The airtight multi-compartment MELiSSA Pilot Plant at the Autonomous University of Barcelona is attempting to recreate a streamlined version of aquatic terrestrial ecosystems – but that adds up to a formidable engineering challenge, requiring the detailed modelling and control of key processes, and the prevention of any contamination or degradation. The 11-nation ESA-led Micro-Ecological Life Support System Alternative programme (MELiSSA) seeks to perfect a self-sustaining life support system that could in future be flown in space, supplying astronauts with all the oxygen, water and food they require.