The history of rockets covers a span of eight centuries, but their use in aircraft armament began during World War II. Rockets answered the need for a large weapon that could be fired without recoil from an aircraft. Since the airborne rocket is usually launched at close range and measured in yards or meters, its accuracy as a propelled projectile is higher than a free-falling bomb dropped from high altitude.

Rockets are propelled by the rearward expulsion of expanding gases from the nozzle of the motor. The necessary gas forces are produced by burning a mass of propellant at high pressure inside the motor tube. It is a common misconception that rockets are pushed forward by the reaction of hot gases against the surrounding air. However, rockets can function even in a vacuum. The propellant contains its own oxidizers to provide the necessary oxygen during burning.

There are two rockets currently used by the Navy. The first is the 2.75-inch, folding-fin aircraft rocket (FFAR) known as the Mighty Mouse. The second, a 5.0-inch, folding-fin rocket known as the Zuni. The Mighty Mouse and the Zuni are discussed in detail later in this chapter. 

Some of the more common terms peculiar to rockets and rocket components used in this chapter are defined as follows: 

Acceleration/deceleration. These terms apply to fuzes that use a gear-timing device in conjunction with the setback principle. Prolonged acceleration completes arming the fuze, and deceleration or proximity initiates detonation. 

Igniter. The initiating device that ignites the propellant grain. It is usually an assembly consisting of an electric squib, match composition, black powder, and magnesium powder. 

Hangfire. A misfire that later fires from delayed ignition. 

Misfire. A rocket does not fire when the firing circuit is energized.

Motor. The propulsive component of a rocket. It consists of the propellant, the igniter, and the nozzle(s).

Propellant grain. The solid fuel used in a rocket motor, which, upon burning, generates a volume of hot gases that stream from the nozzle and propel the rocket (also known as the propellant or propellant powder grain).

Rocket. A weapon propelled by the sustained reaction of a discharging jet of gas against the container of gas.

Setback. This term is applied when internal parts react to the acceleration of the rocket. Setback is a safety feature designed into those fuzes that use a gear-timing device.

Thrust. The force exerted by the gases produced by the burning of the rocket motor propellant.

Rockets are propelled by the rearward expulsion of expanding gases from the nozzle of the motor. Burning a mass of propellant at high pressure inside the motor tube produces the necessary gas forces. Rockets function in an even vacuum. The propellant contains its own oxidizers to provide the necessary oxygen during burning.

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.

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 wrapped ethyl cellulose tape bonded to the propellant surface. Inhibitors cause the propellant grain to burn from the center outward and from forward to aft uniformly. If inhibitors weren't used, the burning surface of the propellant grain would increase, and result in an increased burning rate. This could cause the motor tube to explode from excessive pressure. If a motor is accidentally dropped and the propellant grain is cracked, the crack in the grain increases the burning surface and an identical hazard exists.

STABILIZING ROD.—The stabilizing rod, located in the perforation of the motor propellant grain, is salt coated to prevent unstable burning of the propellant. It also reduces flash and after burning in the rocket motor, which could contribute to compressor stall and flameout of the aircraft jet engines. When the propellant ignites, the stabilizing rod ensures that the grain ignites simultaneously forward and aft.

IGNITER.—The igniter heats the propellant grain to ignition temperature. The igniter used in the 2.75-inch motor is a disc-shaped metal container that contains a black powder and magnesium charge, a squib, and electrical lead wires. It is located at the forward end of the motor. The igniter used in the 5.0-inch motor is a disc-shaped metal container that contains a powder or pellets charge, two squibs, and electrical lead wires. It is located at the forward end of the motor.Acontact disc or a contact band transmits the firing impulses to the motor igniter. The 2.75-inch motor has electrical leads that extend from the squib through the wall of the igniter. They are routed through the propellant perforation to the nozzle fin assembly. One of the wires is connected to the nozzle plate (ground), and the other passes through either one of the nozzles or the fin-actuating piston to the contact disc on the fin retainer. In the Mk 66 Mod 2, both lead wires are connected directly to the HERO filter wires, which extend out of the forward end of the stabilizing rod. When the rocket is placed in the launcher, the contact disc is automatically in contact with an electrical terminal that transmits the firing impulse to the rocket. The igniter in the 5.0-inch motor (fig. 2-2) has an electrical lead wire post that protrudes through the forward bulkhead closure. The electrical lead connects the igniter to the contact band. When the rocket is placed in the launcher, the contact band is automatically in contact with an electrical terminal, which transmits the firing impulse to the rocket. The igniter in the 5.0-inch motor (fig. 2-2) has an electrical lead wire post that protrudes through the forward bulkhead closure. The electrical lead connects the igniter to the contact band. When the rocket is placed in the launcher, the contact band is automatically in contact with an electrical terminal, which transmits the firing impulse to the rocket. Until actually loaded into a launcher, a metal shielding band fig. 2-3) is always in place over the ignition contact band.

NOZZLE AND FIN ASSEMBLIES.—The nozzle assembly for the Mk 66 consists of the nozzle body, carbon insert, fins, contact band assembly, and weather seal. Pivot pins attach the fins to lugs machined on the aft part of the nozzle plate. When folded, the fins lie within the 2.75-inch diameter of the rocket. The fins are notched at the tips to allow attachment of a fin retainer. The fin-actuating mechanism is a steel cylinder and a piston with a crosshead attached to its aft end. When the rocket is fired, gas pressure from the motor operates the piston, cylinder, and crosshead. The crosshead is pushed against the heels of the fins, causing the fins to rotate on the fin pivot pins to the open position after the rocket leaves the launcher. After the fins have opened to the final flight position, the crosshead prevents the fins from closing. There are four nozzle inserts and the detent groove in the aft end of the nozzle plate. They hold the rocket in position after it is loaded in the launcher.

The Mk 71 Mods motor has a modified igniter and a modified nozzle and fin assembly. The nozzle and fin assembly (fig. 2-4) contains four, spring-loaded, wraparound fins inside the motor diameter. The steel nozzle expansion cone has flutes that cause the rocket to spin during free flight. This permits the rocket to be launched from high-speed aircraft, helicopters, and low-speed aircraft. The Mk 71 Mods spring-loaded fins (fig. 2-5) deploy after emerging from the rocket launcher tube. They lock in place (open) by sliding into a locking slot in the flange at the aft end of the fin nozzle assembly. When not actually installed in the launcher, the fins are held in the closed position by a fin retainer band, which must be removed when the rocket is installed into the launcher tube. The fin retainer band is not interchangeable with the shielding band.

SERVICE ROCKET ASSEMBLIES

Airborne rockets, consisting of fuzes, warheads, and motors, are combined and assembled in various configurations to meet specific tactical requirements. For example, a rocket assembly that consists of a fragmentation warhead armed with a proximity fuze is entirely unsuitable for use against an armored tank or bunker. Likewise, the GP warhead fuzed only with the Mk 191 base fuze is relatively ineffective against personnel or unarmored targets.With each specific type of target, the right combination of warhead, fuze, and motor is assembled from the wide variety of components available. 

ROCKET SAFETY PRECAUTIONS

The aircraft rocket is no more dangerous than any other explosive weapon. It does have certain peculiar hazards. A completely assembled rocket, if accidentally fired, takes off under its own power in the direction it is pointed, and threatens everything in its path. When fired, an assembled rocket expels a blast of burning gas capable of injuring or killing anyone it strikes. Generally, rocket motors without a head attached won't explode. It is a fire hazard since ballistite or cordite N (SPCG) ignites easily and burns readily. High-explosive heads, either fuzed or unfuzed, present the same risk as gun projectiles under the same conditions. Handle rockets, whether completely assembled or disassembled, with extreme care to avoid damage to parts. 

Only personnel who are certified to handle rockets should be in the vicinity of assembly operations. When handling airborne rockets, rocket components, and launchers, follow all safety practices that apply to airborne armament and weapons. If practicable, all work should be performed from the side of the rocket launcher. Rocket motors should be stowed in the same manner as smokeless powder. Never allow matches and open flames in the stowage area. Smoking is NOT permitted in the loading area within 200 feet of ammunition. Do not stow rocket motors in the same compartments with or near radio apparatus or antenna leads. Induced currents might ignite the motor.DoNOT fire rocket motors when the propellant temperature is outside the safe-firing temperature limits specified on the motor tube. 

If a rocket motor is dropped and any portion impacts on a hard surface after falling 2 feet or more, do NOT use it. Cracks or breaks in the grain increase the carefully calculated burning area and cause excessive internal pressure buildup, which can cause the motor to blow up after ignition. Stow high explosive heads and fuzes (except fuzes that are permanently installed in the head) separately in the same manner as high-explosive projectiles. Ready-service stowage of assembled rockets is authorized for the 2.75-inch and 5.0-inch aircraft rockets according to NAVSEA OP 4 and NAVSEA OP 5. A fuze is relatively sensitive and must be handled with care to avoid extreme shock that might cause damage. Conduct fuzing, unfuzing, assembly, or disassembly operations of all types of ammunition away from other explosives and vital installations. Only the minimum number of persons and rounds required should be in the vicinity. The ideal situation is to permit work on only one round at a time. This work should be done on a deck or at some other location remote from all magazines, ready stowage, explosive supplies, or vital installations. Examination of the exterior of some fuzes will not show if they are armed. If, for any reason, you think a fuze might be armed, the fuze should be treated as an armed and sensitive fuze. You must NOT attempt to remove it from the rocket head. The complete fuzed round should be disposed of according to current directives. When available, explosive-ordnancedisposal (EOD) personnel should dispose of such rounds.

NEVER attempt to remove a base fuze from a rocket head.

You should NOT tamper with (or attempt to repair) any parts of the round. If the round is damaged or defective, remove the head from the motor and mark the defective part for return to the issuing agency. Disassembly or alteration of rocket components isNOT authorized except under specific instructions from Naval Air Systems Command. Fuzes and/or warheads dropped 5 feet or more onto a hard surface and rockets that have been accidentally released from aircraft launchers upon aircraft landing must be disposed of according to current directives. If a loaded launcher is dropped, you should NOT use it until the launcher tubes, latching mechanisms, and rockets are inspected for damage. Rocket launchers should NOT be suspended from a bomb rack that does not have independent ignition and jettisoning circuits. To prevent possible explosion, do NOT expose airborne rockets or loaded launchers to the exhaust from jet engine starter pods or gas turbine compressors. A minimum distance, as indicated on the unit, must be maintained between the gas turbine exhaust path and rocket assemblies upon which the exhaust impinges. In the absence of specific information on the unit, a minimum distance of 10 feet must be maintained. Rockets should NOT be loaded or unloaded from launchers while on the flight deck. RF barriers should remain in place on the launcher while on the flight deck.

The detent pin must be in the breaker switch at all times. The only exceptions are when you are making certain electrical checks, or when the aircraft is ready for flight. Do NOT, under any circumstances, perform an electrical test with rockets in the launcher.