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The Orion Air Monitor (OAM), a derivative of the International Space Station's Major Constituent Analyzer (MCA) (1–3) and the Skylab Mass Spectrometer (4, 5), is a mass spectrometer-based system designed to monitor nitrogen, oxygen, carbon dioxide, and water vapor. In the Crew Exploration Vehicle, the instrument will serve two primary functions: 1) provide Environmental Control and Life Support System (ECLSS) data to control nitrogen and oxygen pressure, and 2) provide feedback the ECLSS water vapor and CO2 removal system for swing-bed control. The control bands for these ECLSS systems affect consumables use, and therefore launch mass, putting a premium on a highly accurate, fast-response, analyzer subsystem. This paper describes a dynamic analytical model for the OAM, relating the findings of that model to design features required for accuracies and response times important to the CEV application.

This paper describes the requirements for and design implementation of an air monitor for the Orion Crew Exploration Vehicle (CEV). The air monitor is specified to monitor oxygen, nitrogen, water vapor, and carbon dioxide, and participates with the Environmental Control Life Support System (ECLSS) pressure control system and Atmosphere Revitalization System (ARS) to help maintain a breathable and safe environment. The sensing requirements are similar to those delivered by the International Space Station (ISS) air monitor, the Major Constituent Analyzer or MCA (1, 2 and 3), and the predecessors to that instrument, the Skylab Mass Spectrometer (4, 5), although with a shift in emphasis from extended operations to minimized weight. The Orion emphasis on weight and power, and relatively simpler requirements on operating life, allow optimization of the instrument toward the mass of a sensor assembly.

Space Station Freedom presents challenges in water contamination and in the preconcentration of trace contaminants for subsequent analysis. Terrestrial methodologies for the trace level determination of mercury, alcohols, and phenols have been evaluated against levels of detection, complexity, and phase separation requirements. Microgravity compatible modifications of standard methods have been developed and tested. A total mercury sensor, employing solid phase sorption of mercury metal from the analyte followed by determination at a gold film electrode, has been breadboarded and shows a minimum level of detection of less than 0.5ppb. The system uses sodium borohydride as a reagent to facilitate mercury reduction and the decomposition of organomercury compounds. Phenols are determined using a modification of the VOC methodology previously described followed by GC/MS analysis; detection levels below 1ppb have been achieved.