The Effects of Microgravity on Horizontal Infiltration.

In order to realize long-term space mission, we need some life supporting systems. A plant growth system under microgravity is part of life supporting systems. In space, plant growth in soil culture requires the understanding of water movement in porous media under microgravity. On earth, Under 1G conditions, water movement is expressed with the Richards’s equation. According to the equation, water moves in accordance with matric potential gradients when it is not necessary to consider pressure and gravitational potentials. However, under microgravity conditions, water movement in soil is still not well understood. Previous study reported that water hardly moved in void spaces. The objective of this study is to compare water movement of under microgravity with water movement on earth. We conducted parabolic flight experiments and make horizontal infiltration experiment. Samples that we use as representative porous media were Toyoura sand and grass beads. Samples are oven-dried and sieved through a 2-mm sieve. Columns filled with the porous media ware installed horizontally. Water source containers were made of a plastic bag that is soft and non-elastic so that it easily changes its shape to avoid building a water pressure inside. We used degassed water to prevent air bubbles from forming in the water container. Infiltration rate is measured using moisture sensors. An infiltration rate under microgravity was slower than it is on earth. The results suggested that water hardly move through porous media.