Multiple on-off solenoid valve control for a launch vehicle propellant tank pressurization system

摘要

Pressure control inside the propellant tanks of a pump-fed space launch vehicle is almost always a flight-critical task. ^Pressures are commonly controlled by admitting He from high pressure reservoirs into the propellant tank free volumes, or ullages. ^Controlled pressures must often satisfy the competing needs of engine net positive suction head, flight dynamic pressures, tank structural stability, and tank Maximum Expected Operating Pressure. ^A new control scheme using on-off solenoid valves to approximate the performance of a proportional flow control valve has been synthesized for both stages of a space launch vehicle. ^This control system uses the same valves required by a competing limit cycle system but significantly improves system robustness in the face of system uncertainties, including initial engine outflow rates, ullage volumes, and helium-to-propellant heat transfer rates. ^Simulations indicate ullage pressures can be maintained within a 5 psi band at all times, despite the slow 25 Hz data communication rate assumed for this vehicle. ^Further, the control logic provides a simple way to incorporate additional feedback signals such as engine pressure into the control loop to further improve tracking accuracy. ^(Author)