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In the closed environment of an inhabited spacecraft, a critical aspect of the air revitalization system is the removal of the carbon dioxide (CO2) and water vapor produced by the crew. A number of different techniques can be used for CO2 removal, but current methods are either non-regenerative or require a relatively high power input for thermal regeneration. Two-bed CO2 adsorption systems that can remove CO2 from humid air and be regenerated using pressure-swing desorption offer mass, volume, and power advantages when compared with the other methods. Two classes of sorbent materials show particular promise for this application: Zeolite sorbents, similar to those in the International Space Station (ISS) CO2 removal assembly Functionalized carbon molecular sieves (FCMS), which adsorb CO2 independent of the humidity in the airstream Pressure-swing testing of these two different sorbents under both space station and space suit conditions are currently underway.

The Lunar-Mars Life Support Test Project (LMLSTP), formerly known as the Early Human Testing Initiative (EHTI), was established to perform the necessary research, technology development, integration, and verification of regenerative life support systems to provide safe, reliable, and self-sufficient human life support systems. Four advanced life support system test phases make up LMLSTP. Phase I of the test program demonstrated the use of plants to provide the atmosphere revitalization requirements of a single test subject for 15 days. The primary objective of the Phase II test was to demonstrate an integrated regenerative life support system capable of sustaining a human crew of four for 30 days in a closed chamber. The third test phase, known as Phase IIA, served as a demonstration of International Space Station (ISS) representative life support technology, supporting a human crew of four for 60 days.

Space environmental control systems must control cabin temperature and humidity. This can be achieved by transferring the heat load to a circulating coolant, condensing the humidity, and separating the condensate from the air stream. In addition, environmental control systems may be required to remove particulate matter from the air stream. An assembly comprised of a filter, a condensing heat exchanger, a thermal control valve, and a liquid carryover sensor, is used to achieve all these requirements. A condensing heat exchanger and filter assembly (CHXFA) is being developed and manufactured by SECAN/AlliedSignal under a contract from Dornier Daimler-Benz as part of a European Space Agency program. The CHXFA is part of the environmental control system of the Columbus Orbital Facility (COF), the European laboratory module of the International Space Station (ISS).

The dual membrane gas trap filter is utilized in the internal thermal control system (ITCS) as part of the pump package assembly to remove non-condensed gases from the ITCS coolant. This improves pump performance and prevents pump cavitation. The gas trap also provides the capability to vent air that is Ingested into the ITCS during routine maintenance and replacement of the International Space Station (ISS) system orbital replacement units. The gas trap is composed of two types of membranes that are formed into a cylindrical module and then encased within a titanium housing. The non-condensed gas that is captured is then allowed to escape through a vent tube in the gas trap housing.

Condensing heat exchangers (CHX) are used in many applications, including space life support systems, to control temperature and humidity. Temperature control is achieved by transfer of the heat load to a circulating coolant. Simultaneously, humidity control is provided by cooling the air below its dew point, and separating the condensed water from the gas flow. In space, the condensate does not drain from the heat exchanger because of the absence of gravity. To overcome this problem, slurping condensing heat exchangers have been developed that combine a hydrophilic coating on the air flow passages and an additional slurping section added to the air outlet of the heat exchanger to achieve efficient air-water separation. For short missions such as those typical for shuttle flights, microbial proliferation in the coatings has not been a major issue, despite the fact that the coatings are continuously moist and an ideal breeding ground for microbial species.

Advanced space suit portable life support systems (PLSS) require high performance fans for the breathing gas ventilation system. AlliedSignal has developed a high speed air bearing fan for this application. This work addresses the development of an advanced electronic controller to drive this fan. Advances in space suit technology required an improved fan controller. The architecture of the controller was modified to enhance performance and facilitate testing in a space environment. These modifications were both physical and functional. To reduce the size of the controller, electrical, electronic and electromechanical (EEE) components were divided into two circuit cards, the housing was redesigned, test points and control knobs were removed, and a higher grade of EEE components were used in the development of the controller. These modifications improved the functional characteristics of the controller.

The Lunar-Mars Life Support Test Project (LMLSTP) Phase III test examined the use of biological and physicochemical life support technologies for the recovery of potable water from waste water, the regeneration of breathable air, and the maintenance of a shirt-sleeve environment for a crew of four persons for 91 days. This represents the longest duration ground-test of life support systems with humans performed in the United States. This paper will describe the test from the inside viewpoint, concentrating on three major areas: maintenance and repair of life support elements, the scientific projects performed primarily in support of the International Space Station, and numerous activities in the areas of public affairs and education outreach.

One of the primary safety concerns for Space Station Freedom pressurized modules is fire. Some Freedom modules are unattended for long periods of time. In other cases, enclosed, pressurized volumes are not open to crew monitoring. As a result, a fire detection system is required to continuously monitor all modules for combustion. This paper briefly reviews the overall design for the Freedom fire detection system, and the design of the two basic types of detectors: smoke and flame. The smoke detectors monitor particulates in small open areas, stand-offs, end-cones, and racks. The flame detectors survey open areas for radiation at wavelengths and intensities characteristic of combustion. Responses from detectors are evaluated by Freedom's data management system to determine the presence of combustion and to recommend appropriate action.

Reversible adsorption on zeolite molecular sieve material allows selective removal of carbon dioxide (CO2) from spacecraft air without the use of expendables. The four-bed molecular sieve (4BMS) CO2 removal subsystem chosen for use on space station is based on proven Skylab technology and provides continuous CO2 removal from the cabin atmosphere and concentration for further processing downstream or venting overboard. A 4BMS subsystem has also been chosen to remove CO2 from air in the Systems Integration Research Facility (SIRF) at NASA/Johnson Space Center (JSC). After installation in the SIRF in 1992, the subsystem underwent extensive testing in which cycle time, process air flow rate, and process air inlet CO2 composition were varied. In order to obtain performance data required for integration, the subsystem was operated under both nominal and off-nominal conditions. Results of this testing are presented.

This paper reviews designs of urine distillation systems for spacecraft water recovery. Consideration is given to both air evaporation and vacuum distillation cycles, to the means for improving cycle performance (such as heat pumps, multistaging, and rotary evaporators), and to system concepts offering promise for future development. Vacuum distillation offers lower power consumption, at some increase in system complexity; air evaporation distillation is capable of providing higher water recovery efficiency, which could offset the lower power consumption advantage of vacuum distillation for long-duration missions.

The two-phase pump assembly (TPPA) supports advanced thermal control systems (TCS) being developed for future orbital and deep space missions that continuously demand technological advancements to reduce cost, schedule, size, and weight. The TCS provides cooling to onboard personnel and systems by utilizing a coolant in which the working fluid undergoes vaporization and condensation while circulating in the coolant fluid loop. The considerable latent heat associated with these liquid-vapor phase transitions allows the working fluid to absorb and transport a given amount of heat energy with a significantly reduced coolant flow rate resulting in a smaller system size, volume, and mass. Properly designed heat exchangers which utilize boiling and condensation phase transitions can be made smaller and lighter than single-phase systems for a given heat dissipation load.