Interception of spiraling ballistic missiles

During re-entry the rolling velocity of the non-separating tactical ballistic missile caused by configurational asymmetries will normally pass through the missile pitch frequency. This may result in a large amplitude circular yaw and a severe spiraling of the vehicles center of mass. The presence of a static aerodynamic induced rolling moment may cause the roll rate to lock-in at the critical frequency in which case the severity of this spiraling motion is greatly increased. Both the amplitude and frequency of spiraling generally increase as the missile descends in altitude. The frequency of the motion is in the range 0.5 to 1 Hz which is the range of target weave frequencies most critical for fast-response proportional navigation interceptors. These motions can cause significant miss distance in a conventional proportional navigation guidance system. This paper demonstrates the advantages of using a weave guidance law. The paper shows that an alternative approach to improving interceptor performance is by improving the guidance law used to steer the missile. If the target weave frequency can be estimated the paper shows that the compensated weave guidance law substantially improves system performance.