Exo-Atmospheric JR Tracking of Ballistic Objects

Infra red seekers are now considered viable alternative to MMW seekers for exo-atmospheric tactical Ballistic Missile (TBM) interceptors. Only gimbal angle and inertial sightline rate signals are available from such seekers. Both of these are corrupted with random noise and residual body motion signals. The inertial or earth reference based bearing angle signal may be obtained from the INS and the seeker gimbal angle. The initial relative co ordinates and velocities may be obtained from the INS and the ground radar. In the penultimate phase of the interception, the interceptor trajectory may be approximated by a straight line making a shallow angle with the near straight line TBM trajectory. The intercepting platform (seeker) moves towards the ballistic object, though the velocities are several magnitudes higher and inertial sightline rate as well as bearing angle are available as measurement. Two cases have been studied. In the first case, only the gimbal angle information is used and three estimation techniques are compared namely Extended Kalman filter (EKF), Unscented Kalman Filter (UKF) and pseudomea surement filter. It is shown that EKF and UKF fail to track in a considerable number of cases but the pseudomeasurement filter has a performance close to the theoretical optimum described by the Cramer Rao bound. In the second case, the raw noisy sight line rate available from the seeker is considered as a second measurement. It is shown that the tracking performance improves substantially.