Adaptive attitude control of launch vehicles in atmospheric flight

The inclusion of an adaptive augmenting control (AAC) component in the flight control system (FCS) of launch vehicles can be highly effective for enhancing control stability and robustness with respect to parametric uncertainties and dealing with off-nominal conditions, so as to extend the envelope of failures and flight anomalies that can be managed by the vehicle control system. In this paper the adoption of an adaptive notch filter in a control architecture consisting of proportional-derivative (PD) elements, bending filters and AAC is proposed and discussed. The main goal of the study is to investigate the feasibility of implementation and the possible benefits of filter adaptation, such as overcoming critical limitations that degrades the AAC effectiveness for large uncertainties on elastic mode characteristics. To this end, the frequency of first bending mode is estimated during the flight in order to adapt the design parameters of the notch filter. Adaptive control performance is evaluated by simulation of vehicle motion in the atmospheric flight phase in selected stressing cases. Results of Monte Carlo simulations are also discussed for a broader assessment of the effects of adaptive filter on the robustness of integrated FCS.