Drag Perturbations of Near-Circular Orbits in an Oblate Diurnal Atmosphere

Abstract

An improved theory is developed specifically for orbits of very small eccentricity (e = 0 to 0.01). Analytic expressions are derived which describe perturbation rates in orbit period, eccentricity, and perigee argument. The equations include the combined effects of earth flattening, oblate earth mass, and the diurnal bulge. Singularities and ambiguities encountered with existing theory are removed by employing mean orbital elements. Comparisons of analytical averaging with numerical integration methods demonstrate intrinsic perturbation accuracies to within 2%, with an accomplished improvement of two orders of magnitude in computation time.