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. The European Space Agency has therefore been investigating the design of highly compartmentalized man-made model ecosystems together with associated mathematical modelling and control functions.This paper discusses, from the particular point of view of the control system the advantages of compartmentalized artificial ecosystems. Control requirements are formulated and an attempt is made to translate these requirements into a preliminary design concept for MELISSA (Micro-Ecological Life Support System Alternative).