Abstract: In order to meet the requirements of research which use two line element (TLE) as data source, ballistic coefficient estimation methods based on the variation in mean semimajor axis derived from TLE were studied. A direct estimation method based on two TLEs was introduced, and the influence of the TLE interval on the ballistic coefficient result accuracy was analyzed. In order to reduce the influence of outliers, an iterative estimation method based on multiple TLEs was proposed. Comparative analysis was made for these two methods. The results show that these two methods have their own advantages and disadvantages. The ballistic coefficient results estimated by the iterative method have higher stability and are less affected by the TLE accuracy. Due to the shorter data interval, the estimation results using the direct method respond more accurately to the short-term orbital variation characteristics, and this method is recommended to be used in the last phase of re-entry.

Key words: ballistic coefficient, two line element, LEO, re-entry prediction, orbit decay