Ch. Lasseur

MELISSA: Global control strategy of the artificial ecosystem by using first principles models of the compartments

MELISSA is a micro-organisms based ecosystem conceived as a tool for understanding the behaviour of artificial ecosystems, and developing the technology for a future biological life support system for long term space mission. The driving element of MELISSA is the recovering of oxygen and edible biomass from waste (faeces, urea). Due to its intrinsic instability and the safety requirements of manned missions, an important control strategy is developed to pilot this system and to optimize its recycling performance. This is a hierarchical control strategy. Each MELISSA compartment has its local control system, and taking into account the states of other compartments and a global desired functioning point, the upper level determines the setpoints for each compartment. The developed approach is based on first principles models of each compartment (physico chemical equations, stoichiometries, kinetic rates, ...). Those models are used to develop a global simulator of the system (in order to study the global functioning). They are also used in the control strategy, which is a non linear predictive model based strategy. This paper presents the general approach of the control strategy of the loop from the compartment level up to the overall loop. At the end, some simulation and experimental results are presented.

Growth monitoring of a photosynthetic micro-organism (Spirulina platensis) by pressure measurement

An on-line measurement technique for estimating biomass production rate in a photosynthetic micro-organism culture was developed and tested experimentally. The technique is based on monitoring O2 production from the increase in pressure inside a closed photobioreactor. The data obtained by this method correlated with the direct measurement of the biomass concentration. A material balance on the components in the system allows the validity domain of the method to be defined. The method was applied to batch cultures of the cyanobacterium, Spirulina platensis, in a cylindrical photobioreactor validating existing physiological and light energy models.

Light intensity and production parameters of phytocenoses cultivated on soil-like substrate under controled environment conditions

To increase the degree of closure of biological life support systems of a new generation, we used vermicomposting to involve inedible phytomass in the intra-system mass exchange. The resulting product was a soil-like substrate, which was quite suitable for growing plants (Manukovsky et al. 1996, 1997). However, the soil like substrate can be regarded as a candidate for inclusion in a system only after a comprehensive examination of its physical, chemical, and other characteristics. An important criterion is the ability of the soil-like substrate to supply the necessary mineral elements to the photosynthesizing component under the chosen cultivation conditions. Thus, the purpose of this work was to study the feasibility of enhancing the production activity of wheat and radish crops by varying the intensity of photosynthetically active radiation, without decreasing the harvest index. The increase of light intensity from 920 to 1150 μmol·m−2·s−1 decreased the intensity of apparent photosynthesis of the wheat crops and slightly increased the apparent photosynthesis of the radish crops The maximum total and grain productivity (kg/m−2) of the wheat crops was attained at the irradiance of 920 μmol·m−2·s−1. Light intensity of 1150 μmol·m−2·s−1 decreased the productivity of wheat plants and had no significant effect on the productivity of the radish crops (kg/m2) as compared to 920 μmol·m−2·s−1. The qualitative and quantitative composition of microflora of the watering solution and substrate was determined by the condition of plants, developmental phase and light intensity. By the end of wheat growth under 1150 μmol·m−2·s−1 the numbers of bacteria of the coliform family and phytopathogenic bacteria in the watering solution and substrate were an order of magnitude larger than under other illumination conditions. The obtained data suggest that the cultivation of plants in a life support system on soil-like substrate from composts has a number of advantages over the cultivation on neutral substrates, which require continual replenishment of the plant nutrient solution from the systems store to complement the macro- and micro-elements. Yet, a number of problems arise, including those related to the controlling of the production activity of the plants by the intensity of photosynthetically active radiation. It is essential to understand why the intensity of production processes is limited at higher irradiation levels and to overcome the factors responsible for this, so that the soil-like substrate could have an even better chance in the competition for the best plant cultivation technology to be used in biological life support systems.

FEMME: a precursor experiment for the evaluation of bioregenerative life support systems

Abstract In long term manned space missions, oxygen, water and food supplies are a critical issue. Bioregenerative systems, and among them those relying on microbial processes, represent one of the most promising alternatives. Studies of these systems from the engineering point of view, requires the development of mathematical models and their validation with small scale experimental systems (breadboards, pilot plants, etc.). Usually, these studies do not take into account the effects of space environment (i.e. reduced gravity or microgravity, radiation, direct sunlight, temperature, etc …). Despite several scientific experiments, intending to qualify such effects, only few quantitative results are available. In this paper, the possibility of an autonomous off-board experiment, named the First Extraterrestrial Man Made Ecosystem, is investigated. The experiment is based on a very simplified ecosystem consisting in a photoautotrophic compartment and a heterotrophic one, linked by their gas phase. According to its biological concept, this experiment should provide data on microbial growth kinetics in space, and the effects of radiation and gravity. It has been conceived as an entirely automatic device. Its design involves several technological concepts such as thermal control, the use of direct sunlight and radiation shielding. This work is done under the framework of ESA biological life support systems research program. The aim of this document is to provide a preliminary concept of the experiment.

Femme: A precursor ecosystem on the Moon

Abstract An efficient regenerative life Support system for manned base cannot be conceived without biological processes. Therefore since the 1960s, numerous projects have been initiated to close, as far as possible, the biological loop. Based on the selected concepts (i.e. carbon and/or nitrogen cycles, microbial organisms and/or higher plants) mathermatical models have been studied and built. Unfortunately, to our knowledge these robust models do not take into account the effects of the space environment (i.e. reduced gravity, radiation,…). In the past, a large number of scientific studies has been performed to understand these effects but only a few of them have tried to quantify them. In this paper we present a very simplified concept of an ecosystem. Its objectives, which are compatible with a non-pressurised mission, are on one hand to quantify microbial kinetics and on the other hand to demonstrate the validity of several technologies and technical concepts.

Effect of Growing Conditions on Wheat Hormonal Status and Productivity in Experimental Ecological System

The levels of free and bound forms of IAA, ABA, cytokinins (CK), and gibberellins, as well as growth characteristics and productivity were investigated in two wheat lines. The plants were grown under controlled conditions in an artificial ecosystem that allowed the irradiance, CO2 concentration, and rhizosphere temperature to be changed. The main difference in the hormonal status of leaves of tall spring wheat, line 232, and dwarf wheat, line 95-3, was the absence of GA9 gibberellins in the latter. It was found that the light intensity and temperature of rhizosphere insignificantly affected the balance of endogenous phytohormones and HI in wheat. The elevation of CO2 concentration resulted in a considerable increase in the content of free IAA, an appearance of free GA9, and a rise in the productivity of wheat, line 232. The concentration of CO2 was shown to be a major parameter that determined HI in the experimental ecological system.