Abstract
In this paper, a mathematical pressure dynamics model for a variable thrust solid propulsion system with an electric actuator was derived from the mass conservation of gas. To solve the problem induced by modeling uncertainties in the propellant model and the dead zone of the actuator, a nonlinear pressure controller combined with a nonlinear disturbance observer was designed using a mathematical model of the system. The simulation results showed that the proposed pressure controller could reduce tracking errors compared to another conventional nonlinear controller even in situations where input disturbances were present.