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Abstract: Autonomous and magnetometer-based orbit determination algorithm in target pointing satellite based solely on magnetometer measurements for speeding up filter convergence is proposed. The cosine angle between geomagnetic field vector and target direction vector, as viewed from the satellite, provides some quantity that is sensitive to satellite position, more regular and periodical than the magnetic field magnitude as a satellite moves around its orbit, and easily observable from magnetometers. An algorithm is formulated by applying the unscented Kalman filter (UKF) based on the laws of orbital mechanics, the measurement models of geomagnetic field magnitude and the cosine angle. The algorithm is tested and verified by using real-flight data obtained from Korea Multi-Purpose Satellite-1 (KOMPSAT-1) and Magnetic Field Satellite (MAGSAT). The results obtained from numerical simulations using KOMPSAT-1 and MAGSAT data illustrate the significant convergence speed up and the robustness against both noise and bias of magnetic measurements. The proposed orbit determination is adequate as a primary routine for a target pointing satellite mission that requires fast convergence. Otherwise, it is sufficient as a secondary routine to provide redundancy. [Copyright &y& Elsevier]