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Successful trace chemical contamination control is one of the components necessary for achieving good cabin atmospheric quality. While employing seemingly simple process technologies, sizing the active contamination control equipment must employ a reliable design basis for the trace chemical load in the cabin atmosphere. A simplified design basis that draws on experience gained from the International Space Station program is presented. The trace chemical contamination control design load refines generation source magnitudes and includes key chemical functional groups representing both engineering and toxicology challenges.

The trace contaminant control system (TCCS) located in the International Space Station's (ISS) U.S. laboratory module employs physical adsorption, thermal catalytic oxidation, and chemical adsorption to remove trace chemical contamination produced by equipment offgassing and anthropogenic sources from the cabin atmosphere. The chemical adsorption stage, consisting of a packed bed of granular lithium hydroxide (LiOH), is located after the thermal catalytic oxidation stage and is designed to remove acid gas byproducts that may be formed in the upstream oxidation stage. While in service on board the ISS, the LiOH bed exhibited a change in flow resistance that leading to flow control difficulties in the TCCS. Post flight evaluation revealed LiOH granule size attrition among other changes. An experimental program was employed to investigate mechanisms hypothesized to contribute to the change in the packed bed's flow resistance.

The maintenance of the cabin atmosphere aboard spacecraft is critical not only to its habitability but also to its function. Ideally, air quality can be maintained by striking a proper balance between the generation and removal of contaminants. Both very dynamic processes, the balance between generation and removal can be difficult to maintain and control because the state of the cabin atmosphere is in constant evolution responding to different perturbations. Typically, maintaining a clean cabin environment on board crewed spacecraft and space habitats is a central function of the environmental control and life support (ECLS) system. While 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, perturbations associated with logistics, vehicle construction and maintenance, and ECLS system configuration influence the resulting cabin atmospheric quality.

The management of off-nominal situations on-board the International Space Station (ISS) is crucial to its continuous operation. Off-nominal situations can arise from virtually any aspect of ISS operations. One situation of particular concern is the inadvertent release of a chemical into the ISS atmosphere. In sufficient quantities, a chemical release can render the ISS uninhabitable regardless of the chemical's toxicity as a result of its effect on the hardware used to maintain the environment. This is certainly true with system chemicals which are integral components to the function and purpose of the system. Safeguards, such as design for minimum risk, multiple containment, hazard assessments, rigorous safety reviews, and others, are in place to minimize the probability of a chemical release to the ISS environment thereby allowing the benefits of system chemicals to outweigh the risks associated with them. The thermal control system is an example of such a system.

The design and operation of crewed spacecraft requires identifying and evaluating chemical compounds that may present reactivity and compatibility risks with the environmental control and life support (ECLS) system. Such risks must be understood so that appropriate design and operational controls, including specifying containment levels, can be instituted or an appropriate substitute material selected. Operational experience acquired during the International Space Station (ISS) program has found that understanding ECLS system and environmental impact presented by thermal control system working fluids is imperative to safely operating any crewed space exploration vehicle. Perfluorocarbon fluids are used as working fluids in thermal control fluid loops on board the ISS. Also, payload hardware developers have identified perfluorocarbon fluids as preferred thermal control working fluids.

The International Space Station (ISS) Internal Active Thermal Control System (IATCS) uses a water based heat transport fluid with specific chemical parameters and additives for corrosion and microbial control. The fluid and hardware have experienced anomalies since activation of the United States Laboratory (USL), including chemical and possibly, microbial corrosion. The required sampling of the fluid has the crewmembers removing samples via an in-line sampling tool to perform real-time trace ammonia contamination tests using color change strips, and filling a 150 ml bag from each loop for the ground laboratory analyses. The former activity requires stable storage of the strips, and for the latter activity, it is highly desirable to return the ground sample as stable as possible. This paper describes the process for materials selection, test methods/set-up, results, and final recommendation for a replacement outer bag.

Environmental Control and Life Support (ECLS) system functionality aboard the International Space Station (ISS) includes responding to various emergency conditions. The ISS requirements define three types of emergencies: fire, rapid depressurization, and hazardous or toxic atmosphere. The ISS has automatic integrated vehicle responses to each of these emergencies. These automated responses are designed to aid the crew in their response actions to the emergencies. The response to a hazardous atmosphere on board the ISS, including the automatic integrated vehicle response and crew actions, is the focus of this paper. Philosophies regarding the detection of and response to emergencies involving chemical releases are described. Vehicle configuration is discussed for currently supported automatic responses, and crew actions are defined for modules on orbit up to the addition of the Docking Compartment (DC1) in the assembly sequence.

Trace chemical contaminants produced by equipment offgassing and human metabolic processes are removed from the atmosphere of the International Space Station's U.S. Segment by a trace contaminant control subassembly (TCCS). The TCCS employs a combination of physical adsorption, thermal catalytic oxidation, and chemical adsorption processes to accomplish its task. A large bed of granular activated charcoal is a primary component of the TCCS. The charcoal contained in this bed, known as the charcoal bed assembly (CBA), is expendable and must be replaced periodically. Pre-flight engineering analyses based upon TCCS performance testing results established a service life estimate of 1 year. After nearly 1 year of cumulative in-flight operations, the first CBA was returned for refurbishment. Charcoal samples were collected and analyzed for loading to determine the best estimate for the CBA's service life.

For long-duration space missions, the life support and In-Situ Resource Utilization (ISRU) systems necessary to lower the mass and volume of consumables carried from Earth will require more sophisticated chemical processing technologies involving gas-liquid two-phase flows. This paper discusses some preliminary two-phase flow work in packed columns and generation of bubbly suspensions, two types of flow systems that can exist in a number of chemical processing devices. The experimental hardware for a co-current flow packed column operated in two ground-based low gravity facilities (two-second drop tower and KC-135 low-gravity aircraft) is described. The preliminary results of this experimental work are discussed. The flow regimes observed and the conditions under which these flow regimes occur are compared with the available co-current packed column experimental work performed in normal gravity.

THE LOW-POWER SPACE NUCLEAR ROCKET conceived by NASA engineers is described in this paper. It is compared with the chemical rocket and the nuclear turboelectric ion propulsion system. In developing the concept for this low-power rocket, NASA engineers concentrated on attaining low weight and high hydrogen temperature, and on solving problems concerned with automatic control and operation of high-temperature reactors. It was presumed that the NASA 1.5 million-lb thrust engine would be available, and could place 25,000 lb in orbit, at the time the nuclear rocket is ready for test. As experience is gained reactors of higher power can be developed. These can, perhaps, be used as second stages of larger chemical boosters. Finally, high-power, high-temperature rockets for booster application can be undertaken.