Farming in Space

In previous posts I’ve described plans for space habitats which include allowances and techniques for the closed system recycling we will need to establish self-sustaining life in space.

This post describes in some detail just what is needed, and where I found the information. Fundamentally, we will need to provide recycling for nearly everything in space.

Humans breathe oxygen which is plentiful in the form of oxides and silicates, but rare as the free element in space. We each need a bit less than a kilogram of oxygen per day (0.83kg on average, more under high work loads). Note that processes such as smelting metallic ores use heat and a reducing agents such as carbon to turn metal oxides into the metal plus oxides such as CO2. Green plants turn the CO2 into carbon (or carbohydrates), freeing the oxygen, and the carbon can be fed as raw material into the smelter. The only net products of smelting are metal (such as iron) and oxygen.

Humans consume water for drinking, food growth and preparation, cleaning, even entertainment. Since hydrogen is in short supply (until we can gather and use the resources of a comet, in which case we’ll have more than enough to throw away), we’ll need to carefully recycle water. Each human drinks or eats about 2.6 kg of water daily; more is needed for hygiene and growing crops, a lot more.

Working humans need to eat, on average, about 2500 Calories per day (some estimates suggest 2000, my wife’s diet suggests 1500). This can be provided by about 540 grams (dry weight) of food (50g protein, 70g fats, 420 carbohydrates).

The total consumption of a human is about 4 kilograms of oxygen, water, and food per day, and it should come as no surprise that that the same human produces 4 kilograms of waste (in the form of carbon dioxide, exhaled water, sweat, urine, and feces) per day.

Also unsurprising is that green plants (such as algae) can take those 4 kg of wastes and produce the needed food and oxygen with only the addition of energy in the form of light.

The complications arise from the need for a balanced, nutritious, and tasty diet containing all of the essential amino acids and fatty acids, and from the fact that we do not digest all portions of plants. Cellulose (fiber) is undigestible,  and we don’t even attempt to eat most of the plant material of a crop (stems, roots, leaves, bark).

The ecosystem we create in space must be perfectly balanced. When plants produce food for us to eat, they simultaneously produce the exact amount of oxygen needed to metabolize that food. But they also produce those stems, roots, leaves, etc., and excess oxygen to match. All of that extra plant matter must be fed to some other animals (such as rabbits or goats), or to fungi, or to bacteria, or burned. The excess CO2 must be captured and fed back to the growing plants of the next crop, because we don’t exhale enough CO2 to feed the plants, only enough to grow the food we ate – a fraction of the total plant material.

Note that we can meet all of our dietary needs by growing a variety of algae such as blue-green algae including spirulina, and chlorella.

Somewhat surprising is how little water is needed to grow adequate volumes of algae – as little as 6 to 10 liters per person. This is due to the extremely high growth rates of alga under optimal conditions.

However, an algae diet is not only boring, it doesn’t taste good. It is likely to only be used for long space missions where space and payload is at a premium, and even then at least 4 varieties must be cultivated to meet our dietary requirements.

Whether we are growing alga or traditional crops, much of human waste is not readily usable as fertilizer. Portions are, and some bacteria excel at producing nitrates out of urea and ammonia. But much solid waste cannot be so easily processed. Luckily, a technique is available to solve the problem: a Supercritical Water Oxidizer applies high pressure, modest temperatures, and oxygen to burn the carbohydrates to water and CO2, freeing nitrates and mineral salts in the process. This is called the Zimmerman Process.

The process boils down to:

1. feed CO2 and light to growing plants
2. harvest human-edible feedstuffs
3. feed much of the rest to animals such as rabbits, goats, and chickens, as well as vegetarian fish such as tilapia.
4. burn the rest of the plant matter to produce CO2 and ash (which is fertilizer)
5. feed food byproducts (and table scraps) to animals such as chickens or pigs (which when harvested produce still more byproducts)
6. use that Supercritical Water Oxidizer on animal and human wastes to convert them back into CO2 and fertilizers for the plants.
7. Condense water out of the air for drinking, and recycle irrigation water (which holds excess fertilizers) for plants.

Remember, as we are growing crops we need to feed them extra CO2 (much more than humans exhale), and store the excess oxygen they produce; we’ll restore the balance when we burn the crop residues and wastes. The “burning” doesn’t have to be an open fire. Feeding crop residues to goats counts as burning, as does using the plant matter as a reducing agent in the production of iron – both produce CO2 and free the water in the carbohydrates.

What crops should we grow? In general, dwarf varieties of grains, beans, and vegetables will satisfy most of our needs. We’ll have bread and pasta from wheat, rice, soybeans, oatmeal, lettuce, tomatoes, melons, potatoes, sweet potatoes, onions, herbs, etc.. I’m sure we’ll grow strawberries and other fruits, and eventually our parks will also serve as a source for nuts and fruits such as apples. I’m also quite certain we’ll grow grapes for wine, barley and hops for beer, coffee, and tea. Some human appetites insist on being satisfied.

That does leave the question of space. Just how big must our farm be? According to T.A. Heppenheimer’s excellent book Colonies in Space, the answer is derived from existing studies and experiments in high-intensity farming. Using dwarf varieties that have also been selected for short planting-to-harvest times, using interplanting (sowing the next crop before the current one is harvested), and optimizing CO2, water, light, and humidity, Heppenheimer calculates that 60 acres of farmland will support ten thousand people. This is only about 25 square meters per person.

I propose to average less than half that efficiency and allocate 64 square meters per person to include space for crop tending, to support a greater variety of foods, and to allow some extras to feed goats (for milk, cheese, and meat), rabbits (for meat), and chickens (for eggs and meat). Note that crops don’t require high ceilings; a single meter is good enough (on average), yielding a volume requirement of 64 cubic meters per person. This is less than the 100 cubic meters per person of living space I recommend in Designing a Space Habitat, where I also recommend about 33 cubic meters of workspace volume and an equivalent amount of overhead.

In that previous post, I assumed that 3 levels of living space would be allocated for the farms, but that may not be the best option. Rather, the farms are the primary source of waste heat. All that light energy ends up as heat and must be dissipated. The end caps of our cylinder expose a great deal of surface, so it makes the most sense to place our primary heat sources – the farms - adjacent to them. Using 8 meters along both end caps as our farms provides 64 cubic meters per person, independent of the size of our habitat (as long as we use the Kalpana geometry). Many plants need little gravity, indeed aquaculture (raising algae and fish) may require none, and these may be placed near the center. I expect that we’ll place livestock near the outer rim, as their needs for gravity are likely to mirror our own.

A future post will describe the lighting needs of the crops, and the technologies we’ll use to provide it.

Evolution

Evolution - or survival of the fittest (or luckiest) - is a readily provable fact, and one not limited to species: Evolution also applies to ideas (memes) with areas as diverse as religion, music, fairy tales, and urban legends.

The concept of evolution is simple: That which successfully reproduces, survives. If pressures (due to competition or predation) limit the growth of something which has a natural variation (a choice of religions, or music genres, or tales, or an ecosystem, or apes), those variants which most successfully reproduce will succeed versus those less suitable, or less lucky.

Note how few successful religions abound which forbid sex. There have been short term experiments in this direction. More subtly, religions that don't have a strong philosophy of proselytism tend to be dominated by those that do. Remember, survival of the fittest is really just survival of those that successfully reproduce. See The Purpose of Life.

Evolution of species continues today. Mankind is forcing change, which drives evolution. Some of this is merely speeding long term trends (such as reduced success of amphibians in general, or the loss of many marginal species like the spotted owl). Other changes are more worrisome (such as the evolution of anti-biotic resistant bacteria).

Especially with animals (including humans), there are two forces that dominate evolutionary pressures. In addition to reproductive success due to superior survival characteristics, there is reproductive success due to sexual selection (ie, how members of each sex choose mates). More colorful animals are easier to find, and the most showy male is likely to get the most females and successfully reproduce even though he is also the most visible to predators and ends up living a shorter life. Sexual selection may also explain extremely large sauropod dinosaurs; perhaps the males/females liked (or could see) tall females/males better - and sought them as mates - leading to runaway selection for this feature.

Even mankind continues to evolve in several ways, and indeed demonstrates evidence of very recent evolution.

For example, there is strong evidence that people have been evolving for external sexual characteristics. Human females have proportionally larger breasts, narrower waists, and broader hips than other primates. (As a human male, I do love that shape.) Human males have shapes that illustrate upper body strength, and have a penis that is larger in proportion to body size than any other ape. Apparently males have been selecting for large breasts and hips (especially in contrast to waist size). And women have been selecting men with broad shoulders, large muscles, and a big penis. And bad boys, at that.

Watching many reality shows (and especially MTV) suggests that human females are still actively selecting for strength, size, and sexual prowess; intelligence is clearly not a requirement. Likewise for human males, actively selecting voluptuous, athletic females with exotic eyes, long hair, and aggressive sexual attitudes.

Our technology is also having a significant effect on the human specie: we are becoming less diverse, as our ability to travel globally is reducing regional and racial disparities at measurable rates. In a few thousand years, there may be no remaining significant racial differences at all as we continue to interbreed and blend. Personally, I think this is a good thing.

We are also enabling the survival and allowing the reproduction of humans who would never live to adulthood without technology and/or large social organizations to care for them. I think this is a bad thing (when genetically caused), as I prefer that our children be smarter, stronger, and healthier. I know many people find my attitude offensive, but really, people, it is not in humanity's best long term interest to support or encourage the reproduction of serious genetic defects or low intelligence. Again, see my post The Purpose of Life.

A few other rambles:

Humanity is the ocean's most effective predator, and our fishing techniques are rapidly changing (evolving) fish to have less desirable characteristics. Fish are maturing younger and at smaller sizes as we select only the largest (previously most successful) fish. Fish that humans like to eat are being selected out - made extinct - versus undesirable, bony, badly tasting, or hard-to-capture fish. A tight school of fish may have worked to confuse dolphins or sharks, but it is an bright sonar target easily capture by our mile-wide nets today. And small and mid-size fish that avoid schooling behaviors make poor (unprofitable) targets.

Note that the world's most successful plants and animals are those whose evolution has made them desirable food for humans (cows, chickens, pigs, wheat, corn, rice, etc.). Then we help them thrive and reproduce, in numbers far exceeding natural populations.

Some people have argued against the use of windmills as a source of renewable electric power, based upon the fact that the turning windmills kill many birds. Tear down the windmills, drill for oil, save the birds. The reality is that more birds are killed by cars and trucks on the highway. (The activists would probably like to outlaw cars and trucks, too.)

I believe in the value of evolution: the birds that learn to avoid the rotating windmill blades will survive and reproduce. We can already see this effect along our highways: fifty years ago it was much more common to hit a bird on the highway, even though speeds were significantly lower then. Think of it as evolution in action (thank you, Larry Niven).

Last, the implications of evolution to a field near and dear to my heart: science fiction.

Contrary to nearly every movie alien, any intelligent life we meet in outer space will not be highly effective carnivorous killing machines. Au contraire, they will be (on their home planet) relatively weak and defenseless, needing superior intelligence to survive and reproduce. A dominant carnivore, or a herbivore that does not need to fear predation due to successful defenses (armor, size, quills, poisons) will cease to evolve. Every intelligent alien ever depicted with huge fangs, great strength, speed, armored skin, etc.,  is absurd, as they would never have evolved intelligence.

No, the most intelligent species will be those that are slow, weak, need protection from the elements, need to build and use tools to thrive, and need a civilization to defend against the superior strength, speed, and teeth of their planet's versions of lions, and tigers, and bears.

Of course, there is some evidence that intelligence is not a long term survival characteristic. We haven't yet met a single intelligent alien.

The Earth's Fragile Ecology

Most of my readers know that I'm fundamentally an optimist (see I am an optimist), and that I believe that science and technology (along with human ingenuity) can and will solve most (hopefully all) of our problems caused by technology and the resulting global population growth.

But it won't be easy, or cheap.

Most people seem unaware of the major ecological problems we face, focusing instead on a few relatively minor (but well publicized) potential problems such as Global Warming or loss of biodiversity.

Here are a few more for your consideration.

Loss of topsoil: Globally, current farming techniques results in topsoil being lost to erosion at rates far greater than natural replenishment. Topsoil (the only part of the Earth's regolith that can readily support crops) is being lost at a huge rate, resulting in reduced crop yields and even desertification in some areas. Currently, the recommended solution is to globally convert to no-till farming, which has the problem of requiring greatly increased use of herbicides and insecticides with their attendant and largely unknown long term effects.

Ocean anoxia: The huge influx of topsoil and fertilizer into the oceans is producing larger and more frequent dead zones, where nearly everything larger than a bacteria dies due to lack of oxygen. All of the nutrients lead to bacterial blooms which consume all free oxygen, and while some mobile fish can swim to the surface to gulp oxygenated water or swim out of the region, bottom dwellers and the myriad small critters that comprise the bulk of the food chain have no such ability. They die, and so do other life forms that depend upon them. This process happens to thousands of square miles every year, and the area and event duration is increasing.

Overfishing: The oceans are being depleted of desirable foodstocks are rates far greater than can be maintained. Already, many once common seafoods are becoming rare, and many fisheries are now effectively ocean deserts, completely devoid of large fish. At present, there are two approaches to solve the problem. One is to create huge "no fishing" zones to serve as replenishment stocks for the regions around them. This works in the short run (assuming enforcement by fast, armed ships), but eventually the fish will evolve to avoid fishing zones. The second solution is one that our leaders have done completely backwards. They have established minimum take sizes, where the fisherman is allowed to keep only fish above a certain size. Sounds good at first, as the young fish are allowed to live, feed, and grow. Unfortunately, there is something called evolution. Fish which once grew quickly to a large size (to avoid predation) are now evolving to grow more slowly and to reproduce at a much smaller size (avoiding predation by the most effective ocean predator, us). As a consequence, reproductive success is reduced, and the remaining fish are becoming less and less desirable. The solution? Capture (and eat) medium sized fish, encouraging these species to grow quickly to a large (safe) size and to produce large numbers of offspring to ensure that enough of them escape us to maintain their species. But this will take technology, and leadership.

Falling water tables: Everyone has heard of (or experienced) the relative and growing shortage of fresh water. Many people don't realize how serious the problem has become. Many cities (especially in desert areas but including many water-rich areas such as Orlando, Florida, USA) are pumping fresh water out of the ground at rates much greater than natural replenishment. Eventually the wells will run dry. Going deeper is often not a solution because of salt water, no water, or pollutants such as oil, lead, or arsenic. Along the oceans, pumping fresh water out of the ground encourages salt water incursion, a serious problem. One side effect of excessive ground water pumping is that springs dry up, and rivers that once ran to the ocean now shrivel and disappear. Water wars will result when cities / states / nations consume the fresh water that other downstream cities / states / nations need to survive.

Chemical pollution: To me, the most serious pollution issue is from the long term unanticipated side effects of biochemicals we create and dump into the environment. These include insecticides, herbicides, drugs, hormones, and especially antibiotics. We don't understand the long term effects of insecticides and herbicides; we ignore the possible unintended effects of long exposure to low doses of hormones and many other drugs (traces of which can be detected in many or most municipal water supplies), and we are rapidly breeding (thanks to evolution and the overuse of antibiotics) new bacteria (and likely viruses) which are immune to all known antibiotics. This alone could result in a plague which could destroy most human life.

The growth of cities: We tend to put cities (especially large, growing ones) at the worst possible places: in river valleys, along flatland floodplains, along the mouths of rivers. The same places that are the best possible farmland. We should build them on mountains, in deserts, rocky, hilly terrain, even floating on the oceans. Leave the good farmland to farming. Leave the river deltas for farming and allow the annual floods that replenish their topsoils and ecologies. Our cities continue to grow at alarming rates, covering the surrounding land with buildings and asphalt. And polluting or burying the former topsoil in the process.

Are there long term solutions? My favorite is to move humanity off of Planet Earth and into space habitats. See Colonizing the Solar System and Population Unlimited. Unfortunately, I expect that humanity will tend to continue to exploit the Earth in ever greater degree until the point is reached where most of the population will abruptly die. And then the survivors just might be smarter and do it right the next time. That, my friend, is evolution in action.