The Role of Nutrient Solution Volume and Buffering Capacity in Hydroponic Bioregenerative Life Support System Design and Operation

Total fluid volume in a hydroponic bioregenerative life support system for in space use is a critical design parameter because it drives system mass and the design of control systems. Total fluid volume, thermal effects, nutrient solution buffering capacity, and pH setpoint have been examined theoretically and experimentally in a Bioregenerative Life Support Test Bed (BLSTB). Aqueous solution pH control loop responses were characterized for simulated loads from growing lettuce plants, and tuning parameters developed for minimal overshoot and offset. Results are discussed that indicate these parameters play a significant role in designing sensor and control systems to maintain stable characteristics in minimized nutrient solution volumes.