New Interceptor Guidance Law Integrating Time-Varying and Estimation-Delay Models

The paper presents a synthesis of a new guidance law, derived using differential games concepts, for the interception of highly maneuvering targets. The synthesis is based on the integration of two recently demonstrated improvementfeatures:namely,theuseofa time-varying linearkinematicsgamemodelandthecompensationofthe inherent estimation delay of thetarget acceleration. The new guidance law is implemented in a genericyet realistic noise-corruptedthree-dimensionalnonlinearballisticmissiledefensescenariobyusingasuitablethree-dimensional estimator.Thetestagainstworst-casetargetmaneuversdemonstratesasignie cantimprovementcomparedto other known guidance laws indicating a potential breakthrough in interceptor guidance. I. Introduction H ISTORICALLY, the typical target of interceptor missiles has been a manned aircraft, against which the missile had substantial advantage in speed, maneuverability, and agility. Moreover, miss distances of a few meters, compatible with the lethal radius of the missile warhead, were considered admissible. Because of these facts, even a simple guidance law such as proportional navigation (PN) could guarantee the target destruction. The Gulf War introduced the tactical ballistic missile (TBM), able to carry nonconventional warheads, as a new type of target. Successful interception of a TBM, much less vulnerable than an aircraft, requires a very small miss distance or even a direct hit. Several ballistic missile defense systems are currently in development. Because of advances in technology, these systems (such as ARROW and PAC-3) succeeded to demonstrate, using conventionalguidance concepts, excellent homing accuracy against such nonmaneuvering targets. 1;2 Although known TBMs were not designed to maneuver because of their high reentry speed, they have a substantial maneuverability potential in the atmosphere. Moreover, this potential can be made applicable by a modest technical effort. The same is true for future high-speed antiship or cruise missiles.Paradoxically, the successful current development of ballistic missile defense systems can serve to motivate the future development of maneuverable antisurface missiles. Against such threats interceptor missiles will have only a marginal maneuverability advantage. Hence, the required small miss distances are not achievable by using conventional guidance laws even in a noise-free environment, as it was demonstrated by recent simulation studies. 3;4 Most missile guidance laws used at the present, including PN, were derived using a linear quadratic optimal control formulation assuming perfect information. 5 Such a formulation requires an assumption on the future evolution of the target maneuver. If this