Orbit and attitude determination are studied as a single combined estimation problem, and the coupling between the orbit and attitude dynamics is included. The focus is on missions with large spacecraft in low-altitude Earth orbits. The orbit and attitude motions are coupled by the gravitational forces and torques and the aerodynamic forces and torques, which are the dominant environment effects for the class of missions under consideration. A computer simulation of the combined orbit and attitude determination problem, including the coupled orbit and attitude equations of motion, was implemented. Two combinations of measurement types are studied: ground tracking with onboard star observations, and onboard tracking of known landmarks combined with star observations. The effect of the dynamic orbit-attitude coupling on the position and attitude estimates was studied. It is shown that the inclusion of the dynamic coupling improves the position and attitude estimates substantially. Using covariance analysis techniques, it is demonstrated that the attitude uncertainties are unrealistically small without coupling, and that this lead to divergence in the attitude estimate. The use of process noise to prevent this divergence in the attitude estimate is studied. A process noise model which includes some of the coupling effects is also applied to the problem.


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