Space explorers and settlers who are far from the farms and fields of Earth will need a reliable way to produce food. A continuous supply of nutritious, safe, and appealing food is essential for people who are living and working under unusual conditions that require peak physical condition. Food also plays an important role in the psychological welfare of crewmembers by providing familiarity and variety in the diet. The ability to continually produce food is an important element of long-term survival in space that cannot be accomplished by physical or chemical means. Food will have to be grown as quickly, reliably and efficiently as possible.
Methods of Production
Astronauts on long-duration space missions or settlers on other planets will have to maintain crops in growth chambers protected from the outside environment, but they will still need to supply adequate lighting, nutrients, and a suitable atmosphere. Natural sunlight in transparent greenhouses or artificial lights could satisfy the lighting requirement, but there are tradeoffs. On Mars, for example, sunlight is available for only half of each Martian day, and more light is required for optimal growth of many plant species. In addition, the Sun can be obscured for months by giant dust storms. Higher radiation doses and possible damage from meteoroid impacts are other dangers. On the other hand, artificial lighting systems would be costly to transport and may require a great deal of energy.
Nutrients could be provided to crops by a form of hydroponics , with the roots in contact with a thin film of liquid or a porous material such as vermiculite. Alternatively, the surface regolith of the Moon or Mars could be used as soil after any hypersalinity or toxic materials are washed out. Organic wastes and microbial soil communities could be added to the regolith to render it closer to the fertile soil found on Earth. On-site resources could also be processed to provide air and water for growing crops. On Mars, water can be extracted from the regolith and condensed from the atmosphere. Carbon dioxide could be taken directly from the Martian atmosphere. Atmospheric nitrogen could also be extracted and reacted with hydrogen to produce ammonia for fertilizers. Nitrogen-fixing microorganisms could be added to the soil to chemically alter this gas into a form usable by the plants.
What Kinds of Food Would Be Produced?
Foods produced in space will be carefully balanced for caloric content, nutritional quality, and palatability. Some plants may be genetically modified to alter or enhance their nutrient composition, and efforts will need to be made to optimize conditions for plant growth. Processing will also be required to convert crops into palatable, safe, and satisfying foods. In addition, processing will be needed to preserve food for storage in case of crop failure. The chosen foodstuffs will have to be versatile and capable of being converted into different types of foods. For example, soybeans can be pressed to release oils, and the remaining high-protein soybean meal can be manipulated to provide different foodstuffs. Soy milk can be used in place of cow's milk or can be used to make curd in the form of tofu or tempeh.
Adding different plant food will enhance the palatability of the diet. For example, various brassicas (similar to wild mustard) produce oils similar in quality to that of canola, and peanuts have an interesting flavor. Black-eyed peas are a good low-fat complement to oily legumes such as soybeans and peanuts. Besides being heat and drought tolerant, cowpeas are a staple crop eaten in Africa as a dry bean, snap bean, or raw salad green. In addition, their low oil content allows cowpea meal to be incorporated into formed or extruded vegetarian food products.
Rice is an excellent cereal crop to complement protein from legumes in a balanced vegetarian diet. Rice protein is tolerated by virtually all people, and it is more versatile than most other cereal grains. Wheat in the form of breads and pastas is a very important and common foodstuff in many cultures. In addition, the plants can be grown in high density, and the grain is very versatile. Potatoes, whether white or sweet, can make good and hearty additions to the diet. Much of the potato plant is edible, and the tubers are versatile and consumed throughout the world. Other crops such as tomatoes and lettuce may also be grown. Tomatoes can be used in stews, sauces, and salads, while lettuce makes good salad greens and can be grown efficiently. Spices and herbs will surely be grown to make the diet seem more varied, and hot peppers could enrich mealtime. Apples, oranges, and other fruits, however, will probably be rare because many fruits grow on bushes or trees that use space inefficiently and are comparatively nonproductive relative to the resources required for cultivation.
Other Uses for Plant Material
Despite efforts to maximize crop yields, about half of the plant material produced cannot be digested by humans. However, indigestible cellulose can be converted into sugars for use as food or as nutrients to grow yeasts, fungi, or plant cell cultures . Cellulose-digesting animals could also be raised on a small scale. While they would not be raised primarily for food, animals could on occasion provide high-quality protein and would make creating a balanced diet easier. At the other end of the spectrum, "microbial crops" could be good source of single-cell protein. For example, brewer's yeast and algae could be used as a dietary supplement, and green algae are a good source of protein as well as essential fatty acids and vitamins. In addition, algae can help provide oxygen to the atmosphere. Although not suitable as the only source of food, algae could be grown very quickly in an emergency and provide needed sustenance for the crew.
see also Biotechnology (volume 4); Food (volume 3); Living on Other Worlds (volume 4).
John F. Kross
Boston, Penelope J., ed. The Case for Mars. San Diego, CA: American Astronautical Society, 1984.
Eckart, Peter. Spaceflight Life Support and Biospherics. Torrence, CA: Microcosm Press,1996.
Nelson, Allen J. Space Biospheres. Malabar, FL: Orbit Book Co., 1987.
Oberg, James E. Mission to Mars: Plans and Concepts for the First Manned Landing. Harrisburg, PA: Stackpole Books, 1982.
"Growing Crops in a CELSS." Purdue University. <http://www.bio.purdue.edu/nscort/cea.html>.
"Plant Physiological Research in the KSC-Breadboard Project." Kennedy Space Center. <http://bioscience.ksc.nasa.gov/oldals/plant/physio.htm>.