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

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1 June 2012
Ratnasingham Tharmarasa, Thiagalingam Kirubarajan, Nandakumaran Nadarajah, Yaakov Bar-Shalom, Thayananthan Thayaparan

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This paper considers the estimation of the Launch Points (LP) of ballistic targets from two or more passive satellite-borne sensors by fusing their angle-only measurements. 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 the backward prediction. The LP estimate and the corresponding error covariance are obtained by incorporating the above uncertainties. Simulation results illustrating the performance of the proposed approach are presented.