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The development of a spaceflight-rated Porous Tube Insert Module (PTIM) nutrient delivery tray has facilitated a series of studies evaluating various aspects of water and nutrient delivery to plants as they would be cultivated in space. We report here on our first experiment using the PTIM with a software-driven feedback moisture sensor control strategy for maintaining root zone wetness level set-points. One-day-old wheat seedlings (Tritium aestivum cv Apogee; N=15) were inserted into each of three Substrate Compartments (SCs) pre-packed with 0.25–1 mm Profile™ substrate and maintained at root zone relative water content levels of 70, 80 and 90%. The SCs contained a bottom-situated porous tube around which a capillary mat was wrapped. Three Porous Tubes were planted using similar protocols (but without the substrate) and also maintained at these three moisture level set-points. Half-strength modified Hoagland’s nutrient solution was used to supply water and nutrients.

The WONDER space flight experiment will compare the operation of both substrate-based and porous tube nutrient delivery systems (NDS) under microgravity conditions. Each NDS will be evaluated with three moisture availability regimes, and moisture sensing will be critical for the operation and evaluation of the systems. Orbital Technologies (Madison, WI) has developed a space flight-rated temperature and moisture acquisition system (TMAS) for measuring water content of plant growth medium. The sensors were evaluated in 0.25-1 mm and 1-2 mm baked ceramic aggregate (Profile and Turface, respectively). The sensors' pooled standard deviations ranged from approximately 2% to 5% relative water content (RWC), and root mean square error between sensor RWC and measured RWC was greater than 3% using linear calibration.

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.

A study was conducted evaluating the Temperature and Moisture Acquisition System (TMAS; Orbital Technologies, Madison, WI) and the Specific Heat Sensor (Thermal Logic, Pullman, WA) for root zone moisture level monitoring. Each design used a heat pulse and measured the transient temperature response to determine soil moisture changes. The sensors were placed in a polycarbonate compartment filled with oven-dried 1-2 mm Turface. Data was collected from the dry media, then the media was saturated with water and evaporation was monitored using the sensors and a digital balance. Generally, the TMAS sensors tended to over-estimate, while the Thermal Logic sensors under-estimated changes in soil moisture.

The Porous Tube Insert Module (PTIM) is a plant growth apparatus utilizing a porous tube design. The PTIM is under development by the Bionetics Corporation and has been designed as an insert to the Plant Generic Bioprocessing Apparatus (PGBA: Developed by Bioserve Space Technologies). The Water Offset Nutrient Delivery ExpeRiment (WONDER) will perform a side by side evaluation of the PTIM's Porous Tube Nutrient Delivery System (PTNDS) and a Substrate Nutrient Delivery System (SNDS). The PGBA will serve as the environmental chamber and environmental control system for the PTIM. The PGBA will also host the WONDER sequencer software within its control computer. The PTIM integrates six porous tubes wrapped with seed mats. In the SNDS, the tubes and mats are embedded within a substrate material while in the PTNDS, they are exposed to the chamber environment. The PTIM hydraulic equipment includes porous tubes fed by computer controlled miniature pumps and valves.

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.