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Recent NASA-funded studies of Allied-Signal metal-oxide-based absorbents demonstrated that these absorbents offer a unique capability to remove both metabolic carbon dioxide (CO2) and water (H2O) vapor from breathing air; previously, metal oxides were considered only for the removal of CO2. The concurrent removal of CO2 and H2O vapor can simplify the astronaut portable life support system (PLSS) by combining the CO2 and humidity control functions into one component. A further benefit is that the removal processes are reversible, permitting a regenerative component. Thus, a metal oxide absorbent offers many advantages over the current system, which is nonregenerative and uses separate processes for CO2 and H2O vapor removal. These advantages include lower complexity, lower maintenance, and longer life. The use of metal oxide absorbents for removal of both CO2 and H2O vapor in the PLSS is the focus of an ongoing NASA program.

In several previous studies, metal-oxide-based absorbents have been investigated as a regenerative means of removal of carbon dioxide (CO2) from recycled breathing gas in an astronaut portable life support system (PLSS). In most cases, the significant effect of water vapor on the successful absorption of CO2 was noted. Under an ongoing NASA-funded program, parametric studies have been conducted to characterize the performance of a silver-oxide-based absorbent, developed by Allied-Signal researchers, in terms of its ability to remove both gaseous CO2 and water vapor. This phenomenon is highly desirable and could lead to a much simplified PLSS. These studies included an investigation of the effects of preconditioning the absorbent, the effects of cooling the absorbent bed, and the impact of various levels of inlet CO2 and water vapor partial pressures.

A regenerable metal oxide carbon dioxide (CO2) removal system was developed to replace the current means of a nonreusable chemical, lithium hydroxide, for removing the metabolic CO2 of an astronaut in a space suit. Testing indicates that a viable low-volume metal oxide concept can be used in the portable life support system for CO2 removal during Space Station extravehicular activity (EVA). A canister of nearly the same volume as that used for the Space Shuttle, containing 0.10 ft3 (2.8 liters) of silver-oxide-based pellets, was tested; test data analysis indicates that 0.18 ft3 (5.1 liters) of the metal oxide will result in an 8-hour EVA capability. The testing suggests that the metal oxide technology offers a low-volume approach for a reusable CO2 removal concept applicable for at least 40 EVA missions. The development and testing of the breadboard regeneration package is also described.

Supply of oxygen (O2) and hydrogen (H2) by electrolyzing water in space will play an important role in meeting the National Aeronautics and Space Administration's (NASA's) needs and goals for future space missions. Both O2 and H2 are envisioned to be used in a variety of processes including crew life support, spacecraft propulsion, extravehicular activity, electrical power generation/storage as well as in scientific experiment and manufacturing processes. Life Systems, Inc., in conjunction with NASA, has been developing an alkaline-based Static Feed Electrolyzer (SFE). During the development of the water electrolysis technology over the past 23 years, an extensive engineering and scientific data base has been assembled.

Hamilton Standard has developed a non-venting Metal Oxide Regenerable EMU CO2 Removal Subsystem (MORES) for the NASA Johnson Space Center. This system has the potential for application to an Advanced EMU or retrofit to the existing Shuttle EMU. The MORES system uses a catalyzed, silver based metal oxide to achieve the CO2 removal during Extravehicular Activity (EVA) and uses no supplemental cooling. Regeneration is easily accomplished using cabin air in a simple hot air regeneration process. The MORES technology has been demonstrated in a full size EMU Contaminant Control Cartridge (CCC) using a conventional packed bed and also an improved sheet matrix configuration. The packed bed MORES used pellets encased in a porous shell to meet the design performance goal of 3.5 - 5 hours per simulated EVA for more than 50 cycles. The sheet matrix configuration has demonstrated performance of 6 - 8 hours for greater than 50 cycles.

The use of metal oxide absorbents in a portable life support system (PLSS) for regenerative removal of both CO2 and H2O vapor is the focus of an ongoing NASA program. This program addresses the rigorous extravehicular activity (EVA) requirements for Space Station Freedom and future long-duration missions. The concurrent removal of CO2 and H2O vapor can simplify the PLSS by combining the CO2 removal and humidity control functions in one component. A further benefit is that the reversible gas/solid chemical reaction of the removal processes permits a regenerative component that does not vent to space. Recently a preprototype full-scale metal oxide carbon dioxide and humidity remover (MOCHR) and a regeneration module were delivered to NASA Johnson Space Center (JSC). Prior to delivery, preliminary testing of the MOCHR and regeneration module was conducted at AiResearch.

A regenerable solid amine CO2 control system, which employs water vapor for desorption, is being developed for potential use on long duration space missions. During cyclic operation, CO2 is first absorbed from the cabin atmosphere onto the granular amine. Steam is then used to heat the solid amine bed and desorb the CO2. This paper describes the solid amine system operation and application to the Shuttle Orbiter, Manned Space Platform (MSP) and Space Operations Center (SOC). The importance and interplay of system performance parameters are presented together with supporting data and design characteristics.

The Sabatier reactor is an exothermic, heterogeneous catalytic reactor that has the function of reducing carbon dioxide to methane and water vapor. Sabatier reactor operation is affected by gravity through the effects of buoyant forces. The buoyant forces affect the transfer of heat and can be significant in determining the temperatures of the various portions of the reactor. The temperatures then affect the fundamental processes such as the chemical reaction rate. This paper presents the results of zero “G” computer model simulations of Sabatier reactor operation. Groundbase experiments were made for various manned loadings under normal ambient and gravity (l-G) conditions and were correlated with normal gravity simulations. The zero “G” simulations show the reactor will run significantly hotter in a zero “G” environment if cooling air flow is not increased to compensate for the loss of natural convections.

This paper briefly discusses the development history of solid amine CO2 control systems, describes two distinct CO2 control system concepts, and presents the performance characteristics for both system concepts. The first concept (developed under NASA Contract NAS9-13624) incorporates a solid amine canister, an automatic microprocessor controller, and an accumulator to collect CO2 and to provide regulated CO2 delivery to an oxygen recovery system. This system is currently operating in the Crew Systems Division's Advanced Life Support Development Laboratory (ALSDL). The second system concept (being developed under NASA Contract NAS9-16978) employs multiple solid amine canisters, an advanced automatic controller and system status display, the ability to regulate CO2 delivery for oxygen recovery, and energy saving features that allow system operation at lower power levels than the first concept.

Regenerative-type subsystems are being tested at JSC to provide atmosphere revitalization functions of oxygen supply and carbon dioxide (CO2) removal for a future Space Station. Oxygen is supplied by an electrolysis subsystem, developed by General Electric, Wilmington, Mass., which uses the product water from either the CO2 reduction subsystem or a water reclamation process. CO2 is removed and concentrated by an electrochemical process, developed by Life Systems, Inc., Cleveland, Ohio. The concentrated CO2 is reduced in a Sabatier process with the hydrogen from the electrolysis process to water and methane. This subsystem is developed by Hamilton Standard, Windsor Locks, Conn. These subsystems are being integrated into an atmosphere revitalization group. This paper describes the integrated test configuration and the initial checkout test. The feasibility and design compatibility of these subsystems integrated into an air revitalization system is discussed.

Breathing oxygen supply for long-duration manned space missions such as the NASA Space Station may be generated by electrolysis of water produced by the reaction of metabolic carbon dioxide and hydrogen in a Sabatier Methanation Reactor (SMR). A Space Station probable restriction on venting of carbonaceous gases to space will require onboard management of SMR product methane. This may be accomplished via methane decomposition to hydrogen and carbon. The hydrogen could be recycled to the SMR and the carbon would be stored onboard. Under contract with the NASA Johnson Space Center (JSC), Hamilton Standard is currently developing a Carbon Formation Reactor (CFR) that decomposes methane to gaseous hydrogen and dense solid carbon via high temperature pyrolysis. In this paper, the fundamentals of methane pyrolysis to carbon are described and the results of CFR development efforts to date are presented.

Recent development of the solid amine/water desorbed (SAWD) CO2 control system technology has resulted in two preprototype systems. The SAWD I system was developed under NASA Contract NAS9-13624 and is currently under test in the NASA Johnson Space Center, Crew Systems Division Advanced Environmental Control Systems (ECS) Laboratory. The SAWD II system is being developed at Hamilton Standard Division of United Technologies (HSD) under NASA Contract NAS9-16978. This paper reviews the development history of solid amine CO2 control systems and describes the SAWD I and SAWD II systems. In the development of the SAWD II system, special attention was given to reducing its power requirements and to designing the system to be compatible with zero-gravity operation. Energy saving features are discussed, and the zero-gravity solid amine canister test program and selected design are described.

The direct electrochemical reduction of carbon dioxide (CO2) is achieved without catalysts and at sufficiently high temperatures to avoid carbon formation. The tubular electrolysis cell consists of thin layers of anode, electrolyte, cathode and cell interconnection. The electrolyte is made from yttria-stabilized zirconia which is an oxygen ion conductor at elevated temperatures. Anode and cell interconnection materials are complex oxides and are electronic conductors. The cathode material is a composite metal-ceramic structure. Cell performance characteristics have been determined using varying feed gas compositions and degrees of electrochemical decomposition. Cell test data are used to project the performance of a three-person CO2-electrolysis breadboard system.

The Extravehicular Activity (EVA) operations for Space Station (SS) require that a regenerable carbon dioxide (CO2) absorber be developed for the manned Extravehicular Mobility Unit (EMU). A concept which employs a solid amine resin to remove metabolic CCL and water vapor from the breathing air within the space suit is being developed by the Hamilton Standard Division of United Technologies Corporation under Contract NAS 9-17480 with the National Aeronautics and Space Administration (NASA) Johnson Space Center (JSC). The solid amine is packed within a water cooled metal foam matrix heat exchanger to remove the exothermic heat of chemical reaction. After completion of the EVA mission, the amine is regenerated on board the Space Station within the heat exchanger using a combination of heat and vacuum. This paper describes the concept design features, operational considerations and test results during simulated laboratory conditions.

The extravehicular activity (EVA) requirements for Space Station Freedom and future long-duration space missions demand advanced technologies for the life support subsystems in the astronaut portable life support system (PLSS). A NASA-funded program is currently underway to develop a full-scale, breadboard, regenerate metal oxide carbon dioxide (CO2) removal system. This technology is a promising concept to replace the lithium hydroxide absorber presently used for removing CO2 in the recycled breathing gas in the PLSS, but cannot be efficiently regenerated to be used for another EVA mission. In the metal oxide carbon dioxide removal system, an “active” metal oxide compound, contained within a solid absorbent material, effectively removes the CO2 by chemically reacting to form a metal carbonate during astronaut EVA. The absorbent is then regenerated thermally, by decomposing the resulting carbonate and thereby releasing CO2, to reform the metal oxide.

Reduction of metabolic carbon dioxide is one of the essential steps in physiochemical air revitalization for long-duration manned space missions. Under contract with NASA Johnson Space Center, Hamilton Standard is developing an Advanced Carbon Reactor Subsystem (ACRS) to produce water and dense solid carbon from carbon dioxide and hydrogen. The ACRS essentially consists of a Sabatier Methanation Reactor (SMR) to reduce carbon dioxide with hydrogen to methane and water, a gas-liquid separator to remove product water from the methane, and a Carbon Formation Reactor (CFR) to pyrolyze methane to carbon and hydrogen. The hydrogen is recycled to the SMR, while the produce carbon is periodically removed from the CFR. The SMR is well-developed, while the CFR is under development. In this paper, the fundamentals of the SMR and CFR processes are presented and results of Breadboard CFR testing are reported.

A five hour regenerate, nonventing Humidity and CO2 Control Subsystem (HCCS) technology demonstration unit is being developed for potential use in an Advanced Extravehicular Mobility Unit (AEMU) for Space Station application. The HCCS incorporates a weak base anion exchange resin packed in a metal foam matrix heat exchanger. This system simultaneously removes CO2 and water vapor with the resulting exothermic heat of reaction rejected to the heat exchanger. The system has no moving parts resulting in a highly reliable, simple configuration. Regeneration may be accomplished via internal heating and vacuum.