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NASA is investigating the use of plant growth chambers (PGCs) for space missions and for bases on the moon and Mars. Key to successful development of PGCs is a system to recover and reuse the water vapor that is transpired from the leaves of the plants. In this paper a design is presented for a simple, reliable, membrane-based system that allows the recovery, purification, and reuse of the transpired water vapor through control of temperature and humidity levels in PGCs. The system is based on two membrane technologies: 1) dehumidification membrane modules to remove water vapor from the air, and 2) membrane contactors to return water vapor to the PGC (and, in doing so, to control the humidity and temperature within the PGC). The membrane-based system promises to provide an ideal, stable growth environment for a variety of plants, through a design that minimizes energy usage, volume, and mass, while maximizing simplicity and reliability.

For long-duration space missions, the mass of the initial stock of supplies (e.g., food, water, air, spare parts) must be limited and the number of items that require resupply during the mission must be minimized. Given these constraints, regenerative environmental control and life support systems (ECLSS) are a necessity. Membrane processes are ideal for regenerable ECLSS because membrane processes 1) operate reliably for long periods, 2) are simple to repair and maintain, and 3) do not require consumable or expendable materials. In this paper, the uses of membranes in a regenerable ECLSS are reviewed. System designs and experimental data are presented on the use of membranes for the purification and recycling of water (e.g., the treatment of hygiene water, urine, humidity condensate and phase-change distillate) and for the treatment and purification of air (e.g., removal of water vapor and carbon dioxide).

Humidity control is essential in the extravehicular mobility unit (EMU). Excessive humidity can lead to visor fogging; accumulation of water, which can block air flow through the vent loop and corrode system components; and uncomfortable conditions for the person inside the EMU, reducing productivity. This paper describes the development of a membrane-based process for dehumidifying the EMU. The membrane process promises to be smaller, lighter, and more energy efficient than the other technologies being considered for dehumidification, and it requires no expendables. The system employs novel dehydration membranes, which were tested for 90 days at conditions expected to be present in the EMU. The results of these tests indicate that membrane-based technology can effectively control humidity in the EMU.

This paper describes the continued development of a non-phase-change waste-water subsystem for use in the planned manned space station. Comparisons of various membrane-based technologies when operated side by side on feed solutions of synthetic wash water are presented. The effects of soap type and operating temperature on membrane-module performance were determined. A preliminary ranking of these modules indicated that several of the reverse-osmosis and ultrafiltration technologies are excellent candidates for use in the subsystem. At this time, a hybrid system configuration consisting of a first-stage ultrafiltration module followed by a second-stage reverse-osmosis module appears to be the most appropriate for use in the subsystem.

This paper describes the preliminary development of a wash water recycle system utilizing an inside-skinned hollow-fiber membrane developed by Bend Research, Inc. This module configuration is based on tube-side feed and is highly resistant to fouling with a minimum of pretreatment. During an ongoing research program for NASA, these modules were operated on actual wash waters with no significant fouling for a period of 40 days. Due to the tube-side-feed flow in these hollow-fiber membranes, the fibers themselves become the pressure vessels, allowing the development of extremely lightweight membrane modules. During the NASA research program, a pre-prototype membrane module capable of processing 6 gallons per day (2.3×10-2m3/day) of wash water at 97% recovery was developed that can be dry-stored and that weighs 120 g.