Types of Guidance
As we mentioned earlier, missiles have a path
control system and an attitude control system.
Guidance systems are usually classified according to
their path control system, since many missiles use the
same type of attitude control. The type of attitude
control used in the fleet is inertial. The following is a
discussion of the types of path control (guidance) in
use in SMS missiles.
INERTIAL GUIDANCE.—An inertial guidance
system is one that is designed to fly a predetermined
path.
The missile is controlled by self-contained
automatic devices called accelerometers.
Accelerometers are inertial devices that measure
accelerations.
In missile control, they measure the
vertical, lateral, and longitudinal accelerations of the
controlled missile (fig. 1-19). Although there may not
be contact between the launching site and the missile
after launch, the missile is able to make corrections to
its flight path with amazing precision.
During flight, unpredictable outside forces, such
as wind, work on the missile, causing changes in speed
commands. These commands are transmitted to the
missile by varying the characteristics of the missile
tracking or guidance beam, or by the use of a separate
radio uplink transmitter.
BEAM-RIDER GUIDANCE.—A beam-rider
guidance system is a type of command guidance in
which the missile seeks out the center of a controlled
directional energy beam. Normally, this is a narrow
radar beam. The missile’s guidance system receives
information concerning the position of the missile
within the beam.
It interprets the information and
generates its own correction signals, which keep the
missile in the center of the beam. The fire control radar
keeps the beam pointed at the target and the missile
“rides” the beam to the target.
Figure 1-20 illustrates a simple beam rider
guidance system. As the beam spreads out, it is more
difficult for the missile to sense and remain in the
center of the beam. For this reason, the accuracy of the
beam-rider decreases as the range between the missile
and the ship increases. If the target is crossing (not
heading directly at the firing ship), the missile must
follow a continually changing path. This may cause
excessive maneuvering, which reduces the missile’s
speed and range. Beam-riders, therefore, are effective
against only short- and medium-range incoming
targets.
HOMING GUIDANCE.—Homing guidance
systems control the path of the missile by means of a
device in the missile that detects and reacts to some
distinguishing feature of (or signal from) the target.
This may be in the form of light, radio, heat, sound
waves, or even a magnetic field. The homing missiles
use radar or RF waves to locate the target while
air-to-air missiles sometimes use infrared (heat)
waves.
Since the system tracks a characteristic of the
target or energy reflecting off the target, contact
between the missile and target is established and
maintained. The missile derives guidance error signals
based on its position relative to the target. This makes
homing the most accurate type of guidance system,
which is of great importance against moving air
targets.
Homing guidance methods are normally
divided into three types:, active homing, semi-active
homing, and passive homing (fig. 1-21).
Active Homing.—With active homing, the missile
contains both a radar transmitter and a receiver. The
transmitter radiates RF energy in the direction of the
1-16
Figure 1-19.—Accelerometers in a guided missile.
