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A computer-controlled bioreactor system was developed to study various aspects of microbially-mediated nitrogen cycling. The system is used to investigate methods for controlling microbial denitrification (the dissimilatory reduction of nitrate to nitrous oxide and dinitrogen) in hydroponic plant growth chambers. Such chambers are key elements of advanced life support systems being designed for use on long duration space missions, but nitrogen use efficiency in them is significantly reduced by denitrification. Control software architecture was designed which permits the heterogeneous control of system hardware using traditional feedback control, and quantitative and qualitative models of various system features. Model based control entails prediction of future system states and automated regulation of system parameters to achieve desired, and avoid undesirable, system states.

A part of the CELSS Test Facility design effort is the Engineering Development Unit (EDU), a closed crop growth system. The crop growth chamber and system hardware are contained in an enclosure that isolates them from the laboratory environment. The control system includes active differential pressure control. This paper describes a linear optimal quadratic performance index design technique that was used to synthesize a state feedback controller. Performance results of the closed loop linear system as predicted by simulation is presented.

This paper presents details of the mathematical modeling and simulation of the shoot side subsystem of a closed crop growth chamber. A discussion of the derivation of the mathematical model and the development of the simulation is presented, including a computer simulation with temperature control. The objective is to design a temperature and pressure control system.