Integrated Guidance And Control For Endo-Atmospheric Interceptors

In traditional flight control systems, the outer-loop relative position dynamics is assumed to be slow mode, while the inner-loop missile rotational dynamics is assumed to be fast mode. Thus, the separation principle is utilized to split missile dynamics into guidance and autopilot subsystems. However, in the terminal homing phase of highly maneuvering tactical ballistic missile (TBM) defense scenario, the relative position changes fast as well as the missile attitude. Therefore, the separation principle might not be valid, and this can cause instability and unacceptable miss distance. Therefore, to improve the homing performance and to guarantee an perfect interception of TBM, the present research addresses the endoatmospheric interceptor flight control problem by casting it as an integrated guidance and control (IGC) problem.Through taking complete dynamics into account, the IGC formulation can automatically account for the coupling between guidance and autopilot subsystems, and then enhance the homing performance. Through using all the available measure-ments, the IGC can also deal with missile-dynamic performance constraints. Therefore, the interceptor maneuverability saturation can be anticipated and precompensated.Motivated by the requirement of TBM interception, the IGC design has been widely investigated in last decade. Firstly, the guidance and control system of an endoatmospheric interceptor steered by aerodynamic tails and reaction jets is designed separately in this paper. And then the IGC design is investigated.Firstly, the kinematics and dynamics models between the interceptor missile and TBM are outlined with linear and nonlinear assumptions. Then the conventional guidance and control methods and the connections between them are overviewed. Then, the simplified dual control system model is applied to describe the game model of an interceptor launched against a re-entry TBM with high maneuverability. Through the well-known zero-effort miss (ZEM), the vector problem can be reduced to a scalar problem, and by taking the missile maneuverability into account we can get a bounded differential game guidance law. The guidance law can utilize the maneuverability of the interceptor effectively. Therefore, there is a significant improvement in homing accuracy. Otherwise, for a low-altitude endoatmospheric interceptor, the propellant of reaction-jet control system (RCS) is restricted. Increasing RCS thrust decreases operation time, but also increases the acceleration contribution. Game space structures are used to investigate the effect of RCS thrust on homing performance. Moreover, the appropriate timing to initiate the RCS is also investigated through the game space structure.Control allocation methods are useful for control of overactuated systems, and it can separate the actuator selection task from the regulation task. Hence, the sliding mode control with optimally selected sliding surface is employed to specify the virtual moment. Consequently, the system will be robust to model uncertainty and parameter disturbance created by jet interactions, and obtain a desired system response. Then, the virtual control is distributed among the actuators with the dynamic control allocation, through which the required pitching moment will be distributed to the tails through a low-pass filter and to the RCS through a high-pass filter. This is motivated by the desire to get a fast initial response, produce by the RCS, while the tails are known to produce more pitching moment, and are therefore used to generate the required moment at steady state. For the RCS thrust with on-off type, the PWPF modulator is employed to turn the continuous commands into discrete pulse.Based on above researches, the IGC is investigated with ZEM and virtual moment. Defined the ZEM as a single sliding surface, the sliding mode control is used to design the virtual moment. And the control allocator is then utilized to distribute the virtual moment among the actuators. Due to including complete dynamics of the missile, a high-accuracy interception can be guaranteed in engagements against highly maneuvering TBM compared to conventional separated design. Since the ZEM-based IGC design cannot improve the miss dynamic response, two improved approaches are proposed. In the first way, another component based on autopilot design is introduced to make up the single sliding surface with the ZEM. It can make the acceleration profile much smoother, but the dynamic response is not improved basically. Therefore, another IGC design based on inner loop stability is presented. Before the missile dynamics model is taken into IGC design, the linear quadratic regulation is applied to improved the dynamic response. Consequently, the IGC can guarantee high homing performance and airframe stability simultaneously. Meanwhile, a novel control allocation logic is proposed, in which the working state of the reaction jets is decided by the value of the zero-effort miss, and to restrain the system to a collision course. Simultaneously, the tails are mainly used as a compensator, and to generate the required moment.Finally, an estimator is designed, using sliding mode observer/differentiator, to supply the target's information. It can follow the target's acceleration steadily and quickly. And then the Monte Carlo simulation is used to investigate the effect of measurement noise on homing performance. It is shown that there is a significant improvement in homing performance compared to conventional separated design. When the single-shot kill probability (SSKP) is equal to 95%, the miss distance is smaller than 1m, and an effective interception can be guaranteed.