Browsing by Author "Opperman, B. D. L."
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- ItemPrecision propagation and orbit decay predication of low earth orbit satellites(Stellenbosch : Stellenbosch University, 2003-12) Opperman, B. D. L.; Milne, G. W.; Bredenkamp, B. V.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.ENGLISH ABSTRACT: This study investigates the theory of precision satellite orbit propagation and satellite lifetime prediction and lead to the development of two necessary software tools for analysis in these fields. Precision propagation was achieved through the implementation of Cowell's method of special perturbations, considering perturbations due to a 70x70 asymmetrical gravity field, atmospheric drag, Luni-Solar attraction and Solar radiation pressure. The satellite's perturbed equations of motion were integrated utilizing a seveneighth order Runge-Kutta-Fehlberg numerical integration procedure, limiting error propagation by employing adaptive step size control. The MSlS-90 atmospheric density model, providing for diurnal and semi-annual variations, was employed to determine atmospheric density. Care was taken in the precision modelling of the motion of the 12000 equator and equinox. Propagation results for this test case proved to be superior to the SGP4 propagator and a commercial package. The long-term effects of Earth oblateness and atmospheric drag on a satellite's orbital elements were investigated and applied to the orbit decay prediction problem. Orbit decay was predicted by integrating the rates of change of the orbital elements due to Earth oblateness and atmospheric drag. A semi-analytical technique involving Runge-Kutta and Gauss-Legendre quadrature was employed in the solution process. Relevant software was developed to implement the decay theory. Optimum drag coefficients, estimated from drag analysis using precision propagation, were used in decay prediction. Two test cases of observed decayed satellites were used to evaluate the theory. Results for both test cases indicated that the theory fitted observational data well within acceptable limits.