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

Crop production in microgravity may ultimately provide critical 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 flows, channel fill levels, and analog root densities. The microgravity 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. This report provides a draft of subsequent publications, but more importantly at present serves as background information in support of the PWM 5 & 6 video archive uploaded to the NASA PSI website: https://psi.nasa.gov (see Fluid Physics PSI-187).