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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.

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.

Advances in carbon dioxide removal technology for spacecraft air revitalization promise to reduce the size and power consumption of carbon dioxide removal systems on future space missions. AlliedSignal has developed a Functionalized Carbon Molecular Sieve (FCMS) that can simultaneously remove carbon dioxide and water vapor. A thermally-coupled pressure-swing adsorption system has been designed using FCMS as the sorbent to provide regenerative carbon dioxide removal. The low regeneration temperature of FCMS results in lower power consumption than is required for conventional adsorbents, which typically desorb carbon dioxide at higher temperatures. The thermally-coupled pressure-swing system was tested, and results were compared to the Space Station Carbon Dioxide Removal Assembly (CDRA) as a reference design. The comparison indicated that a thermally-coupled pressure-swing system with FCMS offers significant savings in mass, volume and power consumption.

As the architecture of environmental control and life support systems (ECLSS) transitions to moderate-length missions, accommodating transports such as the crew exploration vehicle (CEV), vacuum regenerated carbon dioxide and water vapor removal systems becomes more practical. Carbon dioxide and water vapor partial pressure may be controlled through the use of zeolite molecular sieve adsorption systems as previously demonstrated by the Skylab missions. The design and performance of vacuum regenerated adsorption systems are governed by many factors, including process interface conditions, operational and interface configurations, and adsorbent bed configurations. The effects of these various factors were simulated using a transient adsorption model, and the results were correlated through design of experiments (DOE) methodology to identify the most critical factors.

Next generation ion exchanged X zeolites have been evaluated as replacements for the zeolites used in the spacecraft carbon dioxide removal systems. Most recently, zeolites have been used in the International Space Station (ISS) Carbon Dioxide Removal Assembly (CDRA). The zeolites used in the ISS CDRA are termed ASRT 5A and have 50% improvement in adsorptive capacity for carbon dioxide compared to commercial zeolites. Relative to the ASRT 5A zeolites on ISS, the ion exchanged X zeolites provides a factor of 1.6 improvement in carbon dioxide capacity, and an improved isotherm shape. Further improvement in capacity, along with improved resistance to attrition or cracking is obtained if the X zeolite is immobilized using a polymeric binder into a porous composite which fills the adsorbent canister. Together, these improvements allow the zeolite to be used in an adiabatic pressure-swing mode, or in the temperature/pressure swing mode now used in ISS.