Coarse alignment of a shipborne strapdown inertial navigation system using star sensor

This study presents a novel estimation method for fast initial coarse alignment of a shipborne strapdown inertial navigation system. Unlike several current techniques, the alignment accuracy of the presented estimation method is not reduced by the shipborne disturbances causing by wave action (when moored) and the inertial measurement unit output constant error. The coarse alignment method is based on the acceleration sensed by accelerometers and the attitude matrix respect to the inertial frame sensed by star sensor. The specific force along the inertial frame is derived from the acceleration sensed by accelerometers, and the information characteristics of the specific force along the inertial frame are discussed. The analysed results show that the constant and periodical information is included in the transformation specific force along the inertial frame. Therefore Butterworth low-pass filter is used to extract the constant information to calculate the attitude of the vehicle. The effectiveness of this approach was demonstrates by simulation and experimental study. The results showed this coarse alignment method can estimate attitude information, and the attitude errors of the alignment result are small angles. Therefore the alignment accuracy meets the demands of fine alignment.