Abstract

The paper proposes two attitude motion determination algorithms based on an extended Kalman filter dealing with asynchronous measurements of the star tracker and angular velocity sensor. The satellite control system tracks a complex angular velocity profile during the Earth-point stabilization of the remote sensing camera axis. The star tracker measurement accuracy decreases with higher satellite angular velocity; when a certain angular velocity value threshold is exceeded, the star tracker measurements might be unavailable. These star tracker aspects, along with the variable bias of the angular velocity sensor, are addressed by the developed algorithms. The first algorithm uses kinematic relations; it estimates the attitude quaternion and the angular velocity sensor bias. It does not require information on satellite inertia parameters and on current control torque; it is characterized by low computational burden, though the angular velocity estimation accuracy is limited by the standard deviation of the sensor random noise. The second algorithm is based on both kinematic and dynamic motion equations: it estimates the attitude quaternion, angular velocity sensor bias, and angular velocity vector as well. The satellite tensor of inertia, reaction wheels’ parameters, and history of control inputs are required for the state vector estimation. The performance of these algorithms is compared under the scenario of Earth-point stabilization attitude motion, taking into account different levels of angular velocity measurement errors. It is obtained that the algorithm based on kinematic equations only is characterized by lower stabilization and estimation accuracies compared to the algorithm based on both kinematic and dynamic motion equations, though the latter is significantly more computationally complex. The influence of the state vector estimation errors on the Earth-point stabilization accuracy is studied. The paper contribution is an algorithm performance study considering star-tracker accuracy degradation with angular velocity during the Earth-point flyby.

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