|
|
 |
|
|
|
|
RESEARCH Soil physics in
microgravity Abstract - Plants grown in porous media are part of a bioregenerative life support system designed for long-duration space missions. Reduced gravity conditions of orbiting spacecraft (microgravity) alter several aspects of liquid flow and distribution within partially saturated porous media. The objectives of this study were to evaluate the suitability of conventional capillary flow theory in simulating water distribution in porous media measured in a microgravity environment. Data from experiments aboard the Russian space station Mir and a U.S. space shuttle were simulated by elimination of the gravitational term from the Richards equation. Qualitative comparisons with media hydraulic parameters measured on Earth suggest narrower pore size distributions and inactive or nonparticipating large pores in microgravity. Evidence of accentuated hysteresis, altered soil-water characteristic, and reduced unsaturated hydraulic conductivity from microgravity simulations may be attributable to a number of proposed secondary mechanisms. These are likely spawned by enhanced and modified paths of interfacial flows and an altered force ratio of capillary to body forces in microgravity.
Abstract - The selection of plant growth media remains an empirical endeavor often focusing on available materials rather than on the physical principles that govern water retention and flow. Apparent water- and -O2- induced stresses affecting plant growth experiments in microgravity (10 23 –10 26 go) have prompted the need for refinement of selection criteria for optimal growth media. The objective of this work was to develop a comprehensive approach for selecting the physical characteristics of plant growth media that optimize the dynamic availability of liquids and gases to plant roots. Physically based models describing the relationship between content and fluxes of liquids and gases were written in terms of media parameters and were used to cast a multi objective optimization problem. Plant physiological target values, growth container design, and other system considerations provided constraints for the optimization problem. The optimized media parameters designated a pore-size distribution (psd) that is scaled to a corresponding particle-size distribution (PSD) by inversion of the Arya and Paris model. The iterative process resulted in an average scaling of psd to PSD and led to the synthesis of an optimal medium. Sand and glass bead mixtures were well matched to the optimized media characteristics resulting from the optimization procedure. This methodology is amenable to horticultural, greenhouse, and research applications where optimal porous media design is of value.
Poster - Bingham, G.E., D. Or, S.B. Jones, R.C. Morrow. Optimization of root zone substrates (ORSZ) for reduced gravity experiments. Workshop on reduced gravity flight experiments. January 16-19, 2001, Houston, Texas. Abstract - This newly funded flight experiment will measure root zone gas exchange through important plant growth substrates at varying water content levels in microgravity. This information is critical for proper water management and the prevention of root zone hypoxia during plant growth experiments and ALS biomass production. Microgravity data suggest that mechanisms such as enhanced hysterisis in water retention alters the gas diffusion process, changing the optimum control setpoint. Measuring gas diffusion in microgravity will determine the maximum water content at which plants can be grown without root zone oxygen stress, and will allow the development of models needed to determine improved substrate properties and management protocols. These data will directly support substrate selection and management for NASA's initial ISS plant experiments PESTO and MPNE-02, guide BIO-Plex protocols and guide NASA's new generation flight growth chambers (PRU, etc.) development. Funding agency: NASA |
|
|
