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, h erbivore and carnivore). Simple one limiting nutrient reactor equations pro vide a starting point for the analysis. Optimum surface illumination intens ity for a given reactor depth and population density has been calculated. L inking reactors in a cascade enables decoupling of equations, easier analys is, control and optimisation. Greater stability is thereby also achieved. M aximum sustainable yield for a given nutrient input is found in a general c ascade. Needed nutrient input for desired output from each reactor has been calculated as well. In contrast to a single reactor food chain, we found l inear dependence of the highest trophic level in each reactor on the nutrie nt input. Model provides a theoretical basis for acquiring desired yield fr om 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. (C) 2001 Elsevier Science B.V. All rights reserved.