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The control of temperature and humidity in spacecraft cabins is a vital component of environmental-control and life-support systems. Separating the two phases (i.e., water and air) that result from cooling air for humidity control represents a major technical challenge in the microgravity environment of space. With NASA funding, Bend Research has developed a membrane-based condensate-recovery heat exchanger (CRX) to address this challenge. The CRX offers substantial advantages in simplicity, reliability, mass, and volume over competing technologies. The high heat transfer and mass transfer in this device promise to provide superior humidity control without the need for complex mechanical separators. Moreover, these high transfer rates are achieved with minimal pressure drop, reducing power requirements.

Long duration missions in space will require regenerative processes to recover water for crew reuse. Membrane processes are attractive as a primary processor in water recovery systems (WRS) because of their design simplicity, low specific energy requirements, small size, and high water recovery. However, fouling has historically been regarded as a disadvantage of membrane-based processes. This fouling is often caused by micelle buildup on the membrane surface by high-molecular-weight organics (e.g., from soaps and laundry detergents). This paper describes a two-stage fouling-resistant ultrafiltration (UF)/reverse osmosis (RO) prototype subsystem, which was designed and constructed for a WRS in the Life Support Systems Integration Facility (LSSIF) at NASA Johnson Space Center (NASA/JSC). The first stage of the subsystem is a tube-side-feed hollow-fiber UF module that removes contaminants that tend to foul spiral-wound modules.

Controlled ecological life support systems will require subsystems for maintaining the concentrations of atmospheric gases within acceptable ranges in human habitat chambers and plant growth chambers. The goal of this work was to develop a membrane-based atmosphere control (MBAC) subsystem that allows the controlled exchange of atmospheric components (e.g., oxygen, carbon dioxide, and water vapor) between these chambers. The MBAC subsystem promises to offer a simple, nonenergy intensive method to separate, store, and exchange atmospheric components, producing optimal concentrations of components in each chamber. In this paper, the results of a preliminary analysis of the MBAC subsystem for control of oxygen and nitrogen are presented. Additionally, the MBAC subsystem and its operation are described.

One of the key challenges facing NASA engineers is the development of systems for separating liquids and gases in microgravity environments. In this paper, a novel membrane-based phase separator is described. This device, known as a water recovery heat exchanger (WRHEX), overcomes the inherent deficiencies of current phase-separation technology. Specifically, the WRHEX cools and removes water vapor or water droplets from feed-air streams without the use of a vacuum or centrifugal force. As is shown in this paper, only a low-power air blower and a small stream of recirculated cool water is required for WRHEX operation. This paper presents the results of tests using this novel membrane device over a wide range of operating conditions. The data show that the WRHEX produces a dry air stream containing no entrained or liquid water--even when the feed air contains water droplets or mist. An analysis of the operation of the WRHEX is presented.

Processes to remove and recover carbon dioxide (CO2) and water vapor from air are essential for successful long-duration space missions. This paper presents results of a developmental program focused on the use of a liquid- sorbent/membrane-contactor (LSMC) system for removal of CO2 and water vapor from air. In this system, air from the spacecraft cabin atmosphere is circulated through one side of a hollow-fiber membrane contactor. On the other side of the membrane contactor is flowed a liquid sorbent, which absorbs the CO2 and water vapor from the feed air. The liquid sorbent is then heated to desorb the CO2 and water vapor. The CO2 is subsequently removed from the system as a concentrated gas stream, whereas the water vapor is condensed, producing a water stream. A breadboard system based on this technology was designed and constructed. Tests showed that the LSMC breadboard system can produce a CO2 stream and a liquid- water stream.

This paper describes four membrane-based subsystems to use in the wastewater treatment system of the manned space station being planned by NASA. These membrane-based subsystems involve the recycle of the various wastewater streams and result in increased energy efficiency. Furthermore, in these four subsystems, the membrane acts as a barrier between the wastewater source and the wastewater treatment and consumption systems, thus increasing the reliability of these systems. Finally, the membranes are highly impermeable to the contaminants in the wastewaters and thus help to reduce the load on such expendables as post-treatment adsoption beds.