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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.

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 recycling of water will be critical for the successful long-term cultivation of plants in space. The capture of transpired water via humidity control systems and subsequent refilling of water reservoirs feeding into plant nutrient delivery systems is an approach that accomplishes this objective, but results in a progressive dilution of the nutrient levels initially present. As part of pre-spaceflight protocol development efforts for the Water Offset Nutrient Delivery ExpeRiment (WONDER), we have evaluated the reestablishment of reservoir nutrient concentration levels via the periodic injection of 60 and 90 mL pulses of concentrated (10x) Hoaglands nutrient solution. In space this will involve crew-facilitated injections via a quick disconnect port on the payload's front panel. A study demonstrating the efficacy of this approach is presented using wheat grown on porous tubes.

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.

Engineers and scientists from BioServe Space Technologies and Kennedy Space Center (KSC) are developing a flight-rated payload for the evaluation of two space-based plant nutrient delivery systems (NDS's). The hardware is comprised of BioServe's Plant Generic Bioprocessing Apparatus (PGBA) and KSC's Porous Tube Insert Module (PTIM). The PGBA, a double-middeck locker, will serve as the host carrier for the PTIM and will provide computer control of temperature, relative humidity, and carbon dioxide levels. The PTIM will insert into the PGBA's growth chamber and will facilitate the side-by-side comparison of the two NDS's: 1) the porous tube NDS, consisting of six porous tubes with seeds mounted in close proximity to the tubes, and 2) a substrate-based NDS, with three compartments each containing a porous tube embedded in a particulate substrate.

A plant cultivation material known as the Fibrous Ion Exchange Resin Substrate (FIERS) was assessed for its ability to provide nutrients to wheat plants growing hydroponically on a porous tube nutrient delivery system. Seeds were imbibed and grown on six porous tubes; three at different wetness levels utilizing only the FIERS (as a source of nutrients) and three at comparable wetness levels but with Hoagland’s solution used as the source of nutrients. Although there were significant differences between wetness levels and methods of nutrient provision treatments, the FIERS demonstrated the capability to support plant growth through seed production.