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Cooperation between Russia and the United States on manned spaceflight has led to unprecedented openness, resulting in the ability to now compare the characteristics of environmental control/life support hardware selected to generate oxygen (O2) by water electrolysis for space station applications. This comparison in this paper focuses on the characteristics that have the greatest effect on the cost of assembling and maintaining the hardware in space: launch weight, volume, power consumption, resupply requirements and maintenance labor.

The Static Feed Electrolyzer (SFE) has been under development by NASA through Life Systems, Inc. (Life Systems). Eighteen years of effort has characterized the SFE through extensive hours of testing, ancillary component development, and complimentary advancement in control and monitor instrumentation. The SFE technology is applicable to multiple Space Station systems, e.g., the Environmental Control and Life Support System (ECLSS), the Electric Power System (EPS), Extravehicular Activity (EVA), and the Propulsion and Reboost System. The ECLSS uses the SFE to generate metabolic oxygen (O2) for the crew, to provide reactants for carbon dioxide (CO2) removal, and to furnish hydrogen (H2) for reduction of the CO2. As part of the EPS, the SFE regenerates reactants from water to be used in producing electricity in the Regenerative Fuel Cell system (RFCS). For EVA, the SFE is used to replenish backpack and airlock O2, and regenerate the CO2 absorbent.

This paper will present a status review of Spacecraft Air Revitalization System (ARS) integration using regenerable techniques. The paper will address concepts of integration of individual subsystems into an Air Revitalization System, as well as integration of components within subsystems. An ARS design is presented based on the Electrochemical Depolarized Carbon Dioxide Concentrator Subsystem, the Sabatier Carbon Dioxide Reduction Subsystem, the Static Feed Water Electrolysis Subsystem, a condensing Humidity Control Subsystem, and a Water Handling Subsystem to perform the functions of CO2 removal, CO2 reduction, O2 generation, humidity control and by-product water distribution, respectively. The paper will also highlight the numerous advantages of this integration. Trace contaminant control and the nitrogen supply are not included in the ARS described in this paper.

Vapor Compression Distillation technology has proved its readiness as a spacecraft wastewater processor as evidenced by selection of this technology for the Urine Processor Assembly aboard Space Station Freedom. In conjunction with Boeing Aerospace Company and the National Aeronautics and Space Administration, Life Systems' technical team has made significant advances in both flight hardware design and software operational aspects. The flight hardware design has focused on Orbital Replacement Unit (ORU) design, ORU rack packaging and ORU weight reduction. On orbit operational aspects of software include operating modes, process control loops, fault detection and fault isolation. These improvements are further indication that Vapor Compression Distillation will be the key to providing wastewater regeneration essential for long-term human survival in space.

The future National Aeronautics and Space Administration (NASA) Space Station will require a high level of Control/Monitor Instrumentation (C/M I) for the operation of its critical subsystems. Automatic control and monitoring of subsystem operation will provide the crew with more time to conduct space operations for scientific experiments and commercial processes. Subsystem control and monitoring involves real-time data processing, subsystem fault tolerance and redundancy management, caution and warning, health monitoring and trend analysis, data management and support for on-orbit maintenance and repair. This paper addresses the control and monitor requirements for the Space Station’s Environmental Control and Life Support Systems (ECLSS). Sensor and actuator requirements are detailed. These are identified, along with the required controllers for the ECLSS complement of equipment. A controller hierarchy is also provided.

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.

The Fluid Systems Servicer (FSS) is designed to drain, purge, fill, and recirculate fluids while performing on-orbit start-up, scheduled, and unscheduled maintenance for fluid lines on the International Space Station (ISS). The FSS will utilize space vacuum for purging operations, thus, providing essentially unpowered vacuum back-filling capability. There is also a fluids pump in the FSS which is used for draining and recirculating water. The recirculation mode fulfills an additional design requirement of removing gas bubbles by directing water through a static membrane separator. Several flex-lines and adapters which interface various ISS lines via self-sealing Quick Disconnects (QD), are part of the FSS assembly. The FSS has its own power cord enabling excellent transportability. This feature, as well as, the QD adapters, enables the FSS to be used anywhere on station for numerous servicing tasks.

Progressive development of Electrochemical Carbon Dioxide (CO2) Concentration (EDC) technology by Life Systems under the sponsorship of the National Aeronautics and Space Administration (NASA) has resulted in subsystem hardware and Control and Monitor Instrumentation (C/M I) that are ideally suited for application to the Space Station program. The development effort has simplified the mechanical assembly to where only seven Orbital Replacement Units (ORUs), including two integrated components, are required to perform the process function. This simplification results in subsystem weight, power and volume requirements that are less than those of competing technologies. Further, process simplification provides both superior reliability and enhanced maintainability. Control and Monitor Instrumentation development has focused on utilization of state-of-the art electronics and software features that enhance subsystem reliability through fault detection and isolation.

There are two techniques being considered for carbon dioxide (CO2) removal and concentration for application in a regenerable Environmental Control and Life Support Systems (EC/LSS) aboard the projected Space Station. One uses the continuous Electrochemical Depolarized CO2 Concentration (EDC) technique while the second uses the cyclic absorption and desorption (with steam) from an amine resin bed. While the technologies involved with these techniques are substantially different, each must interface with other elements of a regenerable EC/LSS. This paper presents a comparison of the two competing technologies and includes the design and sizing of the respective subsystems for a Space Station application. The analysis includes identification of assumptions and groundrules with particular attention given to defining subsystem boundaries.

Regenerable carbon dioxide (CO2)/moisture removal techniques that reduce the expendables and logistics requirements are needed to sustain people undertaking extravehicular activities (EVA) for the Space Station. Life Systems, working with NASA, has been developing the Electrochemically Regenerable CO2 Absorption (ERCA) technology to replace the nonregenerable lithium hydroxide (LiOH) absorber for the, advanced Portable Life Support System (PLSS).(1) During EVA the ERCA uses a mechanism involving gas absorption into a liquid absorbent for the removal and storage of the metabolically produced CO2 and moisture. Following the EVA, the expended absorbent is regenerated on-board the Space Station by an electrochemical concept based on the Life Systems' Electrochemical CO2 Concentrator (EDC) technology. The ERCA concept has the ability to effectively satisfy the high metabolic CO2 and moisture removal requirements of PLSS applications.

The preliminary design of the nation’s Space Station is presently being developed. The Environmental Control and Life Support System (ECLSS), consisting of regenerative and nonregenerative technologies, has progressed through a series of trade studies including evaluation of the closure and distribution within the evolutionary Space Station configuration. The analysis has included the identification of the time-critical functions, redundancy (backup) management, definition of common subsystem interfaces and quantification of technology options for the process equipment. Each technology has been characterized by its physical characteristics of weight, power, volume, heat rejection, etc. Summaries of the trade study findings for the overall ECLSS in terms of physical characteristics and the impact of selected technologies is presented.

There is an assortment of hardware designed to work together to provide fluid servicing, seal leak checking and other plumbing-type services on the International Space Station (ISS). The Fluid Systems Servicer (FSS) is designed to drain, purge, fill, and recirculate fluids for on-orbit start-up, scheduled and unscheduled maintenance. The FSS will utilize space vacuum for purging operations on-orbit via the Vacuum Access Jumpers (VAJ), thus providing vacuum back-filling and static leak check capability with minimal power consumption. The FSS services Internal Thermal Control Systems (ITCS) and Environmental Control & Life Support (ECLS) System hardware in the pressurized elements of the ISS. The FSS gas/liquid separator fulfills an additional design requirement of removing entrained gas from fluids by means of a static membrane separator. The FSS and some ancillary equipment also perform Seal Leak Check (SLC), pressure removal and equalization, and window assembly maintenance on ISS.

The Fluid Systems Servicer (FSS) is designed to drain, purge, fill, and recirculate fluids while performing on-orbit start-up, scheduled and unscheduled maintenance for fluid lines leak check ports, and window assemblies on the International Space Station (ISS). The FSS will undergo extensive functional testing to verify that all design requirements have been met. The FSS will utilize space vacuum for purging operations on-orbit, thus providing vacuum back-filling capability with minimal power consumption. For ground testing, the application of space vacuum will be simulated. A full scale mock-up of the Space Station 20″ Window Assembly has been built for requirements verification. Two desiccator assembly Orbital Replacement Units (ORU)s will be tested to assure the FSS can perform window servicing requirements. The FSS gas/liquid separator fulfills an additional design requirement of removing gas bubbles from fluids with a static membrane separator.

The Space Station Environmental Control and Life Support System (ECLSS) consists of 51 functions. These functions are mostly independent of interactions. One exception is the regenerative air revitalization functions of carbon dioxide (CO2) removal, carbon dioxide (CO2) reduction and oxygen (O2) generation. Integration of these interdependent functions and humidity control into a single system provides significant opportunities for process simplification and reductions in power, weight and volume requirements compared to the use of discrete subsystems. An example of the magnitude of the opportunities provided is given by the ARS-1 developed by Life Systems under the sponsorship of National Aeronautics and Space Administration (NASA). Information presented in this paper quantifies the savings achieved by this integration and identifies other advantages available through process integration.

Vapor Compression Distillation (VCD) technology for phase change recovery of potable water from wastewater has evolved as a technically mature approach for use aboard the Space Station. A program to parametrically test an advanced preprototype Vapor Compression Distillation Subsystem (VCDS) was completed by Life Systems for the National Aeronautics and Space Administration (NASA) Johnson Space Center (JSC) during 1985. In parallel with parametric testing, a hardware improvement program was initiated to incorporate and verify certain key improvements into the advanced preprototype VCDS following initial parametric tests. Specific areas of improvements included long-life, self-lubricated bearings, a lightweight, highly-efficient compressor and a long-life magnetic drive. These improvements are now incorporated and verification testing started.

Regenerative processes for the revitalization of spacecraft atmospheres are required for extended duration space missions like the Space Station Freedom. A major atmosphere revitalization function is the recovery of oxygen from metabolic carbon dioxide by means of carbon dioxide reduction. The Sabatier carbon dioxide reduction technology is the baseline technology for the Space Station Freedom for this purpose. Life Systems has performed characterization and endurance testing of Sabatier reactor assemblies that has been used to design a prototype Sabatier reactor that complies with the performance requirements of the Space Station Freedom Carbon Dioxide Reduction Assembly. Information presented in the paper defines the testing that was used to design the prototype reactor and presents the successful test results that have been achieved using this reactor as part of an automated Sabatier based Carbon Reduction Assembly.

The Space Station requirements are divided into eleven systems. One of these systems, the Environmental Control/Life Support System (ECLSS) is further divided into seven functional categories as follows: Atmosphere Revitalization System, Atmosphere Pressure and Composition Control System, Module Temperature and Humidity Control System, Water Management System, Waste Management System, EVA Support and Safe Haven. The paper reviews the requirements for ECLSS in terms of the initial and growth operational capabilities of the Reference Space Station architecture. The paper reviews some of the results of a systems engineering study under way. Both regenerative and nonregenerative ECLSS techniques are reviewed. A design for all of the primary and backup technologies was established so that accurate trade studies could be performed. Each technology design started at a common interface condition for competing technologies.

The Static Feed Electrolyzer (SFE) is being developed by the National Aeronautics and Space Administration (NASA) through Life Systems, Inc. (Life Systems) as part of NASA's effort to mature water electrolysis technology for application in the Space Station Environmental Control/Life Support System (ECLSS), Propulsion and Reboost System, Extravehicular Activity (EVA) and Electric Power System (EPS). The water electrolysis process generates metabolic oxygen (O2) for the crew cabin, EVA backpacks and air lock, and provides reactants for carbon dioxide (CO2) removal, CO2 reduction, propulsion/reboost systems and fuel cell electric power generation. The use within all of these applications will make water electrolysis a fundamental utilitylike technology for the Space Station.

Long-term manned operation of NASA's Space Station will dictate use of regenerative processes for the revitalization of the Spacecraft atmosphere. An alkaline Static Feed Water Electrolysis System (SFWES) is being developed by Life Systems, Inc. and NASA to generate metabolic oxygen (O2) for the crew, provide hydrogen (H2) for reduction of concentrated carbon dioxide (CO2) and compensate for O2 lost overboard due to Space Station leakage. The SFWES employs highly efficient electrodes with rugged unitized cell construction. Integrated mechanical components and advanced automated Control/Monitor Instrumentation (C/M I) are used to reduce system complexity while enhancing overall reliability and maintainability. Crew size and the unique environment of space drive the system design.