Tuesday, November 6, 2007
183-11

Oxygen Diffusion Measurements in Partially Saturated Porous Media on Board the International Space Station.

Scott Jones1, Robert Heinse1, Dani Or2, Shane Topham3, Darwin H. Poritz4, Igor Podolskiy5, and Gail E. Bingham3. (1) Utah State University, Dept. Plants Soils and Biomet, Logan, UT 84322-4820, (2) EPFL Ecole Polytechnique Federale, GR B1 399 (Bātiment GR) Station 2, Lausanne, 1015, Switzerland, (3) Space Dynamics Laboratory, Logan, UT 84322-9700, (4) Crew and Thermal Systems Division, MEI Technologies Inc. MS JE77, Johnson Space Center, Bulding 7A, Room 150, Houston, TX 77058, (5) Institute of Biomedical Problems, 76a Khoroshevskoe shosse, Moscow, 123007, Russia

Oxygen delivery to plant roots in soil or porous media is regulated by the quasi-equilibrium water content resulting in part from the pore size distribution. Optimization of plant growth media’s particle size, which form pores, is a function of the gravitational force it is subjected to. For microgravity conditions aboard spacecraft novel management approaches are needed to provide optimal rooting conditions for plant growth. Our objective was to develop a test system for microgravity to facilitate measurement of oxygen diffusion in partially saturated porous media. A sealed dual-chamber automated oxygen diffusion cell was constructed with porous medium water addition and removal capability. The gas diffusion cell designs were horizontally oriented to minimize gravitational effects using a ‘thin rectangular profile’ cell on earth and a cylindrical cell design for flight. Porous media water content was controlled using a porous membrane coupled with a metered pumping system and tensiometers to measure matric potential. Continuous measurement of oxygen concentration in the diffusion cells provided transient response data for fitting water content-dependent diffusion coefficients to earth-based models. Gas diffusion was modeled as a function of air-filled porosity in mm-sized aggregated particles. Results between microgravity and earth-based measurements were compared using statistical sampling from triplicate cell measurements in 3 different porous medium particle size distributions (i.e., a 3x3 cell treatment combination). Data was collected on the International Space Station between July and September 2007 as part of the ORZS-MIS experimental flight package.

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