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We report here on a series of KC-135 parabolic flight studies investigating various aspects of water distribution in plant nutrient delivery systems being developed for spaceflight applications. Several types of porous tubes were evaluated. Under microgravity conditions, fluid was observed to creep up the end walls of polycarbonate substrate compartments. Capillary mats wrapped around the porous tubes wetted up in a uniform fashion regardless of the level of gravity to which they were being exposed, and they were found to eliminate the end-wall creep wetting-up pattern. Results from observations using 1-2 mm glass beads and 1-2 mm Turface substrates are presented. The Turface’s absorption of water effectively minimized fluid redistribution as the compartment alternated between microgravity and 1-1.8g conditions.

Wheat seeds were automatically imbibed and germinated within a Porous Tube Insert Module (PTIM) apparatus developed to support both porous tube and substrate-based nutrient delivery systems (PTNDS, SNDS) in space. The PTIM was operated under both; (1) a programmable fixed feed mode, and (2) a moisture sensor feedback control mode. For the former, increased levels of water use efficiency were evident within the PTNDS component of the study. For the latter, moisture sensors within the SNDS were evaluated at setpoints of 65-85% relative water content. Data demonstrating the ability of this approach to control moisture levels and the vertical moisture distribution patterns obtained over an 18 d grow-out interval are presented.