Adaptive control for lateral motion of reusable launch vehicle using retrospective cost estimator

An in-flight aerodynamic coefficient estimation method is proposed for nonlinear lateral motion of reusable launch vehicle via retrospective cost adaptive control theory. The estimated aerodynamic coefficient is then utilized for adaptive controller switch to cope with unexpected polarity change of LCDP(Lateral Control Departure Parameter) online. First, the nonlinear lateral dynamics of a reusable launch vehicle rewritten to a form where the lateral moments are expressed linearly by aerodynamic coefficients related to LCDP. Then, the identification problem is converted to an adaptive control problem for a virtual system to track the angular velocity of the vehicle. The adaptive control problem is then solved by utilizing retrospective cost adaptive control algorithm. The estimation error dynamics is analyzed and an update law is proposed. Simulation on attitude three degree-of-freedom nonlinear model along a standard trajectory shows the performance of the proposed estimator to capture time-varying LCDP with multiple zero crossing in flight and the performance of the adaptive switch controller to yield converging lateral motion.