Line-of-sight rate estimation and linearizing control of an imaging seeker in a tactical missile guided by proportional navigation

Acceleration commands in missiles guided by proportional navigation require the measurement of line-of-sight (LOS) rate. It is often obtained by filtering the output of a 2-DOF rate gyro mounted on the inner gimbal of the seeker. This paper describes the modeling of an imaging seeker and the formulation of an extended Kalman filter (EKF) for the estimation of LOS rate from measurements of relative angular displacement between seeker gimbals and a low-cost strapdown inertial unit. The approach aims at circumventing the need for the rate gyro on the seeker. A linearizing feedback control law for decoupling missile motion from that of the seeker is proposed based on the filter model and its estimates. Additionally, the control law uses visual information from the image sequence for target tracking. Seeker dynamics and control are then integrated into a dynamic model of a cruciform missile equipped with canards and rollerons and guided by proportional navigation in 3D interception tasks. Monte Carlo simulation is employed to evaluate the overall system accuracy subject to different initial conditions and the impact of rolling motion during high-g maneuvers on miss distance. Initial engagement geometry and roll-rate damping at high incidence angles have significant effect.