Robust Trajectory and Attitude Control of a Flexible Launcher

This paper aims to find a robust attitude controller for a small launcher during the first stage burning, which takes 100 seconds, in the presence of variable dynamics and of scattering. The launcher is a variable mass system so, during the mission, its inertial characteristics, hence its frequencies and mode shapes, vary. Because of the great variation of the velocity in the examined part of the mission, also the dynamic pressure and the aerodynamic coefficients change. The thrust profile is not constant at all, since the actuator is the nozzle deflection, it is necessary to include this uncertainty in the control design. A set of controllers was necessary to control the launcher. In the pitch plane a controller and the following one coexist for one second and the command for the actuator is given by the sum of the two suitably weighed commands. In the yaw plane a controller and the following can not coexist without making the system unstable, so they are turned on and off instantaneously.