A Quaternion Formulation for Boost Phase Attitude Estimation, Guidance and Control of Exoatmospheric Interceptors

This paper describes the boost phase guidance of the space interceptor system for exoatmospheric missile engagements. A space interceptor equipped with 2 booster motors is considered. The boost phase guidance is realized through the attitude control, which, in turn, controls the direction of the thrust vector of booster motors. A quaternion method devoid of trigonometric function computations is proposed for the attitude command generation. The quaternion attitude command is expressed as an error quaternion that represents the difference between the current attitude and the desired attitude determined by the guidance law. The error quaternion computation is then combined with existing quaternion algorithms for attitude determination and attitude control, resulting in a pure quaternion method for the boost phase guidance. The quaternion based guidance method is computationally efficient and free of singularities while the conventional methods based on Euler angles are not. An algorithm for the prediction of intercept point is also included for the sake of completeness. A 6-Degree-Of-Freedom simulation including an interceptor and a target is conducted to demonstrate that the quaternion based method is suitable for the boost phase guidance for exoatmospheric interceptors.