Moisture and Oxygen Content Sensor Suite for Nutrient Delivery Systems

This project will develop a small, low power instrumentation package which includes a two part sensor suite: 1) sensor for monitoring profiles of moisture content, and 2) sensor to detect O2 concentration in porous substrate nutrient and water delivery systems designed to support plant growth in space. Long-term plant growth experiments aboard the Mir Orbital Station have demonstrated that management of water and O2 in porous substrates is substantially more difficult than in similar systems on earth. The instrument package will consist of several pairs of moisture-oxygen sensors used to measure concentration profiles simultaneously. The substrate moisture content sensor will use the thermal pulse method, which detects changes in thermal conductivity as the substrate moisture content changes. Significant innovations exist in the concept and design of each sensor as well as the integration of the sensor into a usable electronics module with calibrated control. Innovative improvements in moisture sensor construction, reliability, and improved sensor design will allow calibration transfer from earth to microgravity. The companion O2 concentration sensor will monitor O2 in close proximity to the moisture content sensor to allow the two profiles to be compared simultaneously. The innovative design of the O2 sensor includes features permitting the miniaturization of an existing commercial sensor core to provide safe use in wet, O2 diffusion limited environments.