ROCKET COMPONENTS

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.