Fighter Combat - Tactics and Maneuvering

36 FIGHTER WEAPONS
straight path. The numbers along each trajectory denote time intervals
after launch for ease in visualizing the geometry involved. The missiles are
fired at time "1."
The missile following the "pure-pursuit" path keeps its nose (and its
velocity vector) pointed directly at the target at all times, generating a
curved flight path that ends in a tail-chase with the target and intercept at
about point "5."
The "lead-pursuit" trajectory results from the missile leading the target
somewhat, keeping its nose in front by a small amount. This is the
trajectory that would be expected of a single-beam beam-rider or a command-to-LOS
system where the launcher, missile, and target positions
always lie in a straight line. This trajectory also terminates in a tail-chase,
but the inherent lead of this system results in a slightly earlier intercept,
between points "4" and "5."
The most efficient trajectory depicted here is the "lead collision,"
which is a straight line with an intercept near point "4." Such a path is
possible for preset, command, or beam-rider guidance systems with separate
tracking and guidance beams.
Homing guidance systems may be programmed to follow any of these
trajectories to the target. Pure pursuit is probably the simplest course to
follow since it requires a less sophisticated guidance computer. For heat
seekers, pure pursuit has the added benefit of tending to keep the missile
farther into the target's rear hemisphere, which aids in maintaining a good
view of a jet aircraft's tailpipe. Pure pursuit has some serious problems,
however. One is reduced maximum range under many circumstances, a
result of the inefficient trajectory. Another is the great amount of maneuvering
required when significant AOT exists as the missile nears a fast
target. This requirement is accentuated if the target turns toward the
missile, and the required maneuvering may easily exceed the weapon's
turn capability.
Lead collision is probably the optimum missile trajectory, since it is
generally the most efficient and ideally requires the least maneuvering. It
does, however, require a more sophisticated guidance system.
A lead-pursuit course, in which the missile pulls some lead but not
enough for a collision course, requires essentially the same guidance
complexity in a homing system as lead collision and has nearly all the
problems of pure pursuit. Thus, it is seldom used by homing systems, but it
is quite common with beam-riders and command guidance. Another
trajectory type, known as "lag pursuit," causes the missile to point its nose
behind a moving target. Because of trajectory inefficiency it is not commonly
used by missiles, but it may result of necessity if the missile is
unable to make its intercept turn and overshoots the target's flight path.
Passive homing has become quite popular among AAM systems because
of its simplicity and resultant reliability. The first AAM to score a
kill in combat [1958] was the passive heat-seeking Sidewinder missile
developed by the U.S. Navy. Since that time many versions of heat-seeking
missiles have emerged worldwide. The high heat output of jet engines
makes heat seekers especially effective, but to some extent they may also