What is the optimal selection for a small self sustaining space farm?

Question

There are a multitude of resources about growing food in space, NASA research indicates we have been growing foods in space for years. Colonies in Space by T. A. Heppenheimer seems to have some research behind it, but it measures production in acres, and assumes large colonies of thousands of people.

For a long space journey or a planetary settlement, abundant solar energy or sufficient electrical energy to simulate solar energy would be a basic requirement. Everything else would need to be self sustaining in the food energy life cycle. After sufficient air and water recycling have been addressed the next concern is meeting the human dietary requirements.

Assuming a small group of humans with limited area for growing, and a hostile environment (space or planet) what would be the optimal garden/farm products for self sustaining indefinitely?

Answer 1

One of the longest lasting (tiny) self-sustaining ecosystems is the Ecosphere. You can't eat it, but it's completely sealed and lasts for about two years, but can be as long as seven. It contains tiny shrimp, algae, some bacteria, and seawater. You need to keep it at about room temperature in indirect sunlight, but other than those requirements you could keep it anywhere(although most people have them as desk toys).

Because of thermodynamics and trophic levels, you would probably need about 10 times the weight of the crew in plants at minimum, and probably more like 100. Humans would probably not provide adequate nutrient recycling on their own, so they probably couldn't be the only herbivore species. If nothing else, you'd need something that could eat our banana peels, etc. So that puts a lower bound on the size of such a farm.

I would expect the actual participants in the farm wouldn't make as much of a difference as you think, but I suppose things like the oxygen crisis are a counterargument.

Answer 2

Allow me to try and describe to you that magnitude of this question

The crux science here isn't necessarily genetic engineering, its ecological engineering with a comprehensive understanding of microbiology. To create a self sustaining environment as you describe is in reality synonymous with a self contained ecosystem. These are very hard to create (I've been looking into them alot lately with a curiosity of Koi).

There are several reasons why engineering such ecosystems are incredibly hard.

1) Diversity - One of the reasons we (humans) haven't killed ourselves off yet is because we live in a global ecosystem that has overcome an Eon of ecological disasters. When something goes wrong somewhere organisms can rapidly emerge to balance out that imbalance. Like the Oil Spill in the Gulf of Mexico that was thought to wipe out all life in the ocean barely caused a blip. That is because extremophiles exploded into the imbalance and took care of it. Engineered ecosystems lack the diversity to handle imbalances (this is mostly due to our rather limited knowledge of the microbial world). So when one species for one reason or another dies then all the other organisms in the engineered system die as well.

2) Decomposition - This is related to the above which is the main fact but this warranted a distinction. To exist in a closed ecosystem that is self sustaining, every waste item must be decomposable back into a nutrient structure that your flora can absorb. This is actually a very complicated process. In koi ponds there are things called live filters which contains 2-3 species capable of decomposing fish waste into nitrates and phosphates which plants love. However, these arent designed to handle a dead fish. This is the problem when making a self sustaining ecosystem. You need to be able to decompose ALL the parts of the members in that ecosystem.

So in a self sustaining human ecosystem you need to be able to break down human bodies, bone included. This also includes plant matter not consumed by humans like leaves and branches. This brings us to the problem with decomposition. The very organisms adapted to decomposing a dead organism also tend to adapt well to decomposing living members of that organism. This one of MANY reasons why human infections are becoming more prevalent and adept. This is also an entry point into modern waste management processes and advancement.

To Conclude

What you are asking is not impossible, it is just not fully researched yet. The question isn't what could be grown to be self sustaining. The question is what do you need in order to support the members of your ecosystem. We humans can survive off a wide variety of diets, but which members do you want and how do you support them is the real challenge.