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CONTROLLED ECOLOGICAL LIFE SUPPORT SYSTEM (CELSS) 69 4 Controlled Ecological Life Support System (CELSS) DEFINITION To date, all manned space explorations have been relatively short, both in terms of overall time from start to completion of the missions, and also in terms of distance traveled from the Earth. Mission lengths have been limited by the carrying capacity of the spacecraft, the number of crew, and their life support requirements; all food and life-sustaining materials and supplies had to be carried in the craft when it was launched. When these consumables were nearly depleted, the mission space crew would return to Earth. For long ventures in space, the resupply of life-sustaining materials from Earth is impractical, both technologically and in terms of cost. Extended Space Station missions, or longer term manned expeditions to the Moon or to Mars and beyond, will remain improbable until systems capable of regenerating life- sustaining materials (air, water, and food) become a reality. To this end, NASA is investigating the necessary scientific and technological requirements for a bioregenerative system, the Controlled Ecological Life Support System (CELSS).
CONTROLLED ECOLOGICAL LIFE SUPPORT SYSTEM (CELSS) 70 RESEARCH OBJECTIVES A two-pronged program is required to achieve the CELSS capability. First, the ability of plants and animals to grow, mature, and reproduce efficiently in the altered gravity of the spacecraft environment must be assessed. Through the normal photosynthetic mechanisms these same plants will serve in part as atmospheric purifiers. Whether we are concerned with life support in a spacecraft bound for the planets, or the establishment of a lunar base or martian colony, the basic principles are the same: we must know that biological systems will function productively under the environmental conditions at hand. Second, the ability to cleanse and recycle the air and water needed to sustain human, plant, and animal life must be demonstrated. This requires engineering and development efforts of considerable magnitude. The engineering requirements include a plant growth chamber with appropriate light, humidity, and temperature controls; a dehumidifier to control excess moisture produced in the growth chamber by plant transpiration; a water purifier, to remove accumulations of toxic compounds; a food processing system to convert raw materials into edible material and convert, where possible, inedible matter into nutritionally usable matter; a waste processing system to recycle (chemically or biologically) human, plant, and animal waste into reusable materials; and an air purifier to remove toxic molecules from the atmosphere. The achievement of such a system clearly represents a difficult undertaking requiring long lead times. Foremost among several important factors that must be considered in the design of CELSS is the rate at which organisms or physical-chemical devices produce or consume biomass, food, oxygen, carbon dioxide, potable water, and fixed nitrogen in response to variables such as temperature, light intensity, humidity, the nutrient medium used, and the composition of the atmospheric gas in which the organisms or devices operate. Automated sensing and data collection and interpretation are being emphasized in an effort to improve the efficiency, stability, and control of bioregenerative systems. Specific research objectives in the CELSS development program include: 1. The development of practical methods for bioregeneration.
CONTROLLED ECOLOGICAL LIFE SUPPORT SYSTEM (CELSS) 71 2. The determination of optimum environmental requirements of higher plants used in recycling systems. 3. Refinement of hydroponic and aeroponic plant growth techniques. 4. The investigation of lighting requirements. 5. Research into the use of algae as human food sources. 6. Definition of factors influencing algal productivity. 7. Inquiry into efficient biological waste processing methods. 8. Development of computer methods for operating and controlling bioregenerative systems. ACCOMPLISHMENTS Previous studies have indicated the approximate size, volume, and power requirements to accomplish water recycling, atmosphere regeneration, waste recycling, and plant growth sufficient to feed four to six humans on a space trip of several years' duration. This ranges from a minimum of 150 cubic feet to well over 200 cubic feetâthe better part of a space station module. Specific plants have been studied in the laboratory (for example, potatoes and wheat) for applicability to the CELSS environment. Optimum conditions for growth are understood and the utility of these plants as food sources and atmosphere regenerators is being evaluated. A growth chamber capable of simulating the various environmental parameters in space (except microgravity and the complete radiation spectrum) and of the approximate size required is being designed to test the various systems needed for a working CELSS. These research and development programs ultimately will lead to the selection of a set of plants and animals for use in a controlled chamber that could be included in a spacecraft or planetary or lunar habitat, and which would be capable of sustaining human life in extraterrestrial environments for very long periods of time. The CELSS project is of great basic scientific interest as it involves research into large-scale, complex ecological systems involving humans. Also, it is of crucial operational importance for long-duration missions outside earth orbit. It is a program of formidable size and complexity from the management point of view. Nevertheless, it should be a project of high priority, both now and for the two decades beyond the Space Station era. Indeed, CELSS research could provide a connecting roleâa focus of interestâfor many of the scientific activities of the life sciences in NASA.
