Life support in space

Wheeler, R. M., Stutte, G. W., Subbarao, G. V., Yorio, N. C. (2001). Plant growth and human life support for space travel. In M. Pessarakli (Ed.), Handbook of Plant and Crop Physiology, (2" Edition) (pp. 925-941). Marcel Dekker, Inc, New York. 

Life-Support Applications. Exploration of outer space by humans has focused considerable attention on maximum as weU as minimum limits in the oxygen content of life-support atmospheres. Above the earth, both the atmospheric pressure and the partial pressure of oxygen decrease rapidly. The oxygen content of air remains constant at 20.946% to an altitude of ca 20 km, after which it decreases rapidly (1). 

Stoichiometry has important practical applications, such as predicting how much product can be formed in a reaction. For example, in the space shuttle fuel cell, oxygen reacts with hydrogen to produce water, which is used for life support (Fig. L.l). Let s look at the calculation space shuttle engineers would have to do to find out how much water is formed when 0.25 mol 02 reacts with hydrogen gas. 

The problem was solved by Francis Bacon, a British scientist and engineer, who developed an idea proposed by Sir William Grove in 18.39. A fuel cell generates electricity directly from a chemical reaction, as in a battery, but uses reactants that are supplied continuously, as in an engine. A fuel cell that runs on hydrogen and oxygen is currently installed on the space shuttle (see Fig. L.l). An advantage of this fuel cell is that the only product of the cell reaction, water, can be used for life support. 

NASA conducted studies on the development of the catalysts for methane decomposition process for space life-support systems [94], A special catalytic reactor with a rotating magnetic field to support Co catalyst at 850°C was designed. In the 1970s, a U.S. Army researcher M. Callahan [95] developed a fuel processor to catalytically convert different hydrocarbon fuels to hydrogen, which was used to feed a 1.5 kW FC. He screened a number of metals for the catalytic activity in the methane decomposition reaction including Ni, Co, Fe, Pt, and Cr. Alumina-supported Ni catalyst was selected as the most suitable for the process. The following rate equation for methane decomposition was reported ... 

The similarities in products and pathways between interstellar molecules and terrestrial laboratory experiments imply a unity of physical and chemical laws in the universe. Given certain conditions and appropriate energy sources, the same chemical pathways will be followed to create certain products from the elements. That is not to say that life, even in primitive form, could be supported in interstellar space. The significant precursor molecules found in interstellar space are at extremely low concentrations, but if they were transported to planetary atmospheres, perhaps by comets, they might then react in the proper environment and evolve into self-replicating systems. 

Figure 17.2 Dr. Ted Tibbitts of the University of Wisconsin, Madison, Wl, USA, working with potato plants in a growth chamber. Ted Tibbitts was the principal investigator for NASA-sponsored studies with potatoes from 1982 through 1994, and work from his laboratory has provided baseline information on controlled environment production techniques bioregenerative life support systems in space.

Mitchell, C. A., Dougher, T. A. O.,Nielsen, S. S., Belury, M. A., Wheeler, R. M. (1996). Costs of providing edible biomass for a balanced diet in a controlled eeologieal life support system. In Ft. Suge (Ed.), Plants in Space Biology (pp. 245-254). Tohoku Univ. Press, Sendai, Japan. 

Wheeler, R. M. (2003). Carbon balance in bioregenerative life support systems Effects of system closure, waste management, and crop harvest index. Adv. Space Res., 3J(1), 169-175. 

Wheeler, R. M., Tibbitts, T. W. (1986a). Utilization of potatoes for life support systems in space. I. Cultivar-photoperiod interaction. Amer. Potato J., 63, 315-323. 

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