System Analysis of Plant Production in Greenhouse Modules as an Integrated Part of Planetary Habitats

Kurzfassung

The establishment of planetary outposts and habitats on the Moon and Mars will help foster further exploration of the solar system. In-situ operating crews live and work in these facilities and will, eventually, rely on bio-regenerative closed-loop systems and principles, such as algae reactors and higher plant chambers, in order to minimize resupply needs and improve system resiliency. Greenhouse modules will play a major role in closing loops regarding oxygen, carbon-dioxide and water supply, but also by providing fresh food for the crew. Within the frame of the present thesis a holistic system analysis is performed in order to layout the benefits and challenges of integrating plants into an extra-terrestrial habitat. A detailed literature review on past-, present- and future greenhouse research outlines six decades of plant cultivation research for the space sector. An evaluation method on plant selection is developed, facilitating fundamental resource and benefit related criteria, important for plant cultivation during different mission scenarios. The present thesis contributes to the effort of selecting the right composition of plants to benefit the crew, the habitat functions, and the mission architecture. A crop section strategy for future mis-sions to Moon and Mars has been worked out. A systematic functional breakdown of the subsystems and relationships within the habitat and the greenhouse module is performed. The three main Controlled Environment Agriculture (CEA) technologies, essential for plant cultivation within closed-loop regimes, are examined: Illumination Control System, Atmosphere Management System, and Nutrient Delivery System. Through the implementation of CEA technologies that carefully control and optimize the provision of nutrients, environmental conditions, and light (including spectral composition), it is possible to achieve higher yields and shorter growth cycles. The systems were tested within dedicated breadboard installations within DLR’s EDEN laboratory and the Closed-Loop Test Facility, which represents an adequate greenhouse analogue test environment for the system validation and operation testing. Qualitative interface strategies to link the greenhouse with the habitat have been worked out. Further, an investigation of the greenhouse design is conducted, where three dedicated evaluation campaigns investigate the outer layout design in order to incorporate the necessary systems. The aspect of plant placements within the production system of a greenhouse is evaluated and applicable design suggestions are provided for achieving high plant densities, while still allowing subsystems integration and crew handling operations. Key findings of the crop selection, CEA testing, and the plant accommodation considerations serve as input for a plant production analysis. The research results of a 400-day biomass and crew time simulation of an adapted EDEN ISS Future Exploration Greenhouse are presented. This greenhouse is an experimental cultivation system that will be used in an analogue test mission to Antarctica (2018-2019) to test plant cultivation technologies for space. Applying a net cultivation area of ca. 12 m², 11 crops have been simulated. Detailed work procedures are established for each crop according to its production lifecycle requirements. With this work, future mission planning, crop selection, and greenhouse design studies will op-timize the tailoring of the implementation challenges of greenhouse modules into the habitat infrastructure. While the realization for these systems has to be seen in a long-term perspective, a more present outlook regarding the transformation of closed-loop greenhouses into terrestrial applications, such as Vertical Farming, are discussed and analyzed, as well.