Plant Water Management Experiments 5 & 6 on ISS: Hydroponics and Ebb and Flow

Crop production in microgravity will be important to provide whole food nutrition, dietary variety, and psychological benefits to astronauts exploring deep space. Unfortunately, terrestrial plant watering methods face significant challenges when applied aboard spacecraft due to rogue bubbles, ingested gases, ejected droplets, and various unstable liquid interface configurations that arise in microgravity environments. To address these issues, we present the recent results of the Plant Water Management (PWM 5 & 6) technology demonstrations conducted on ISS, where recirculating hydroponic and ebb and flow watering processes are studied using engineered root modules varying solution flow rates, serial and parallel channel fill levels, and analog root densities. The micro-gravity demonstrations employ plumbing elements that exploit the near absence of body forces to achieve passive bubbly flow aeration, bubble separation, gas diversion, bubble mergers and migration, droplet capture, nutrient/water delivery, and the use of plant root geometry for complete microgravity fluid phase separations at different stages of growth. Practical demonstrations of system priming, start-up, shut-down, draining, and plant installation and changeout are highlighted. Such advances offer a variety of plug-and-play solutions for effective plant watering in low- and variable-gravity environments, despite the challenging wetting properties of contaminated aqueous nutrient solutions. This research is funded by NASA Biological and Physical Sciences Division.