Maintaining and Monitoring the Habitable Environment of the International Space Station

The maintenance of cabin air-quality aboard spacecraft requires a proper balance of contamination generation and removal, and environmental monitoring. Achieving this balance is paramount to a spacecraft's ability to sustain human life and maintain functionality. Spacecraft cabin atmosphere can best be described as an equilibrium. As with other systems in equilibrium, the cabin air-quality of the International Space Station (ISS) has a remarkable ability to respond to constantly applied perturbations and restore balance. This is a function of not only design, but also a proficient understanding of the ISS atmosphere. Active air quality control equipment is deployed on board every vehicle to remove carbon dioxide, water vapor, and trace chemical components from the cabin atmosphere. Proper management of various logistics, vehicle construction, and system configuration are applied to ensure that cabin atmospheric quality is preserved. Safeguards, such as design for minimum risk, multiple containment, hazard assessments, rigorous safety reviews, and others, are in place to minimize the probability of any long-term detrimental effects perturbations may have on the ISS environment. In addition to engineering controls, procedural controls and requirements are implemented to address strategies which can mitigate off-nominal situations crew may encounter and a rigorous air-quality monitoring program offers candid snapshots and long-term trending of the ISS environment. The underlying nature of engineering controls is primarily static despite the increases in size and crew of the ISS, and the programmatic changes involved with the ISS Program. This is not necessarily true for the strategies developed for mitigating off nominal situations, and for monitoring the ISS habitable environment. Environmental health monitoring is addressed as well as why and how the fundamental philosophy of air-quality monitoring may or may not evolve.