feb 17 at 10:23

If you are traveling on a one way trip to some far off planet you make plans with the expectation that there WILL NOT be anything there to help immediately feed you and keep your power supplies going.

What I'm saying is you are going to be sent with enough supplies to feed everyone for a reasonable time and enough supplies to start gardens and likely even livestock would be in cryofreeze to help start up a colony.

So you will be bring seeds, and even bacteria needed to start producing a soil for plants to grow in, since even a habitable planet will still need these things.

Most likely if most/everyone is frozen for the trip, then 'unfreezing' would be a regulated process. A few people at first to start. Maybe finding an asteroid to hollow out and terraform (with the help of robots) and then starting up a hydroponics lab in the ship to start growing fresh foods and producing needed bacteria and soils.

as systems expand and more and more people are 'thawed' out to help out and continue expanding the livable spaces and generating foods, creating soils etc. Some of this stuff might have come along with ship. Maybe some good soil to begin with, some grass growing in a 'yard' etc.

But there is no way anyone would travel with the expectation that when they get there they can all thaw out, disembark on a planet and start tilling the soil, let the cattle graze and start a western movie.

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Non-biological food synthesis is likely to be an iffy proposition, if for no other reason than the issue of trace elements. You've mentioned the obvious elements: carbon, hydrogen, oxygen, nitrogen, sulphur, and phosphorous.

You've left out a whole slew of others: sodium, chlorine, iodine, zinc, selenium, copper, molybdenum, chromium, calcium, iron, magnesium, bromine, manganese, silicon, nickel, boron and vanadium, at the least. See here, for instance.

Management of these elements is likely to be tricky, since many of them are notably toxic in large quantities. Note that some elements seem to be needed in ng/kg quantities. Plus, the issue of bioavailability needs to be considered, especially since many of these require ingestion in certain classes of compounds, and may or may not be usable if not in the appropriate form.

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In principle, yes. The formose reaction starts with formaldehyde (a simple molecule consisting of one carbon atom, one oxygen and two hydrogens) and produces an array of different sugars.

Unfortunately the result is poisonous to eat, both because not all sugars are edible and possibly also because it still contains some formaldehyde, which is fairly nasty stuff by itself. However, with sufficient investment in chemical techniques this could probably be tamed to produce only a specific type of sugar, which could then by used as a starting point to synthesise more complex food molecules, such as larger carbohydrates, fatty acids and proteins. Again this assumes considerable investment in chemical expertise, but it's not far beyond what's achievable even with present technology, if there were sufficient reason to perfect it and make it safe.

However, it may well be that it's cheaper and easier to just use bacteria instead. After all, a bacterium is already a machine that can break down existing organic material into its basic constituents and then (with the help of some energy) build them back up again into sugars, fats, proteins and carbohydrates. Doing all this chemically would be very expensive and it may well be hard to beat 4 billion years of evolution in terms of efficiency. (Though for the sake of a story, it's not completely implausible that you could.)

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