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As part of NASA's initiative to develop an advanced portable life support system (PLSS), a baseline schematic has been chosen that includes gaseous oxygen in a closed circuit ventilation configuration. Supply oxygen enters the suit at the back of the helmet, passes over the astronaut's body, and is extracted at the astronaut's wrists and ankles through the liquid cooling and ventilation garment (LCVG). The extracted gases are then treated using a rapid cycling amine (RCA) system for carbon dioxide and water removal and activated carbon for trace gas removal before being mixed with makeup oxygen and reintroduced into the helmet. Thermal control is provided by a suit water membrane evaporator (SWME). As an extension of the original schematic development, NASA evaluated several Helmet Exhalation Capture System (HECS) configurations as alternatives to the baseline.

Independent temperature and humidity control may be required for a variety of reasons. One application under study at the NASA Johnson Space Center is the environmental control of completely sealed plant growth chambers. The chambers are used to optimize plant growth and to develop engineering prototypes of future plant growth chamber modules for long duration space travel. One chamber at the Johnson Space Center which is part of the Early Human Test Initiative was rebuilt and upgraded during 1994. Requirements called for a thermal control system which could supply the plants with a wide range of air temperatures and independently control humidity. A math model was developed using G189 thermal/environmental modeling software to simulate the internal environment of the plant growth chamber. The model was used in the design of the chamber thermal control system.

Growth of higher plants In closed environments requires a great deal of energy for lighting systems. Even the most efficient lights deliver only about a quarter of the energy they use as useful radiation for plant growth (photosynthetically active radiation or PAR). The remainder of the energy, as well as most of the PAR, ends up as waste heat which must be removed from the plant growth chamber. The thermal control system (TCS) which does this job can require a significant amount of volume, mass and power. Efficient and effective design of the TCS is therefore important to the overall feasibility of the plant growth chamber, either for terrestrial or aerospace purposes. As part of the Early Human Testing Initiative being conducted by the Crew and Thermal Systems Division at the Johnson Space Center, a plant growth chamber has been designed and built which has instruments for research and is outfitted for human testing.