Crew Member/Extravehicular Mobility Unit Thermal Interactions Affecting Cooling Preferences and Metabolic Water Removal

An Extravehicular Mobility Unit (EMU) Portable Life Support Subsystem (PLSS) has among its primary functions requirements to remove metabolically generated heat and respiratory byproducts to maintain an atmosphere which is both physiologically safe and comfortable for the Extravehicular Activity (EVA) crew person. The EMU thermal control system interacts with the crew member through the Liquid Cooling and Ventilation Garment (LCVG), which circulates the ventilation gas to remove carbon dioxide, humidity, and trace contaminants, and the cooling water to remove metabolically produced heat. To maintain thermal comfort, the crew member may vary the LCVG inlet water temperature. The thermal interaction between the EMU and the crew member is very complex and highly dependent upon the individual crew member's cooling preferences and the exterior environment. Changes in metabolic activity will create EMU thermal cooling transients which affect both crew member cooling preferences and vent loop heat balances. In particular, the interactions between the person, the water cooling system, and the ventilation gas circulation system have a substantial impact on the evaporative heat transfer. Under certain transient conditions, condensation of metabolic water may occur. Under other conditions, this water reevaporates, resulting in some cases in transient evaporative cooling effects for the crew person.

This study defines the effects that the ventilation loop/LCVG operation has on overall crew cooling and total EMU heat balances, with special focus on EMU metabolic water removal. The results of a vacuum test series conducted at the Johnson Space Center using the current configuration EMU (closed loop with human test subjects) are presented. Operational differences as well as thermal physiological differences between individual crew members were evaluated to measure the impacts on EMU performance.