Attitude determination methods using pseudolite signal phase measurements

In this paper, new attitude determination algorithms using pseudolite signal phase measurements are developed and presented with realistic simulations. Pseudolite signals are used to replace GPS signals which are often not available due to blocking by nearby large structures, for example, a crew return vehicle under the International Space Station. A new observation model needs to be applied because spherical wavefronts are present for pseudolite signals, which are much closer to the antennas than GPS signals. Both static and filtering methods are developed. An iterative algorithm using the Levenberg-Marquardt method and a nonlinear Predictive filter provide a deterministic solution; however, they are not suitable for moving cases. Instead, the nonlinear Predictive filter, the extended Kalman filter and the Unscented filter using angular velocity measurements as well as pseudolite signal phase measurements are developed. In the convergence comparison, the Unscented filter and the Predictive filter show more robust behavior than that of the extended Kalman filter.