Evaluation of recent atmospheric density models

Abstract

Precision radar tracking data taken in 1985 on two spherical satellites has been used to evaluate atmospheric density models: Jacchia 1971 [CIRA 1972], Jacchia 1977, and MSIS 1983, using Cook's definition of Cd /2/. The satellites have perigee heights of 270 km and 780 km. For each day, using numerical integration, an independent trajectory was computed, including a drag scale factor (S). The difference of S from unity represents the error in the atmospheric model used to compute the drag. At 270 km the three models performed equally well, as S was consistently close to unity. This was true for all hour angles and latitudes. At 780 km the scale factors ranged from 0.1 to 1.8 for all models. However, for the Jacchia 1977 model, the average scale factor was 0.943, and represents the best model at that altitude. Computer timing was also done. For orbit computation, drag models need further improvement, and the Jacchia 1977 model seems the best available today in terms of accuracy and computational efficiency.