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Every ecosystem, whether natural or man-made, has a natural tendency to increase its organisational level inducing a maximal utilisation of its resources and consequently, minimising the net output from the system. In order to obtain useful net output from an ecosystem, therefore, it is necessary to stop and to stabilise the evolution at an intermediate organisational level by proper control. “Ecological” life support systems for manned space missions will be required to maximise productivity and safety whilst at the same time respecting tight size constraints, which implies powerful control and regulation systems. However the behaviour of complex ecosystems is relatively poorly understood, their stability/evolution is greatly influenced by intrinsic internal controls and classical control theories cannot be easily applied.

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.

The MELISSA (Micro-Ecological Life Support Alternative) project was initiated in 1989. The recycling system is conceived as a micro-organisms and higher plants based ecosystem. As a matter of fact, it is intended as a tool to gain understanding of closed life support, as well as the development of the technology for a future life support system for long term manned space missions, e.g. a lunar base or a mission to Mars. The collaboration was established through a Memorandum of Understanding and is managed by ESA. It involves several independent organisations: University of Ghent, EPAS, SCK, VITO (B), University of Clermont Ferrand, SHERPA (F), University “Autonoma” of Barcelona (E), University of Guelph (CND). It is co-funded by ESA, the MELISSA partners, the Belgian (DWTC), the Spanish (CIRIT and CICYT) and Canadian (CRESTech, CSA) authorities. The driving element of MELISSA is the production of food water and oxygen from organic waste (inedible biomass, CO2, faeces, urea).

Initiated in March 1989, the MELISSA (Micro-Ecological Life Support Alternative) has been conceived as a micro-organisms and higher plants based ecosystem intended as a tool to gain understanding of the behaviour of artificial ecosystems, and for the development of the technology for a future biological life support system for long term manned space missions, e.g. a lunar base or a mission to Mars. The collaboration was established through a Memorandum of Understanding and is managed by ESA/ESTEC. It involves several independent organisations: IBP Orsay (F), University of Ghent (B), University of Clermont Ferrand (F), VITO Mol (B), ADERSA (F), University “Autonoma” of Barcelona (E), University of Guelph (CND). It is co-funded by ESA, the MELISSA partners, the Spanish (CIRIT and CICYT) and Canadian (CRESTech) authorities. The driving element of MELISSA is the recovering of edible biomass from waste (faeces, urea), carbon dioxide and minerals.

Study of bio-regenerative life support system is a critical issue for long term manned spaceflight applications. An engineering approach of such systems, consists in experimental stoichiometry and growth kinetics determination and building up structured and predictive mathematical models, in order to test simplified biological processes. Up to now, the main results obtained by such an aproach are in good agreement with ground-based data. Despite several scientific experiments performed in space, results on microbial kinetics study remains rare, and the real influence of space environment (micro-gravity, radiation, light spectrum, ..) on micro-organisms growth is still not quantified. Precursor space missions are therefore justified to expand current knowledge and check for the changes affecting such biological processes.