Water Movement in T- and Y- Shaped Capillary Tubes Under Microgravity.

International Space Exploration Coordination Group are planning Extended Duration Crew Missions on Moon, or on Near-Earth Asteroids in the 2020s to create the Deep Space Habitat and the path to Mars. As the space mission getting longer, the food production in space takes an important role to save the launching cost and to create secured life-support systems. Water accessibility is one of the most important factor for plants growth; however, there are few reports about water movement under microgravity. Our objective of this study was to reveal how water moves in porous media under microgravity, especially on the branch point of a water-flow path. To visualize the water movement, T- and Y- shaped capillary tubes were used to observe water movement driven by the capillary force under microgravity made by a free-fall tower. The Y- shaped tubes were also compared with different diameters (2.3, and 5.5 mm). Although water in all shapes of the tubes moved upward and went beyond the branch point, the speeds of water movement were almost half after the branch comparing with the speed before the branch. A small diameter tube before the branch, which did not provide enough water to the water front, and the friction between water molecules and the wall of the tubes made water movement slower after the branch point. There were no significant differences of water movement between T- and Y- shaped tubes; however, water movement was faster in the 2.3 mm diameter tubes than in the 5.6 mm diameter tubes.