Inertial Navigation Systems: Prelaunch Alignment

A conventional inertial navigation system navigates by sensing components of the acceleration vector along three mutually perpendicular axes held stable after some initial alignment. This paper discusses the need for initial alignment, followed by a review of the effects of alignment errors on navigation in order to establish the order of accuracies desired. Several alignment techniques are described and compared including synchro memory, optical autocollimation, self-leveling, gyrocompassing, and alignment from a moving vehicle. Transfer functions are developed for each alignment method, and trends in alignment techniques are discussed.