Comparative analysis of architectures for the control loop of launch vehicles during atmospheric flight

Most of architectures used for the control loop of launch vehicles are based on attitude angle, attitude rate and lateral acceleration feedbacks. Related controllers are usually chosen to be stable. The main purpose of this paper is to give a comparison between a few architectures, pointing out the benefits of an unstable attitude angle feedback design for the control of an aerodynamically unstable launch vehicle. Such a design indeed is appropriate to reduce significantly the aerodynamic load during atmospheric flight. This is an issue of practical interest as it has become a design driver for mechanical sizing of modern launchers.The paper recalls the various goals the control loop is trying to reach all along the atmospheric flight (stability, set point tracking, aerodynamic load minimization …). For each phase of the flight, priorities are discussed. The paper then focuses on two critical phases of the atmospheric flight, i.e. high dynamic pressure period and atmospheric stages separation.