Air-to-air missile guidance for strapdown seekers

This paper presents results of a study on advanced guidance for short range air-to-air BTT missiles using an active strapdown seeker. The guidance laws, based on modern control theory, utilize an Extended Kalman Filter (EKF) and a Pursuit plus Proportional Navigation type law for autopilot command generation. The nine state EKF estimates relative position, relative velocity and seeker scale factor errors. Low frequency glint is studied in detail and both software and hard-ware solutions to reducing the effect of glint noise are proposed. Other topics considered are: (i) the effect of different coordinate systems on EKF performance, and (ii) robustness of the guidance law with and without the target acceleration term. Detailed sensitivity and performance analyses are performed with respect to all the sources of errors (gyro, accelerometer, seeker, initial conditions, filter parameters) against constant g and ´smart targets. The results show that a modern control theory approach using EKF for on line estimation of scale factor errors is essential for satisfactory guidance loop performance using strapdown seekers.