Head Pursuit Guidance

Abstract

DOI: 10.2514/1.27737 Aguidancelawforintercepting high-speedtargetsinanovelheadpursuitengagementispresented.Theguidance law imposes a geometric relation in which the interceptor missile is positioned ahead of the target so that both fl yi n the same direction. The missile speed is planned to be lower than that of the target, and therefore the target closes in on the interceptor missile and it is intercepted from its front end. The guidance law also enables enforcing a predeterminedinterceptionanglerelativetothetarget’s flightdirection.Analyticconditionsenablinginterceptionin this novel engagement are provided. The guidance law is implemented using the sliding mode approach, and simulation results confirm its viability in several representative engagements against maneuvering high-speed targets. NTERCEPTION of high-speed targets, such as reentering ballistic missiles, is a formidable challenge. The interception in these scenarios is typically head-on, with a very high closing speed. This imposes severe requirements on the interceptor systems such as precise detection of the target from a large distance by the onboard seekers, and very fast response time of the missile subsystems. To overcome these difficulties, a different approach was suggested in [1],inwhichtheinterceptorvelocityismatchedwiththatofthetarget by a preliminary maneuver. If the target path is predictable, as in the case of ballistic missiles, the maneuver can be designed such that the interceptor missile is positioned ahead of the target on its predicted flight path, flying in the same direction but at a slightly lower speed. This way the target closes in on the interceptor that is conducting the necessary lateral maneuvers to achieve interception. The interceptor speed along the target’s predicted path can be selected to achieve a desired closingrate. Asimilar lowclosingspeedcanbe obtainedina tail-chase scenario. However, tail chase requires that the interceptor will be faster than the target, and therefore more energy is needed during the preliminary maneuver to reach the desired closing speed. Various guidance methods have been examined for implementation in the different stages of high-speed exo- or endo-atmospheric interception scenarios of ballistic missiles. Some of these methods are described next. In [2] a modified version of proportional navigation (PN) guidance law [3] was proposed for implementation in the coast phase. A variable bias was applied to the actual line of sight (LOS) to account for engine burn. The terminal guidance in a hyper-velocity exo-atmospheric orbital interception was studied in [4]. The control energy expenditure is reduced by constraining the expected final state to a function of the estimation error. An optimal guidance algorithm was proposed in [5] for the interception of a nonmaneuvering target decelerated by atmospheric drag. Its implementation requires knowledge on many scenario states, obtained from a nonlinear state estimator. In a recent paper [6] a differential game guidance law was proposed against targets having knownspeedandlateralaccelerationlimitprofiles.Itwasshownthat in a ballistic missile interception scenario such a guidance law provides a significant improvement in the homing accuracy