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Completed TRL 5 (started at 2, targeting 5)
To enable sustainable food production in future human exploration missions, plant growth is being studied by the Space Crop Production Team at KSC. Microgreens are good candidates for food supplements and contain specific nutrients that are lacking in the prepackaged diet, including vitamin C and vitamin K. Because they are densely sown, typical growth methods do not allow the ability to distinguish between the levels of evaporation from the rooting substrate and transpiration from the leaves. With larger plants, the root and shoot zone can be separated to distinguish these fluxes and accurate transpiration measurements of plant canopies are feasible. Furthermore, separation of the root and shoot zone may also be beneficial when harvesting microgreens in microgravity as it may reduce microbial contamination of the edible biomass by the roots, which have high microbial loads. Using a root and shoot separator box when harvesting may help with microbial contamination, but these tiny plants are challenging to handle in microgravity, so harvest management remains an open question.
The innovation proposed here is a microgreen root/shoot partitioned planting box, which offers a solution to these challenges with accurate gas exchange measurements and a safe microgreen harvest in low gravity environments. Being able to measure transpiration of a microgreen canopy will be important for modeling plant growth in reduced gravity environments, so the first objective was to develop a planting unit with a seal between the root zone and the shoot zone. With an unsuitable harvesting technique, freshly harvested microgreens may add debris to the cabin, so the second objective was to test different harvesting techniques and management approaches associated with this innovation. These two objectives were pursued in parallel since many goals were the same: develop a planting unit that 1) separates the shoots from the roots, 2) allows acceptable germination rate, and 3) allows for seedlings to emerge and develop. What differed was the need to have a seal, which was only applicable for our gas exchange goal, and the need to have an embedded harvesting mechanism and bagging method which only applied to our harvesting goal.
Testing of the various harvesting mechanisms and bagging methods was performed during a series of parabolic flights. All parabolic flight procedures took place inside a rented secondary containment chamber (e.g., glovebox) that was developed by the University of Louisville specifically for experiments involving fluids and other materials that may become airborne during reduced gravity flight. Three different harvesting methods and two different bagging collection methods were tested for microgreens. A third bagging method was initially tested but found to be unsuitable. Human factors were also taken into consideration, to identify which harvest and bagging collection methods would be easiest to use with favorable results in microgravity. Three parabolic flight tests were performed in total, one in November 2021 and two in December 2021.
For long duration missions (Mars transit and Lunar and Martian surface), growing food will be required on a larger scale to reduce resupply, storage, and launch costs. In addition, the prepackaged diet degrades over time, so supplemental food production may be required to ensure food security – the condition that the crew have continuous access to sufficient safe and nutritious food that meets both their dietary needs and food preferences to maintain peak health and performance. Additionally, plants enable air regeneration, since they remove CO2 from the air and generate O2, and water recycling, since they transpire pure water. This research aligns with NASA’s Technology Taxonomy areas TX06.1.5 ECLSS Modeling and Simulation Tools and TX06.3.5 Food Production, Processing, and Preservation. KSC’s space crop production work aligns with our role as the NASA center leading Plant Research and Plant Production and advancing the growth of microgreens also helps to fill gaps identified by the Human Research Program for a risk of inadequate nutrition. Microgreens are a nutrient-dense crop that has been targeted to serve as an easily grown dietary supplement for a variety of spaceflight applications. Crews on the ISS or the Lunar Gateway could benefit from growing microgreens as supplement for their diet in the near future. The 3D-printed microgreens planting box and associated approaches developed as part of this project would make microgreens harvests easier and improve food safety when compared to conventional techniques. Ensuring microgreens can be grown, harvested and handled safely without food safety risks is key for assessing readiness of this type of crop for spaceflight. Additionally, this planting box could be directly printed on an ISS 3D printer and thus allow the crew to adjust the microgreens content of their diets or easily replace a box that is damaged.
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