A new method to identify active decoys from ballistic targets in the course of ballistic missile penetration is proposed based on the time invariant of orbital elements

while the effects of radar placement upon the identification are analyzed as well.And a novel approach named Inverse Track Filter (ITF) based on the principle of kinetic track reciprocity of two bodies is put forward to decrease the initial error and shorten the convergence time.Simulations are presented to verify the effectiveness and feasibility of the proposed methods.