Abstract:

The long-term success of human space exploration hinges on the development of sustainable, closed-loop life support systems, including the ability to produce food autonomously. Astro-agriculture, the cultivation of crops in space, presents unique challenges, particularly the energy demands associated with controlled environment agriculture. This study investigates the impact of diffused, full-spectrum lighting on wheatgrass (Triticum aestivum) growth under low-energy conditions, a crucial factor for minimizing the cost and complexity of extraplanetary greenhouses. Our findings demonstrate the potential of diffused light to enhance yield consistency and, in some cases, overall yield, offering valuable insights for optimizing lighting strategies in future space farming endeavors. A more detailed account of this research, originally conducted under my mentorship, is forthcoming in a publication currently in preparation.

Introduction:

As humanity progresses toward extraplanetary colonization, the ability to produce food autonomously becomes essential. Long-duration missions, like a Mars expedition, necessitate on-site food production due to the prohibitive cost and logistical challenges of resupply. Astro-agriculture, the cultivation of crops in space, is a critical area of research. However, establishing and maintaining extraplanetary greenhouses presents significant hurdles, primarily the energy requirements for lighting, climate control, and other essential systems. Minimizing energy consumption is paramount for the long-term viability of astro-agricultural systems.

One promising candidate for space-based cultivation is wheatgrass (Triticum aestivum). Its rapid growth cycle, high nutritional value (rich in vitamins, minerals, and chlorophyll), and ability to thrive in relatively low-light and temperature conditions make it an attractive option. Furthermore, the consistency of crop yield is crucial for nutritional planning in closed-loop life support systems. This study explores the effects of diffused lighting on wheatgrass growth under varying power and photoperiods, aiming to identify optimal lighting strategies for maximizing yield and consistency in low-energy astro-agricultural settings. Diffused lighting has shown promise in improving yield consistency in terrestrial agriculture, making it a key area of investigation for space-based applications.

Materials and Methods:

Growth chambers were constructed from cardboard boxes, lined to minimize light leaks. LED grow lights, providing full-spectrum illumination, were attached to the top of each chamber. For diffused lighting treatments, diffusion film was placed around the LED strips. Wheatgrass seeds were pre-soaked and then sown in potting soil within the growth chambers. Water was provided to the plants through a bottom-watering system. Temperature and humidity were maintained within the growth chambers, and the photoperiod and light intensity were controlled externally. Light intensity (lux) was measured at multiple points within each chamber.

The experiment investigated the effects of both light power and photoperiod on wheatgrass growth. Three power levels (3.75W, 5.63W, and 7.50W) were tested under an 8-hour photoperiod. Subsequently, the impact of photoperiod was examined at the 5.63W power level, comparing 4-hour and 8-hour photoperiods. Wheatgrass was grown for one week before harvesting. Harvested wheatgrass was weighed, and the maximum and minimum heights were recorded. In some trials, wheatgrass juice was extracted, and the color of the juice was qualitatively assessed as an indicator of potential chlorophyll content.

Results:

Our results indicate that diffused lighting can positively influence both the consistency and, in certain conditions, the yield of wheatgrass harvests, particularly in low-energy environments. At the lowest power level (3.75W), diffused lighting significantly improved the consistency of the harvest compared to direct LED light. While the difference in consistency was less pronounced at higher power levels, diffused lighting consistently resulted in a more uniform yield across the growing area.

Interestingly, the heaviest yields were observed in the low-energy trials under diffused light. This suggests that diffused light may enhance the efficiency of light utilization for wheatgrass growth, even at lower light intensities. However, at higher power levels, the difference in yield between diffused and direct lighting was less significant.

The photoperiod experiments further revealed the interplay between diffused light and energy input. While diffused lighting consistently improved yield consistency across both photoperiods (4 hours and 8 hours), the effect on overall yield varied. In the 4-hour photoperiod, diffused light appeared to promote slightly higher yields, whereas in the 8-hour photoperiod, direct LED light resulted in marginally higher yields.

Qualitative analysis of the wheatgrass juice suggested potential differences in chlorophyll content depending on the lighting conditions. Juice from wheatgrass grown under low-energy, diffused light appeared darker and more opaque than juice from wheatgrass grown under low-energy, direct light, potentially indicating higher chlorophyll levels. However, this observation requires further quantitative analysis.

Conclusions:

This study provides preliminary evidence that diffused lighting can be a valuable tool for optimizing wheatgrass growth in low-energy astro-agricultural systems. Our findings suggest that diffused light can enhance yield consistency and, in some cases, increase overall yield, particularly at lower light intensities. The observed variations in juice color also highlight the need for further investigation into the impact of lighting conditions on the nutritional content of wheatgrass.

Future Directions:

Future research should focus on quantifying the nutritional content, including chlorophyll and vitamin levels, of wheatgrass grown under different lighting conditions. Hydroponic growing methods could also be implemented to provide more consistent nutrient delivery and reduce variability. Further exploration of different diffusion materials and light spectra could also lead to further optimization of wheatgrass growth for space-based applications. Ultimately, a comprehensive understanding of the interaction between light quality, energy input, and wheatgrass growth is crucial for designing efficient and sustainable food production systems for future space missions.

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