<h2>AAS 99-175</h2>
<h2>Determination and Modeling of Error Densities in Ephemeris Prediction                                                                            </h2>
<h4>J.P. Jones, M. Beckerman                                                                                                                                                            </h4>
Oak Ridge National Laboratory, TN                                                                                                                                         
<h2> Abstract </h2>
We determined the distributions of error in position predicted by a Special Perturbations orbit propagator for a population of 14 low-earth orbiting satellites. Errors in the along-track, radial and cross-track directions were extracted by aligning and combining 72-hour ephemerides calculated sequentially for periods of time spanning several months for each satellite. The along-track errors dominate, and together with the radial increase uniformly in time. The growth rate for the along-track errors is correlated with the decay rate of the semi-major axis and the growth rate for the radial errors is correlated with the eccentricity.