As you read this section, refer to figure 2-1. To
understand how a rocket operates, visualize a closed
container that contains a gas under pressure. The
pressure of the gas against all the interior surfaces is
equal (view A). If the right end of the container is
removed (view B), the pressure against the left end will
cause the container to move to the left.
In the rocket motor, gases produced by the burning
propellant are confined to permit a buildup of pressure
to sustain a driving force. A Venturi-type nozzle (view
C) restricts the size of the opening. The Venturi-type
nozzle decreases the turbulence of escaping gases and
increases the thrust. In this design, gas pressure inside
the container provides about 70 percent of the force,
and the escaping gases provide about 30 percent of the
force necessary to move the container forward.
ROCKET COMPONENTS
A complete round of service rocket ammunition
consists of three major components—the motor, the
warhead, and a fuze. A general description of these
components is given in the following paragraphs.
Motors
The rocket motor consists of components that
propel and stabilize the rocket in flight. Not all rocket
motors are identical, but they do have certain common
components. These components are the motor tube,
propellant, inhibitors, stabilizing rod, igniter, and
nozzle and fin assembly. The rocket motors discussed
in the following paragraphs are for the 2.75-inch Mk 66
Mods 2 and 4, and 5.0-inch Mk 71 Mod 0 and 1.
MOTOR TUBE.—The motor tube supports the
other components of the rocket. Presently, all motor
tubes are aluminum, threaded internally at the front end
for warhead installation, and grooved or threaded
internally at the aft end for nozzle and fin assembly
installation.
The Mk 66 Mods rocket motor tube is an integral
bulkhead type of motor tube and is impact-extruded
from aluminum stock. The forward end contains the
head closure and threaded portion for attachment of the
warhead. The integral bulkhead closure does not
rupture when accidentally fired without a warhead and
becomes propulsive when ignited. The center portion of
the motor tube contains the propellant. The nozzle and
fin assembly attaches to the aft end by a lock wire in a
grove inside the tube.
The Mk 71 Mods rocket motor tube is basically an
aluminum tube with an integral bulkhead closure. The
forward end contains the head closure, igniter contact
band, igniter lead, RAD HAZ barrier, and a threaded
portion for attachment of the warhead. The center
section is the combustion chamber and contains the
igniter, propellant grain, stabilizing rod, and associated
hardware. The aft end of the motor tube is threaded
internally to accept the nozzle and fin assembly.
PROPELLANTS.—The
propellant
grain
contained in the Navy's 2.75-inch and the 5.0-inch
rocket motors is an internal burning, star perforation,
double-base solid propellant. The star perforation is
designed to produce a nearly constant thrust level.
The Mk 66 rocket motor has the star points
machined off (conned) to reduce erosive burning.
INHIBITORS.—Inhibitors restrict or control
burning on the propellant surface. In the 2.75-inch and
the 5.0-inch motors, the propellant grains are inhibited
at the forward and aft ends, as well as the entire outer
surface. The forward and aft end inhibitors are molded
plastic (ethyl cellulose) components bonded to the
propellant ends. The outer surface inhibitor is spirally
2-2
Figure 2-1.—Principles of rocket propulsion.
