Porous Substrate Water Relations Observed During the Greenhouse-2 Flight Experiment

The Greenhouse-2 experiment was conducted on the Mir Space Station as a part of the SpaceLab-Mir-1 (SLM-1) mission. The Russian-Bulgarian plant growth unit (Svet), used in the 1990 Greenhouse-1 Mir Space Station experiment, was refurbished for use in this experiment. The Svet root module was loaded with the same type of substrate (Balkanine) that was used in the 1990 experiment except that the grain size was reduced and packing density increased. Heat pulse type moisture sensors developed jointly by Russian and American scientists provided additional monitoring of water distribution inside each module. These sensors determined moisture movement and distribution in real time, thus permitting the crew support team to monitor the moisture level in the root module and estimate the water delivery needs of the root module. The water relations results obtained during the Greenhouse-2 experiment are discussed in this paper. The data indicate that heat pulse moisture sensors provide excellent, long-term water status documentation and can be made small enough to provide accurate water content distribution data in microgravity experiments. Speed of water propagation in Bulkanin and rate of evaporation in microgravity have been estimated along with water potential distributions.