Duri, Luigi Giuseppe (2022) In-Situ Resource Utilization (ISRU) for life support in Space. [Tesi di dottorato]

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The 21st century is an era rich in scientific findings with rapid technological development. Hence space travels and the colonization of other celestial bodies would result no longer an image close to the world of science fiction but would be desirable soon. With this aim, many Space Agencies, Research Centers, and Universities are working to establish colonies self-sustaining. The establishment of such a complex system is expensive, in addition, it must be considered the commitment to planning and managing the replenishments, which makes it even more complicated. So, it is mandatory the costs reduction through the implementation of Bioregenerative Life Support Systems (BLSSs). The in situ resource utilization (ISRU) approach aims to reduce terrestrial input into a BLSS by using native regoliths and recycled organic waste as primary resources. A sustaining and auto-regenerating solution could be permanent agriculture, through the combination of BLSS and ISRU may allow sustainable food production on Moon and Mars, in a future long-term settlement. This research addresses this issue by seeking to improve the characteristics of extraterrestrial "soils" (regolith) and evaluating their effects on plants. Lunar and Martian regoliths are not available on Earth; therefore, space research studies are conducted on regolith simulants that replicate the physicochemical properties of extra-terrestrial regoliths. In our case, two simulants have been selected; one lunar (LHS-1) and one martian (MMS-1). Green compost and monogastric manure were involved in the experiments as surrogates of waste and excreta from the crew. To use as amendments to improve the simulants' characteristics. The lettuce (Lactuca sativa L.) was selected as a candidate crop to test, due to its agronomic and qualitative characteristics. Although the simulants can be a source of nutrients, it lacks organic matter, nitrogen, phosphorus and sulphur, which may be supplied by compost. So, in the first experiment, four different mixtures of Mars simulant and compost (0:100, 30:70, 70:30, and 100:0; v:v) were involved to assay the response of two butterhead lettuce (Lactuca sativa L. var. capitata) cultivars (green and red Salanova®) grown on, and physico-chemical and hydraulic properties of the different mixtures were evaluated. The experiment was performed in a phytotron open-gas-exchange growth chamber for 19 days under fertigation. The 30:70 mixture proved to be optimal in terms of crop performance, photosynthetic activity, intrinsic water use efficiency, and quality traits of lettuces. But, the 70:30 mixture was the best substrate in terms of pore-size distribution for water-plant relationship. By the cultivar comparison, the Red Salanova produced statistically higher dry biomass, leaf number, and area than Green Salanova; and showed the best performance in terms of quality traits, especially about phenolic content. With the idea of reducing inputs, the subsequent experiment assessed the nutritional supply of amendment. For this purpose, was involved one lettuce cultivar (Lactuca sativa L. cultivar ‘Grand Rapids’), grown on different substrates consisting of MMS-1 or LHS-1 simulants mixed with monogastric manure at varying rates (100:0, 90:10, 70:30, 50:50, w/w), for 30 days in an open-gas-exchange climate chamber with no fertilization. Specifically, we evaluated the lettuce growth on these substrates, the plant physiology and nutrient uptake, the microbial biomass C and N, enzymatic activity and nutrient bioavailability in the mixtures after plant growth. A better agronomic performance, in terms of fresh biomass production and physiology, nutrient availability and enzymatic activity, was provided by substrates containing MMS-1, in comparison to LHS-1-based ones. Amendment with a monogastric-based manure significantly improved the ability of both simulants to sustain plant growth. The best crop growth response was achieved on the 70:30 simulant/manure mixture. Our findings indicate that the addition of manure at specific rates (30%) may increase the biomass production of lettuce plants cultivated in MMS-1 simulant. In addition, considering the importance of supplementation of bioactive compounds in astronauts' diets. Was also evaluated how the substrates can modulate some qualitative traits as the organic acids, carotenoids content, antioxidant activity, and phenolic profile. The phytochemical composition is variably affected by manure addition, depending on the simulant. Indeed, was recorded an increment in lutein and β-carotene content by +181% and +263%, respectively, when applying the highest percentage of manure (50%) compared with pure simulants. The 50:50 MMS-1/manure treatment contained the highest amounts of individual and total organic acids. While the highest antioxidant activity (ABTS assay) was recorded when no manure was added. Matching crop growth performance and chemical, mineralogical, and physical-hydraulic characteristics of possible plant growth media for space farming allows a better understanding of the processes and dynamics occurring in the experimental substrate/plant system, potentially suitable for an extra-terrestrial BLSS. Therefore, the agronomic practice of amendment showed promising results. However, it must be tested with other species to verify its applicability in space colonies for food production purposes; or in combination with other factors such as fertilization rates or biostimulants application to reduce the stressors and allow better plants performance.

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