Computing Bounds of Estimator Time-lag for Homing PN Guidance Loop Considering Autopilot and Airframe Dynamics

Stability analysis of a realistic linearized PN homing loop has been presented in this paper with an objective to compute the allowable time constant of the guidance estimator. Bounds of estimator time constant over the flight time have been computed for a PN guidance loop comprising of a first order seeker, third order autopilot and airframe. Incorporating a third-order autopilot and airframe, the current paper yields a more practical bound of allowable bandwidth of a first-order LOS rate estimator for successful intercept of a ballistic target. It has been established that the state dependent Lipschitz nonlinearity of the nominal plant in the loop is bounded for estimator time constant within the computed stability bounds. Finally it has been shown by numerical simulation that beyond the specified bound of the estimator time constant the deviation of the homing trajectory from that obtained using ideal kinematic feedback exhibits divergence.