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Accuracy in Orbital Propagation: A Comparison of Predictive Software Models

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Technical Report

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Naval Postgraduate School Monterey United States

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Current analytical satellite vulnerability planning in the U.S. Space Surveillance System is reliant on two orbital propagators, PPT3 and SGP4, both of which have a foundation in similar theory. Since their first operational use, both propagators have incorporated updated theory and mathematical techniques to model additional forces in the space environment, causing their calculation methods to diverge over time. The aggregate effects of these diverging mathematical techniques cause calculation differences for perturbations of an orbit over time, resulting in differences in future predicted positions from PPT3 and SGP4, as well as differences in their accuracy. The atmospheric model within each propagator is determined to be the most effective component of each propagator to test, as the theoretical atmospheric drag calculation methods of PPT3 and SGP4 differ greatly. PPT3 and SGP4 both perform well within the expected accuracy limits inherent with analytical models, with neither propagator demonstrating an accuracy rate decay that was significantly better or worse than the other. Compared to ground truth observations, both propagators demonstrate decreased accuracy for satellites under greater effects from atmospheric drag, i.e., satellites that are closer to the Earth. Satellite vulnerability planning with these propagators should therefore utilize the most current TLE data available to avoid accuracy errors.

Subject Categories:

  • Celestial Mechanics

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