In-flight alignment of laser strapdown systems

This paper describes an in-flight alignment technique developed for a laser strapdown system. In-flight update is required to compensate for the large error in the initial attitude determined from prelaunch gyrocompassing. The approach, known as the position velocity matching, involves the comparison of navigator output at booster cutoff with an a priori nominal trajectory data for position and velocity dispersion. Attitude information is estimated from these dispersions based upon two covariance matrices: one to characterize the correlations between navigator error and initial attitude error, and the other to shape the statistics of actual trajectory deviations from the nominal. Results obtained from both covariance analysis and time history simulation indicate that the performance of the proposed technique satisfies overall system accuracy requirements.