Zhou, W., Zeltner, W., and Meyers, R., "Advanced Photocatalytic Ethylene Degradation Technology to Support Plant Research in the Enclosed Environment," SAE Technical Paper 2003-01-2610, 2003, doi:10.4271/2003-01-2610.
Conducting research to assess the impact of microgravity environment on plant growth and development requires a research facility that has the capability to provide an enclosed, environmentally controlled plant chamber. Since plants are sensitive to a number of atmospheric gaseous materials, the chamber atmosphere must be isolated from the space vehicles' atmosphere, which typically contains high levels of CO2 and other trace contaminants and volatile organic compounds (VOCs) that can be detrimental to the plant growth. However, an enclosed chamber may result in a high concentration of ethylene, a potent hormone produced by the plants, which can accumulate to levels well above what plants are able to adapt to. The physiological effects of excessive ethylene on plant development include severe interruption of the pollen process and significant reduction of seed production. Hence, the enclosed plant research unit must be capable of removing the ethylene to assure healthy plant growth and development.The Wisconsin Center for Space Automation and Robotics (WCSAR) at the University of Wisconsin Madison has recently developed an enhanced ethylene scrubber using a thin-film coated photocatalyst and homogeneous surface configuration. Comparisons between this new design and the previous version using particulate catalyst show a fundamental difference in photocatalytic behavior and reaction rate, especially under significantly elevated relative humidity in the test chamber. Since the photocatalytic material is not consumed during the oxidization process, this technology is particularly suitable for long-term space-based operations where the supply of consumable materials becomes a challenge.