Inertial Navigation for Guided Missile Systems
INTRODUCTION
Inertial navigation has been a key element of missile system design since the 1950s. Traditionally, the focus has been on strategic- and precision-strike systems. In these applications, terminal-position accuracy is the primary objective of the navigation system. In guided missile systems in which a terminal seeker is used to sense and track an air or ballistic missile threat, a critical function of the inertial navigation system (INS) is to provide accurate seeker-attitude information and, therefore, allow accurate pointing of the seeker for the acquisition of a target. In addition, the navigation system provides essential data for guidance and flight-control functions.
This article also discusses more recent advances in navigation for guided missiles. These advances have been motivated by several factors. The historical use of a semi-active RF seeker with a wide field of view placed less demand on the accuracy of the navigation system for pointing information. The use of wide-field-of-view seekers also was consistent with the fact that accurate navigation systems were high in cost, heavy in weight, large in volume, and, therefore, not suitable for tactical guided missiles. However, as lower-cost, smaller, and more reliable inertial measurement units (IMUs) have become readily available, missile systems have been able to employ higher-accuracy, smaller-field-of-view seekers such as infrared or high-frequency RF technology without the need to perform an angle search. The use of advanced seeker technology naturally leads to better overall performance against more stressful targets. A second consideration is that targeting information may be improved by the use of multiple sensors. As sensor alignment errors and target-track errors are taken into account, it is desirable to minimize the alignment error between the missile seeker and the targeting reference. A third consideration is the missile guidance system configuration before seeker acquisition. Typically, a missile is guided by uplinks that are based on filtered radar measurements of both the missile and the target. In an alternative approach, called inertial midcourse guidance, the tracking radar still provides filtered targeting data and unfiltered missile-position measurement data, but the missile itself computes the guidance commands. This latter approach places greater reliance on the missile navigation and guidance systems in an attempt to improve overall system performance. This article provides a general overview of inertial navigation and describes the basic navigation-system design approach. Also included is a discussion of the navigation functions of a guided missile system during the various phases of flight. Finally, we present a summary of the future of advances in inertial navigation for guided missile systems.