State and Disturbance Estimation using Higher Order Sliding Modes for Seeker System

A seeker system is the target detection mechanism of a missile. It consists of a two axis gimbal system with an optical sensing device as pay load. The estimation approach is required for the angular position and displacement rates of the seeker pitch and yaw gimbals. The performance of seeker is affected by cross coupling between the two gimbals and the external disturbance. This paper presents estimation of the lumped disturbance term in each channel using higher order sliding modes (HOSM). The lumped disturbance is considered as additional state to formulate extended state system. HOSM Estimator is designed for the extended state system. The effectiveness of the method is validated in simulations. The advantage of HOSM observer over Sliding Mode Observer (SMO) with respect to instability for increased initial conditions is validated in simulation.