This paper provides the development of a simplified covariance model for predicting the along-track error uncertainty and error uncertainty growth rate for the single-pass, angles-only orbit update, the validation of the model using simulation and real data cases, and a summary of efforts made to characterize the uncertainty of general-perturbations-based element sets. The analysis shows that one of the limiting factors in obtaining a high-accuracy orbit update from a single pass of angles-only data is the eccentricity uncertainty. For the observation characteristics considered, a high-accuracy orbit update could not be obtained if the initial eccentricity uncertainty is 10 -5 or greater. Analysis of general perturbation element set uncertainties showed that typically the eccentricity uncertainty is no smaller than 10∼5, so the eccentricity uncertainty is a limiting factor in obtaining an accurate orbit update with a single pass of angles-only data with general perturbations element sets.