Design of a module for cultivation of tuberous plants in microgravity: the ESA project “Precursor of Food Production Unit”

Plant cultivation systems for Bioregenerative Life-Support Systems in Space developed on Earth need to be tested in Space, where reduced gravity alters the liquid and gas behaviour within the plant and between the plant and the surrounding environment, making critical the distribution of water and nutrients. The ESA project “Precursor of Food Production Unit” (PFPU) aims to design a modular cultivation system for edible tuberous plants (such as potato and sweet-potato) in microgravity, to be preliminary tested in ground conditions in the view of successive Space application. Among the different modules of the PFPU demonstrator, the Root Module (RM) is the component physically hosting the plant, accommodating tubers and roots. This paper describes the step-by-step procedure adopted to realize the RM, including the design, the building and the ground testing of its prototype. Specifically, the hydrological characterization of possible cultivation substrates, the set-up of the water distribution system, and the validation test of the assembled prototype in a tuber-to-tuber growing cycle of potato plants are described. Among 6 substrates tested, including 3 organic materials and 3 synthetic materials, cellulosic sponge was selected as the best one, based on the hydrological behaviour in terms of air and water transport and water retention capacity. The water sensor WaterScout was successfully calibrated to monitor the water status in cellulosic sponge and to drive to irrigation and fertigation management. The designed porous tubes based distribution system, integrated with water sensors, was able to provide water or nutrient solution in a timely and uniformly way in cellulosic sponge.