Research on Thermospheric Densities Derived from Two-line Element Sets

Two-line Orbital Element Sets (TLEs) consist of mean orbital elements at epoch, along with the NORAD (North American Aerospace Defence Command) catalog number, international designator, epoch and additional fitting parameters. These information can be used to derive thermospheric densities through integration of differential equation for mean motion. For near-circular orbit satellites, derived thermospheric density can be seen as real density because of their stable orbit height, while for elliptical orbit satellites, thermospheric density at perigee and apogee can be different as much as several orders. So different methods were applied to derive thermospheric density according to different satellite orbits. This paper chooses CHAMP and Explorer 8 satellites, whose orbits are respectively near-circular and elliptical, as our research cases. The inverse ballistic coefficient B (B-factor) was firstly derived based on TLEs data, then thermospheric densities were derived with different methods according to different orbit characters. Finally, a comparison was made among TLEs-derived density, NRLMSISE-00 model density and observed (or reference) density. The result shows that the average error of TLEs-derived density and empirical model density with respect to observed value for CHAMP is 7.94% and 13.94% respectively, and the average error with respect to reference value for Explorer 8 is 9.04% and 14.32% respectively. This result indicates that TLEs-derived density is closer to the real density than empirical model density, and this method provides an effective way to obtain extensive and reliable atmosphere density data.