Introduction
As human space exploration expands beyond low Earth orbit and ventures further into the solar system, establishing sustainable food production capabilities will become increasingly important. Long term bases on the Moon and eventually Mars will require life support systems capable of growing crops to provide fresh food and regenerate vital resources like oxygen, water, and soil. With this goal in mind, the Japan Aerospace Exploration Agency (JAXA) established the Lunar Farming Concept Study Working Group in 2017 to conceptually design a lunar agricultural system capable of sustainably feeding crew members without dependency on regular resupply missions from Earth.
Over the course of multiple meetings between 2017-2018, the working group brought together experts in fields like plant cultivation, environmental control, robotics, recycling, and systems engineering. They divided into four subgroups – cultivation technology, unmanned technology, recycling, and overall system design – to holistically examine the technical challenges and propose solutions. This article summarizes the working group’s efforts to conceptualize a robust and self-sufficient lunar farming system based on applying the latest Earth-based agricultural advancements to the unique constraints of the Moon.
Background and Motivation
With the retirement of the Space Shuttle program in 2011, low Earth orbit became the proven domain for long duration human spaceflight aboard the International Space Station (ISS). However, to truly establish humanity as a multi-planetary species will require venturing beyond LEO to destinations like the Moon and Mars. The working group was motivated by JAXA’s mandate to help enable sustainable exploration and development of lunar surfaces. They recognized that establishing agricultural production capabilities will be crucial to support long term inhabited outposts beyond Earth’s proximity.
Relying solely on pre-packaged rations and regular resupply missions from Earth would be profoundly inefficient and unsustainable for permanent settlements. The working group established several key goals and assumptions to guide their conceptual study: designing a system that could support 6-8 crew members initially while minimizing inputs from Earth, closing material loops to regenerate vital resources, applying Japan’s world-leading agricultural technologies, and accounting for the 1/6 Earth gravity environment on the Moon. They sought to build upon past lunar agriculture studies by incorporating 30+ years of technological advances not previously considered.
Selection of Crop Species
A crucial first step was determining the appropriate crop portfolio capable of meeting crew dietary needs. The crop species subgroup began by defining reference daily intake levels for energy, macronutrients, vitamins, and minerals required by Japanese individuals based on health guidelines. They then screened candidates based on their production suitability for controlled plant factories, variances in growth requirements, virus screening status, traits favorable for automation, and overall nutritional profiles.
Eight crop species were selected that could together provide a balanced daily meal for crew members: rice and soy as staple grains supplying protein, carbohydrates, and fats; sweet potato and potato as bulk carbohydrate sources; lettuce as the primary leafy vegetable; tomato and cucumber as supplemental vegetables; and strawberry as a source of vitamins and minerals. Computational analysis determined these eight crops, if cultivated together, could meet over 90% of crew daily nutritional needs through balanced combination in meals without supplements. Their selection established the foundation for further examining cultivation and life support system requirements.
Cultivation System Design
Precise environmental control is essential for plant growth in artificial lunar greenhouses. The cultivation subgroup analyzed key growing condition parameters of lighting, temperature, moisture, carbon dioxide, air circulation, and root zone environments. They also evaluated challenges of cultivating in lunar surface facilities versus potential uses of in-situ resources. Microgravity effects on leaf gas/heat exchange and nutrient delivery were also studied.
State-of-the-art plant factory techniques from Japan like LED lighting and multi-shelf hydroponic systems were proposed for adaptation to lunar conditions. Recirculating hydroponic or aeroponic systems with nutrient film technique or mist propagation were identified as the most resource efficient cultivation methods. Automating environmental monitoring and controls was also emphasized to minimize crew labor demands. Overall cultivation system design centered on tightly regulating all plant growth factors while optimizing resource usage.
High Efficiency Food Production
Maximizing crop yields within the limited cultivable area was another central goal. The production subgroup broke down specific growth cycle monitoring needs and management strategies for each crop. Batch and continuous cultivation cycles were proposed depending on species traits. For example, rice and soybeans would use batch hydroponic trays, while lettuce, tomatoes and cucumbers employed continuous nutrient film technique shelves. Sweet potatoes and potatoes could be continuously recirculated via hydroponic channels.
Advanced food production technologies from Japanese plant factories were suggested for implementation. These included controlled germination, automated transplanting, multi-wavelength LED lighting optimized for each growth phase, computerized nutrient dosing, non-destructive harvest monitoring via light/hyperspectral sensors, and machine vision for crop inspection/grading. Adapting these cutting-edge automation and precision agriculture approaches aimed to maximize harvests from a limited greenhouse area.
Sustainable Material Circulation
Closing biogeochemical loops to regenerate life support system resources was a paramount concern. The recycling subgroup focused on designing modular waste processing facilities using microbial conversion. Methane fermentation was proposed to break down organic wastes from crops, crew, and greenhouse cleaning into methane biogas for energy production. The remaining digestate could then be further composted and reused as soil amendment/growth media.
Lunar regolith properties and potential agricultural uses were also investigated. Initial experiments demonstrated that lunar regolith simulants could retain moisture and nutrients when amended with organic materials or minerals, showing promise as a growth substrate. Overall the recycling concept aimed to reuse all gaseous, liquid, and solid wastes through thermochemical and biological processing without discarding anything overboard, achieving sustainability through complete material cycling.
System Integration and Analysis
Finally, the overall system subgroup integrated all preceding technical analyses. Mass balance modeling determined necessary life support hardware scales and throughputs to sustain the proposed crew size based on estimated crop yields, oxygen generation rates, and inorganic resource regeneration abilities. Various configurations for modular crop production, waste processing, resource recovery, and environmental control units were computationally compared.
Key metrics like minimum cultivation area, power requirements, resource throughputs, and equivalent system mass were evaluated. Comparative assessments provided insights on optimization tradeoffs between maximizing resource regeneration capacities versus minimizing physical scale and mass demands. The end goal was to define a baseline functional lunar agro-industrial complex capable of long term sustainable operation with minimal Earth resupply needs or physical footprint.
Future Challenges
While the working group’s conceptual design demonstrated the viability of establishing self-sufficient lunar farming, it also highlighted many remaining technological hurdles. Plant cultivation experiments must further evaluate microgravity effects and adaptation needs. Equipment hardening, automation, and standardization for manned and remote operation need development. Seed stock storage, crop disease control, and pollination solutions also require research. Expanding the range of cultivable crops for diversified nutrition presents opportunities.
Closing biogeochemical loops tighter through advanced life support systems integration and waste processing remains an engineering challenge. Quantifying resource requirements and establishing standards for system sustainability also demands ongoing refining. Verifying theoretical models through physical prototypes and tests will be needed. International cooperation on shared technical challenges can accelerate progress, as can continued ground-based demonstrations and applications of spin-off technologies.
Overall the working group’s conceptual study provided a systems-level framework and starting point for further technically refining the vision of sustainable, autonomous lunar farming capabilities. Their holistic, multi-disciplinary approach incorporated global agricultural innovations with prudent resource mitigation strategies required for long term space missions. Continued advances from both the space and terrestrial technology sectors will be imperative to help realize humankind’s aspirations for permanent settlement beyond Earth.
