Fighter Combat - Tactics and Maneuvering

44 FIGHTER WEAPONS
Missile Fuzes
The purpose of a missile fuze system is to cause the detonation of the
warhead at the time that produces the maximum target damage, while also
ensuring the safety of the firing platform and personnel. Typically, a fuze is
"armed" (made capable of causing warhead detonation) when it senses that
firing has occurred and that safe separation from the firing platform has
been achieved. The acceleration of the missile during motor burn may be
used to start a timing mechanism for arming, or any number of other
methods may be employed. Once a fuze is armed, another fuze function is
required in order to detonate the warhead.
Fuzes can be classified as contact, time delay, command, and proximity.
Contact fuzes were discussed previously in conjunction with explosive
cannon projectiles. Nearly all anti-aircraft missiles have such a fuze, either
alone or in combination with another type. Time-delay fuzes are preset
before launch to explode at a given time that is calculated to place the
missile in the vicinity of the target. This is a fuze commonly used by
large-caliber anti-aircraft artillery, but seldom by missiles because of its
lack of accuracy. Command fuzes are activated by radio command from
the guidance platform when the tracking system indicates that the missile
has reached its closest point of approach to the target. This method is most
applicable to command-type guidance systems and generally requires relatively
large warheads to be effective against airborne targets.
Proximity fuzes are probably the most effective fuzes against maneuvering
aircraft; they come in many designs, including passive, semi-active,
and active. Passive fuzes rely for their activation on a phenomenon associated
with the target. This might be noise, heat, radio emissions, etc.
Semi-active fuzes generally function on an interaction between the guidance
system and the target, such as rapidly dropping Doppler frequency or
high target LOS rates. An active fuze sends out some sort of signal and
activates when it receives a reflection from the target. Popular designs
include radio-proximity fuzes and laser fuzes. For maximum effectiveness
the proximity fuze should be capable of detecting the target out to the
maximum lethal radius of the warhead.
Because of the wide range of intercept conditions possible in engagements
with aircraft targets, fuze design is one of the weakest links in
missile systems. Proximity fuzes are usually tailored to the guidance
trajectory of the missile, the most probable target, and the most likely
intercept geometry. "Functional delays" are generally used for this purpose.
For instance, if a missile is expected to approach the target from the
rear with a relatively low closure, a fairly long functional delay might be
incorporated to allow the missile to travel from the target's tailpipe area
(where detection would presumably occur) to some point near the middle
of the target, where an explosion would probably do the most damage.
However, if this missile intercepted the target from the side or head-on,
such a time delay might cause detonation past the target, resulting in little
or no damage.
All-aspect missiles, because of their larger variety of possible intercept
conditions, offer the greatest challenge to the fuze designer. One approach