Managing Soil for Plant Growth in Microgravity: Lessons Learned from Vomit Comet and Space Station Experiments.

Water distribution patterns in pore spaces of particulate porous media directly control the resulting diffusion pathways required for plant root respiration. Choosing porous media and managing them for future plant-based life-support systems in space must therefore account for effects of microgravity (≈10⁻⁶g_earth) conditions on fluid behavior.  We present oxygen diffusion and water retention data measured in near zero (micro-) gravity aboard the International Space Station and the Vomit Comet (parabolic flight aircraft). Porous-ceramic aggregates tested included 1- to 2-mm Turface, 0.25- to 1-mm Profile, and a 50:50 mixture of both. Results suggest higher percolation thresholds and tortuosities during drainage that are caused by heterogeneities in the water distribution not observed for hydrostatic conditions on Earth. These findings are important to control water and gases in root zones for successful plant growth in space.