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The Controlled Ecological Life Support Systems (CELSS) program is evaluating higher plants as a means of providing life support functions aboard space craft. These plant systems will be capable of regenerating air and water while meeting some of the food requirements of the crew. In order to grow plants in space, a series of systems are required to provide the necessary plant support functions. Some of the systems required for CELSS experiments are such that it is likely that existing technologies will require refinement, or novel technologies will need to be developed. To evaluate and test these technologies, a series of KC-135 precursor flights are being proposed. A general purpose free floating experiment platform is being developed to allow the KC-135 flights to be used to their fullest. This paper will outline the basic design for the CELSS Free Floating Test Bed (FFTB), and the requirements for the individual subsystems.

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.

Understanding the dynamics of capillary flow through unsaturated porous media is very important for the development of an effective water and nutrient delivery system for growing plants in microgravity. Experiments were conducted on Mir Space Station with an experimental cuvette called “Capillary Testbed.” The results of these experiments showed a need for continued experimentation in microgravity and that major modifications to the cuvette were needed. Preliminary microgravity tests of the new, modified Capillary Testbed device were conducted during parabolic flights on KC-135. In spite of the short duration microgravity portion of a parabola, the performace of the modified Capillary Testbed was evaluated. An experiment was conducted on the Space Shuttle, STS-63 mission, using a modified Capillary Testbed device. This experiment studied the effect of bead diameter on capillary flow by comparing the capillary flow in three different granular beds.

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.