Capillary Hydroponic Plant Watering System for Spacecraft
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Soil-based systems for crop cultivation aboard spacecraft suffer mass penalties due to the transport, storage, and disposal of the nutrient soil mass. In contrast, hydroponic systems purport to require only nutrient water solutions for optimal plant growth. Though low-g soil systems present their own challenges regarding optimal water delivery to the ever-changing root zone, successful low-g hydroponics systems must address the challenges of large length scale capillary flow phenomena. Recent technology development investigations conducted by NASA have demonstrated that such capillary fluidics phenomena can be successfully exploited for the advancement of numerous spacecraft fluids management systems—despite the poor and often highly variable wetting properties of water. Following a brief review of such demonstrations we outline the development of an automated omni-gravitational hydroponic system for applications aboard transit and orbiting spacecraft as well as for surface laboratories on Earth, Moon, and Mars. Our approach exploits capillary fluidic elements for passive water-nutrient delivery, stable fluid containment, flow control, aeration, bubble phase separations, and more. Specific challenges such as passive methods to adjust nutrient delivery to the plant throughout the highly variable plant growth cycle are discussed. Terrestrial benchtop and scaled model low-g drop tower tests are presented that support expectations of successful operations in space.