Toward a closed life support system for interplanetary missions

A theoretical model of a life support system, composed of a cascade of well-mixed continuous culture reactors, is investigated (e.g. photoautotroph, herbivore and carnivore). Simple one limiting nutrient reactor equations provide a starting point for the analysis. Optimum surface illumination intensity for a given reactor depth and population density has been calculated. Linking reactors in a cascade enables decoupling of equations, easier analysis, control and optimisation. Greater stability is thereby also achieved. Maximum sustainable yield for a given nutrient input is found in a general cascade. Needed nutrient input for desired output from each reactor has been calculated as well. In contrast to a single reactor food chain, we found linear dependence of the highest trophic level in each reactor on the nutrient input. Model provides a theoretical basis for acquiring desired yield from each reactor, thus enabling formation of balanced diet for users (e.g. a spaceship crew). Nutrient cycling is achieved with bacterial degradation. A buffer, which acts as a low pass filter, is inserted in a cycle.