The European Space Agency's MELiSSA (Micro-Ecological Life Support System Alternative) is a multidisciplinary project which 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 regenerative life support system for long term manned space missions, e.g. a lunar base or a mission to Mars. The driving element of MELiSSA is the recovery of edible biomass from waste, carbon dioxide and minerals, using light as source of energy to promote biological photosynthesis. MELiSSA has five compartments colonised respectively by thermophilic anoxygenic bacteria, photoheterotrophic bacteria, nitrifying bacteria, photosynthetic bacteria and higher plants, and the crew.