There is a need for microgravity-based plant culture nutrient delivery systems (NDS’s) for both bioregenerative Advanced Life Support and plant research functions. The provision of adequate levels of water (without causing waterlogging) and oxygen to the root zone is the most crucial component deterring major advancements in this area. The dominance of the surface tension of water under microgravity conditions has often been found to lead to either severe waterlogging or excessive drying in the root zone. Consequently, differences in plant growth responses between spaceflight experiments and their ground controls are expected based merely upon differences in moisture distribution patterns between the two conditions. The Water Offset Nutrient Delivery ExpeRiment (WONDER) will address the question of “comparability of environmental conditions” between spaceflight and ground control experiments for both a porous tube plant NDS and a substrate-based NDS by employing three different wetness level treatments for each of these approaches. It is anticipated that different preset wetness levels than those used on Earth will be required to support optimal plant growth in space. Dry wheat seeds (N = 60-72) will be loaded 3 days prior to Orbiter liftoff, and the system will be initiated by the crew on orbit. Time-lapsed video recording of the plants will monitor growth over time. At recovery, the plants will be measured, and extensive tissue analyses relating to gene expression and stress-associated metabolites will be undertaken.

Figure 1. The Porous Tube Insert Module (PTIM) Design
(Alternating porous tube and substrate-based NDS’s are visible. An array of 25 cameras to monitor and document plant growth over time is also evident along one side wall. A similar array is present on the opposite wall.)

The Porous Tube Insert Module (figure 1) was designed to fulfill the requirements of this project specifically and to provide a testbed for a multitude of space-based plant studies. PTIM delivers water to both a series of “naked” porous tubes (figure 2) and porous tube/substrate compartments (figure 3). PTIM software will allow the crew to interact with the system’s watering initiation protocols. The PTIM incorporates moisture sensors to both monitor and control the wetness levels on both the three “naked” porous tubes and within the three substrate compartments contained within the PTIM. A fixed-feed water provision mechanism functions as a backup mode in the event of a system failure.