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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 Carbon Dioxide Removal Assembly (CDRA) is a part of the International Space Station (ISS) Environmental Control and Life Support (ECLS) system. The CDRA provides carbon dioxide (CO2) removal from the ISS on-orbit modules. Currently, the CDRA is the secondary removal system on the ISS, with the primary system being the Russian Vozdukh. Within the CDRA are two Desiccant/Adsorbent Beds (DAB), which perform the carbon dioxide removal function. The DAB adsorbent containment approach required improvements with respect to adsorbent containment. These improvements were implemented through a redesign program and have been implemented on units on the ground and returning from orbit. This paper presents a DAB design modification implementation description, a hardware performance comparison between the unmodified and modified DAB configurations, and a description of the modified DAB hardware implementation into the on-orbit CDRA.

A new water recovery system architecture designed to fulfill the National Aeronautics and Space Administration's (NASA) Space Exploration Policy has been tested at the Marshall Space Flight Center (MSFC). This water recovery system architecture evolved from the current state-of-the-art system developed for the International Space Station (ISS). Through novel integration of proven technologies for air and water purification, this system promises to elevate existing system optimization. The novel aspect of the system is twofold. First, volatile organic compounds (VOC) are removed from the cabin air via catalytic oxidation in the vapor phase, prior to their absorption into the aqueous phase. Second, vapor compression distillation (VCD) technology processes the condensate and hygiene waste streams in addition to the urine waste stream. Oxidation kinetics dictate that removing VOCs from the vapor phase is more efficient.

Operation of the Internal Thermal Control System (ITCS) Cold Plate/Fluid-Stability Test Facility commenced on September 5, 2000. The facility was intended to provide advance indication of potential problems on board the International Space Station (ISS) and was designed: To be materially similar to the flight ITCS. To allow for monitoring during operation. To run continuously for three years. During the first two years of operation the conditions of the coolant and components were remarkably stable. During this same period of time, the conditions of the ISS ITCS significantly diverged from the desired state. Due to this divergence, the test facility has not been providing information useful for predicting the flight ITCS condition. Results of the first two years are compared with flight conditions over the same time period, showing the similarities and divergences.

To facilitate life support system loop closure on board the International Space Station (ISS), the Node 3 Oxygen Generation System (OGS) rack contains a functional scar to accommodate a future Carbon dioxide Reduction Assembly (CRA). This CRA uses a Sabatier reactor to produce water from CO2 scrubbed from cabin air and hydrogen byproduct from OGS electrolysis. As part of the effort to better understand and define the functional scar, significant risk mitigation activities have been performed. To address integration risks, a CRA Engineering Development Unit (EDU) has been developed that is functionally equivalent to a flight CRA and is suitable for integrating with ground based carbon dioxide removal and oxygen generation systems. The CRA EDU has been designed to be functionally equivalent to the Sabatier Reactor Subsystem (SRS) portion of the CRA. This paper discusses the CRA design and the major issue expected with the flight unit integration.

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.

The International Space Station (ISS) IATCS (Internal Active Thermal Control System) includes two internal coolant loops that use an aqueous based coolant for heat transfer. A silver salt biocide was used initially as an additive in the coolant formulation to control the growth and proliferation of microorganisms in the coolant loops. Ground-based and in-flight testing has demonstrated that the silver salt is rapidly depleted and not effective as a long-term biocide. Efforts are now underway to select an alternate biocide for the IATCS coolant loop with greatly improved performance. An extensive evaluation of biocides was conducted to select several candidates for test trials.

Since activating the International Space Station's (ISS) Service Module in November 2000, archival air quality samples have shown highly variable concentrations of octafluoropropane in the cabin. This variability has been directly linked to leakage from air conditioning systems on board the Service Module, Zvezda. While octafluoropropane is not highly toxic, it presents a significant challenge to the trace contaminant control systems. A discussion of octafluoropropane concentration dynamics is presented and the ability of on board trace contaminant control systems to effectively remove octafluoropropane from the cabin atmosphere is assessed. Consideration is given to operational and logistics issues that may arise from octafluoropropane and other halocarbon challenges to the contamination control systems as well as the potential for effecting cabin air quality.

Spacecraft cabin air quality is influenced by a variety of factors. Beyond normal equipment offgassing and crew metabolic loads, the vehicle's operational configuration contributes significantly to overall air quality. Leaks from system equipment and payload facilities, operational status of the atmospheric scrubbing systems, and the introduction of new equipment and modules to the vehicle all influence air quality. The dynamics associated with changes in the International Space Station's (ISS ) configuration since the launch of the U.S. Segment's laboratory module, Destiny, is summarized. Key classes of trace chemical contaminants that are important to crew health and equipment performance are emphasized. The temporary effects associated with attaching each multi-purpose logistics module (MPLM) to the ISS and influence of in-flight air quality on the post-flight ground processing of the MPLM are explored.

Spacecraft for long duration deep space missions will need to be designed to survive micrometeoroid bombardment of their surfaces some of which may actually be punctured. To avoid loss of the entire mission the damage due to such punctures must be limited to small, localized areas. This is especially true for power system radiators, which necessarily feature large surface areas to reject heat at relatively low temperature to the space environment by thermal radiation. It may be intuitively obvious, that if a space radiator is composed of a large number of independently operating segments, such as heat pipes, a random micrometeoroid puncture will result only in the loss of the punctured segment, and not the entire radiator. Due to the redundancy achieved by independently operating segments, the wall thickness and consequently the weight of such segments can be drastically reduced.

A new water recovery system designed towards fulfillment of NASA's Vision for Space Exploration is presented. This water recovery system is an evolution of the current state-of-the-art system. Through novel integration of proven technologies for air and water purification, this system promises to elevate existing technology to higher levels of optimization. The novel aspect of the system is twofold: Volatile organic contaminants will be removed from the cabin air via catalytic oxidation in the vapor phase, prior to their absorption into the aqueous phase, and vapor compression distillation technology will be used to process the condensate and hygiene waste streams in addition to the urine waste stream. Oxidation kinetics dictate that removal of volatile organic contaminants from the vapor phase is more efficient.

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.

Contaminated air and process gases, whether in a crewed spacecraft cabin atmosphere, the working volume of a microgravity science or ground-based laboratory experiment facility, or the exhaust from an automobile, are pervasive problems that ultimately effect human health, performance, and well-being. The need for highly-effective, economical decontamination processes spans a wide range of terrestrial and space flight applications. Adsorption processes are used widely for process gas decontamination. Most industrial packed bed adsorption processes use activated carbon because it is cheap and highly effective. Once saturated, however, the adsorbent is a concentrated source of contaminants. Industrial applications either dump or regenerate the activated carbon. Regeneration may be accomplished in-situ or at an off-site location. In either case, concentrated contaminated waste streams must be handled appropriately to minimize environmental impact.

An integrated sorber-based Trace Contaminant Control System (TCCS) and Carbon Dioxide Removal Assembly (CDRA) prototype was designed, fabricated and tested. It corresponds to a 1-person load. Performance over several adsorption/regeneration cycles was examined. Vacuum regenerations at effective time/ temperature conditions, and estimated power requirements were experimentally verified for the combined CO2/trace contaminant removal prototype. The current paper details the design and performance of this prototype during initial testing at CO2 and trace contaminant concentrations in the existing CDRA, downstream of the drier. Additional long-term performance characterization is planned at NASA. Potential system design options permitting associated weight, volume savings and logistic benefits, especially as relevant for long-duration space flight, are reviewed.

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.

The NASA Heavy Lift Rotorcraft Systems Investigation examined in depth several rotorcraft configurations for large civil transport, designed to meet the technology goals of the NASA Vehicle Systems Program. The investigation identified the Large Civil Tiltrotor as the configuration with the best potential to meet the technology goals. The design presented was economically competitive, with the potential for substantial impact on the air transportation system. The keys to achieving a competitive aircraft were low drag airframe and low disk loading rotors; structural weight reduction, for both airframe and rotors; drive system weight reduction; improved engine efficiency; low maintenance design; and manufacturing cost comparable to fixed-wing aircraft. Risk reduction plans were developed to provide the strategic direction to support a heavy-lift rotorcraft development.

The baseline environmental control and life support (ECLS) systems currently deployed on board the International Space Station (ISS) and that planned to be launched in Node 3 are based upon technologies selected in the early 1990's. While they are generally meeting or exceeding requirements for supporting the ISS crew, lessons learned from years of on orbit and ground testing, together with new advances in technology state of the art, and the unique requirements for future manned missions prompt consideration of the next logical step to enhance these systems to increase performance, robustness, and reliability, and reduce on-orbit and logistical resource requirements. This paper discusses the current state of the art in ISS ECLS system technologies, and identifies possible areas for enhancement and improvement.

The factors affecting noise from small propeller driven airplanes are reviewed to quantify their affects where possible, and to indicate the potential for noise reduction. The main sources of external noise are noted to be the propellers and engines; the airframe being of less importance for both aural detection and community annoyance. Propeller noise is a strong function of tip speed and is affected adversely by non-uniform inflows. Reciprocating engine exhausts are noisier than those of comparably rated turboshaft engines, but their noise can be reduced by the use of flight certified exhaust mufflers. Presently, there are no generally accepted engineering methods for development of optimized propellers and exhaust muffler designs from weight and performance penalty standpoints. Flight demonstration results, however, suggest that required noise reductions for future certification should be possible with potentially small penalties.

Aerodynamic effects of trailing edge geometry, hole size, angle, spacing, and shape have been studied in two- and three-dimensional cascades and in a warm turbine test series. Heat transfer studies have been carried out in various two- and three-dimensional test facilities in order to provide corresponding heat transfer data. Results are shown in terms of cooling effectiveness and aerodynamic efficiency for various coolant fractions, coolant-primary temperature ratios, and cooling configurations.

Vehicles capable of lifting very large and heavy payloads into low earth orbit (LEO) will be needed to support certain large-scale space missions being considered for the late 1990-2000 time period. These missions include the support of strategic national commitments, large space power systems, and interplanetary and lunar exploration. Nearer term missions will utilize the Space Shuttle and its direct derivatives, the Shuttle-Derived Vehicles (SDV), currently being defined under NASA and DOD sponsored studies. A conceptual design of a Heavy Lift Launch Vehicle (HLLV) that will lift a half million pounds to low earth orbit is presented. Design alternatives and key system design problems and issues are discussed. The new developments required, such as a new large liquid booster engine and Space Shuttle Main Engine (SSME) modifications, are identified. New candidate launch locations and launch facility requirements are also discussed.