Construction of closed integrative system for gases robust stabilization employing microalgae peculiarity and computer experiment

Bioregenerative life support system (BLSS) is an artificial ecosystem providing life support for crewmen on space or ground mission in terms of biological unit components. It is critically important to maintain gases (O2 and CO2) concentrations in the system to robustly stabilize at nominal levels, nevertheless BLSS is a complex system, its control law could not be sufficiently and profoundly investigated merely by traditional approaches, i.e., prototype experiment and open-loop control. In our research, a closed integrative system (CIS) composed of lettuce, silkworm and microalgae was constructed as a specific prototype of BLSS, studying the gases dynamics in system and their closed-loop regulation and control adopting microalgae as a bioregenerative tool in combination with computer simulation. Firstly, a precise kinetic model of CIS was developed for fully describing the dynamic characteristics of gases concentrations by means of system dynamics and artificial neural network based on relevant ecological mechanisms and experimental data. Secondly, a closed-loop CIS with Linear-Quadratic Gaussian (LQG) servo controller was established depended on microalgae peculiarity, such as high growth rate, metabolism flexibility, controllability, and so on. Thirdly, the closed-loop CIS was optimized via predetermined gases dynamic responses to control inputs and digital simulation. Finally, the effectiveness of the closed-loop CIS was fully tested and accredited by real-time simulation. The result showed that the closed-loop CIS could effectively regulate the light intensity and aerating rate to stimulate or inhibit the growth of microalgae based on real-time measurements of gases concentrations, and indirectly control them to come back to their nominal levels with desired dynamic response performances after deviation from originally equilibrium points. Therefore, the closed-loop control of microalgae might greatly enhance the safety and reliability of BLSS operation.