Advanced Technology for Human Support in Space (1997)

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.)

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

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.

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

• 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.

The functions to be provided by ALS systems are shown in Table 2-2.¹

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.

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.

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

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.

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

contribute to the removal of many trace contaminants; however, they might also produce other trace compounds.

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.

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

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 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.

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

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.

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,

roots exude a wide variety of low molecular mass carbon compounds that increase microbial activity on the root surfaces. These microbes decompose most organic compounds to CO₂. Perhaps undesirable inorganic compounds could be concentrated on root surfaces and could be harvested with the crop. Cost-effective options for recycling, storing, or eliminating the inedible portions of plants after harvest need to be modeled and investigated.

Figures 2-2 and 2-3 show plants using CO₂ during photosynthesis to produce carbohydrates (food) and oxygen. The harvest index, which is the ratio of edible biomass to total biomass produced, is assumed to be 0.5 for both figures. Figure 2-2 represents a fully closed food loop that provides 100 percent of the crew's diet and oxygen, as well as oxygen for recycling solid inedible waste material. Figure 2-3 represents a partially closed food loop, which provides approximately 50 percent of the crew's diet, all of their oxygen, but no oxygen for recycling solid waste materials. Full closure of the food loop is not necessary for atmosphere revitalization (removing CO₂ and providing O₂) or for water processing. Closure of the food loop above about 50 percent to reduce the need for food resupply places additional burdens on the temperature and humidity control system to remove excess transpired water and on the waste processing system to recycle CO₂ from inedible waste material. For these reasons, the degree of food loop closure and the recycling of inedible biomass are key issues that must be addressed by careful systems analysis.

Figure 2-2

Fully closed food loop. Source: Wheeler, 1996.

Figure 2-3

Partially closed food loop. Source: Wheeler, 1996.

The specific mission environment can play a significant role in the selection of plants to be grown in space. Mission constraints may mean that a small area of plants can be used only for water recycling and diet supplementation. Crops with a high ratio of edible to total biomass (high harvest index) and crops that require little post-harvest processing may be particularly attractive in this scenario. Examples of such crops are leafy greens, like lettuce and spinach. Radishes and strawberries require little processing, but have lower harvest indexes. All of these crops are short and can be grown in a small growth chamber. Food production on a planetary surface must be done under different conditions from those encountered in microgravity. Volume and energy (if ample power is available) may be less constraining, and a larger variety of crops could be grown.

The optimal conditions for some plants may not always be suitable for humans, so the plant growth area might have to be separated from the crew quarters. For example, the optimum temperature for several plants is higher than the optimum temperature for people, and some plants (e.g., wheat) grow best in continuous light. Neither plants nor humans require sea-level atmospheric pressure for growth and development. A significant portion of the food on Earth is grown at an atmospheric pressure of 0.85 atmospheres (1.5 km elevation [5000 ft.]), and some food is produced at pressures as low as 0.6 atmospheres. Normal growth and development of plant seedlings has been observed at pressures as low as

0.2 atmospheres (Musgrave et al., 1988). Low-pressure, enclosed volumes for plant growth environments may enhance the engineering economy of food production on planetary surfaces because the strength and mass of the structure can be decreased as the internal/external pressure difference is reduced. However, the structure must still provide protection from radiation and micrometeoroids. Other factors associated with low pressure plant growth environments may offset any mass savings benefit, such as special provisions required for crew access, the development of support equipment designed to operate under low pressure conditions, and the expense of conducting life support system R&D at low pressure on Earth.

Low-pressure experiments are expensive to conduct on Earth because of the need for hypobaric chambers with gas composition and humidity control. But additional studies of plant productivity at low pressure are necessary if pressures less than about 0.6 atmospheres are to be utilized in space. Because different plant species have different optimal temperatures, some separation of environments for different species will probably be cost effective. It will probably not be cost effective to provide the exact optimum conditions for each crop. The cost/benefit trade-offs between the increased structural and system costs of separation and maximum food production have not been well documented. Optimal photo-periods and temperatures are likely to be driving parameters for separate environments. Separation for disease control may also be a useful precaution. The decreased production in less than optimal, shared environments needs to be modeled and studied to determine cost-effective alternatives for designing the plant growth facility.

The optimal CO₂ levels for plants may also be different from the CO₂ level in the crew compartment. Despite the fact that plants require CO₂ to survive and humans do not, some plants appear to be adversely affected by CO₂ levels at which humans suffer few or no ill effects. Although plant productivity increases with elevated CO₂ (to about 0.1 percent), preliminary evidence indicates that the productivity of some plants begins to decrease when CO₂ levels exceed about 0.2 percent. NASA currently tolerates CO₂ levels of up to 1.3 percent for up to 24 hours on its spacecraft, and 0.7 percent for 180 days (NRC, 1996b). A separate, low CO₂ area for plant production may be useful. The following section discusses some of the requirements and issues for growing plants in space and identifies where advances in technology could contribute significantly.

The roots of healthy plants absorb water and consume oxygen rapidly. If water is not continuously resupplied to all root surfaces, cell expansion decreases in a few seconds. If oxygen is not resupplied, anaerobic conditions occur, and respiration becomes highly inefficient. The simultaneous requirement for water and oxygen is satisfied in controlled plant growth environments on Earth, either by rapidly flowing hydroponic solutions or by multiple air/water interfaces in a porous matrix. Gases and liquids do not separate in microgravity, so delivering water and oxygen to root surfaces is a significant challenge. The challenge is compounded by the small root volumes that are necessary to minimize volume in

space. Several technologies are promising, especially microporous tubes that allow controlled leakage of nutrient solution to the root zone.

Plants require high levels of light for optimal growth. For a 10-year lunar base with a crew of four, it has been projected that 90 percent of the total mass of the systems will be required to support the plant component of a bioregenerative life support system, with one-third of that mass devoted to lighting (Drysdale, 1995). When electric lamps are used, most of the energy input for plant growth is used to provide radiation for photosynthesis. Electric lamps range in efficiency from 9 percent (incandescent) to 19 percent (fluorescent) to a high of 37 percent (high pressure sodium lamps). In addition to electrical efficiency, the cost of lighting in space includes the lamp mass and volume, heat rejection requirements, and mass and labor for replacing light bulbs. NASA is investigating many lighting technologies, but when all factors are taken into account, light-emitting diodes (Bula et al., 1991) and microwave lamps (MacLennan et al., 1995) seem to have good potential for near-term and long-term use in space (Drysdale, 1995). The development of lighting that is efficient in terms of mass, energy, and volume is extremely important. However, in the next decade and beyond, NASA is likely to benefit from lighting technologies being developed or advanced elsewhere.

The direct use of sunlight could dramatically reduce the energy requirement but would require an extremely strong, durable, highly transparent window that could efficiently filter out cosmic and ultraviolet radiation. Fiber optics are a promising new technology, particularly when coupled with a fresnel lens to selectively focus photosynthetic radiation on the end of the fiber-optic bundle. Unfortunately, sunlight is not available during the 14-day lunar night, so other options must be considered for use on the Moon. The direct use of sunlight in space (when it is available) is one area where technology advancement could yield significant cost benefits.

The questions of when resource recovery is actually needed and whether the partial recovery of resources might be adequate remain to be answered by systems analysis. In general, however, as mission duration and crew size increase, the recovery and recycling of nutrients from solid wastes to support food production becomes an economical consideration. Microbial bioreactors can be used to break down plant and human waste so that the primary inorganic nutrients (N, P, K, Ca, Mg, and S) are retained in a water-soluble form that can be directly returned to plants. Although plants and their associated rhizosphere microbes can facilitate the recycling of gray water, the effects of chronic exposure to the chemicals present in gray water have not been well characterized. Work has begun at KSC and ARC to study the impact of combustion or bioreactor wastes on plant growth. NASA's use of biological waste conversion and control is in the early stages, despite the maturity of, and conceptual similarity to, terrestrial

transformation systems, which have been produced after many years of R&D and have been used in large-scale operations.

Analyses of various closure scenarios, including partial conversion of waste residues, the roles of various oxidation reactions, and the challenges of final disposal, can be used to evaluate the applicability of specific resource recovery technology options. The conversion/transformation of biodegradable materials to substances that might be useless in space, but useful on a planetary surface (for example, lignin as a contribution to the eventual creation of a root-zone media for plant growth), is an additional consideration in determining the circumstances under which the recovery of resources from solid waste is warranted.

Systems analysis, engineering, and integration include methods to guide investments in technology, resolve and integrate competing needs, and guide the evolution of complex systems. Systems analysis is particularly important for ALS where multiple technologies can perform the same function. In the absence of a defined target mission, it is essential that systems analysis and trade-off studies be conducted to support strategic planning and to provide direction for decisions about technology development. Systems analysis tools then evolve into tools that can help determine the best technology for a given application. The best technology becomes apparent only after a rigorous quantitative analysis of system inputs and outputs within the context of mission parameters and constraints.

The realization of a closed, reliable, autonomous life support system will require complex integration. The complexity of this task will require the conscious application of systems engineering principles to ensure a low life cycle cost and a safe final product. Systems engineering of a complex system typically starts with an understanding of the mission or product requirements. The life support systems being developed in the ALS program must be engineered for many different mission scenarios. The system analysis must be flexible enough to identify high-leverage technology needs so cost-effective designs can be generated when detailed mission requirements become available.

Design factors for future missions need to be determined, even in the absence of specific missions. Table 2-3 outlines some differences in design drivers between past and future missions. Even from a top-level view, it is clear that the evolution of current capabilities is unlikely to meet all of the design challenges for future life support systems. Revolutionary steps in regenerable processes, autonomous controls, and repairability and reliability will probably be required. As advances are made in EMC, a concerted effort will be required to integrate them during the transition from the current conventional controls to a more highly automated control system that utilizes sensor feedback. Systems engineering and program management capabilities must be developed to encourage and incorporate revolutionary developments throughout the development process and to

provide a means for evaluating competing new technologies against the current technology baseline.

As life support systems become increasingly complex, and particularly as the integrated components of life support systems operate across a wide range of time constants, the capability to use analytic/computational simulations will become critical to verifying requirements and designs. The reliability requirements for an integrated, long-term life support system will also require the use of high-fidelity simulations and will lead to other challenges, such as the need for new materials, simplified designs for mechanical components, and multiply-redundant systems (e.g., sensors or computers). On-mission maintenance will require careful ''design-for-assembly/design-for-disassembly" analyses that account for work being done in reduced gravity.

The development of closed-loop, regenerable systems presents new challenges in mass and elemental partitioning within the system, adding reserves to accommodate system perturbations, understanding the varying time constants for P/C and biological processors, monitoring and controlling the generation and accumulation of microbial contaminants, and integrating biological processes into existing P/C-based life support systems. As the need to address these issues becomes more pressing, especially in the absence of specified mission scenarios, assessing the capabilities of ALS systems will become even more dependent on the development of adequate computer design tools and system models that can simulate processor performance, compare alternative design scenarios, understand system dynamics, develop reliability, availability and maintainability requirements and models, conduct both broad and focused trade-off studies, and perform analyses that support all elements of determining the cost of the program, from the technology development stage to the testbed stage to space-qualified designs.

System studies necessarily require test data. The combination of computer/system models and testbed-acquired data makes adequate and increasingly detailed system assessments possible. System modelers must be in close contact

with those making the measurements to maximize the efficiency of the modeling process. Because testbed testing is costly, it is essential that specific test goals be established and that an analysis of test parameter sensitivity be conducted before each test is run to ensure that goals are reasonable and attainable. Initial system assessments typically produce "quick-look" results that identify areas where data are either poor or lacking altogether. The identification of data gaps enables the development of requirements for testbeds and, thus, for the structure and format of a testbed program. This iterative process should be carefully considered during the development of multiyear funding plans to avoid the potential difficulties caused by accelerating the development of one component past the others before the next series of requirements has been established.

In the past, system studies programs have been initiated in the ALS program. But, apparently, they were not sustained or integrated and yielded little follow-up and no integrated effort to guide the overall ALS program. For example, in the 1970s and 1980s, CELSS and P/C trade-off studies were conducted with gross calculations of the relative benefits of growing higher plants in a closed life support system. These studies were mostly proof-of-concept models for a CELSS, single processor trade-off studies, and life support analyses of the early stages of the ISS.

In the late 1980s and early 1990s, the development of ongoing system analysis was begun at ARC (where decision analysis was applied to life support system trade-off studies and where system analysis models of lunar and Mars outpost missions were developed) and at JPL (where the life support systems analysis [LiSSA] code was developed and lunar and Mars outpost missions were analyzed). The analysis work at both centers came to a halt when funding was redirected. These efforts were never integrated, and data gaps and methods for dealing with them were never addressed. Many of the viewgraphs shown to the committee on "break-even points" for bioregenerative systems were derived from this relatively old work.

A wide variety of modeling tools are used to conduct systems analyses, from very basic spreadsheets to expert system interfaced models with sophisticated chemistry codes. Systems engineers have sometimes been limited in conducting analytical studies because many codes do not have the chemistry, biology, or dynamic capabilities to truly represent regenerative systems, especially systems with biological components. The most glaring problem for analysis of life support system studies is the clear lack of integration across the various programs. Several comprehensive assessments of modeling and system analysis tools are available,³ but there is little evidence that any of these have been analyzed or used in the ALS program.

The committee found few examples of systematic methodology development. Both JPL and ARC had brief programs in the early 1990s (Ganapathi et al., 1992, and Zookin, 1993), and some ongoing work by contractors includes methodological development as well as modeling. But the committee found little or no evidence that this work has ever been integrated in the planning for the ALS program or for feeding the results of system modeling into testbed development, following the iterative process described above. There appears to be one effort at ARC (Finn and Srinivasan, 1995), but this was discovered by the committee by reading a paper, and was neither presented to the committee nor recognized by any of the other centers in their presentations.

The objectives of the NASA OLMSA ALS program are managed or carried out at NASA headquarters, JSC, ARC, KSC, and MSFC. The program also funds work at universities and in industry. Other parts of NASA fund additional work relevant to ALS. These include: the Small Business Innovative Research (SBIR) Program (managed until recently by OSAT and now managed by the Office of Aeronautics), which funds a considerable number of projects; OLMSA, which sponsors one of the relevant NASA Specialized Centers of Research and Technology (NSCORT) at Rutgers University; OLMSA and the Office of Equal Opportunity, which jointly sponsor a University Research Center (URC) at Tuskegee University; OSF and JSC, which fund considerable work at JSC through the JSC Crew and Thermal Systems Division (CTSD) directly related to ALS; and OSF alone, which also funds other relevant work at JSC and MSFC under the auspices of the Space Shuttle and ISS programs.

A breakdown of NASA work related to ALS during FY96 is shown in Figure 2-4. The total of $16.8 million is an estimate based on data from NASA. OLMSA funding constitutes $10.46 million (62 percent of the total), and non-OLMSA funding constitutes $6.34 million (38 percent). ISS and Space Shuttle work on operational life support systems are not included in this estimate. Perhaps most noteworthy are the facts that SBIR funding comprises nearly a quarter of the NASA funding dedicated to ALS and that the human-rated test programs at JSC are the largest elements of the OLMSA program. At the time of the final meeting of the committee on August 31, 1996, there were no official estimates available from NASA regarding ALS or related funding beyond FY96. Like all NASA programs, the OLMSA ALS program budget depends on the overall NASA and OLMSA budgets determined by the administration and Congress. The ALS program budget also depends on NASA for its priorities because there is no line item in the NASA budget for the ALS program (or for any of the other three human

Figure 2-4

FY96 NASA funding for advanced life support. Source: NASA.

support programs). The ALS program is funded primarily from the portion of the NASA OLMSA budget allocated to supporting research and technology (SR&T). With this accounting method, there are no official projections of funding levels for the next several years, as there are for programs that have dedicated line items (such as facilities for the ISS).

At the committee's request, NASA provided detailed information on all the ALS-related projects under way in FY96 at ARC, KSC, and JSC. A summary of this information is provided in Appendix E. Funding for these projects falls under the SBIR, SR&T, and center office and discretionary funds identified in Figure 2-4. The figure also shows that the present ALS funding profile is heavily oriented toward in-house projects, with more than 50 percent going to NASA centers and NSCORTs. University involvement primarily falls under the SR&T portion of the OLMSA program. Allocation of this funding is primarily based on projects selected by peer review from proposals submitted in response to NASA Research Announcements (NRAs). The 13 percent ($2.2 million) for SR&T is based on funding data from JSC, ARC, and KSC. SBIR awards accounted for a significant percentage of NASA ALS technology funding in FY96, i.e., $4.5 million of the $16.6 million total. The current ALS program described to the committee includes a relatively minor role for industry other than small businesses.

Traditional prime and first-level subcontractors are not significant participants in NASA-funded technology development projects, but industry is funding some of their own projects, and interaction with NASA appears to be initiated primarily by industry.

Historically, challenges in spacecraft life support technology, from the beginning of human space flight through the ISS, have been met by strong ties between NASA and industry. This has encouraged industry to invest financial resources, as well as company talent and facilities to support NASA goals. Independent research and development (IR&D) by industry is typically directed to near-term business opportunities. In the absence of explicit exploration projects for a return to the Moon or a mission to Mars, IR&D funding will most likely be concentrated on evolutionary improvements to P/C systems that can benefit the Space Shuttle or the ISS. If there is no reasonable expectation of NASA advanced development funding as a follow-on to industry contributions, industry funding will probably be shifted to more promising business opportunities. This will diminish the industrial base and industry's ability to make contributions in the future. The lack of industry participation is likely to result in a less cost-effective and less innovative program.

The NASA headquarters ''road map" for ALS R&D is shown in Figure 2-5. There are four key elements of the road map: science and technology R&D; low-gravity research on the ISS; ground integrated testbed; and zero-gravity integrated testbed on the ISS. Note that a technological capability for a lunar/Mars base appears on the schedule in approximately 2010, preceded by a technological capability for a lunar/Mars planetary outpost. Neither the NASA nor the HEDS Strategic Plans yet supports actual missions. Note also that the schedule for closing the food loop is apparently driven by the requirement to have such a technological capability for a planetary base by 2010. The road map assumes that there will be a significant ability to do research and technology demonstrations and tests on the ISS. However, at the time of this study, no ISS facilities or resources had been designated for ALS research.⁴

The JSC CTSD plans for future work in ALS are primarily directed toward the "Ground Integrated Testbed" portion of the NASA headquarters road map. These plans are shown as detailed road maps in Figures 2-6a and 2-6b. Figure 2-6a shows JSC projects, beginning in 1995 and continuing through 2010 and beyond. The key aspects of this road map are the "Early Human Testing Initiative," which began in 1995, and the "Human Rated Test Facility," which is projected to be used beginning in about 2000. Figure 2-6b shows the post-2010 scenarios assumed by JSC, that the life support system for a new space vehicle for transportation beyond Earth orbit would be based on P/C technologies and that the life support system for a habitation on a planetary surface would be biologically based.

At the outset of this study in March 1996 and at the final meeting in August 1996, the committee was informed that NASA was in the process of transferring program management of the ALS program from NASA headquarters to JSC. However, no definitive steps were made during this period to establish JSC as the NASA organization responsible for the program. Throughout the study, JSC CTSD was identified as the group most likely to be responsible for the management of the ALS program. The CTSD organization has worked with the staff at NASA headquarters to take increasing responsibility for the program during the period of the study. This seems to have been done by individuals on their own personal initiative to fill a definite need, without specific guidance from NASA upper management.

JSC has directed life support technology R&D for human space flight since 1962. In addition, JSC has provided oversight for industry to provide life support systems for all of the crewed space programs, from Project Mercury through the Space Shuttle. For the ISS, NASA assigned life support design, development, and oversight responsibility to MSFC. Much of the technology used in the ISS was developed under the direction of JSC through advanced development programs in the 1970s and 1980s. From the standpoint of technical and programmatic continuity, many found this shift to MSFC confusing. It is not clear to the committee why the overall NASA policy statement released in February 1996 (NASA, 1996a) calling for the transfer of most program management functions from NASA headquarters to the NASA centers had not been implemented for the ALS program. This was particularly difficult to understand because the NASA 1996 Strategic Plan lists JSC as the lead NASA center for human exploration.

At the first meeting of the committee, NASA presented a study approach for developing requirements and R&D priorities to support the exploration scenario with the following tasks:

• to establish ALS technology requirements
• to assess current technology capabilities
• to prioritize technology development needs
• to develop a technology maturation process

NASA's proposed approach for developing requirements and prioritizing projects is logical. Although the planning process has not yet been implemented, if it is followed by scheduling, funding, and implementation plans, it appears likely to produce an integrated technology development plan that would meet mission needs.

Large human space flight programs have historically taken about 10 years from authorization to first flight. Despite reorganizations and redesigns, experience with the ISS and Space Station Freedom has shown that developing technology and building hardware and facilities for human space missions is not a straightforward proposition. As the ALS program develops its plans, the proper

mix of evolutionary and revolutionary technology development to be funded by the ALS program should be considered. It is a truism that although revolutionary breakthroughs can lead to the greatest gains, trying to achieve these gains is risky in terms of the allocation of resources (i.e., projects with the potential to produce revolutionary gains are also the projects most likely to fail). It is reasonable for the ALS program to pursue evolutionary improvements in mass, power, volume, reliability, life-cycle cost, maintainability, and durability of existing systems, while simultaneously investigating revolutionary improvements. A significant point to remember in seeking a balance between revolutionary and evolutionary projects is that there is no consistently successful way to solicit, find, or fund proposals for revolutionary technologies with a reasonable probability of success. Standard evaluation criteria for assessing the advantages of a new technology over the baseline technology must also be developed (e.g., cost/risk to benefit/need analysis).

Summary Finding. High priority areas for ALS R&D include systems analysis and P/C technologies for system loop closure to minimize resupply.

Finding. Current systems analysis is inadequate to support strategic planning or to provide direction for making decisions about technology development.

NASA has not targeted a specific mission, such as a return to the Moon or a mission to Mars, as the next definitive step to follow the ISS. Therefore, it is essential that the ALS program conduct systems analysis and trade-off studies with the objective of creating a comprehensive set of generic requirements for meeting future mission needs. More work needs to be done to update trade-off studies and "crossover" charts and to standardize analysis approaches for determining conditions that warrant different degrees of closure. A good example of the lack of analysis is the widespread acceptance of the value of 2.6 years (Winkler and Henninger, 1996) as the break-even point at which bioregenerative life support systems become advantageous, despite the fact that this figure is not based on a definitive analysis. Models of processes, systems, and subsystems are essential for adequate analysis. Test data for P/C and bioregenerative technologies, under both nominal and off-nominal conditions, are essential for validating models.

Recommendation 2-1. NASA should perform systems analyses using representative reference mission scenarios to develop generic technology development requirements that can be used as a basis for defining advanced life support subsystem and component research and development programs. Systems analysis should also be used to help determine the proper sequence and timing for subsystem and system-level testing, both with and without humans. It is important

that systems analysis work be completed early to ensure proper planning to develop the best technologies to meet the goals of the NASA Strategic Plan and to provide the flexibility to react to a specific mission when it is defined.

Recommendation 2-2. The advanced life support program should evaluate the analytical tools and skills available both inside and outside NASA. The evaluation must include an assessment of the resources, or combination of resources, that can be assembled to meet the needs of the advanced life support program. The best analytical tools, processes, procedures, and skills must be integrated to ensure that the program can conduct the highest quality systems work in the most cost-effective and timely manner. Evaluation criteria should be standardized so that processes, subsystems, and systems can be compared on a consistent basis.

Finding. There is little OLMSA-funded research and development on advanced P/C technologies for use beyond the ISS, particularly in the area of atmosphere revitalization.

Although the P/C and bioregenerative advanced life support programs have been successfully merged into a single program, the current program does not put enough emphasis on developing P/C subsystem technologies. Except for the teams directly involved with the development of P/C life support systems, there is a sense that the technologies necessary for closed systems have already been developed and are available for future use on long-term missions. But P/C life support technology is not fully mature.

Technologies have been developed for the ISS that will come close to closing the water loop, but the current technologies require a significant amount of expendables, such as prefilters and multifiltration beds. There are a few water recovery projects, which appears to be the proper emphasis, but increased efforts to push the envelope of the current technologies could bring benefits. In the area of air revitalization, a few projects investigating improvements in CO₂ removal and trace contaminant control are under way, but virtually none of them explores options for closing the oxygen loop, which will be the next major material closure challenge. There are similar levels of effort in the program for P/C and bioregenerative technologies for waste management.

Recommendation 2-3. Greater emphasis should be placed on developing advanced physical/chemical technologies to reduce dependence on resupply and on closing the oxygen loop. Water recycling initiatives should address technologies or processes that can reduce expendables, and power and volume requirements, either by incremental improvements to the International Space Station baseline system or by the adoption of new technologies. Air revitalization initiatives should concentrate on the recovery of oxygen from carbon dioxide in order to further close the oxygen loop.

Recommendation 2-4. NASA should perform systems analysis to determine when processing waste material is beneficial and what degree of recovery is

needed (e.g., water, carbon, and nutrients). Special attention should be placed on the management of process residues and effluents.

Summary Finding. Advanced life support is a critical technology for the success of long-duration future missions. Current technology cannot provide life support functions for long-duration human exploration in a cost-effective manner.

Finding. At current funding levels, the program plans are overly ambitious and do not represent a balanced approach for meeting future needs in technology for advanced life support. The program schedules appear to be unrealistic and unlikely to be accomplished with the most promising technologies without increased emphasis on early basic and applied research and development.

The current ALS program is operating in the absence of a NASA plan to take humans beyond LEO before 2010. Without a significant increase in resources, the program cannot support an earlier Moon or Mars mission. The ability of the program to support missions in the 2010 to 2020 time period depends on whether the programs will be funded and managed at the levels necessary to support the development of new technologies and systems with capabilities beyond present systems.

Recommendation 2-5. In the absence of specific mission objectives, research and development should be focused on long-term, mission-independent technology needs. When an exploration mission is initiated, research and development should be reexamined and refocussed, and corresponding budget adjustments should be made.

Recommendation 2-6. For now, technology development should focus on micro-gravity and lunar and Mars surface missions. Near-term priorities for physical/chemical, bioregenerative, and hybrid systems should be determined based on these scenarios.

Summary Finding. There is no current program plan for the development of advanced life support technology. In order to establish meaningful milestones, program objectives should be coordinated with an overall plan to develop the advanced life support technologies necessary for long-duration space missions.

Finding. There is no agency-endorsed plan for future missions to meet the HEDS objective of ''establish[ing] a human presence on the Moon, in the Martian System, and elsewhere in the inner solar system." (NASA, 1996b)

Meeting the technology development needs of a specific mission requires a highly focused program. But, if mission objectives change, the relevance of the

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.

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

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.

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

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.

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.

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

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.

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.

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

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

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.

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.

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

and systems for advanced life support in space (the unique goal of the program and the basic reason for its existence).

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