NASA has a strong interest in improving the method to control carbon dioxide (CO2) and water in the Exploration Extravehicular Mobility Unit (xEMU). The goal is to limit the CO2 partial pressure to 2.2 mm Hg at the highest metabolic generation rates. Historically, the Metox, which contains a solid silver oxide sorbent, has been used to remove CO2 from the suit. However, this unit has a finite capacity and therefore limits EVA mission times. The technology currently planned to replace the Metox is the Rapid Cycle Amine (RCA). This device utilizes two beds which alternately are used to remove CO2 and H2O and then are regenerated by exposure to space vacuum during the mission. The RCA currently utilizes an amine-based sorbent designated as SA9T. Although the sorbent has good reversible CO2 uptakes, higher capacities are desired to maintain low CO2 levels and reduce O2 losses. In addition, this sorbent emits low levels of ammonia which must be removed from the suit using a separate technology. In a recently completed SBIR Phase I project, Reaction Systems developed new sorbents that have the potential to outperform SA9T and also reduce ammonia emissions. Reaction Systems used a rapid screening method that provided accurate performance data under relevant conditions along with its expertise in the development of CO2 sorbents to identify materials that have potential to perform better than the SA9T. In this project, Reaction Systems characterized sorbent cycle times as a function of CO2 partial pressure and then estimated the total number of cycles required when applied to simulated EVA missions. Sorbents were identified that resulted in a net reduction in the number of cycles required over the course of an EVA, which reduces power consumption and oxygen losses. The sorbent also emits less ammonia than a SA9T equivalent sorbent.
Wickham et al. (Sun,) studied this question.