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A step in the development of advanced regenerative life support systems is to produce simulation models to guide experimentation and hardware development. This paper discuses the development of detailed simulation models of water reclamation processors using the ASPEN PLUS™ simulation program. Individual models have been developed for Vapor Compression Distillation (VCD), Vapor Phase Catalytic Ammonia Removal (VPCAR) and Supercritical Water Oxidation (SCWO). This paper outlines the methodology which is used to complete this work and discusses the insights which are gained by this type of model development. A discussion of how modeling predictions are used to direct future work in modeling and experimentation is also presented. The initial set of modeled processors were VCD, VPCAR, and SCWO. Future work will cover the modeling of other processors. These models will be linked to form subsystem level models, and evaluations will be performed on various configurations.

Waste management is a vital function of spacecraft life support systems as it is necessary to meet crew health and safety and quality of life requirements. Depending on the specific mission requirements, waste management operations can include waste collection, segregation, containment, processing, storage and disposal. For the Crew Exploration Vehicle (CEV), addressing volume and mass constraints is paramount. Reducing the volume of trash prior to storage is a viable means to recover habitable volume, and is therefore a particularly desirable waste management function to implement in the CEV, and potentially in other spacecraft as well. Research is currently being performed at NASA Ames Research Center to develop waste compaction systems that can provide both volume and mass savings for the CEV and other missions.

A Microwave Enhanced Solid Waste Freeze Drying Prototype system has been developed for the treatment of solid waste materials generated during extended manned space missions. The system recovers water initially contained within wastes and stabilizes the residue with respect to microbial growth. Dry waste may then be safely stored or passed on to the next waste treatment process. Operating under vacuum, microwave power provides the energy necessary for sublimation of ice contained within the waste. This water vapor is subsequently collected as relatively pure ice on a Peltier thermoelectric condenser as it travels en route to the vacuum pump. In addition to stabilization via dehydration, microwave enhanced Freeze Drying reduces the microbial population (∼90%) in the waste.

The inedible portion of plant biomass in closed regenerative life support systems must be reprocessed producing recyclable by-products such as carbon dioxide, sugars, and other useful organic species. High solids biomass slurries containing up to 27 wt% were successfully prepared in a stirred batch reactor and then pumped using a single piston valveless pump. Wheat straw, potato, and tomato crop residues were acid hydrolyzed using 1.2 wt% sulfuric acid at 180°C and 1.2 MPa for 0.75-1.5 hours. Viscosity for a 25 wt% acid hydrolyzed wheat straw emulsion (Bingham-plastic) was 6.5 centipoise at 3 cm/sec and 25°C.

Over the last three years, the University of Utah (UofU), NASA Ames Research Center (ARC), and Reaction Engineering International (REI) have been developing an incineration system for the regeneration of components in waste materials for long-term life support systems. The system includes a fluidized bed combustor and a catalytic flue gas clean up system. An experimental version of the incinerator was built at the UofU. The incinerator was tested and modified at ARC and then operated during the Phase III human testing at NASA Johnson Space Center (JSC) during 1997. This paper presents the results of the work at the three locations: the design and testing at UofU, the testing and modification at ARC, and the integration and operation during the Phase III tests at JSC.

Water is of critical importance to space missions due to crew needs and the cost of supply. To control mission costs, it is essential to recycle water from all available wastes - both solids and liquids. Water recovery from liquid water wastes has already been accomplished on space missions. For instance, a Water Recycling System (WRS) is currently operational on the International Space Station (ISS). It recovers water from urine and humidity condensate and processes it to potable water specifications. However, there is more recoverable water in solid wastes such as uneaten food, wet trash, feces, paper and packaging material, and brine. Previous studies have established the feasibility of obtaining a considerable amount of water and oxygen from these wastes (Pisharody et al, 2002; Fisher et al, 2008; Wignarajah et al, 2008).

The elemental composition of food consumed by astronauts is well defined. The major elements carbon, hydrogen, oxygen, nitrogen and sulfur are taken up in large amounts and these are often associated with the organic fraction (carbohydrates, proteins, fats etc) of human tissue. On the other hand, a number of the elements are located in the extracellular fluids and can be accounted for in the liquid and solid waste fraction of humans. These elements fall into three major categories - cationic macroelements (e.g. Ca, K, Na, Mg and Si), anionic macroelements (e.g. P, S and Cl and17 essential microelements, (e.g. Fe, Mn, Cr, Co, Cu, Zn, Se and Sr). When provided in the recommended concentrations to an adult healthy human, these elements should not normally accumulate in humans and will eventually be excreted in the different human wastes.

This paper builds on a steady-state investigation of waste heat reuse in an Advanced Life Support System (ALSS) for a Mars mission with a low degree of crop growth. In past studies, such a system has been defined in terms of technology types, hot and cold stream identification and stream energy content. The maximum steady-state potential for power and cooling savings within the system was computed via the Pinch Method. In this paper, the next step is taken toward achieving a pragmatic estimate of costs and savings associated with waste heat reuse in terms of equivalent system mass (ESM). In this paper, the assumption of steady-state flows are discarded, and a proposed schedule is developed for activities that are of interest in terms of waste heat reuse. The advanced life support system for the Mars Dual Lander Transit Vehicle is the system of interest.

Solid Waste Management (SWM) systems of current and previous space flight missions have employed relatively uncomplicated methods of waste collection, storage and return to Earth. NASA's long-term objectives, however, will likely include human-rated missions that are longer in both duration and distance, with little to no opportunity for re-supply. Such missions will likely exert increased demands upon all sub-systems, particularly the SWM system. In order to provide guidance to SWM Research and Technology Development (R&TD) efforts and overall system development, the establishment of appropriate SWM system requirements is necessary. Because future long duration missions are not yet fully defined, thorough mission-specific requirements have not yet been drafted.

Long duration missions pose substantial new challenges for solid waste management in Advanced Life Support (ALS) systems. These possibly include storing large volumes of waste material in a safe manner, rendering wastes stable or sterilized for extended periods of time, and/or processing wastes for recovery of vital resources. This is further complicated because future missions remain ill-defined with respect to waste stream quantity, composition and generation schedule. Without definitive knowledge of this information, development of mission requirements is hampered. Additionally, even if waste streams were well characterized, other operational and processing needs require clarification (e.g. resource recovery requirements and planetary protection constraints). Therefore, the development of solid waste management (SWM) subsystem requirements for long duration space missions is an inherently uncertain, complex and iterative process.

A Microwave Powered Solid Waste Stabilization and Water Recovery Prototype system has been developed for the treatment of solid waste materials generated during extended manned space missions. The system recovers water initially contained within wastes and stabilizes the residue with respect to microbial growth. Dry waste may then be safely stored or passed on to the next waste treatment process. Using microwave power, water present in the solid waste is selectively and rapidly heated. Liquid phase water flashes to steam and superheats. Hot water and steam formed in the interior of waste particles create an environment that is lethal to bacteria, yeasts, molds, and viruses. Steam contacts exposed surfaces and provides an effective thermal kill of microbes, in a manner similar to that of an autoclave. Volatilized water vapor is recovered by condensation.

Handling and processing human feces in space habitats is a major concern and needs to be addressed for the Crew Exploration Vehicle (CEV) as well as for future exploration activities. In order to ensure crew health and safety, feces should either be isolated in a dried form to prevent microbial activity, or be processed to yield a non-biohazardous product using a reliable technology. During laboratory testing of new feces processing technologies, use of “real” feces can impede progress due to practical issues such as safety and handling thereby limiting experimental investigations. The availability of a non-hazardous simulant or analogue of feces can overcome this limitation. Use of a simulant can speed up research and ensure a safe laboratory environment. At Ames Research Center, we have undertaken the task of developing human fecal simulants. In field investigations, human feces show wide variations in their chemical/physical composition.

Advanced space life support systems, especially systems that include growing plants to produce food, require the recovery of resources - primarily carbon dioxide and water - from various hydrocarbon wastes. Supercritical water oxidation (SCWO) of wastes is one of several possible techniques for oxidizing waste organics to recover the carbon dioxide and water. Supercritical water oxidation has the advantages of fast kinetics, complete oxidation, and the minimization of undesirable side products. However, the SCWO process requires further development before the process can be implemented in space life systems. One of the SCWO development needs is in the area of destruction of insoluble solids - such as inedible biomass or human wastes. Insoluble solids have to be introduced into a SCWO reactor as particles, and it can be expected that the particle size of the solids will affect the rate of reaction.

Newly outlined missions in the Vision for U.S. Space Exploration include extended human habitation on Mars. During these missions, large amounts of waste materials will be generated in solid, liquid and gaseous form. Returning these wastes to Earth will be extremely costly, and increase the opportunity for back contamination. Therefore, it is advantageous to investigate the potential for wastes to remain on Mars after mission completion. Untreated, these wastes are a reservoir of live/dead organisms and molecules considered “biomarkers” (i.e., indicators of life). If released to the planetary surface, these materials can potentially interfere with exobiology studies, disrupt any existent martian ecology and pose human safety concerns. Waste Management (WM) systems must therefore be specifically designed to control release of problematic materials both during the active phase of the mission, and for any specified post-mission duration.

To ensure that adequate water resources are available during a mission, any net water loss from the habitat must be balanced with an equivalent amount of makeup water. For a Mars transit mission, the primary sources of makeup water will likely involve water contained in shipped tanks and in prepackaged food. As mission length increases, it becomes more cost effective to increase system water closure (recovery and generation) than to launch adequate amounts of contained water. This trend may encourage designers to specify increased water recovery in lieu of higher food moisture content. However, food palatability requirements will likely declare that prepackaged foods have a minimum hydration (averaged over all food types). The food hydration requirement may even increase with mission duration. However, availability requirements for specific emergency scenarios may declare that determined quantities of water be provided in tanks, rather than as moisture in food.

Of the many competing technologies for resource recovery from solid wastes for long duration manned missions such as a lunar or Mars base, incineration technology is one of the most promising and certainly the most well developed in a terrestrial sense. An incinerator was used to recover and recycle part of the waste produced during the Early Human Testing Initiative Phase 3 (EHTI 3) at Johnson Space Center. The fluidized bed incinerator developed for the EHTI testing was a joint initiative between Ames Research Center, University of Utah and Johnson Space Center. Though in no way an optimized system at that time, the fluidized bed combustor fulfilled the basic requirements of a resource recovery system. Valuable data was generated and problem areas, technology development issues and future research directions were identified during the EHTI testing.

Reduction in power requirements for long-term space travel remains a critical technological challenge, since power provision for an advanced life support system determines a significant portion of the system's equivalent system mass (ESM). Optimization of individual processors alone is not sufficient to minimize power needs; system studies must be performed in order to maximize power savings. It is important to develop system designs that are more efficiently integrated from an energy standpoint, so that the equivalent system mass of future life support systems can be reduced. In a procedure referred to as the ‘pinch technique’, hot and cold streams within the system are matched and their energy exchanged in order to lower the external cooling and heating requirements. This paper describes an investigation of power savings by application of the pinch technique to a closed life support system under steady-state conditions.

The electrosynthesis of expendable reagents including acids, bases, and oxidants from simple salts or salt mixtures has been demonstrated using a variety of electrochemical cells. A five chambered electrodialytic water splitting (EDWS) cell with bipolar membranes was utilized to efficiently convert sodium sulfate, sodium chloride, potassium nitrate, and potassium chloride to conjugate acids and bases. With the same cell, selective segregation of cations and anions from mixed salt solutions occurred, resulting in relatively pure acids and bases. These results suggest that pure acids and bases can be produced from composite spacecraft brines. Chemical oxidants such as sodium and ammonium persulfate were also synthesized with high current efficiencies by the electrooxidation of salts and acids in a two chambered electrochemical cell.

A variety of techniques, including supercritical water oxidation, fluidized bed combustion, and microwave incineration have been applied to the destruction of solid wastes produced in regenerative life support systems supporting long duration manned missions. Among potential problems which still deserve attention are the need for operation in a variety of gravitational environments, and the requirement for improved methods of presenting concentrated solids to the reactor. Significant improvements in these areas are made possible through employment of the magnetically assisted gasification process. In this paper, magnetic methods are described for manipulating the degree of consolidation or fluidization of granular ferromagnetic media, for application in a gravity independent three step solid waste destruction process.

Since the mid 1980s, NASA has developed advanced waste management technologies that collect and process waste. These technologies include incineration, hydrothermal oxidation, pyrolysis, electrochemical oxidation, activated carbon production, brine dewatering, slurry bioreactor oxidation, composting, NOx control, compaction, and waste collection. Some of these technologies recover resources such as water, oxygen, nitrogen, carbon dioxide, carbon, fuels, and nutrients. Other technologies such as the Waste Collection System (WCS - the commode) collect waste for storage or processing. The need for waste processing varies greatly depending upon the mission scenario. This paper reviews the waste management technology development activities conducted by NASA since the mid 1980s and explores the drivers that determine the application of these technologies to future missions.