Activation of new aaa units - Air Defense Artillery

19..J.8 THE ANTIAIRCRAFT GUIDED MISSILE 17
onds and to drop away from the missile after the desired
\'C'locityhas been attained. Experience has indicated that
where a large thrust is required for a short time, the solid
propellant rocket motor is simpler in design and operation
and. more important, is lighter in weight than a liquid
propellant motor of the same thrust.
The specific number of solid propellant rocket motors of
a rated thrust which are required during the boosting period
is dependent on the total impulse necessary to accomplish
the design requirements of the missile. In order to calculate
the total impulse required, definite values have to be
selected as to: (1) Total mass (missile plus booster) which
has to be accelerated, (2) Average velocity during the boost
period, (3) Booster burning time. Since specific values of
mass, velocity, and time \vill vary between different system
designs. the requirement on total impulse for each application
will cover rather broad limits. However, in all cases,
a high initial acceleration is desired in order that a control
by external fins may become effective; to reduce the time
spent at subsonic speeds, for \vhich drag is excessive; and
to traverse the transonic zone where control by external
nns is impossible..
The value of total impulse required in each case serves
asa basis for the design of the solid propellant rocket motors
for the booster. Up to the present time it has been rather
dillicult to fulfill the requirements of total impulse by using
a hooster which consists of a single unit rocket motor.
However, future developments in this direction look promising.
The principal disadvantage in using a single unit
rocketmotor is that the booster unit becomes relatively long,
and when attached to the missile, the over-all length of the
booster-missile combination may be undesirable from the
tactical point of view. Although sufficient impulse can be
obtained by using a combination of two or more rocket
motors, the weight and complexity of the booster assembly
increasesconsiderably. In addition, multiple rocket boosters
areinclined to have more dispersion because of the variation
in thrust and burning time bet\veen the individual rocket
units. Again, continued engineering experience in the
solid propellant field will increase the uniformity in performance
between individual motors.
However, because the time element is so critical in the
successful application of the antiaircraft guided missile, a
booster performs several important functions. First, the
boosterprovides a means of accelerating the missile up to
itsdesign speed in the minimum of time. This can be seen
?y the fact that the booster develops a thrust many times
In excessof that developed by the missile power plant alone.
In addition, the booster provides a means of reducing the
~issile weight by dropping off after imparting a high
mitial acceleration. It is essential that the missile weight
be kept to a minimum so that high lateral acceleration can
be obtained at extreme rano-esbv relativelv small control
forces. - •
c. Missile. The missile may be defined as a highly
streamlined bodv which is aerodvnamicallv stable both at
SUbsonicand stipersonic speeds -and is c~pable of being
c~ntrolled in such a manner as to intercept and destroy a
hIgh-speed aircraft taro-et. The missile consists of three
_
pnncipal components: A jet or rocket power plant 'which
IS capable of propelling the missile at supersonic speed for
a sustained period of time; Internal control equipment
which will cause the missile to execute command orders
and to follow a specific course to the target; and third, A
warhead which is sufficiently effective to cause a high kill
probability.
In the present state of deSign, a missile weight of 1000
Ibs. appears to be the minimum that can be met and still
incorporate all the required components to provide maximum
effectiveness. A brief description of the three major
components will complete the picture of the missile itself.
(1) Power Plant. Because of the high operating speeds
required for the successful application of the antiaircraft
guided missile, it is necessary that either a thermo jet or
pure rocket motor be employed for propelling the vehicle
at supersonic speed. Specifically, a high thrust lightweight
unit capable of an operating speed in excess of 1500 miles
per hour is essential.
In the field of thermo jet power plants, the ram jet appears
to be the only type which will meet the above requirements.
The ram jet is classified as a compressorless thermo
jet since the high combustion pressure is achieved by means
of a diffuser inside the unit rather than by a mechanical
device. The kinetic energy of the high velocity air stream
entering the nose of the ram jet is converted into pressure
by means of a diffuser. Fuel is mixed with the air under
high pressure in a combustion chamber and the resultant
products of combustion are expanded through a nozzle
in the rear of the unit. The ram jet is particularly suited
for short duration operation at high speed. By obtaining
oxygen from the atmosphere during flight to support the
combustion process the over-all fuel consumption is considerablv
less than in the case of the rocket motor. The
princip~l disadvantages of the ram jet engine are: (a) The
dependence of the unit on atmospheric oxygen to support
combustion limits the maximum operating altitude to approximately
60,000 feet, (b) Operation of the unit is dependent
on a minimum forward velocity of approximately
350 miles per hour and therefore a ram jet propelled vehicle
must be boosted by an auxiliary poV' .'er plant (booster) up
to the above speed before the ram jet \'Ifillsustain combustion.
The second type of power plant presently being used for
propelling missiles is the liquid fuel rocket motor. In
contrast to the solid propellant motors used in the booster,
liquid propellants are used for the missile motor because
operating times in excess of thirty seconds are normally
required. A gas pressure feed system is used to force one
or more liquid propellants into a combustion chamber at a
specified rate. Ignition is in some instances spontaneous
but ,,-hen necessary, an auxiliary ignition device is used.
The products of combustion are then ejected as a high
velocity gas stream through a nozzle in the rear of the unit.
Although the specific fuel consumption of rocket motors is
extremely high (approximately six times that of the ram
jet) their over-all ,,-eight is still light enough to make them
\,-ell suited for short duration applications. Also, the performance
of the rocket motor is not affected bv altitude since
one of the propellants known as the o)cidiz~rprovides the
oxygen to support combustion. For efficient operation, the
flight yelocity of the yehicle should be relatiyely high. In
fact. maximum efficiencyis attained ,,,hen the flight yelocity