Food
Proper nutrition is central to the maintenance of good health. The primary purpose of a diet, whether on Earth or in orbit, is to provide adequate levels of essential nutrients and energy. However, nutritional requirements change under microgravity conditions and diets need to reflect these changes. There are a number of physical constraints on the presentation and preparation of foods during piloted space missions. These include issues of weight, volume, preparation time, and waste generation. The psychosocial benefits of mealtime on motivation and morale also must be considered.
Food products for spaceflight need to be safe, easy to prepare and consume, compact, and produce little waste. For short-term missions of two weeks or less, such as those of Apollo and the space shuttle, foods are stored at room temperature. Food products are thermostabilized, freeze-dried, or specially packaged to prevent microbial spoilage. Water is plentiful on spacecraft that use fuel cells, so dried foods are easily rehydrated for consumption. Many of the precooked foods are commercially available canned or foil-packaged products.
Longer missions, such as Skylab and the International Space Station, are provided with refrigerated-and frozen-food storage units. Short-duration missions are characterized by intense workloads for the crew. Little time is available for food preparation and meals. Many of the food products available require no preparation and are provided as individual portions. Early missions used food products packaged in tubes that could be squeezed into the mouth. Apollo used hot water (about 65°C [150°F]) to warm foods. The space shuttle has a small convection oven to warm foods at temperatures of 145 to 185°C [293 to 365°F]. No cooking is done during spaceflight. For longer missions, more preparation time and effort is acceptable.
Lifting materials into orbit and beyond is costly, making weight and volume considerations important. Dehydrated foods help to limit these costs. The consumption of foods is made simpler in a microgravity environment by providing bite-sized products or by using special packaging. Crumbs and splatters disperse throughout the cabin on orbit, so their generation must be minimized. Given the closed environment of the spacecraft, food odors also should be minimized.
Space Diets
Space shuttle astronauts meet with dieticians well before the start of their mission to design a suitable diet. Menus are chosen from a list of more than 100 foods and beverages. Many of these are prepackaged, widely available, and familiar food products. Fresh fruits can be included. Tortillas act as a bread substitute to limit the generation of crumbs. Beyond the menu chosen by each astronaut, a communal pantry is stocked with a variety of snack foods and an extra two-day supply of food. Astronauts aboard the International Space Station can choose from an even richer variety of foods. Approximately one-quarter of the foods are ethnic or international in origin. The menu rotates through a twenty-eight-day cycle. The station also has a "salad machine" to grow fresh lettuce and salad greens onboard. This technology has been tested and used on the space shuttle and on the Mir space station.
The Impact of Diet During Short-Duration Missions
For short-duration missions, nutritionists follow the basic U.S. National Research Council recommended daily allowance guidelines. Additional considerations are necessary for long-duration missions. Studies have found that individuals who consume the space shuttle diet on the ground obtain proper energy intakes and no loss of lean body mass. However, during shuttle missions adequate energy intake is an issue, mainly because of decreased food consumption. In part this can result from space adaptation syndrome, which causes malaise, vomiting, and the loss of fluids and electrolytes. A more prevalent cause may be the excitement of spaceflight and the demanding work schedule. Astronauts simply do not take the time to eat proper meals while on orbit. During spaceflight, liquid intake is generally too low. Microgravity causes bodily fluids to redistribute. It is possible that thirst is not triggered in the same way under these altered physiological conditions.
Changes in Nutritional Needs During Longer Missions
Over the course of longer missions, studies have identified a variety of physiological changes that may reflect changes in nutritional needs. The most striking changes are the loss of minerals from the bones and a decrease in muscle mass. There are changes in the metabolism of calcium that leads to bone loss. The cause is unclear, but may be due to reduced load on the bones in the absence of gravity, reduced Vitamin D production in the absence of ultraviolet-rich sunlight, and changes in fluid balances and endocrine function. Nitrogen balance also is affected during long-duration spaceflight, and this, combined with changes in energy metabolism due to endocrine alterations, may be responsible for the loss of muscle mass that has been observed.
The Challenges of Very-Long-Duration Missions
Very-long-duration flights, covering years, such as a human expedition to Mars, pose unique challenges. As the length of the voyage extends past several months, it becomes increasingly cost-effective to grow foodstuffs in the spacecraft rather than launching with a full supply of foods. Closed ecological life support systems would provide the crew with oxygen and remove carbon dioxide, as well as provide food and potable water. Vegetarian diets are under consideration that include a limited number of hydroponic crops such as rice, wheat, potatoes, and soybeans. Fewer crops are easier to manage, but a diet lacking in variety is less palatable. It will be important to develop the means to create a variety of food products from each crop. Soybeans can provide soy milk, tofu, tempe, and other products. Extensive use of spices also can be helpful.
As mission lengths increase, it is likely that the crew's emphasis on food and mealtimes will increase, a phenomenon observed at the permanent station at the South Pole and during the two-year enclosure of people in the closed environment of Biosphere 2 in Oracle, Arizona. The psychosocial benefits of feasting are likely to become more important as the distance between the crew and Earth increases and real-time communication and interaction with Earth decreases. In addition, cumulative nutrient deficiencies become more important over long time spans. Food processing can affect nutrient availability and protein digestibility. Cumulative toxicological effects may be observed as a result of by-products of food processing, storage, or water recycle. Extensive ground-based testing will need to be performed to ensure a safe food supply for long-duration human space missions.
Bibliography
Eckart, Peter. Spaceflight Life Support and Biospherics. Torrance, CA: Microcosm Inc.;Dordrecht, Netherlands: Kluwer Academic Publishers, 1996.
Holick, Michael F. "Perspective on the Impact of Weightlessness on Calcium and Bone Metabolism." Bone 22, no. 5., supplement (1998):105S-111S.
Lane, Helen W. "Nutrition in Space: Evidence from the U.S. and the U.S.S.R." Nutrition Reviews 50 (1992):3-6.
Lane, Helen W., Barbara L. Rice, Vickie Kloeris, et al. "Energy Intake, Body Weight, and Lean Body Mass Are Maintained in Healthy, Active Women Consuming the U.S. Space Shuttle Diet." Journal of the American Dietetic Association 94 (1994): 87-88.
Lane, Helen W., S. M. Smith, Barbara L. Rice, et al. "Nutrition in Space: Lessons from the Past Applied to the Future." American Journal of Clinical Nutrition 60, supplement (1994):801S-805S.
Seddon, M. Rita, Martin J. Fettman, and Robert W. Phillips. "Practical and Clinical Nutritional Concerns during Spaceflight." American Journal of Clinical Nutrition60, supplement (1994):825S-830S.
Stadler, Connie R., et al. "Food System for Space Shuttle Columbia." Journal of the American Dietetic Association 80 (1982):108-114.
Stein, T. P., M. J. Leskiw, and M. D. Schulter. "Diet and Nitrogen Metabolism during Spaceflight on the Shuttle." Journal of Applied Physiology 81 (1996):82-97.
