Date of Award
Mechanical and Aerospace Engineering
NASA and other organizations are preparing to send humans deeper into space, including a NASA manned mission to Mars in the 2030s, in order to learn more about our universe and the origin of life and to ensure the survival of the human race. Long journeys in space require efficient, dependable, and sustainable methods to provide for astronauts' metabolic needs such as oxygen, water, and food. In order for microgravity plant growth chambers to become a viable solution, several challenges encountered by past growth chambers must be resolved.
One problem with existing space food growth chambers is hypoxia, or lack of oxygen, in the root zone, which decreases growth and causes epinasty and leaf chlorosis. Plant leaves produce oxygen and consume carbon dioxide through photosynthesis while roots consume oxygen and produce carbon dioxide through root respiration. Consequently, there are high levels of oxygen near the leaves and high levels of carbon dioxide near the roots.
In microgravity, surface tension forces dominate. Instead of filling the pores from the bottom up, water tends to collect on the surface of the soil pores and trap air bubbles from which roots remove oxygen. Oxygen from the plant atmosphere is slow to diffuse into the water-trapped bubbles and the water doesn't naturally drain from the pores without gravity. These factors prevent oxygen near the leaves from quickly diffusing to the roots and carbon dioxide and ethylene near the roots from diffusing out of the substrate. A method is needed to enable continuous quick gas diffusion between the leaf chamber and the root zone in space food growth chambers.
Our project was to assess whether an additively manufactured lattice plant substrate composed of nylon facilitates gas diffusion between the leaf chamber and the root zone in a passively watered hydroponic space food growth chamber. In space, water collects on the sides of tubes first, leaving a column of air in the middle. We designed a substrate so that in space the columns would have the optimal balance of water and air for the plant roots. In order to test out design on Earth, we created a plant substrate lattice that has columns of various diameters. Water is then drawn upward at varying heights depending on the diameter of the substrate column. This creates spaces of water and air for the plant roots. We found the optimal column diameters through analytic calculations, simulations in the program HYDRUS, and experimental testing.
We designed and built a complete microgravity food growth chamber and tested our substrate in it. Our growth chamber is passively watered. As plants absorb water from the substrate, the pressure difference causes water from the reservoir to naturally diffuse into the root zone. We planted mizuna in the substrate and it successfully grew for 30 days. We plan to continue experimental testing over the summer in order to further improve our substrate design.
Stacey, Nathan I., "XHAB Microgravity Food Growth Chamber" (2016). Undergraduate Honors Capstone Projects. 601.
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Departmental Honors Advisor
R. Rees Fullmer