Design, Modeling, and Initial Characterization of a Subscale Variable Conductance Radiator for CO2 Deposition System in Deep Space Transit

Deep space, long-duration human exploration missions require critical technical advancements in areas such as air revitalization, since resupply is not accessible and resources including mass, power, and volume must be minimized for all subsystems. NASA is currently conducting research on a CO2 capture technique that involves using cryogenic coolers to create cold surfaces. By cooling cabin air to extremely low temperatures, CO2 is deposited onto these surfaces. This process is performed in a continuous, cyclic manner to demonstrate concept of operation. However, since the implementation of cryogenic coolers results in high power consumption, alternative methods are needed to achieve energy efficient air revitalization systems. As Mars transit missions provide a capability to view deep space at low temperatures, utilizing radiators for heat rejection is emerging as an opportunity to complement or replace cryogenic coolers for CO2 deposition. This study focuses on the Variable Conductance Radiator (VCR)-based CO2 deposition system that mainly features two internal CO2 capture/recovery panels and one external heat rejection panel (radiator). The closed-loop system circulates a working fluid between two panels: the CO2 capture panel and the heat rejection panel. The CO2 capture panel is maintained at approximately 130K, allowing CO2 from the cabin air to be deposited on it. The heat rejection panel, exposed to the deep space environment at around 4K, dissipates the heat absorbed from the air stream. The two internal panels operate alternately; while one panel involves circulating working fluid to maintain a cold surface for CO2 deposition, the other one involves stagnant, non-condensable gas and is heated for CO2 sublimation. A subscale, VCR-based CO2 deposition system is investigated to demonstrate its feasibility for deep space applications. Initial efforts include developing the design geometry and performing analytical and numerical analysis to evaluate various design parameters for the external heat rejection panel (radiator).