A method for propagating ephemeris data for a satellite in Earth orbit is
provided. The method includes the steps of receiving orbital positional
data for a first time period of a satellite's Earth orbit, propagating
orbital positional data for the satellite's Earth orbit during a second
time period extending beyond the first time period, fitting a Keplerian
ephemeris model to the propagated orbital positional data to estimate
model coefficients, and sending the estimated model coefficients to
receivers for determination of receiver position at a time during the
second time period.