Development and simulation of an illumination unit for microalgae cultivation in the context of a life support system of a crewed habitat on Mars

Abstract

To ensure the sustainability of future bases and settlements on the surface of Mars, bioregenerative life support systems shall be developed. For this purpose, the Institute of Space Systems (IRS), at the University of Stuttgart, works in the development of cultivation systems of algae (Chlorella vulgaris) in a photobioreactor (PBR), which uses natural sunlight to make photosynthesis, producing edible biomass and oxygen. A system of mirrors -the illumination unit- would be used to appropriately collect and focus the sunlight to reduce the demand of artificial illumination. In this Thesis, it has been investigated -both through numerical simulations and an experiment- the feasibility of this system. 4 different scenarios have been defined, which are considered representative of the environmental conditions on the surface of Mars. After that, a thermal model of the PBR and the illumination unit has been created, which has allowed to compute the temperature variation of the microalgae culture medium and the received irradiance during the day in each scenario. A control algorithm for the illumination unit has been designed and implemented, and the previous model has been used to demonstrate that the temperature of the culture medium could be kept constant. Then, the experimental part of the Thesis has been conducted, which has consisted in the cultivation of Chlorella vulgaris under similar illumination conditions to those obtained in one of the simulations. Finally, a model of a life support system with the PBR-illumination unit has been created. Its initial Equivalent System Mass (ESM) and the resupply demand have been computed. This data has been used to compare its performance with that of a Physico-Chemical Life Support System.