The American (NASA), European (ESA), Russian (FKA), Japanese (JAXA) Chinese (CNSA) and Indian (ISRO) space agencies have successfully put a great deal of satellites into orbit. But, as far as manned missions to space are concerned, only the American and Russian agencies have experience, and what´s more, in a field limited to exploring the Moon and the international space station (ISS). The main difficulty when carrying out manned space missions bound for planets or more or less distant satellites, lies in the distance that must be travelled, which determines the amount of food and oxygen necessary for the crew to survive throughout the mission. To tackle a long term manned mission, for example to Mars, which would last at least around 1,000 days, supplies for the crew (food, water and oxygen) would weigh around 30,000 kg. This load is too heavy and greatly exceeds the maximum launch load for current space shuttles.
The feasibility of any long term manned mission to Mars or any other place, depends on developing an enclosed artificial ecosystem which recycles urine, faeces and CO2 from the respiration of the crew, and provides water, food and oxygen.
The European Space Agency (ESA) is leading the MELiSSA project (Micro-Ecological Life Support System Alternative), which was conceived as a tool for studying and understanding how artificial ecosystems behave and to develop the technology needed for future life support systems that will allow long term manned space missions to take place.
Project MELÍSSA is based on recreating an artificial ecosystem capable of creating oxygen, water and food from recycling the waste produced by the crew from a space ship (organic waste, urine, faeces and CO2). The concept is based on five interconnected compartments operating independently which are colonized by anaerobic thermophilic bacteria, photoheterotrophic bacteria, nitrifying bacteria, photoautotrophic bacteria and superior plants. Each of the compartments has a specific function assigned to it in order to reach the overall objective, which is none other than to transform the waste into supplies:
- Compartment 1: here all the waste products of the system are collected (faeces, urine, paper, inedible biomass and the inedible part of the plants). Its purpose is the anaerobic thermophilic transformation of the waste into ammonium , volatile fatty acids and minerals. These operations are carried out under thermophilic conditions in order to increase the efficiency of the degradation process and to guarantee that the potentially pathogenic microorganisms are destroyed.
- Compartment II: the volatile fatty acids produced in compartment I are transformed into a source of inorganic carbon under anaerobic conditions by means of photoheterotrophic bacteria growth which uses light as the energy source. The biomass created is returned to compartment I to be degraded.
- Compartment III: its purpose is to transform the ammonium produced in compartment I into nitrate which is the preferred source of nitrogen by the superior plants and bacteria in compartment IV. The oxidization of the ammonium is produced by the Nitrosomonas europaea bacteria and the oxidization of the nitrates is undertaken by Nitrobacter winogradskyi. Both use CO2 as a source of carbon. It grows very slowly so very little biomass is created.
- Compartment IV: is responsible for transforming carbon dioxide into oxygen, for creating edible biomass which can be used to feed the crew and to recover water. All this is carried out through two subcompartments (IVa and IVb) which compartment IV is divided into. Subcompartment IVa is colonized by photoautotrophic Arthrospira platensisbacteria which use light as a source of energy and CO2 as a source of carbon and they produce oxygen and water. The biomass created is in itself edible, so it would feed the crew. Subcompartment IVb is made up of a selection of superior plants, which carry out the same role as the photoautotrophic bacteria. However, the superior plants allow CO2 to be transformed into oxygen at a greater specific speed than with the photoautotrophic bacteria. Moreover, they help to achieve a more balanced diet for the crew.
- Compartment V: is made up of the crew, it is the one in which food, water and oxygen is transformed into faeces, urine and CO2, thereby closing the cycle.
In the figure the distribution of the five compartments can be seen in such a way that they allow the flow of the different material to operate in a loop, and it is clear that, given the materials referred to, this is a closed artificial ecosystem.
Project MELiSSA is being developed by an international conglomerate of universities, research centres and private companies, coordinated by the ESA. More specifically, the following organizations are participating in the project: the technological research institute VITO and the Nuclear Energy Studies Centre SCK/CEN (both in Mol, Belgium), the University of Ghent (in Ghent, Belgium) the Autonomous University of Barcelona (in Barcelona, Spain), Blaise Pascal University (in Clermont-Ferrand, France), the University of Guelph (in Guelph, Canada) and SHERPA Engineering (in Paris, France).
This project requires multidisciplinary knowledge, so within it experts in genomics, proteomics, modelling, microbiology, nutrition, process engineering, biotechnology, systems engineering, automation, etc.. are participating, both from an academic and industrial point of view.
The pilot plant made up of the five compartments on a pilot scale is being implemented and developed at the Autonomous University of Barcelona. All the progress made by the project in the different disciplines are integrated and reviewed in the pilot plant.
The technology developed in the MELiSSA project has also opened a new field of possible solutions in matters such as water management, reuse of waste and regenerating the atmosphere for applications that bear no relation with the space missions. Perhaps in the near future, when according to forecasts the petrol reserves on Earth have run out and global warming makes the world an increasingly inhospitable place, the technology developed by MELiSSA will help us survive. Then it will not be necessary to travel so far for its application to be useful.
