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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).

At present there is no valid approach to the problem of incorporating human solid and liquid wastes and plants wastes into the organic matter turnover of bioregenerative life support systems (BLSS). As a rule, these waste products are currently either stored inside a system or subjected to processing by physicochemical methods. Thus, it is too early to speak of a full value return of human and plant wastes in intrasystem matter turnover. This study discusses the combination of physicochemical and biological methods for human and plant waste utilization allowing an increased degree of closure of matter turnover. The human solid wastes following physicochemical processing were included in intrasystem turnover together with plants wastes by using biological oxidation in soil-like substrate (SLS). The next stage was the inclusion of salt-tolerant plants (halophytes) into the BLSS so that mineral elements contained in urine could be recycled into matter turnover.

This work concerns the model of a biological life support system consisting of higher plants, a unit of “biological combustion”, a physicochemical reactor, and 1/30 of a human. The cycling of the main biogenic elements of the system, water, and carbon dioxide was closed to a high degree (more than 95%). Experimental-theoretical analysis of the cycling processes in the system was based on the calculations of mass exchange rates dynamics and some stoichiometric equations. The model was designed for the study of mechanisms of material transformation and the directions of mass exchange processes in the artificial ecosystems.

If man leaves Earth for a long time to settlements on the Moon or Mars, he will be dependent of Closed Ecological Life Support Systems (CELSS) for the recycling of waste and the production of food. A large amount of the inedible plant material has to be pretreated and converted into a form which can be recycled. The main portion of this biomass is lignocellulosic material which cannot or only slightly be degraded by micro-organisms. White-rot fungi like Pleurotus spp. (oyster mushroom) or Lentinus edodes (shiitake or black Chinese mushroom) degrade these fibrous material more efficient than other micro-organisms and produce edible and also tasteful mushrooms which will increase the quality and nutritional value of the settlers diet. In the MELISSA (Micro-Ecological Life Support Alternative) project, a project under the management of ESA to study CELLS, it was observed that also human faeces contain a considerable amount of fibrous materials which pile in the loop.

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.

For the last 10 years, ESA has initiated Life Support activities to prepare long-term manned missions. Although a large part of these activities were based on physico-chemical technologies, biological processes were considered as well. A few projects were initiated: air contaminants removal (e.g. BAF) up to the complete and complex approach of artificial ecosystems (e.g. MELISSA). In order to make a complete survey of the existing developments, to evaluate their advantages and weaknesses, to identify the needs of future projects, as well as to understand the interest of industry, an Advanced Life Support Workshop has been organised in April 1999 by ESA. This paper reviews the existing developments and presents the recommendations of the workshop. A specific part is devoted to the projects in collaboration with the ESA Life Sciences community and the results of the 1999 announcement of opportunity, which included Biological life Support.

Trace contaminants originating from both material off-gassing and human metabolism may cause human safety and welfare issues, when they accumulate in the spacecraft cabin air. For long duration missions and planetary bases, biological oxidation is a viable solution for the removal of these contaminants. The Biological Air Filter, BAF, a development of Stork and Bioclear is a continuously operating system, which degrades trace organic contaminants to harmless components like water and CO2. The BAF forms an interesting alternative to the existing physical-chemical trace contaminant control systems. This ecological system is low in weight, volume and power consumption. Due to the nature of the system, the maintenance requirements are also very limited. The applied micro-organisms are harmless and the system is operated at atmospheric pressure, which makes the system extremely safe within the operating environment.

Support media for the fixation of nitrifying bacteria were compared. Polystyrene beads were found to be the most effective among the media tested. It was shown that axenic cultures of pure strains of bacteria do not lead to better performance than bacteria seeded from the waste water. Loads as high as 1.6 Kg N-NH4/m3 reactor.d-1 could be eliminated on the selected media, and oxygen was found to be limiting under 3.5 mg/l of concentration for the fixed bacteria.

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 (Microbial Ecological LIfe Support System Alternative) project has been set up to be a model for the studies on ecological life support systems for long term space missions. The compartmentalisation of the loop, the choice of the micro-organisms and the axenic conditions have been selected in order to simplify the behaviour of this artificial ecosystem and allow a deterministic and engineering approach. In this framework the MELISSA project has now been running since beginning 1989. In this paper we present the general approach of the study, the scientific results obtained on each independent compartment (mass balance, growth kinetics, limitations, compound conversions,..), the tests of toxicity already performed between some compartments and their effect on the growth kinetics. The technical results on instrumentation and control aspects, and the current status of the ESA/ESTEC hardware are also reviewed.

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.