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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.

The BRIC-LED (Biological Research In Canisters-Light Emitting Diode) PDFU (Petri Dish Fixation Unit) apparatus was originally developed to support the on-orbit growth and subsequent fixation of any biological material amenable to petri dish culture in space. The PDFU component has been modified to support a two-stage fluid provision option so that investigations can incorporate an initial injection of a biologically active solution followed by a subsequent fixative injection to terminate the experiment in space. Crew-operated actuator tools initiate the delivery of the liquid treatments. Aseptic protocols have been developed which permit the entire experiment to be conducted under sterile 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.

The Plant Growth Facility (PGF) is under development as a Shuttle middeck apparatus to support research on higher plants in microgravity. It is designed to operate for 15 days, and will provide (1) fluorescent lighting at a minimum of 220 μmol m-2 s-1 evenly distributed (±10%) over the growth area, (2) temperature control to a set point of ±10°C of cabin ambient with a control accuracy of ±1°C, (3) humidity control ±5% for set points between 30-80% RH, and (4) carbon dioxide control ±5% over a range of 300-5000 ppm. Filters will be provided to remove ethylene and trace organics from the internal air flow.