Autonomous positioning utilizing star sensor and inclinometer

An autonomous positioning method independent of satellites is introduced in this study. When the location of vehicles cannot be covered by navigation satellites or the signals of navigation satellites are denied or under disturbance, the presented method can offer accurate position information for the vehicles. The designed system contains two parts: a star sensor that determines the attitude of the vehicle through starlight imaging, and a dual-axis inclinometer that measures the tilt angle between the vehicle and the horizontal plane. In addition, a precision clock is needed to provide current time and synchronize the data from the star sensor and the inclinometer. Base on principle of star sensor and inclinometer, the measurement model of the system is established and error analysis is carried out. It is noticed that the systematic error caused by the misalignment of the star sensor and the inclinometer influences the positioning accuracy significantly. In order to eliminate this systematic error, a calibration method based on QUEST (QUaternion ESTimator) is proposed to obtain the misalignment matrix and refine measurement model. The night sky experiments prove the proposed calibration method is effective, and the autonomous positioning system can achieve accuracy of 20-70 m in distance by continuous measurement in several minutes.