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Investigating Local Impacts of Heat-Pulse Sensors for Growth Media Moisture Content. H.G. Levine1, M. A. Ask2, J. J. Prenger3, and D. Rouzan-Wheeldon3  1NASA Biological Science Office, Kennedy Space Center, FL; 2Kennesaw State University, Kennesaw, GA; 3Dynamac Corporation, Kennedy Space Center, FL.

Fresh food production and advanced life support functions on a transit mission or planetary base will require automated water and nutrient delivery for crops in the systems.  The Water Offset Nutrient Delivery ExpeRiment (WONDER) investigates two types of nutrient delivery systems (NDS) that use a porous tube and capillary mat wicking material: the “substrate” module includes arcillite-based particulate media and the lower mass “bare tube” alternative uses the wicking material only.  Miniature heat-pulse sensors (TMAS, Orbital Technologies, Madison, WI) are being evaluated to measure the root zone (particulate or wicking material) moisture content, which is crucial for irrigation control and monitoring.  The thermal-based TMAS sensor operation is operated with a sustained energy output that could cause bias in its measurements.  An investigation was conducted to examine the sensors’ effect on their local environment and to determine the minimum sampling interval required to dissipate the energy of the sensor operation.  TMAS sensors were embedded individually in double-layer 7.5 cm x 7.5 cm capillary mat assemblies and the sensors sewn in place.  Three levels of sampling frequency (12, 4, and 1.33 samples per hour) were applied, with 2 sensors per frequency level.  A thermal infrared camera was used to monitor the heat pulse of the sensors in the wicking mat, and time lapsed infrared thermography was analyzed to determine the characteristics of the thermal changes near the heat-pulse sensors.  Measurements of the thermal responses and heat dissipation times were taken before and after applying the sampling frequency treatments for seven days.  Results presented illustrate the effects of thermal-based sensors on their local environment. 

(Supported by NASA: NCC10-52)