Development and Testing of a Two-Stage Air Drying System for Spacecraft Cabin CO2 Removal Systems

The use of molecular sieves such as zeolite for the removal of CO2 in spacecraft cabin atmospheres necessitates thorough water removal prior to processing. This is because water also binds readily with these sieves, and will lead to reduced CO2 loading capacity and water-contaminated CO2 streams for resource recovery. A two-stage air drying system has been under development at NASA Ames Research Center to address this need. The system consists of a membrane-based bulk dryer designed to passively remove up to 80% of the inlet water using the ultra-dry exhaust airstream from the CO2 removal system, and a regenerable, thermal-swing, structured-sorbent residual dryer that removes the remaining water to a nominal exit dew-point of -65oC. Individual unit testing of both of these units was conducted and indicates both are potential candidates for use in future missions. This paper provides that data from these tests.