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Mathematical Problems in Engineering
Volume 2013, Article ID 530516, 8 pages
Research Article

Onboard and Real-Time Artificial Satellite Orbit Determination Using GPS

1Grupo de Dinâmica Orbital e Planetologia, FEG/UNESP, 12 516-410 Guaratinguetá, SP, Brazil
2Division of Space Mechanics and Control—INPE, Avenida dos Astronautas, 1758, 12 227-010 São José dos Campos, SP, Brazil

Received 21 September 2012; Accepted 9 January 2013

Academic Editor: Maria Zanardi

Copyright © 2013 Ana Paula Marins Chiaradia et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


An algorithm for real-time and onboard orbit determination applying the Extended Kalman Filter (EKF) method is developed. Aiming at a very simple and still fairly accurate orbit determination, an analysis is performed to ascertain an adequacy of modeling complexity versus accuracy. The minimum set of to-be-estimated states to reach the level of accuracy of tens of meters is found to have at least the position, velocity, and user clock offset components. The dynamical model is assessed through several tests, covering force model, numerical integration scheme and step size, and simplified variational equations. The measurement model includes only relevant effects to the order of meters. The EKF method is chosen to be the simplest real-time estimation algorithm with adequate tuning of its parameters. In the developed procedure, the obtained position and velocity errors along a day vary from 15 to 20 m and from 0.014 to 0.018 m/s, respectively, with standard deviation from 6 to 10 m and from 0.006 to 0.008 m/s, respectively, with the SA either on or off. The results, as well as analysis of the final adopted models used, are presented in this work.