Autopilot Design for Velocity-varying Missile Based On Sliding Mode Control Scheme

Abstract

Solid propellant rockets are widely used for anti-air missiles, including anti-ballistic missile and anti-ship missile interceptors. The missiles undergo immediate acceleration during the boost phase after launch and experience deceleration due to the aerodynamic drag during the glide-phase after burnout. Expanding the time devoted to the mid-course guidance and the terminal homing guidance, wherein the missile is precisely guided by the guidance loop, can increase the target interception probability. Moreover, the need for guaranteed control performance during the entire flight envelope, including the boost-phase and the glide-phase, is necessary. Therefore, for efficient and effective target interception, missile autopilot exhibiting acceptable performance over the entire flight-envelope is required. The problem posed in terms of the autopilot design for the velocity-varying missile, however, is that the missile experiences rapid parameter variation, including the velocity and inertial characteristics. Additionally, cross-coupled dynamics and aerodynamics due to large attitude change or rapid maneuvering are experienced

therefore, integrated autopilot control design is required. When the missile is launched from a vertical launch system, the initial attitude control, which is used to make the missile fly toward a target by controlling the pitch and yaw attitude, is required. Consequently, an integrated attitude and acceleration controller is required to achieve the desired attitude during the initial boost phase and to track the given guidance command for the target interception. In this study, sliding-mode-based, nonlinear missile autopilots are designed for a velocity-varying missile. The purposes of the autopilots are initial attitude control and acceleration control for skid-to-turn missiles. To perform integrated attitude and acceleration control associated with the input channel cross-coupling effects, precise mathematical modeling of the missile is conducted. For the autopilot design, multiple sliding surfaces are simultaneously considered. The sliding mode attitude controllers are designed in the form of single-loop and two-loop architectures regarding the time-scale separation. Moreover, a virtual control input is employed to relax the requirements for the higher-order sliding mode controller. For the acceleration control, a baseline autopilot is designed considering the nominal missile dynamics and the aerodynamics. To address the uncertainties due to the parameter variations, such as external disturbances and imperfect modeling, an adaptive sliding mode autopilot is designed in addition to the baseline autopilot. Numerical simulation using a six-degrees-of-freedom, nonlinear missile model is performed to demonstrate the performance of the autopilots.