An alternative erection procedure for on-ground transfer alignment

Abstract

This paper presents a procedure for computing the relative orientation between two static inertial navigation systems: a primary and a secondary. The primary system is assumed to be of navigation quality and therefore capable of gyro-compassing to the desired accuracy. The secondary is lower quality and requires external aiding for azimuth and accurate leveling initialization. The assumption that allows the transfer alignment is that the primary and the secondary are rigidly mounted on a mechanical structure that allows for joint rotation around one or more axis while maintaining the relative orientation between the two systems. A pitch axis is typical in practical systems and hence the name “Erection Procedure.” As opposed to the Kalman-filter based procedures in use in several systems today, the new method does not require the computation of a navigation solution while the mechanical system is been erected. Instead, measurements from the navigation sensors are required at a number of discrete stages, and then these measurements are processed to compute the relative orientation between the primary and the secondary. The procedure is easy to implement and yields an exact solution to the problem whenever the underlying assumptions are exactly met. It has been shown to work well both in simulations and in practice. In addition to its practical relevance, this work also sheds additional light into the general question of aligning two static navigation systems.