If humans were to establish colonies on the moon, and travel to Mars and beyond, what would they eat? Import from the Earth might be extremely expensive. Would we build greenhouses and/or microbiological farms, that we would irradiate by sunlight and/or artificial light? Could we possibly have a closed system based on recycling, or would we harvest planetary soil and water?
Greenhouses, gently spun in their own small centrifuges 50m wide or so, equipped with freshwater tanks sporting algae (for waste water treatment) could support a thriving farm fish population.
Warmer, wetter greenhouses could raise tropical crops such as banannas, coconuts, etc. Papayas, oranges, you name it.
Dryer, hotter (more desert like) greenhouses could even be used to grow desert crops (such as agave for Tequila fans in the cosmos!)
Corn, wheat, etc could also be grown. No reason why rabbits, chickens, perhaps even cattle for that matter.
Seperate rotating greenhouses could be set to simulate different climates on Earth. Then it is just a matter of tending to the crops and letting them grow. No reason why it couldn't work: provided energy, and resources, and trace minerals, just about anything could be made to grow whether plant or animal.
It's all dependent upon the area (volume) and energy (light) devoted to it.
I don't remember right off hand where to find it, but an old (from when they still expected to get out there any old time now) book on astronautics included an Air Force (or NASA) study on output value versus input value for crops and animals in space. It was a pretty large study, taking into acount (and sorting in multiple tables) the habitat volume, raw material(dirt, rock, water, air, light, etc), mass, gravity(or psuedograv), upkeap work(taking care of the garden, fixing equipment the goat chewed on), etc... necessary, and the food(sorted by nutrients, type, etc), recycling(as in algae), coproduction(leftovers from one thing making it easier to have another, like fish in the algae tank, etc), psychological effect(actually on both sides) and several other things I can't remember right off hand.
Their conclusion were that most of the standard farm animals didn't produce enough usable products for the quantity of supplies (especcially space and food) that they took up. And with plants, some common ones would work, like sweet potatoes and some beans(soy), but others, like corn, wouldn't be very useful. And then there were the more exotic items, algae, yeast, etc. They even had tables showing which combinations to use to get the most out of several of the potential colony and base mission designs that NASA was working on at the time.
And as a side note, pound for pound, rabits convert the largest percentage of their food into usable materials, and they are perfectly satisfied with being kept in a series of small boxes on shelves and being fed dried algae. Just don't let them out of their cages unless it's into a connected exercise ring or the stew pot. And their are several plants that provide food, yet can also to produce things, include some that can be used for makeshift electronics, tho I'm not sure what you would do with that.
And if you want to get such information now, you might try the Echo Foundation, they specialise in determining what combination of plants and animals will produce the most, for the least cost, in any situation, especially ones where resupply is limited(third world countries). Tho you would have to pay for their work, they know what they are doing, as many missionaries can attest.
I think I remember hearing about that Air Force Study. The one I've seen is the PDF's and other documents in a CD bundled with the book: The High Frontier by Dr. Gerard K. O'Neill. The fairly detailed study included water and materials cycling in a closed loop life support system for moderate and large sized space colonies (with between ten thousand and several hundred thousand inhabitants.) The studies looked at crop yields and ways to boost them, the efficiency of utilizing chickens, fish, cattle and rabbits for animal protein--rabbits seemed to be fairly efficient with cattle, I think, being about the worst.
Another excellent book is T.A. Heppenheimer's classic: Colonies in Space. This is another detailed look at Dr. O'Neills concepts, and has a slightly different perspective.
An interesting device that is mentioned in these works is unique, and I'm not sure has ever been tested: A wet oxidation combustor. A heavy pressure vessel is charged with a mixture of solid and liquid wastes--these wastes could be sewage sludge, animal byproducts/wastes, grass clippings, whatever. The mixture is mulched and then pumped into the pressure vessel with plenty of water. It is then heated to perhaps 200 to 300 degrees Celsius under pressures approaching 100 atmospheres (well over 1000 psi) and then pure oxygen is allowed to slowly bubble through the mixture as it tumbles. Hot steam and carbon dioxide are drawn off, cooled--the water condensed and sent to a 'treated' waste water tank. Makeup water and more oxygen are pumped into the wet oxidation reactor. If oxygen is introduced slowly, and is not allowed to build up inside the reactor, then the organic sludge can be completely 'burned' in place.
After several hours, the device will cool off when everything combustable has been oxidized and consumed. The pressure is reduced and remaining water (rich in ammonia) is tapped off for storage in a treated waste water tank. The remaining slurry is a mineral rich fluid which, with the treated waste water, ought to make a pretty good medium for feeding hydroponic crops or even regular crops planted in treated lunar regolith.
In a 'mature' space industrial society, with large amounts of materials extracted from the moon (by mass driver) and from asteroids and comets, then oxygen should be a plentiful byproduct of metal 'smelting' from lunar regolith. other organics and volatiles are presumably fairly easily extracted from near Earth Orbit crossing asteroids, and the occasional comet. Given sufficient regolith processing on the moon, then volities such as hydrogen, carbon, nitrogen, and others could be extracted directly from the upper surface of lunar regolith that has been doped by the solar wind for billions of years. Not to mention the strong possibility of ice in the perpetual shade of craters in the moon's polar regions.
No life support system will likely ever be completely 'closed' [there will always be small leaks, no matter how 'tight' a design is!] but the real question would be at what rate will 'makeup' materials need to be imported to sustain a viable colony? And is that rate sustainable with the likely infrastructure needed to build the colony in the first place?
Interesting questions that will probably not be definitively answered until we take a shot at it!
