1. A method for providing an extended propagation ephemeris model for a satellite in Earth orbit comprising: obtaining within a ground station data associated with a satellite's orbital position over a first period of time; calculating within the ground station, from the data, coefficients defining osculating Keplarian orbital elements and harmonic perturbation parameters associated with a coordinate system defining an extended propagation ephemeris model that can be used to estimate the satellite's position during the first period; applying a Fourier transform to data derived from the calculated coefficients to determine dominant frequencies of the harmonic perturbation parameters; weighting the extended propagation ephemeris model according to a weighing function so that the extended propagation ephemeris model generates a highest level of accuracy at a beginning of the first period; and providing the weighted extended propagation ephemeris to a receiver.