The dominant error source in force models used to predict low perigee satellite orbits is atmospheric drag, hence improvements in its estimation is vital for many applications such as orbital evolution. Errors in ballistic coefficient estimation cause significant errors in predicted satellite translational states which may lead to inaccurate orbit determination and prediction. This paper presents an improved method for estimating ballistic coefficients of low perigee objects from their historical two-line elements. The publicly available two-line element data provide orbital ephemeris with a limited accuracy, therefore deriving accurate ballistic coefficient requires robust estimation techniques. The method uses the drag perturbation equation of the semi-major axis of the orbit. The method is demonstrated using a small number of objects with external ballistic coefficient reference values, and generally produces agreement within 10% of the expected value. The motivation for this work originates from the study of space debris object characterisation.
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