Velocity Control of Solid Upper Stages Using Attitude Modulation

A closed-loop scheme for controlling the speed of solid rocket propelled spacecraft is described. Using a proportional plus integral control law, this scheme superimposes pitch-yaw attitude oscillations on the nominal guidance commands to control the spacecraft speed during the motor burn. Oscillation frequency is selected based on the permissible lateral acceleration magnitude. Feasibility of this approach is demonstrated using a nonlinear point-mass simulation of a typical spacecraft performing an orbit transfer mission. Acceptable accuracies are found to be achievable even with the use of a simple control logic.