Liquid CO2 as a coolant will not contaminate the area as it is sublimated from the life support system for heat rejection.
Two fundamental problems facing the development of a portable system to sustain life on extraterrestrial surfaces are (1) heat rejection and (2) rejection of metabolically produced CO2 to an environment with a ppCO2 of 0.4 to 0.9 kPa as is present on Mars. Portable life support systems typically use water for heat rejection via sublimation. Consequently, the water is removed from the life support system and into the surrounding environment after use. This wastes a valuable resource required for human life that is expensive to transport from Earth. Furthermore, rejecting the water vapor to the surrounding environment contaminates it, severely interfering with any search for life on extraterrestrial surfaces. A portable life support system should be able to use a variety of fluids for heat rejection, especially liquid CO2, as it can be easily acquired and cheaply stored on the surface of Mars. The use of liquid CO2 as a coolant has the advantage that it will not interfere with scientific investigations by contaminating the area as it is sublimated from the life support system for heat rejection.
A subsystem has been developed for a portable life support system (PLSS) called Metabolic heat regenerated Temperature Swing Adsorption (MTSA). MTSA simultaneously addresses heat rejection and CO2 rejection to an environment ranging from vacuum to a ppCO2 of 0.9 kPa or greater. The invention utilizes an adsorbent-based subsystem that is cooled with liquid CO2, and is used to cleanse the vent loop of metabolically produced CO2. Once the adsorbent is fully loaded with metabolically produced CO2, metabolic waste heat from the expired breath is used to warm and regenerate the adsorbent bed. Exhausted adsorbent cooling fluid is used to aid in additional heat rejection and further cool the user.
The basic principle is removal of CO2 by an adsorbent with regeneration through temperature swing adsorption (TSA) over the temperature range bound by the sublimation temperature of CO2 (less than 195 K) and the metabolic vent loop (310 K). There are two beds to facilitate continuous removal of metabolically produced CO2 from the vent loop: one for loading the adsorbent via a vent loop exiting the helmet/ undergarment of an astronaut’s portable life support system, and another for regenerating the adsorbent.
This work was done by Taber MacCallum of Paragon Space Development Corp. for Johnson Space Center. MSC-24859-1