2
Advanced Life Support Systems

Introduction

Life support systems, as addressed in this report, provide the following functions: temperature and humidity control; atmosphere control, supply, and revitalization; water recovery and management; waste management; and food management. NASA work in advanced life support (ALS) systems is directed toward scientific research and technology development related to physical/chemical (P/C) and bioregenerative processes needed to support humans in space, on the Moon, and on Mars. P/C processes use traditional engineering methods, such as filtration, distillation, and oxidation; bioregenerative processes are performed by living organisms.

Life support systems are described as "open-loop" or "closed-loop," depending on the flow of material resources through, or within, the system. Open-loop life support systems provide all required resources, such as water, oxygen, and food, from storage or resupply, and store waste materials for disposal or return to Earth. In an open-loop system, the resources required increase proportionally as mission duration and crew size increase. Closed-loop life support systems require an initial supply of resources but then process waste products, such as carbon dioxide, urine, and wastewater, to recover useful resources, such as oxygen or water for reuse, thus reducing dependence on resupply. Both open-and closed-loop systems require energy from outside the system. The ultimate combination of technologies will be chosen based on results of system trade-offs to determine the optimal degree of closure, which is defined as the percentage of the total required resources provided by recycling. (Zero percent closure indicates that no resources are provided by recycling, and 100 percent closure implies that all resources are provided by recycling.)



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2 Advanced Life Support Systems Introduction Life support systems, as addressed in this report, provide the following functions: temperature and humidity control; atmosphere control, supply, and revitalization; water recovery and management; waste management; and food management. NASA work in advanced life support (ALS) systems is directed toward scientific research and technology development related to physical/chemical (P/C) and bioregenerative processes needed to support humans in space, on the Moon, and on Mars. P/C processes use traditional engineering methods, such as filtration, distillation, and oxidation; bioregenerative processes are performed by living organisms. Life support systems are described as "open-loop" or "closed-loop," depending on the flow of material resources through, or within, the system. Open-loop life support systems provide all required resources, such as water, oxygen, and food, from storage or resupply, and store waste materials for disposal or return to Earth. In an open-loop system, the resources required increase proportionally as mission duration and crew size increase. Closed-loop life support systems require an initial supply of resources but then process waste products, such as carbon dioxide, urine, and wastewater, to recover useful resources, such as oxygen or water for reuse, thus reducing dependence on resupply. Both open-and closed-loop systems require energy from outside the system. The ultimate combination of technologies will be chosen based on results of system trade-offs to determine the optimal degree of closure, which is defined as the percentage of the total required resources provided by recycling. (Zero percent closure indicates that no resources are provided by recycling, and 100 percent closure implies that all resources are provided by recycling.)

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The cost of recycling increases dramatically as closure approaches 100 percent. Table 2-1 shows the quantities of resources required for metabolism and hygiene activities for one crewmember. If we assess the resupply reduction potential for water (hygiene and potable), oxygen, and food based on the magnitude of the mass of each resource, it appears that the recovery of water provides the greatest opportunity for savings, making up the majority of the total. Also, as a rule of thumb, recycling technologies become more "expensive" as the processing requirements become more complicated: the recovery of water requires the removal of impurities; the recovery of oxygen from carbon dioxide requires a basic oxidative process; and closure of the food loop requires photosynthesis. To determine the overall benefit of recovering a particular resource, the trade-off between the mass savings from a reduction in resupply and the additional mass, power, volume, and thermal load requirements imposed by the recovery system should be evaluated. From Project Mercury through the Space Shuttle, life support systems have been open-loop, using expendables and on-board storage for providing resources and handling waste. Exceptions to the use of expendables for atmosphere revitalization were the molecular sieve for CO2 concentration used on Skylab and the recent incorporation of solid amines to control CO2 on some long-duration Space Shuttle missions. These two technologies are regenerable, with the concentrated carbon dioxide either vented into space or stored for further processing to recover oxygen. On spacecraft with fuel cells (Gemini, Apollo Command Module, and the Space Shuttle), potable water was supplied from the water produced by the reaction of H2 and O2 to produce energy. The open-loop life support systems on Mercury, Gemini, Apollo, and Skylab were intended to be used just once. The Space Shuttle life support systems, however, have been used for more than one mission, with ground maintenance and repair between flights. Life support system control has been either manual or by conventional controls peculiar to the subsystems, with little or no interactive control between subsystems. Mass, power, and reliability have been significant design drivers, but because mission durations have been relatively short, the optimum design was a TABLE 2-1 Metabolic Values for Normal Spacecraft Operation of One Astronaut Parameter Resource Requirements Metabolic Oxygen Consumption 0.636-1 kg/day Food (dry ash based) 0.5-0.863 kg/day Potable Water 2.27-3.63 kg/day Hygiene Water 1.36-9 kg/day   Source: Eckart, 1996.

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simple system based on expendables. In-flight maintenance was not a significant design requirement. With the advent of an orbiting space station with a permanent crew, the design drivers have changed significantly. The ISS requires at least 10 years of continuous operation, on-orbit maintenance and repair, and no extended system down time. For the ISS, because of the logistics burden, the operational costs of conventional open-loop systems would have been prohibitive. Therefore, closed-loop designs were seriously considered for some subsystems. The baseline system for the current ISS design incorporates the processing of shower water, condensate, personal hygiene water, and urine into potable water. The CO2 is concentrated by a four-bed molecular sieve and vented overboard. Once assembly of the ISS is complete, oxygen will be supplied via water electrolysis, and nitrogen will be provided from on-board storage, replenished by resupply flights. It will also be necessary to resupply the ISS periodically with water to provide oxygen and make up for losses due to the less than 100 percent efficiency of water recycling technology. Food will be stored on board and resupplied. Therefore, the current ISS design, although more of a closed-loop system than on previous spacecraft, is still mostly an open-loop system (with the exception of water processing) and requires considerable resupply of expendables. For missions beyond the ISS, including the establishment of lunar and Mars bases and Mars transit vehicles, increased system closure, automatic control, and improved reliability will be critical and will drive the design. System trade-off factors to be considered include launch mass, power, heat rejection, resupply mass, safety, reliability, maintainability, and life-cycle costs. It should be noted that a reduction of resupply mass does not necessarily mean a reduction of transportation costs. There is a trade-off between these savings and the mass required for additional resource recovery and power supply systems. The technical challenge for ALS R&D is to provide the designer of future missions with appropriate mature technologies and hardware designs, and extensive supporting performance data. Mature technologies will be necessary to provide the confidence that highly reliable ALS systems can meet future mission constraints. Technical and Scientific Topics Related to Advanced Life Support According to NASA briefing documents, the mission of the ALS program is to "open the space frontier for exploration, utilization, and development by developing safe, efficient, and effective closed-loop life support systems." The goal is to "provide self-sufficiency in life support for productive research and exploration in space, for benefits on Earth, and to provide a basis for planetary exploration." The objectives of the ALS program are: to provide ALS technologies for long-duration missions that significantly reduce life-cycle costs, improve operational performance, promote

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self-sufficiency, minimize the expenditure of resources for long-duration missions, and provide spin-offs to ensure the timely transfer of new life support technologies to NASA missions to resolve issues of hypogravity performance through space flight research and evaluation to develop and apply methodologies for systems analysis and engineering to guide technology investments, resolve and integrate competing needs, and steer the development of systems to transfer technologies for the benefit of the nation These objectives are highly interdependent. System analysis and engineering help identify ALS technologies that will significantly reduce life-cycle costs and resolve issues of hypogravity performance and will be key to providing timely transfer of new technologies to NASA missions. Because of their operational history and relative maturity, initial missions back to the Moon or to Mars are likely to rely on existing P/C technologies until other options have been extensively tested and are shown to be flight ready and to meet reliability and safety requirements. The following sections discuss life support functions provided by P/C technology, potential applications of bioregenerative systems, and systems analysis, engineering, and integration. Development challenges and areas for potential improvement are highlighted in each section. Description of the Life Support Subsystem and Challenges for Physical/Chemical Technologies The functions to be provided by ALS systems are shown in Table 2-2.1 Temperature and Humidity Control Maintaining the temperature and humidity on board a spacecraft requires removing sensible heat produced by the operation of equipment and sensible and latent heat generated by the presence and activities of the crew (e.g., showering). Condensing heat exchangers are a well developed technology for controlling temperature and for condensing moisture from the atmosphere and have been used on all crewed spacecraft to date. Separating condensed water from the air stream in a microgravity environment is usually done with a centrifugal separator, a complicated mechanical device that is subject to failure. In order to simplify the system design, researchers are investigating using membranes instead of mechanical separators. 1    The functions of life support systems for applications in space are discussed in detail in Peter Eckart's Spaceflight Life Support and Biospherics (Eckart, 1996) and in Paul Wieland's Designing for Human Presence in Space: An Introduction to Environmental Control and Life Support Systems (NASA, 1994).

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TABLE 2-2 Summary of Advanced Life Support System Functions Function Details Temperature and Humidity Control Removal of sensible and latent heat loads Atmosphere Control and Supply Partial and total pressure control Atmosphere Revitalization CO2 removal, CO2 reduction, O2 replacement, N2 replacement, trace contaminant and particulate removal Water Recovery and Management Humidity condensate, urine, hygiene and wash wastewater processing; water storage and distribution Waste Management Fecal collection, urine collection and pretreatment, waste processing (including food/plant wastes) Food Management Food production, processing, storage Atmosphere Control and Supply The cabin atmosphere is maintained at the desired total pressure, with a partial pressure of oxygen sufficient to sustain human life (the Space Shuttle, Mir, and the ISS nominally operate at sea level equivalents for total pressure and partial pressure of oxygen). The subsystem to accomplish this requires pressure sensors and regulators, shutoff valves, check valves, relief valves, distribution lines and tanks, and valves and controls to provide the proper concentrations of oxygen and nitrogen. These components are already well developed and, except for improving reliability, are not the subject of ALS research. Atmosphere Revitalization The quality of the cabin atmosphere must be maintained: CO2 must be kept below a critical level; O2 must be kept within a specified range; N2 must be present in sufficient quantity to maintain total pressure; and trace gases and particulates (including microorganisms) must be removed. CO2 Removal. The closed cabin of a spacecraft requires a system that can remove carbon dioxide produced by the crew, other living organisms, and chemical processes, such as the oxidation of waste materials. In early and current U.S. spacecraft (Mercury, Gemini, Apollo, and the Space Shuttle), nonregenerable lithium hydroxide has been used to absorb CO2. This process is well understood and is useful for short missions. The first use of a regenerable CO2 system was in Skylab, which employed a four-bed molecular sieve to remove CO2 and vent it into space. This is the baseline technology for the ISS, with the possibility of processing CO2 to recover oxygen in the future. The Space Shuttle has used a

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solid amine CO2 removal system as an alternative to lithium hydroxide for certain long-duration missions to reduce the need for expendable lithium hydroxide canisters. This reduces mass and saves crew time. The four-bed molecular sieve planned for the ISS will essentially eliminate the need for resupply but still has significant mass and power penalties. Improving the selectivity of sorption materials for CO2 would eliminate problems associated with high humidity in the cabin air and with contaminants in the concentrated CO2. Other technologies for CO2 removal being funded by NASA include metal hydrides and membranes. The current NASA requirement for CO2 levels on board a spacecraft is 0.5 to 1.0 percent, which is an order of magnitude higher than atmospheric CO2 levels on Earth (less than 0.1 percent ambient CO2 ). The elevated CO2 levels complicate the analysis of biomedical and life sciences data as compared to data collected on Earth. Achieving CO2 levels of less than 0.5 percent using P/C technologies becomes increasingly difficult because the removal efficiency typically decreases as CO2 levels decrease. The potential role of plants in the removal of CO2 is important, especially for permanent bases on the Moon or Mars. This is discussed in the section on Potential Applications for Bioregenerative Systems. CO2 Reduction. Currently, the ISS does not include CO2 reduction to recover O2. The exothermic Sabatier process for CO2 reduction, which reacts CO2 with H2 to produce CH4 and H2O, is currently a mature technology but has not yet been qualified for use in space. The H2O produced can be electrolyzed to produce O2 for the atmosphere and H2 for recycling to the Sabatier. The CH4 can theoretically be used in resistor jets for attitude control or can be vented overboard. Because this process results in a net loss of H2 (unless the CH4 is decomposed), the system requires resupply. Another process, the exothermic Bosch process, reacts CO2 with H2 in the presence of a catalyst to produce carbon and H2O. This process does not require venting gas overboard but does require replacing the catalyst bed because of carbon accumulation. Another process that has been investigated is CO2 electrolysis, which converts CO2 to carbon and O2 directly. Plants can also reduce CO2, converting it to edible biomass through photosynthesis. There are currently no fully mature technologies for CO2 reduction. O2 Supply. The oxygen consumed by the crew, experimental animals, or aerobic bioreactors, as well as oxygen lost through leakage, must be replaced. Oxygen can be provided by resupply, by producing it on board, or from in situ resources. Stored gaseous or cryogenic oxygen has been used on every U.S. crewed spacecraft to date. These open-loop technologies have the typical mass penalty as mission duration increases. Although more efficient means of storing oxygen are being investigated, water electrolysis (which dissociates H2O into H2 and O2) to supply O2 is the technology of choice for proposed future systems and the one most developed to date. The H2 can be used in CO2 reduction processes or vented overboard.

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At least three competing technologies are being investigated for water electrolysis: static feed water electrolysis, which uses KOH as the electrolyte; solid polymer water electrolysis, which uses a perfluorinated sulfonic acid polymer, and circulating KOH electrolysis. A circulating KOH electrolysis system is currently being used on Mir. The other two processes have been developed in the U.S. and are candidates for use on the ISS. General concerns that must still be addressed in oxygen generation techniques include: O2 delivery pressure; power consumption; the presence of corrosive materials on board the spacecraft; and operational flexibility. The role of plants in providing oxygen is also an important consideration, especially for a permanent lunar or Mars base. This is discussed in detail in the section on Potential Applications for Bioregenerative Systems. N2 Replacement. Nitrogen is required to produce the desired total atmospheric pressure and to compensate for nitrogen losses from the spacecraft. Nitrogen losses from leakage, airlock operations, and experiment venting are ''nonrecoverable,'' and N2 is generally resupplied from stored gaseous or cryogenic tanks. It is technically feasible to provide N2 by the catalytic dissociation of hydrazine (N2H4) or ammonia (NH3), which may have a lower mass penalty than storing N2. In-flight use of one of these processes depends on the trade-offs of mass, power, heat rejection, and mission length. The investigation of in situ resource availability or the recovery of nitrogen from metabolic waste products may also be worthwhile. Trace Contaminant Removal. Controlling trace contaminants begins with the careful screening and control of materials allowed on board the spacecraft to limit offgassing, which can cause the crew discomfort or sickness. Some contaminants are common to all missions (e.g., the products of human metabolism): others will vary from one mission to another or over time during a given mission. Some experiments require the use of substances that are potentially hazardous to the crew but are necessary for experimental protocol; special efforts are made to ensure that these compounds are highly contained. This can involve double or even triple containment of the substance. Despite these precautions, there will always be contaminants produced by humans, by experimental activity, or by material offgassing that must be controlled and removed. Activated carbon has typically been used to remove organic contaminants; chemisorbant beds are used to remove nitrogen compounds, sulfur compounds, and halogens; and catalytic burners are used to oxidize the remaining contaminants. Dust particles, aerosols, and airborne microbes and allergens are removed by screens and high-efficiency particulate air (HEPA) filters in the return air ducts. Current technologies use significant mounts of expendable materials, especially activated carbon beds. One of the key challenges in the removal of trace contaminants is reducing the use of expendable materials. If plants are integrated into a life support system (primarily for their other uses), they could

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contribute to the removal of many trace contaminants; however, they might also produce other trace compounds. Water Recovery and Management For long-term missions, the recovery and reuse of wastewater produced by humans offers the greatest potential for reducing resupply of any resource in the life support system. A number of P/C and bioregenerative processes are available to process humidity condensate, urine, and hygiene and wash water for reuse as potable water or for other uses. Distillation is an effective means of purifying water, and several distillation methods for use in space are being developed, including vapor compression distillation (VCD), thermoelectric integrated membrane evaporation, vapor phase catalytic ammonia removal, and simple air evaporation. Among the filtration techniques being investigated are reverse osmosis, multifiltration, and electrodialysis. Significant steps have been taken to recover wastewater in space, but for the foreseeable future, some resupply or special storage reserves to make up for losses will continue to be necessary for long-duration space missions. The baseline system for the ISS uses a single system to produce water for hygiene and consumption by the crew. Urine is pretreated and processed in an ambient-temperature VCD system. The distillate from the VCD is delivered to the wastewater network, which also receives humidity condensate and hygiene return water. The wastewater network delivers water to the water processor, which uses multifiltration technology and a volatiles removal assembly. The product water from the system is monitored by the Process Control and Water Quality Monitor. If the water is acceptable, it is delivered to product water storage. If it is not, it is recycled through the system again. Multifiltration technology requires little power and provides 100 percent recovery efficiency but relies on expendable beds. Therefore, it is subject to storage and resupply constraints. Current vapor compression technology has moving parts and provides about 90 percent recovery efficiency. Power consumption is fairly low, and resupply requirements are negligible. Other issues to be addressed in water recovery and management include in-flight maintenance, reliability, the disposal or recycling of brine, as well as the potential for microbial contamination and the accumulation of toxins in long-term water processing, storage, and distribution systems. Waste Management The waste management system includes a toilet subsystem for collecting urine and feces and an overall housekeeping system for managing other wastes, e.g., food waste, refuse, and biomass from bioregenerative components. The toilet subsystem for operation in microgravity has presented particularly difficult mechanical system/human interface design problems. In all U.S. space projects to

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date, feces and refuse have been collected and stored on board for eventual return to Earth. Little or no processing, other than vacuum desiccation, has been done to stabilize or neutralize waste materials. Some processing to render waste material biologically inactive may be required for long-term storage. For planetary missions of extended duration, recovering the water from feces and food waste, and recycling solids will be beneficial, particularly if bioregenerative systems are used to provide food and/or to process waste materials. Food Management Food for space flight has improved dramatically since the early days of Mercury, Gemini, and Apollo, but it is still not as varied or fresh as everyday food on Earth. Food currently provided on space vehicles is preserved using a mixture of old and new technologies, including freeze-drying, canning, radiation-stabilization, thermostabilization, and other methods. Food scientists, often in concert with military programs, have made significant advances in food preservation and storage techniques in recent years, and NASA has been a participant in, as well as a beneficiary of, this work. Applicability of these techniques for space is being investigated by NASA, and foods preserved by these new techniques are now being flown on the Space Shuttle and are expected to be used on the ISS. Food production in space through biological processes is discussed in the following section. The use of significant quantities of food produced in space will raise new issues in food processing, storage, and preparation. (All missions to date have used food produced and packaged on the ground.) In addition to the nutritive value of fresh produce, anecdotal information from the Mir space station, Antarctic stations, and other closed environments indicates that the mere presence of living plants enhances the crew's psychological well-being. Little information is currently available for evaluating the trade-offs between the psychological benefits to the crew and the additional power, mass, and volume that the inclusion of plants would require. Potential Applications for Bioregenerative Systems On Earth, biological agents, acting in concert with a biotic aspects of the biosphere, have provided a closed-loop life support system for millions of years. Bioregenerative life support systems are based on the idea of utilizing the natural biological abilities of living organisms to provide life support in a microcosm. The challenge is to make the microcosm small and reliable. The primary components of a microcosm and their relationships are shown in Figure 2-1. Bioregenerative processes are capable of fulfilling many of the functions listed in Table 2-2, with the exception of temperature and humidity control and atmosphere control and supply. Bioregenerative processes may play a major role in removing CO2 and producing O2, potable water, and food. They may play a

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smaller role in contamination control and waste processing. Incorporating bioregenerative techniques, although increasing system closure, generally comes at the expense of increasing volume, power, and thermal load requirements. Incorporating biological components into an ALS system would increase the self-sufficiency of the system by producing food and reducing the need for expendable air, water processing systems, and other materials. A common perception among some engineers, however, is that biological systems are inherently less reliable than P/C systems because the death of a living organism is more likely than an equipment failure, which is repairable and is not usually propagated to other P/C components. However, ground-based research in the past Figure 2-1 Principal relationships in a bioregenerative life support system.

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decade indicates that microorganisms and higher plants are more reliable than the equipment required to provide environmental control. In other words, equipment failures (of pumps, fans, or sensors) have been shown to be more common than failures caused by biological problems, such as disease. Because biological productivity is highly dependent on the P/C support components, a fundamental understanding of the effects of short-or long-term mechanical failures on biological productivity is essential before biological components can become critical components of a life support system. Real-time monitoring of plant and microbial metabolism will provide detailed data on plant responses to short-and long-term stress. Improved monitoring methods will enable monitoring of parameters such as: carbon and water fluxes associated with plant and microbial metabolism; leaf and canopy temperatures; plant morphology, including stem elongation, leaf number, branching, and reproductive development; as well as machine vision analysis of leaf enlargement. Both biological and P/C systems can purify water and regenerate O2 from CO2, but growing higher plants is currently the only viable approach to producing food in space. Proteins and carbohydrates can be chemically synthesized, but this process is energy-intensive, and the product is a half-and-half mixture of D-and L-rotation isomers.2 Humans can only metabolize L-rotation isomers (which are produced by other living organisms on Earth) because of the way the enzymes in human cells have evolved. Plants require high radiation (light) levels to produce food, but if there is enough light for maximum photosynthesis, the caloric requirements of one person can be met with a growing area as small as 10 m2, when wheat is the only crop (Bugbee and Salisbury, 1988). This level of productivity requires a light level equivalent to full summer sunlight at noon, 24 hours a day. When other crops that cannot tolerate these high light levels are incorporated into the diet, the production area for one person increases to 20 to 50 m2. Through transpiration, this same area can, theoretically, provide at least four times the purified water needed for a single crewmember. Algal systems are photosynthetically efficient, but an excess of indigestible cell wall material, nucleic acids, and chlorophyll make algae unpalatable for more than a few percent of daily calories. Fungal organisms, such as mushrooms, can be grown directly on waste products without a light energy source, but, like algae, mushrooms cannot provide a significant fraction of caloric requirements. The ability of plant/microbial systems to decompose organic wastes and absorb inorganic wastes on a continuous basis has not yet been rigorously quantified. Plants have evolved effective mechanisms for preventing the uptake of unnecessary organic and inorganic compounds, and these compounds might, therefore, accumulate in the water made available to the plant roots. However, 2    D-and L-isomers are two forms of the same compound that are not superimposable. For example, the letter "p" is identical to the mirror image of the letter "q" and, in that sense they are identical, but "p,'' and "q" are not superimposable.

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program may be jeopardized. Fundamental requirements for life support are well known and, with system analysis in areas where fundamental R&D are required, can be identified for a broad range of missions. NASA's goals for human exploration will require that more than one type of mission be supported by advanced R&D. Life support will be required for transportation vehicles with various crew sizes and missions, pressurized work spaces, planetary habitats (either short-term or permanent), and pressurized rovers. Recommendation 2-7. NASA should continue to develop a program plan and road map for technology research and development that (1) is consistent with the NASA Strategic Plan, (2) takes into account the relative benefits of physical/chemical and bioregenerative technologies, and (3) is based on realistic development schedules. If the road map continues to focus on new technologies to enable planetary missions, but no specific mission is identified, then metrics should be put in place to evaluate the relative benefits for a range of possible missions. Finding. A major emphasis of the current NASA ALS program is on integrated ground testbeds, which is only one of the four key elements of the NASA headquarters road map. Developing new technologies at the component and subsystem level is a relatively small portion of the ALS program. The primary focus of the ALS program from 1996 to 1998 is integrated testing, and programs using integrated human testbeds consume a large portion of the NASA resources allocated to advanced life support systems. According to the FY96 budget, almost half of the approximately $10 million OLMSA will spend is designated for human testbeds. The tests are designed to bring existing subsystem concepts to a level of maturity that will reduce the risk of incorporating them into plans for future flight programs; these are the first tests of this kind in the U.S. in more than 20 years. The committee considers the ground testbeds important and valuable but is concerned with the relative balance between testing and advanced technology development. Although it is possible to conduct future interplanetary missions using current technology, new technology will be necessary to reduce the logistics burden, increase reliability, ensure acceptable risk to crew health and mission success, and provide a level of self-sufficiency that could accommodate potential deviations in missions plans. Therefore, it is crucial that the testbeds not consume an inappropriately large portion of the funding and other resources available for work in ALS. Closed system tests of existing technologies with humans is not an appropriate end in itself. There must be an ongoing programmatic and fiscal commitment to the development of new technologies in the near term, or the tests are likely to become less and less valuable. Recommendation 2-8. The emphasis on developing new technologies for advanced life support should be increased and a process established for incorporating them into ongoing programs.

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Recommendation 2-9. The research done using the testbeds could be significantly more valuable if: initial system assessments are performed to identify areas where modeling and system data are either missing or are of poor quality and this information was used to develop requirements for testbed programs rigorous analytical models were developed and validated using an iterative process that utilizes testbed-based data acquisition and increased model fidelity to describe and predict the overall operation of the various functions of life support systems and subsystems (successful models could be adapted to predict the performance of space-based systems) actual flight subsystems were used in tests designed to predict the function of flight subsystems (e.g., when tests use prototypes that represent flight systems but are not identical to flight systems, the test team should carefully document the differences between test hardware and flight hardware so test results can be properly interpreted) ground tests were tied to a commitment that NASA will continue testing promising new technologies in space on the International Space Station or, to a lesser extent, on the Space Shuttle technology demonstration tests were more rigorously integrated with relevant human factors research on people living together in small, closed environments and with related topics, such as hygiene, nutrition, and performance evaluation there were some sort of routine peer review of the test plans by individuals not directly involved in the test program (NASA staff should not be excluded) there were ample time between tests to analyze the results and apply lessons learned to subsequent tests Overall Scientific and Technical Quality Summary Finding. Some of the research performed under the ALS program is of world class status, as evidenced by the publication record in prestigious journals. However, the overall scientific and technical quality is uneven. Finding. Many projects are published only as NASA technical memoranda or as nonreviewed papers. Although proposals written in response to NASA Research Announcements undergo external peer review, some NASA center projects do not undergo adequate internal and external peer review. Recommendation 2-10. NASA scientists should be continuously encouraged to expand their associations with professional societies through participation on committees, publication, and attendance at national meetings. NASA management should ensure the rigorous application of scientific method (which is essential in basic research projects) through internal and external reviews.

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Program Requirements Summary Finding. NASA has a good understanding of the general requirements for advanced life support, but the requirements for continuous, long-term, autonomous control are not well understood, and the baseline requirements for the current program have not been established. Materials presented to the committee did not indicate that all of the important areas were being systematically addressed. The following areas, in addition to those identified earlier as high priority areas for research and development, should be emphasized. Finding. Little testing has been done for off-nominal operating conditions. Data from off-nominal tests would provide valuable information for systems analysis and modeling. Although many traditional physical, chemical, and microbial treatment techniques are technically feasible, linking them to food production through the reuse of gas, liquid, and solid-phase mixtures creates a complex and difficult recycling challenge. NASA has begun to probe this issue, but most work has been conducted under almost ''ideal" conditions for systems optimization that do not incorporate subtle influences that can often lead to instability or even system failure. Recommendation 2-11. System perturbations, including toxicity, inhibition, and adulterations caused by the invasion and/or buildup of alien microbial species and/or refractory chemicals, need to be addressed in a transitory as well as steady-state fashion. Such a protocol would permit an analysis of reliability and outcomes requisite for making recommendations in response to disasters incorporating such loops. Test objectives and procedures should be coordinated with model developers. Finding. Initially, plant-based bioregenerative systems will provide only a fraction of the total food requirement. The requirements for intermediate closure levels of the food loop are currently underfunded. Recommendation 2-12. Intermediate food loop closure levels warrant additional study. Issues to be considered include: the mixture of crop species that should be used; crop sensitivity to high CO2 levels (about 1 percent); crop capacity to recycle gray water; the engineering impact on support systems and waste processing for different levels of food loop closure. Finding. The incorporation of plants into bioregenerative systems and the use of plants for food production impose unique constraints and demands. Although there is a tremendous data base on the efficiency of crop production on Earth, there is considerably less data on growing plants in controlled environments. Recommendation 2-13. Plant growth research should focus on resolving issues unique to growing plants in controlled environments for space applications. Some of these issues include: standardization of procedures for reporting production

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efficiency; optimization of environmental conditions during different periods of plant growth to increase production efficiency; the ability of plants to tolerate high levels of ammonium nitrogen typical of recycled wastes in regenerative systems; techniques for providing aerobic, well watered root zones to reduce plant stress; adaptation of commercial processes for food processing and storage; provision of oil in a primarily vegetarian diet; selection of a plant growth medium; and fluid handling under micro-and hypo-gravity conditions. Program Direction and Organization Summary Finding. The current ALS program is a result of the unification of two NASA programs, in two different NASA headquarters offices (both of which were dedicated to the development of ALS systems). In 1993, the consolidation of the P/C and bioregenerative programs was a significant step toward the formation of a coherent ALS program. However, NASA has still not specified an organizational structure to manage the program. This has resulted in a lack of focus and a delay in program planning and implementation. Finding. Since the reorganization of NASA's ALS programs began in 1993 (which placed P/C and bioregenerative life support programs in a single NASA headquarters office), NASA groups working in the two areas have been more coordinated. The present R&D program has improved because it recognizes the potential systems engineering advantages of both technical approaches. This increases the likelihood that combined ALS systems will be rationally developed to meet long-term needs in space. Finding. NASA headquarters has tentatively assigned responsibility for the ALS program to JSC, the lead center for the HEDS Enterprise. JSC management has not yet identified an ALS program manager or support structure. This has had an adverse effect on the planning and implementation of the program. Recommendation 2-14. Johnson Space Center management should define an advanced life support program management structure. The organization should be headed by a program manager who has the authority and responsibility to plan and execute the program. The program manager, in concert with the supporting centers, should develop a summary document that clearly defines the tasks to be accomplished by each NASA center that receives advanced life support program funds, as well as tasks to be accomplished by industry and universities. Recommendation 2-15. Assuming that management of the program is transferred to the Johnson Space Center, the funding for advanced research and development should continue to be allocated separately from operational programs and responsibilities, such as the Space Shuttle or the International Space Station, to ensure that advanced life support research is not subordinated by immediate operational concerns.

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Finding. Expertise and activities at NASA centers are spread across the ALS spectrum (with some overlap) and generally support the division of responsibility. JSC's primary focus in the ALS program is on integrated testing of humans in engineered systems. JSC's CTSD has a long history of developing technology for spacecraft life support systems and significant expertise in most aspects of ALS systems. Current life support work at MSFC is primarily funded by the ISS program and is directed toward the development and evolution of the baseline ISS Environmental Control and Life Support System (ECLSS). MSFC has ground-based facilities for developing and testing water recycling and air revitalization technologies, using volunteer subjects to supply products for the water recycling tests and metabolic simulators for the air revitalization tests. MSFC has proposed a number of projects for the evolution of the ISS ECLSS. If these are funded and successful, they could reduce resupply and power demands. MSFC also plays a small role in testing advanced subsystems in space on the Space Shuttle, as part of the OLMSA ALS program. Research at KSC is carried out by a small civil service and contractor staff, supplemented by postdoctoral fellowships, university grants, and SBIR contracts. KSC's work in ALS focuses on plant growth and is well grounded scientifically, as demonstrated by papers in refereed journals and presentations at professional meetings. KSC also has expertise in processing Space Shuttle payloads, including life sciences payloads; this provides a skill base and synergy for some aspects of the research focusing on growing plants in space. Work on life support systems at ARC includes research on both bioregenerative and P/C systems. The work at ARC appears to have great potential, although the work on bioregenerative systems lacks a strong focus, and, in general, ARC's work is currently not well integrated with other elements of the NASA program. If the P/C projects and expertise were carefully integrated with work at other centers, ARC could provide a much needed basic research capability to the ALS program. ARC has also done significant work in systems analysis in the past and might be a site for research into the integration of bioregenerative and P/C technologies. Recommendation 2-16. Program management should conduct a comprehensive evaluation of the resources required to conduct the advanced life support program, and determine the technical and organizational roles of NASA headquarters and the relevant NASA centers. Recommendation 2-17. Management of an excellent plant research program should involve a working group with a broad knowledge of basic plant biology, advanced training, and awareness of the special requirements imposed by microgravity and a closed environment. Managers should also encourage active participation in professional societies, a consistent record of publication in peer-reviewed journals, and collegial relationships with other NASA centers, academia, and

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industry. The current program at the Kennedy Space Center exemplifies these attributes, and this center should continue work in plant research and should play a larger role in the management of plant research related to advanced life support. Finding. Current mechanisms for soliciting and supporting ALS contributions from industry are inadequate. NASA has adopted the NRA as the primary method of soliciting proposals from academia and industry. This is appropriate if the objective is to solicit proposals for basic research and revolutionary concepts for new processes, bread board, or prototype developments. Universities should play a role in the development of revolutionary approaches to improving P/C systems, and, most importantly, to improving bioregenerative technologies that are not a high priority for IR&D. In the past, the NRA process has been only marginally successful in attracting such proposals. At the higher technology levels, it is generally better to solicit specific proposals through the competitive request for proposal process or, when appropriate and justified, through a noncompetitive procurement process. Recommendation 2-18. NASA should use the NASA Research Announcements primarily to request proposals at the early levels of technology development. The highest priority technology areas for advanced life support should be carefully and fully communicated in each announcement. Through outreach programs, NASA should attempt to reach a wider population of universities and industrial organizations that have generally not been involved in space research. Recommendation 2-19. For more mature technologies that are closer to being used in operational space systems, NASA should primarily use the competitive request-for-proposals process to attract proposals from companies likely to provide flight systems in the future. Recommendation 2-20. NASA should invite companies to propose cooperative agreements for using the ground system testbeds at the Johnson Space Center and Marshall Space Flight Center to test advanced hardware developed with company funds. Recommendation 2-21. NASA technical and management staff should make a concerted effort to keep abreast of developments in independent research and development projects. Recommendation 2-22. For the present, bioregenerative research should primarily be conducted at universities and NASA centers. However, it is imperative that NASA exert stronger leadership to keep this research focused on NASA goals. Finding. Developing a coherent ALS program has been complicated by individuals other than the ALS program manager selecting SBIR and NSCORT projects, as well as by the inherent unpredictability of new project proposals and funding allocations in response to NRAs.

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Recommendation 2-23. Advanced life support management should provide clear direction and priorities for selecting Small Business Innovative Research (SBIR), NASA Specialized Center of Research and Technology (NSCORT), and NASA Research Announcement (NRA) technology development projects. Advanced life support program management should receive regular status reports for all ongoing projects. Recommendation 2-24. A mechanism/process should be developed and implemented to integrate SBIR, NSCORT, and NRA projects into mainstream NASA technology development programs, including integrated system testing, testbed data acquisition, and the eventual incorporation of promising technologies into flight programs. Synergism with Other Programs Summary Finding. The potential for synergy between the OLMSA ALS program and other NASA programs is significant. Areas for cooperation include SBIR, SHF, EMC, the ISS, and the Space Shuttle programs. The ALS program should continue to recognize and make use of the scientific results generated by other OLMSA programs in areas such as plant biology and microgravity sciences related to transport phenomena. Finding. The SBIR projects are significant contributors to the development of ALS technologies and provide an opportunity for small businesses to bring forward innovative concepts. The SBIR program has proved to be a valuable source of innovative technology initiatives for the ALS program. The funded projects presented to the committee were generally of high quality and addressed appropriate technology areas. However, there appears to be a lack of effective coordination among the NASA centers that manage the individual contracts, and the solicitation and selection process has not ensured that the areas of highest priority are addressed. Recommendation 2-25. NASA should target the Small Business Innovative Research (SBIR) solicitation and selection process to specifically request proposals that address areas of highest priority. Through technical exchange meetings, NASA should fully inform advanced life support researchers throughout the agency about SBIR activities. Finding. There is little quantitative information on the psychological value of plants in closed environments, which may become a significant SHF issue for long-duration missions. Much of the incentive for using higher plants for food, oxygen, and water on short missions (less than two years) is based on the assumption that plants will provide a critical psychological boost. This assumption is based on reports from people in partial isolation (e.g., Mir). There seems to be unanimous agreement

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that plants will be psychologically important, but detailed information on their importance is lacking. For example, how many plants are necessary and where should they be placed to provide a psychological boost? Higher plants make people feel they are living, rather than simply surviving, in space. This has prompted NASA to study the use of plants for purposes beyond their immediate value in reducing resupply and increasing self-sufficiency. Recommendation 2-26. NASA should work to quantify the psychological value of plants in closed environments and take advantage of the advanced life support human rated testing opportunities for space human factors investigations. Finding. ALS systems maintain the parameters that the newly formed EMC program is responsible for monitoring. Currently, monitoring and control functions for the provision of life support have been decoupled and have essentially no direct feedback or automated control of life support system functions (with the exception of oxygen partial pressure). As control systems become more sophisticated and life support systems are required to provide and respond to more variable environmental conditions, control strategies (predicated on the availability of required monitoring equipment) will be critical. Recommendation 2-27. Communication between the advanced life support and environmental monitoring and control programs should be strengthened to allow them to evolve in a coordinated and synergistic manner. Finding. There is little coordination with the Space Shuttle and ISS programs to ensure the utility of ALS projects directed at near-term needs or to make provisions for use of on-orbit facilities to support the development of ALS technology. There is presently no commitment for volume or other resources on the ISS for ALS testing, although since the final meeting of the committee on August 31, 1996, NASA has taken initial steps to allocate some ISS resources for testing and demonstrating new ALS technology. At present, OLMSA has no budget to produce ALS test hardware for the ISS or to sponsor an ISS test facility for ALS. The ALS program is expected to provide upgrades for the ISS, but there is no specific interface between the ALS programs and the ISS. It is imperative that a mechanism be established for transferring information between the ISS and ALS programs. Over its lifetime, the ISS could benefit from ALS developments leading to a system to recover O2 from CO2, systems to reduce the logistics burden of the current water processing design, the addition of laundry facilities to reduce the clothing resupply burden, and other subsystem improvements to reduce logistics and power requirements. Recommendation 2-28. The advanced life support program should recognize the International Space Station (ISS) environmental control and life support system (ECLSS) as a point of departure for technology initiatives. OLMSA along with the Human Exploration and Development of Space Enterprise (with the ISS

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Program Office) should develop a funded plan to use the ISS as an engineering testbed for advanced life support research.5 This plan should address the evolution of the ISS, as well as the development of processes, subsystems, and systems for lunar bases, Mars transit vehicles, and Mars bases. The NASA team at Marshall Space Flight Center, which currently has the most expertise in the ISS ECLSS, should continue to be involved in any long-term projects to provide enhancements to the system. Research and development of bioregenerative or plant-based technology should be included in the plans for any advanced life support testbed on the ISS. If such a testbed were expanded to a module, the module could help form the basis for an ALS module on a Mars transit vehicle or a long-term planetary base. Finding. There are no definitive requirements for the selection of crop types to be included in bioregenerative life support systems. Recommendation 2-29. NASA personnel working in space human factors and the development of foods and meals for space crews need to help establish requirements for the selection of food crops for representative mission scenarios (based on nutritional, cultural, processing, and crew time considerations). Researchers responsible for growing plants in space should consider processing requirements when making crop selections, as well as coordinate with those whose task is to turn the processed crops into acceptable meals. Dual-Use Technologies Summary Finding. The NASA-sponsored research in ALS emphasizes resource recovery from solid waste (primarily to support controlled environment plant growth) and contaminant removal from the water and atmosphere. Spacecraft life support systems are designed to perform these functions to support humans in confined environments at remote locations where resupply is difficult and costly. Other applications that share one or more of these attributes may be dual-use candidates if the economic and/or political environment is favorable. Finding. The processing of solid and liquid waste materials can be motivated either by a need for the recovered resources or by a need to convert waste materials into something more environmentally benign. Spacecraft conditions tend to require the former, while terrestrial spin-offs tend toward the latter. Regardless of the motivation, the same technology can be used. Several projects currently under way demonstrate the potential dual use of ALS waste processing. Both applications described below are in remote locations where living conditions make growing plants in a controlled environment an attractive option. 5    Issues regarding engineering research on the ISS are reviewed in Engineering Research and Technology Development on the Space Station (NRC, 1996).

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NASA is a technical contributor to the collaborative effort, Advanced Life [Support] Systems for Extreme Environments Project, with the University of Alaska, the North Slope Borough, the Ukpeavik Inupiat Corporation, and Llisagvic College. The primary goal of this effort is to establish a research and operational facility in the Alaskan North Slope Borough to introduce and distribute socially, environmentally, and economically compatible technologies to improve life in remote communities. The project emphasizes: waste and wastewater treatment and sanitation; food production; environmental protection and remediation; and the introduction of technologies to the Arctic environment that will not adversely affect the traditional subsistence activities and ways of life of the indigenous peoples. It is expected that some of the waste treatment processes developed in the ALS program will be applicable to this project. A similar project, funded by the National Science Foundation, is under way to apply the waste treatment and plant growth technologies developed in the NASA program to reduce the accumulation of waste at the South Pole Station and to provide a source of fresh vegetables during the winter confinement. The removal of contaminants generated by human occupants and material offgassing from the atmosphere in a confined environment becomes more difficult as the exchange with the external environment decreases. On board a spacecraft, exchange with the external environment is negligible, which means that contaminants will build up over time unless they are actively removed. Other applications, such as energy-tight buildings and aircraft, have varying degrees of exchange with the external environment. In most cases, exchange with the external environment is kept low to maintain the desirable attributes of the internal environment (e.g., air pressure, temperature, etc.). A low exchange can also be used to keep undesirable external elements out (e.g., cold, air pollutants, etc.). Early commercial jet aircraft circulated outside air through the cabin to reduce contaminants and vented it through a thrust recovery nozzle at the rear of the aircraft. The cabin atmosphere was maintained at a higher pressure than the external atmosphere by using bleed air from the engine compressors. Recently, aircraft designers have begun recirculating some air through the cabin to reduce performance penalties from the 100 percent flow-through. Passenger density and the resulting contaminant load (particularly CO2) limits the amount of recirculated air that can be used without additional processing. Other air quality concerns are cabin humidity and microbiological and trace gas contamination. When higher levels of recirculation are necessary or when the outside air quality is not good (e.g., when the plane is sitting on the runway waiting to take off) atmosphere revitalization technologies being developed by the ALS program are potentially applicable. Recommendation 2-30. NASA's work in advanced life support should continue to contribute improvements to technologies and systems for use on Earth, but the program should remain focused primarily on the development of technologies

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and systems for advanced life support in space (the unique goal of the program and the basic reason for its existence). References Bugbee, B., and F.B. Salisbury. 1988. Exploring the limits of Crop Productivity: Photosynthetic Efficiency in High Irradiance Environments. Plant Physiology 88: 869–878. Bula, R.J., R.C. Morrow, T.W. Tibbitts, D.J. Barta, R.W. Ignatius, and T.S. Martin. 1991. Light-emitting diodes as a radiation source for plants. HortScience 26 (2):203–205. Drysdale, Alan. 1995. McDonnell Douglas 1995 Annual Report. St. Louis, Missouri: McDonnell Douglas Corporation. Eckart, Peter. 1996. Spaceflight Life Support and Biospherics. Torrance, California: Space Technology Library, Microcosm, Inc. Finn, C., and V. Srinivasan. 1995. Dynamic simulation of the laboratory-scale CELSS. Life Support and Biosphere Science, International Journal of Earth/Space 2(2): 49–57. Ganapathi, G.B., P.K. Seshan, J. Ferral, and N. Rohagti. 1992. Human life support during interplanetary travel and domicile. Part VI. Generic modular flow schematic for hybrid physical/chemical-biological life support systems. Society of Automotive Engineers Paper 921120. Warrendale, Pennsylvania: Society of Automotive Engineers. MacLennan, Donald, Brian Turner, James Dolan, Michael Ury, Paul Gustafson. 1995. Efficient, full spectrum, long-lived, non-toxic microwave lamp for plant growth. International Lighting in Controlled Environments Workshop, held in Madison, Wisconsin. NASA Conference Publication Number 95-3309. Washington, D.C.: NASA. Musgrave, M.E., W.A. Gerth, H.W. Scheld, and B.R. Strain. 1988. Growth and mitochondrial respiration of mungbeans (Phaseolus aureus Roxb.) germinated at low pressure. Plant Physiology 88: 19–22. NASA (National Aeronautics and Space Administration). 1994. Designing for Human Presence in Space: An Introduction to Environmental Control and Life Support Systems. NASA RP-1324. Marshall Space Flight Center, Alabama: NASA. NASA. 1996a. FY 1996 Administrator's Guidance. Letter from NASA Administrator to NASA Center Directors. February 2, 1996. Washington, D.C.: NASA. NASA. 1996b. Human Exploration and Development of Space: Strategic Plan. Washington, D.C.: NASA. NRC (National Research Council). 1996a. Engineering Research and Technology Development on the Space Station. Aeronautics and Space Engineering Board. Washington, D.C.: National Academy Press. NRC. 1996b. Spacecraft Maximum Allowable Concentrations for Selected Airborne Contaminants. Vol. 2. Committee on Toxicology. Washington, D.C.: National Academy Press. Wheeler, Raymond M. 1996. Gas Balance in a Plant-Based CELSS. Pp. 207–216 in Plants in Space Biology. Sendai, Japan: Institute of Genetic Ecology, Tohoku University. Winkler, Gene, and Don Henninger. Early Human Testing Program Overview. 1996. Briefing presented to the Committee on Advanced Technology for Human Support in Space, at the Johnson Space Center, Houston, Texas, April 24, 1996. Zookin, Gary. 1993. Advanced Life Support System Analysis: Methodological Framework and Application Studies. Society of Automotive Engineers Paper 932129. Warrendale, Pennsylvania: Society of Automotive Engineers.