Alignment of Inertial Guidance Systems by Gyrocompassing-Linear Theory

The performance of an inertial guidance system can be only as good as the accuracy to which the system is initially aligned. Optical alignment can be performed with high precision, but involves external equipment which may be too elaborate for many operational applications. The alternative procedure of gyrocompass alignment uses the system's own instruments, and can be accomplished without any external equipment. When sufficient alignment time is available navigation errors due to gyrocompass alignment are no greater than other errors inherent in the system's instruments. In certain tactical operations it is desirable to sacrifice some accuracy in the interest of more rapid alignment. But, on the other hand, if alignment must be performed on a moving base, base motions may be filtered only by lengthening alignment time. In this paper some simple linear gyrocompassing schemes are described, and the basic dynamic relations are established for the dependency of alignment accuracy upon instrument characteristics, speed of alignment, and base motions during the alignment period. Upper bounds are established for alignment performance achievable under typical circumstances. I t is planned that a subsequent paper will extend the discussion to describe nonlinear effects and sampled-data techniques, and to present operational results including high-latitude, atsea, gyrocompass alignment of inertial ship navigation S3^stems.