Nonventing Thermal and Humidity Control for EVA Suits

Future EVA suits will need processes and systems to control internal temperature and humidity without venting water to the surrounding environment. This paper describes a non-venting absorption-based cooling and dehumidification system and laboratory demonstrations of the key processes. There are two main components in the system: an evaporation cooling and dehumidification garment (ECDG) that removes both sensible heat and latent heat from the pressure garment, and an absorber radiator that absorbs the moisture and rejects heat to space by thermal radiation. This paper discusses the overall design of both components and presents recent data demonstrating their operation. We developed a design and fabrication approach to produce prototypical heat/water absorbing elements for the ECDG, then demonstrated by test that they could absorb heat and moisture at a high flux. Proof-of-concept tests showed that an ECDG sample absorbs sensible and latent heat at a combined rate of 85 W/ft² under conditions that simulate operation in an EVA suit. The heat absorption was primarily due to direct absorption of water vapor. It is possible to construct large, flexible cooling patches using this material that can be incorporated into a cooling garment. Data from the proof-of-concept tests was scaled to calculate area needed for full metabolic loads, showing that it is feasible to use this technology in an EVA suit. Full-scale absorber/radiator modules have also been built and demonstrated. These modules are lightweight, flexible, and made from rugged materials. Tests show that these absorber/radiator modules can reject heat at a flux of 33 W/ft² while maintaining ECDG operation at conditions that will provide a cool and dry environment inside the EVA suit.