Orbit Determination with GNSS

This chapter addresses the fundamentals of global navigation satellite system-based orbit determination, highlighting the unique aspects of the technique relative to conventional terrestrial positioning. The unique challenge in satellite orbit determination is not the formulation or the solution of the estimation problem but, rather, the validation of the solution. Much of the special technology and expertise in precise orbit determination revolves around techniques and approaches for assessing solution accuracy. The inversion of the orbit determination problem to estimate the epoch state and model parameters can be accomplished with a variety of techniques, from classical least squares to various flavors of Kalman filtering or other statistical techniques. Regardless of the employed estimation technique, the first step is always the linearization of the problem around an initial approximation of the solution, consisting of a trajectory and a corresponding set of model parameters.