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Results from plant growth experiments utilizing particulate growth media during space flight revealed difficulties associated with providing reliable reproducible gaseous and water supply to plant roots. These limitations were attributed to insufficient understanding of liquid configuration and growth media transport processes in reduced gravity. The objective of this NASA-funded research program is to develop a framework for modeling and quantitative characterization of physical processes associated with flow of wetting and non-wetting phases in particulate plant growth media in microgravity. This paper provides an overview of research plans and current status of research activities. Characterization and modeling of substrate water retention and transport properties in microgravity is key to management and control of gas and liquid fluxes within plant root zones.

A Nutrient Delivery System (NDS) capable of working in microgravity is an essential component of growing plants in space. A substrate-based NDS is a conventional and mechanically simple way to grow plants in microgravity, especially when a nutrient impregnated substrate is used. A substrate moisture sensor is a key element of the control system needed to successfully grow plants in this type NDS. A heat pulse-type moisture sensor has been developed for use in microgravity that has the advantages of a simple, compact design and a low average power requirement. The heat pulse-type moisture sensor was developed to be used in the “Greenhouse 2” Experiment with the Russian plant growth unit, “Svet.” This experiment is part of the SpaceLab/Mir-1 mission which is being conducted on Mir in 1995 and 1996. The design of the sensor allows installation of the sensors into the Svet root module aboard Mir.