General perturbations method for orbit lifetime analysis incorporating non-spherically-symmetrical atmospheres

A general perturbations method for orbit lifetime analysis is extended to include an analytical non-spherically-symmetrical atmospheric density model. This improvement allows the method to be applied with confidence to highly inclined orbits and special cases such as sun-synchronous orbits where the inclusion of the effects of atmospheric oblateness and the diurnal bulge will be particularly significant. These improvements can be applied to any general perturbations model for lifetime analysis. Using a case study of a sun-synchronous satellite a comparison is drawn between the original and improved methods, showing that by capturing the effects of a non-spherically-symmetrical atmosphere the orbit lifetime predicted could be up to 7% longer or 10% shorter than when using the spherically-symmetrical model. Also notable is the difference between the orbit lifetime predictions made using the spherically-symmetrical model derived from different data sets; for the case study this was approximately a third of the orbit lifetime.