Copyright 1977, 2007 by T. A. Heppenheimer, reproduced with permission
In space colonization, the really interesting questions do not involve things such as rockets or lunar bases or how fast the colony is to spin. They involve matters of how people will live in space. It is necessary to discuss the arrangements which will provide the colonists with a pleasant attractive life. O’Neill has written of lakes and gardens, of parks and of pleasant apartments. How do we know the colonies can actually be like this? How can we say that these prospects will ultimately be realized?
The implications of space colonization are so vast, its potential importance to the human race so great, that it deserves to be approached with care and attention to detail. It is necessary to discuss how the colonists get to the colony, how the colony can contribute to solving the world’s problems, how long it would take to build one. It is equally necessary to look at such questions as breakfast, or what happens after the colonists put the garbage down the kitchen disposal.
How do you feed 10,000 people living in space? How do you provide the air they will breathe? These necessities must come from a space farm. Most people need about ten pounds of food, water, and oxygen per day. If the colony is to get its supplies by rocket from Earth, it will be necessary to launch one each day. Not only is this expensive, but it would contradict one of the major goals of space colonization: to build a self-sufficient human community.
There must be a space farm. And most if not all of the colonists’ wastes will have to be recycled. The space colony will therefore have to be a closed-cycle ecology par excellence. The farm must be small in area, since it will be a long time before colonies grow large enough to offer room for Kansas wheatfields. Yet it must provide an appetizing diet of variety and quality similar to that which we enjoy on Earth.
These goals will not be easy to meet. NASA and the Air Force have done research in space farming and closed ecologies for over twenty years. They have studied algae, yeast, and distilled urine as comestibles. Reports stating that the best strain of algae would be of the genus Chlorella have been issued. In 1960 it was counted a considerable step forward when the Air Force’s Project Hermes succeeded in distilling from urine water which was alleged to be potable. (One Air Force scientist tried it and said, “It’s no worse than some of the stuff you get at cocktail parties.”) Mercifully, this line of research was abandoned and the Apollo astronauts got good fresh water made by combining hydrogen and oxygen in fuel cells.
For the colonists, there will be no algae except for feeding to fish and no yeast except when baking bread and cakes. They will have grain, vegetables, fruits, meat, fish, and poultry as well as eggs and plenty of milk or milk products. Steak may be a rarity and some of the people will miss familiar brand names. On the whole, though, there will be much less change in their diet than they would experience in moving to many places on Earth.
All this means high-intensity agriculture. In ordinary agriculture, Kansas style, a farmer may get 65 bushels of wheat to the acre, or about 1-3/4 tons. In Iowa, if the rain is good, you can get 140 bushels of corn to the acre, which is 3-1/2 tons. But since the middle 1960s, Richard Branfield and his associates at the International Rice Research Institute in the Philippines have consistently been getting 16 tons and more to the acre!
Branfield has been able to do this by taking advantage of several items which favor increased yields. The Philippines get much more rainfall than does Kansas and the growing season is longer. Branfield has been able to grow crops bred for shorter growing times. His rice, for example, matures in 90 to 110 days, instead of the usual 135 to 150. But his main techniques are interplanting and multiple cropping.
Interplanting means planting the seeds of your next crop before you have harvested the existing crop, planting the seeds between the already-growing plants. Crops grow slowly in the first weeks, while they are still seedlings. Interplanting overlaps the time of slow growth of your next crop with the time of rapid growth of the first crop just prior to harvest.
To do multiple cropping properly, Branfield has carefully worked out the proper sequences of crops to grow in succession. His best sequence starts with rice. Then he plants sweet potatoes and then soybeans; next corn and finally soybeans again. As a result, one of his acres will yield 2 tons of rice, 10 of sweet potatoes, 4 of soybeans, and 18,000 ears of corn. The stems and cuttings which are inedible by humans supply ten tons of forage for livestock. Such an acre will yield enough to feed thirty people continuously.
With these techniques, the whole colony of 10,000 population could live off the production of a single half-section, which is 320 acres. These methods are important much closer to 124 home—they were not developed for space colonization. They were developed to feed people in Asia. Just as the technology of high-speed trains points the way to the lunar mass-driver, so do the methods of high-intensity agriculture show the direction to follow in planning the space farm.
Branfield’s results, impressive as they are, can be improved on. It is possible to grow more. The Philippines have a nine-month growing season and less than ideal weather conditions. In the space colony, the growing season is continuous and can be adjusted to any conditions. We can control the temperature, the lighting, the moisture, the level of carbon dioxide in the atmosphere. Even if we give plants the best conditions they would find in the Philippines, but do so continually, the yield will be double what Branfield has obtained.
We should begin to regard the space farm as a continual producer of food. Rather than planting and harvesting at reasonably well-defined times in a well-defined growing season, we must imagine that at any time there will be some crops being planted, others newly growing, others ripening, and still others being harvested. Instead of thinking of yields in bushels or tons per acre over an entire growing season, we should think in terms of the yield as so many pounds per acre per day.
In Branfield’s fields, the yields are about 125 pounds per acre per day. This includes not only food grown and eaten directly, but the daily production of meat from animals which eat the stems and cuttings as forage. By reproducing in the colony’s farm the best Philippine days, the yield goes to about 245 pounds.
This is still only the beginning. In his book, Photosynthesis, Photorespiration, and Plant Productivity, Israel Zelitch of the Connecticut Agricultural Experiment Station reports yields exceeding 500 pounds for corn, sugar cane, sorghum, and millet, when these crops grow under optimum field conditions. In a laboratory experiment in England, plant growth initially at 340 pounds was raised above 1000 pounds by optimizing the atmospheric content of carbon dioxide at 0.13 percent. In the hydroponic garden at Arizona State University, John R. Meyers has grown forage under artificial 24-hour lighting, high ventilation, and controlled temperatures. His yield: an astounding 15,400 pounds per acre per day!
It is entirely reasonable to plan to grow grain in the space farm at a rate of 850 pounds per acre per day. Plants will grow in sand, vermiculite, styrofoam, or nothing at all provided they are supported and receive nutrients and water. Carolyn and Keith Henson, Tucson agriculturalists, propose to support the plants by means of styrofoam boards. The roots would hang below the boards and it would be possible to spray a nutrient solution onto these roots directly. A significant advantage of this method is that the roots could be harvested for animal feed.
The productivity of wheat and grains can be exceeded by vegetables. The best yields for vegetables commercially grown come from greenhouses in the desert of Abu Dhabi:
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Melons would yield about as well as cabbage and potatoes about as much as tomatoes. Potato harvesting would be especially easy with unsupported roots. You could go down the row and pick ripe potatoes as you would pick fruit. Nor do the Abu Dhabi productivities represent the ultimate. By carefully optimizing the growing conditions, these yields might very likely also be doubled.
The colonists can have plenty of grain and vegetables and they can also have fruit. There will be numerous parks and trees throughout the colony—the trees providing shade and making the surroundings pleasant to look at. Trees can have apples or oranges, pears, cherries, plums, or peaches. Even coconuts and bananas will be easy for the venturesome to grow, for the mild, pleasant conditions within the colony will prove suitable for any fruit tree which is desired. Fresh fruit from the parks will be a common item on the colony’s menu.
The colonists will also want meat and this poses a problem. Is it feasible to raise meat in the space farm, when space in the farm is at such a premium? The ideal animal must have high productivity. For instance, if you have a herd of cattle, only 20 percent of its mass can
be harvested as meat per year. But chickens and rabbits reproduce so fast and grow so rapidly that a herd of either animal can produce five times its initial weight in edible meat over a year.
Chickens or hogs grow rapidly and pound for pound eat much less feed than do cattle. They have often been suggested as being suitable for use as meat animals on a space farm. However, for efficient growth these animals require a diet which is suitable for human consumption. Because of the waste involved in feeding animals a diet which puts them in competition with human beings, it does not seem desirable to choose these animals as the main source of the colony’s meat.
Dr. Kenneth Olson, of the University of Arizona and a friend of the Hensons, has proposed raising alfalfa for rabbit feed. Alfalfa gives good yields of protein but has too much fiber for people to accept. The addition of a little salt makes alfalfa suitable as a complete feed for rabbits. Rabbit meat is low in fat and can be cured like ham or made into sausage and liverwurst. It is mild-flavored and can be cooked many ways, even as rabbitburgers.
One square yard will house a doe and her litter. Every two months, a new litter will arrive and that is when the young rabbits will be taken for their meat. Each such doe-and-litter “unit” requires about a dozen square yards of area for its alfalfa. Overall, the production of boneless meat comes to 145 pounds per acre per day. In terms of its protein content, the productivity is as good as that of protein from grain.
This farm produces food for two additional kinds of animals at no additional cost in growing area. Ruminants can convert the waste materials—stems, leaves, and roots from vegetable production—into milk. For instance, tomato vines are up to 24 percent protein. Cucumber vines, melon vines, and cabbage leaves also are valuable feeds. Ruminants could also eat straw or sorghum stalks from the grain production.
There is the question of which ruminant to choose. The two most common milk-producing ruminants are the cow and the goat. Cows weigh ten times as much as goats and eat ten times as much feed. But a cow will produce only four times as much milk as a goat. For a given amount of feed, a goat will produce more than twice as much milk as a cow.
Goats require more care than cows if their milk is to be of high quality. They should not be fed onions, the taste of which will wind up in the milk, and must be kept clean. A dairy goat and her milk will smell bad if there are billy goats around. But the billies can stay on Earth and artificial insemination can be used whenever new goats are needed.
In addition to the forage feeds, such as stems and leaves, goats (as well as cows) require some grain. The space farm can easily raise several times more grain than people will eat as bread or as products made from flour. The excess can be goat feed. Everyone can get two quarts a day of goats’ milk, rich in protein and with higher-quality protein as well as more minerals and vitamins than the grain used as feed. Much of this milk may be made into cheese or butter or cream. And the space farm can produce ice cream!
It will also be possible to raise chickens on the farm, feeding them with kitchen waste as
well as leftovers from meals and the waste from rabbit butchering. These foods have traditionally been fed to hogs as well as chickens, but egg production supplies food more efficiently than the production of pork or lard. Without adding any area to the farm for growing chicken feed, the wastes will support enough hens to give everyone in the colony three or four eggs per week. The colonists can enjoy cakes, waffles, omelets, and mayonnaise.
To grow enough nutritious, varied food for all 10,000 colonists would require a farm of only 100 acres. Even this is not the ultimate. If the production of grains and forage can be doubled again to 1700 pounds per acre per day—given optimum concentrations of carbon dioxide as well as optimum conditions of light, temperature, humidity, and nutrients—the space farm can be cut down to sixty acres.
The inside of the Stanford torus offers a clear area of 200 acres. In addition, the agricultural areas can be built in levels, with sunlight directed by means of mirrors to each level. The space farm will require only a relatively small share of the colony’s space.
There will be an opportunity to expand, to grow additional feed and forage and give even greater variety to the diet. An increase in the number of hens or chickens would be one of the easiest things to do. One of the most popular decisions, along this line, would be to import a small herd of Herefords or other beef cattle and set up a feedlot. (Since feedlots are exceptionally smelly, probably the best place for it would be in the spokes leading inward to the colony hub.) Cattle are rather wasteful at converting feed to beef. They need over twice as much feed as rabbits to produce a pound of edible meat. What is worse, cattle feed includes a lot of corn or grain which can be eaten directly by humans. But people like to eat beef and if the colony can grow the extra feed for cattle, the steers and cows will be very welcome.
There is another popular source of protein which comes from an animal and which may be nearly as productive as the rabbit. This is fish. In a weightless space farm, it may be possible to raise fish without water. On Earth, when a fish is taken from water, gravity makes its gills collapse so that it cannot get oxygen. In weightless space these same fish might easily “swim” through an atmosphere of 100 percent humidity, keeping comfortably moist: hydroponic fish, if you will. In the space farm there will be artificial gravity and this will not be possible. Instead, the fish will grow in ponds at the top levels of the farm, where a quarter million may live. These will be enough to supply everyone with ten one-ounce fillets per week.
In those waters, warm, shallow, rich in phosphates and other nutrients, there is the opportunity to recreate the food chains of the most productive fishing grounds. There will be diatoms, tiny microscopic vegetables, to grow on the minerals, sunlight, and carbon dioxide. These and one-celled algae will be food for the fish. The New Alchemy Institute of Woods Hole, Massachusetts, has developed a “backyard fish farm–greenhouse” which raises crops of fish this way. It grows dense blooms of algae to provide food for herbivorous fish. Tilapia, a herbivore from Africa, has been cultured to edible size in as little as three months. The white amur, a vegetarian fish prized in China, has grown to over a foot in length in less than a year.
Will the space farm actually produce these yields? On Earth, farm yields vary quite sharply from year to year and sometimes fail entirely. However, there are reasons to believe that a space farm would be more stable, more predictable than an Earth farm.
On Earth variations in yield are due to weather, weeds, insects, rodents, and disease. Weather simply does not apply in space, assuming there are no breakdowns in the systems for temperature and humidity control (and no one opens a window!).
The initial seeds for a space farm can be individually inspected to keep out weeds. If a few weed seeds do get through, the farm area is small enough so they will be spotted and removed. Simple fumigation of shipments from Earth should eliminate the insect problems, but if undesirable insects get in, they can be dealt with by the means used to fight disease, or lizards and frogs can eat the insects. This is the method used at the New Alchemy Institute. Rodents are easier to keep out than insects and this will not be a problem if scientists do not bring in rats and white mice. In the event they do and some escape, a cat may be necessary.
Disease organisms will be harder to keep out or control, and may come in with each new shipment from Earth. The space farm environment will be rich, similar to that of a greenhouse. Molds and viruses have been troublesome in greenhouses, but there are a variety of control methods. Steam sterilization, for instance, might be satisfactory. Molds are particularly troublesome in the high humidity of greenhouses, but in space the humidity can be kept as low as desired. For grain crops, in any case, low humidity is essential. Moreover, the sciences of coping with diseases date back to the time of Pasteur and the space farm will certainly stock vaccines and antibiotics. Bacterial and virus diseases usually attack a narrow range of hosts, sometimes even a single species. The wide variety of crops and animals grown on a space farm will give further insurance against a widespread disease-caused failure of the farm.
Nevertheless, for those convinced of the general perversity of things (Murphy’s Law), there are a number of fallback positions. For one thing, the diet available is rather excessive, producing two or three times more protein and somewhat more calories than are actually required. A substantial fraction of the crops could be lost and no one would go hungry. There is a large safety margin in terms of stored food and seeds, food being processed (e.g. cheese being aged), and fish still swimming or meat still hopping.
Even so, imagine a disaster, nature unspecified, that kills every plant on the farm but leaves the people and animals unaffected. This would be similar to an Earth crop failure. What would be done would be to butcher all the animals which could not be fed beyond the next two weeks and freeze or dry the meat. After cleaning up the mess, the farmers would plant the fastest growing seeds available.
The CO2 content of the air would not reach a problem level for at least two weeks even with nothing growing. With planting, in one week the CO2 level would be on its way back down. In two weeks, the production of forage for rabbits would be back to normal and in three months the entire farm would be back to normal. Those two weeks of leeway, before CO2 levels become uncomfortable, would allow time for the ultimate fallback position: the arrival of help from Earth.
In a sense, this ultimate fallback is the way the farm will be started, as well as maintained in the face of slow leaks or losses of material, which will very likely occur. At the outset, it will be necessary to bring from Earth the seeds, the styrofoam boards, and the initial stocks of animals, as well as stores of carbon, hydrogen, and nitrogen. These last will produce CO2, which the plants will use for growth, as well as water and part of the atmosphere. Oxygen will come from lunar rocks and will be continually available for replenishment. The same is not true of carbon, nitrogen, or hydrogen, or of compounds which incorporate these elements. Some of them can come from the moon as trapped atoms released when fine lunar soil is heated. The initial stores, as well as most of any additional quantities needed, must come from Earth. The freight rates will not be cheap. Even when the space transportation is working with maximum effectiveness, the shipment costs for the hydrogen in a gallon of water still will come to $40.
It is essential to have effective means for reclaiming water and for restoring carbon dioxide to the air for the plants. Wastes must be purified and converted into useful products without producing pollution. Minerals and fertilizers must be carefully recycled. The methods used do not need to be totally effective, for the colony is not the same as a starship which will cruise in self-sufficiency for centuries. The recycling must be complete enough, however, to reduce the need for resupply from Earth to a level compatible with normal trade and commerce. Perhaps it will be common for the space freighters on the outward trip to carry a few bags of fertilizer or briquettes of charcoal, a few bred nanny goats or chickens, or 100 pounds of salt. But these should be only minor items on the manifest.
To reclaim water, there are two good methods and both will probably be used. The simplest is to extract it from the air with a dehumidifier. The moisture-laden air passes over a coolant and gives up some of its heat. When cooled, the air passes through a screen made of materials which are hydrophilic (water-loving). The moisture condenses and is extracted, to be pumped to a tank. As with many air conditioners, the dehumidifiers will be tied in with the colony’s temperature-control systems. The heated coolant will pass through a heat exchanger, the excess heat then being taken to the central radiator.
Most of the moisture in the colony’s atmosphere will come from the plants as water evaporates from their leaves in a process called transpiration. Most of the dehumidifiers will be in the farm areas. The temperature and humidity will be controlled by adjusting the temperature of the coolant and the rate at which air passes through the dehumidifiers. In particular, some areas will have to be enclosed and kept at very low humidity—the crop storage areas for instance.
The water from the dehumidifiers will be available for drinking, cooking, and taking showers or baths. It will be a pure water with no chlorine or other chemicals, and it will be free of the dissolved salts which make water hard. It will be like rainwater and it will percolate through no ground strata, need no water softeners; it will simply be condensed from the air and piped to people’s homes.
There is another source of water, which will furnish a product well suited for crops and animals—water reclaimed from wastes. The problem of waste treatment requires a solution which not only gets rid of the wastes, but which turns them into useful products. The usual processes used in Earthside communities, such as biological degradation or incineration, are unsuitable for the colony. These processes either produce pollution, or are incomplete since they produce a very messy sludge which must be disposed of.
There is a process which has neither of these defects—the wet oxidation or Zimmerman process. Wastes are heated with oxygen to a temperature of 500° at 100 times normal atmospheric pressure. They are cooked under these conditions for an hour and a half. What comes out is high-quality water containing ammonia and fine phosphate ash, as well as an effluent gas rich in carbon dioxide but free of oxides of nitrogen, sulfur, and phosphorus. Both the effluent gas and the water will be sterile.
The gas will be fed to the space farm to maintain desired levels of CO2. The water will serve for growing food. The ash and other solids can be filtered, then mixed in with animal feed or with water for the plants as a source of minerals. If more than 2 percent of the initial waste is combustible solids, the process will be self-sustaining. Like an incinerator, it will operate continuously without an outside source of heat, the heat released in the combustion being sufficient to keep the process going.
All the water from the waste processing, as well as much of the water from the dehumidifiers, will first be fed into the fish ponds. From there, the water will be screened to remove fish waste, then pumped to the agricultural areas. What water is not used for the plants will flush human and animal waste to waste processing. In a continuous cycle, water will circulate throughout the colony, being cleaned and purified when necessary and serving all purposes.
The plants will also remove carbon dioxide from the atmosphere. They are entirely adequate for this, and there will be no need for anything but photosynthesis to produce and recycle the oxygen for the colony’s atmosphere.
The atmosphere as a whole will follow the principle, “less is enough.” It will have enough pressure and there will be enough of the different constituent gases to meet all biological needs. Its overall pressure will be at one-half that of Earth’s atmosphere. This will not only make it easier to transport the atmospheric nitrogen from Earth, but also make the Stanford torus much lighter and easier to construct. A thicker atmosphere would need thicker walls for the torus in order to contain it.
It will contain as much oxygen as Earth’s atmosphere at sea level. On Earth this much oxygen represents 21 percent of the total; in the colony, it will be over 40 percent. There will be only half as much nitrogen in the colony atmosphere as there is in Earth’s. There is no clear reason why humans or animals need to have any nitrogen at all in the air they breathe, but the nitrogen will serve some useful purposes. It will make breathing easier and will reduce fire hazards. Nitrogen-fixing bacteria will help provide it to plants, which need nitrogen to grow.
About 2 percent of the atmosphere will be water vapor to supply humidity. The colonists probably will be most comfortable at a temperature of about 72° and a humidity of 40 percent. Less than 1 percent of the atmosphere will be carbon dioxide and pollution will be controlled to very low levels.
Pollution control methods are highly developed from research in submarines. There will be no autos in the colony and industry will have its own recycling arrangements. But there will be unpleasant or polluting chemicals released into the air formed during cooking or operating backyard barbecues, not to mention the smelly gases exuded from wastes. However, these will be easy to remove. They can be concentrated by being adsorbed on activated charcoal, then sent through waste treatment. Or they can be disposed of directly by passing atmospheric air through a catalytic burner. Some substances, such as mercury and Freon, cannot be disposed of this way. There will be few reasons to bring mercury into the colony, but the exclusion of Freon means that aerosol cans will have to use nitrogen or carbon dioxide. The Navy has a rule not to bring anything into a submarine which is harmful after passing through a catalytic burner and this will be a good rule for the colony. As far as monitoring pollutants is concerned, there are instruments such as mass spectrometers and gas chromatographs which can detect incredibly low concentrations.
The colony can be a completely closed ecosystem. The atmosphere can stay pollution-free through two entirely different means. There are also two independent methods to recover water. It should be possible to provide plenty of varied, nutritious food for all with an ample margin against crop failure. The plants, animals, and fish will represent three distinct food sources, each largely independent of the other, providing not only extra variety but an extra margin of safety.
Many people have said the space colony will be a cold, artificial place where people will be cut off from nature. But the colonists may have more involvement with growing things than they would have in a city on the earth. Many of them might well spend several hours a week in the space farm, then go home to eat the meat or cook potatoes and vegetables which they have grown with their own hands.
There is one job which probably will prove too tedious to attract volunteers. This is the hand-pollination of vegetables. For this, the farm should include several hives of docile bees bred without stings or selected as particularly slow to get angry. These bees then will complete the space farm as “a land of milk and honey.”