  The active target defense differential game is addressed in this paper. In
this differential game an Attacker missile pursues a Target aircraft. The
aircraft is however aided by a Defender missile launched by, say, the wingman,
to intercept the Attacker before it reaches the Target aircraft. Thus, a team
is formed by the Target and the Defender which cooperate to maximize the
separation between the Target aircraft and the point where the Attacker missile
is intercepted by the Defender missile, while the Attacker simultaneously tries
to minimize said distance. This paper focuses on characterizing the set of
coordinates such that if the Target's initial position belong to this set then
its survival is guaranteed if both the Target and the Defender follow their
optimal strategies. Such optimal strategies are presented in this paper as
well.
