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The MELiSSA (Microbial Ecological Life Support System Alternative) project was designed as an early model of a future artificial ecosystem for long-term space missions. It centres on the recovery of edible biomass from waste, CO2 and minerals, with direct use of light as a source of energy for photosynthesis. MELiSSA is composed of four axenic compartments colonized by microorganisms, and a fifth compartment formed by the crew on board the craft. Simulation of the entire MELiSSA loop had been performed to obtain mass fluxes and concentrations of microorganisms, and liquid and gas components in all the system streams. This first approach helped to define the process conditions necessary to obtain complete recycling of nitrogen or regeneration of the atmosphere. This paper reports on the simulation of the behaviour of the loop when the photosynthetic compartment is working under various light-limiting conditions.

Mathematical modeling and control of artificial ecosystems, such as MELISSA, require first the study of physical and biological characteristics in optimal and limiting conditions. Following the previous determination of the stoichiometric equations (Spirulina compartment) and regarding the two phototrophic compartments of MELISSA (Rhodospirillaceae and Spirulina), we have first to focus our control study on the growth kinetics for the light source. In this paper, we recall the theoretical equations of microbial growth kinetics and emphasise the problem of the light transfer in a photobioreactor. We present their adaptations to our pilot plant taking into account technological and biological specifics (lamp spectrum, working illuminated volume, growth rate,…). We then develop the principles and structure of the control system and describe tests of both the hardware and software for several steady state configurations.