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In closed environments such as space stations, it is necessary to eliminate CO2 produced by the metabolisms of crew members, for their life support, and to regenerate the air by supplying O2 to make up for the deficiency. If humans are to be in space only a short time, it is in general advantageous to adsorb CO2 with lithium hydroxide, and to supply O2 from tanks. But when the stay in space is long, it is essential to establish a highly reliable and energy-efficient system to recover CO2 in high concentrations and regenerate O2 from this recovered CO2 Fig. 1 shows the system presently conceived, which is roughly divided into the following processes: A process that removes and concentrates CO2 from the air; a CO2 reduction process that separates carbon from CO2 and obtains water; and a water electrolysis process that decomposes water electrically and recovers O2.

A manned Mars mission will be undertaken in the near future. Then the need for ‘water’ will become critical. One of the solutions to the problem is making use of the resources on Mars. We take notice of CO2 reduction. The method is to generate H2O from CO2, which is major composition of Martian atmosphere. Nominally, the reaction of CO2 reduction is performed at atmospheric pressure on Earth. However, the nominal pressure of the Martian atmosphere is below 10 torr. Therefore, it is necessary to confirm whether the reaction of CO2 reduction can be performed with same efficiency as on Earth. This paper summarizes the results of a fundamental study of CO2 reduction system for a Mars mission.

Water is one of the most valuable items in the closed environment such as the space station. It will be used for human habitation and various experiments. However, it will be not supplied from the earth. Therefore, water reclamation is one of the most indispensable technologies in the space station. The water treatment processes used to be combinations of the membrane separation technologies of pre-filter (PF), ultra-filtration (UF) and reverse osmosis (RO) which has been developed for the salt-to-fresh distillation technology. One the other hand, more efficient hydrophobic membranes have been developed recentry. Using these new water treatment technology of hydrophobic membranes, the membrane distillation (MD), combined with the conventional water treatment process in now being investigated for water reclamation. The MD is expected to be most important process of the water reclamation system integrated into the space station in the future.