Performance Analysis And Autopilot Design For A Missile With Blended Lateral Thrust And Aerodynamic Force

With the development of ballistic missile technology, the warheads of ballistic missiles may execute some highly spiral maneuvers to increase their survivability as they reenter the earth’s atmosphere. Therefore a “hit-to-kill” interception becomes the requirement of the new generation of air-defense missiles. One kind of interceptor missile to satisfy the requirement is attitude-controlled agile missile, which is steered by aerodynamic force from tail fins and lateral thrust from pulse thrusters which are located ahead of the center-of-gravity of the missile. The aerodynamic force is continuous and the lateral thrust is pulse-type. It brings some challenges to the autopilot design and stability analysis when the two control inputs work simultaneously. This dissertation take the blended controlled missile missile as the research subject to study the blended control of the lateral thrust and aero-dynamic force. The main study include the analysis of the characteristic parameters of the blended controlled missile and autopilot design for the missile.First of all, the linear and nonlinear control models of a blended controlled missile is deduced. Then the unstable zero dynamics of the nonlinear control system and nonminimum phase zeroes of the linear control system are chosen as the characteristic parameters. The characteristic parameters are applied to analysis the tracking performance of control system and to guide the design of sampled-data controller. The zero dynamics of the traditional tail-controlled missile is unstable, while the zero dynamics of the blended controlled missile is bounded stable. According to the theories of tracking performance limitation, the tracking performance of the aerodynamic control system has a limit while that of the blended control system has none. Therefore, if the requirement of tracking performance exceed the performance limitation of the aerodynamic control system, the blended control must be applied. Take the pulse feature of the pulse thruster into account, if the aerodynamic control law are designed suitably in the sampled-data control, then there exists only one nonminimum phase zero which is far away from the imaginary axis in the complex plane in the controlled object of lateral thrust control. The tracking performance limitation of the blended control system is smaller than that of the aerodynamic control system and can achieve better tracking performance. If the aerodynamic control law are designed unsuitably, there will be some other nonminimum phase zeroes in the controlled object of the lateral thrust control. The extra zeroes will bring bad influence to the blended control. Since the autopilot design depend deeply on the mathematic model of the pulse thruster in the sampled-data control, if the model changes the design process must be changed. Thus, the nonlinear optimal control using two-step design method is proposed for the blended controlled missile. Firstly, the lateral thrust and aerodynamic force are both considered as continuous variables, and a continuous controller is designed based on the nonlinear control model of the missile. Take the dynamics of pulse thrusters and tail fins into account, the actual inputs from actuators are treated as the perturbation feedback of the computed inputs from controller. Then some sufficient conditions are deduced to guarantee the asymptotic stability of the closed-loop system. If the sufficient conditions are satisfied, the closed-loop system is stable. The method is independent of the models of the pulse thruster, and the autopilot design use nonlinear control model, thus its application range is larger than the linear control design. State-dependent Riccati equation (SDRE) approach and θ D(Theta-D) method are applied to design the continuous controller, and two sufficient conditions are deduced to guarantee the asymptotic stability of the closed-loop system. The effectiveness of the proposed method and the independence of the models of pulse thruster are verified by the simulation. The simulation also showed that the performance of the Theta-D control is better than that of the SDRE control.Based on the two-step design method, indirect robust control method is proposed for the blended controlled missile. The errors between the actual inputs and the computed inputs are treated as input uncertainty of the system, then the original acceleration tracking problem with the actual inputs is translated into a virtual robust control problem with the input uncertainties. It can be proved that the robust control problem is equivalent to a nonlinear quadratic optimal control problem, whose performance index was modified with input uncertainty bound. If the solution to the optimal control problem exists, then it is also a solution to the robust control problem, and in the final it is the solution to the origin acceleration tracking problem. The IR-SDRE method and IR-Theta-D approach are used to solve the nonlinear quadratic optimal control problem. Simulation results show that to track the acceleration command quickly enough, the fin deflections in the IR-SDRE control always reach their limits temporarily, while the tail fins in the IR-Theta-D control can avoid the saturations. Thus, the IR-Theta-D control is better than the IR-SDRE control. The numerical results demonstrate that both the Theta-D control and IR-Theta-D control exhibit robustness when the influence of jet interaction is considered.Finally, to test the effectiveness of the proposed methods, we integrate with the motion models of interceptor missile and target, guidance law and control law to simulate the interception processes against a spiral maneuvering ballistic missile. The sampled-data control, Theta-D control and IR-Theta-D control are used in the simulation and their effectiveness are verified by detailed simulation results. The distribution statistics of the miss distance and the consumption of pulse thrusters are obtained by Monte-Carlo simulation. The statistics show that the Theta-D control and IR-Theta-D control are more sensitive to the change of the maneuver amplitude of the target than the sampled-data control, average miss distance becomes larger along with the larger maneuver amplitude, while the average consumption of pulse thrusters nearly unchanged. For the regular maneuver-ing target, the interception performance of the IR-Theta-D control is best: the probability of the3m-miss distance is92%and the average consumption of pulse thrusters is less than80.