Profile-Free Launch Point Estimation for Ballistic Targets Using Passive Sensors

In this paper, the estimation of the Launch Points (LP) of ballistic targets using angle-only measurements from two or more passive satellite-borne sensors is considered. The targets are assumed to have a two stage boost phase with a free-flight phase between the two stages. Due to the passive nature of the sensors, there is no measurement during the free-flight motion. It is also assumed that measurements are available only after a few seconds from the launch time due to cloud cover. In the literature, profile-based methods have been proposed to estimate the target's launch point and trajectory. Profile-based methods normally result in large errors when there is a mismatch between actual and assumed profiles, which is the case in most scenarios. In this paper, a profile-free method is proposed to estimate the target states at the End-of-Burnout (EOB) and LP. Estimates at the EOB are obtained by using forward-filtering with adaptive model selection based on boost phase changes. The LP estimates are obtained using smoothing followed by backward prediction. Uncertainties in the motion model and the launch time must be incorporated in backward prediction. LP estimates and corresponding error covariance are obtained by incorporating the above uncertainties. Simulation results illustrating the performance of the proposed approach are also presented.