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Launching Systems
18.1 OBJECTIVES AND INTRODUCTION
Objectives
1. Be acquainted with the general requirements of a launching system and know the functions that it must perform.
2. Understand the three basic types of launching systems.
3. Understand the purpose of the recoil/countercoil systems to include soft recoil and recoiless systems.
4. Understand the principles of operation of ejector-type reaction-type launchers.
5. Understand the storage, transfer, loading, control, and launching functions of a launching system.
Introduction
The purpose of a launching system is to place a weapon into a flight path as rapidly as the situation demands. Launching must occur at the optimum moment so that the weapon system may function effectively. The launching system must safely withstand the propulsive forces of the weapon, and it must be highly reliable in order for the weapon to achieve the kill probability for which it is designed.
18.2 GENERAL REQUIREMENTS
The most significant general requirements of launching systems are as follows:
18.2.1 Speed
The launcher must be capable of rapid initial employment and a subsequent high rate of fire.
18.2.2 Reliability
No matter what the degree of sophistication adopted in the design of a launcher, it must be capable of a certain level of repeated use without failure. It must also be repairable.
18.2.3 Safety
The vehicle upon which the launcher is mounted and the personnel who operate and control the launcher must be able to function without damage or injury.
18.2.4 Compatibility
The launching system must complement the mission of the delivery vehicle and consequently other weapon systems installed. It must be designed to withstand the particular rigors of deployment associated with the mission of the delivery vehicle as well (corrosive environment, strong dynamic forces, vibration).
18.3 FUNCTIONS
Any launching system must perform certain distinct functions in order to successfully launch the weapon associated with it. In the operational configuration, these functions do not necessarily occur in isolation, but frequently integrate as processes in achieving the designed goal of the system. These basic functions are as follows:
18.3.1 Storage
A safe and readily accessible area must be provided for the storage of weapons until they are needed.
18.3.2 Transfer
The weapons must be moved from the storage position to the loading position and vice versa.
18.3.3 Loading
Before the weapon may be put into flight, it must be placed on the launching device in a ready-to-fire position.
18.3.4 Control
Once the weapon has been loaded, it must be oriented in space. Typically a launching system functions in response to the solution of the fire control problem. Specifically, the launcher receives the position error signal from the computational systems, in the form of a DC voltage. Most launching systems are configured with angle-tracking servo systems for train and elevation. The angle-tracking servo system responds to the analog (DC voltage) input in a manner identical to the angle-tracking system described in Chapter 5.
18.3.5 Launching
Flight initiation occurs during the process of launching as a result of a propelling force provided to the weapon by gravity, an impulse, or a reaction. A launching system is classified by the propelling force employed.
18.4 GRAVITY LAUNCHING SYSTEMS
Gravity launchers are characteristically simple in design because they rely upon gravity to cause separation of the weapon from the launcher. Since the initial velocity and orientation of the weapon is supplied by the delivery vehicle, no additional forces are applied to the weapon at release, and the launcher incurs no sudden shock. Airborne platforms used this type of system in the past. However, with the high speeds of high-performance aircraft, gravity launching of all but small practice weapons has become unfeasible. Because of the air-flow patterns about the weapon and launch platform, aerodynamic forces are created that can result in the weapon not separating from the aircraft or separating and then striking the aircraft. Therefore, pure gravity-launching systems are seldom used.
18.5 IMPULSE LAUNCHERS
In this case a force is applied to the weapon either to project it along the entire path of its trajectory or, to a lesser degree, to clear the weapon from the delivery vehicle. Two basic launcher types employ this method: cannon launchers and ejector launchers.
18.5.1 Cannon Launchers
Cannon launchers are more common and may be further subdivided into guns, howitzers, and mortars. The basic differences among these subdivisions are trajectory, initial velocity, and size of the launcher, with guns having the highest muzzle velocities and flattest trajectories. Since the functional operations of the three cannon-launcher types are similar, gun launchers will be examined.
18.5.1.1 Gun-type Launchers. A gun launcher not only imparts Initial Velocity or IV to the weapon (more commonly referred to as a projectile), but it also provides projectile flight guidance in the most simple application. Specially designed projectiles may be fitted with a rocket motor (rocket assisted projectile--RAP) or with a guidance package (Laser, IR). A major consideration in gun launcher design is energy dissipation of the reaction force (recoil) created by the impulse employed to propel the projectile.
In Chapter 17, various propulsion principles were discussed, all of which led to the generation of heat and gas in a confined space. Gun barrels must be constructed with enough inherent strength to withstand the pressures developed by propellant heat and gas. Additionally, most gun launchers are characteristically large and heavy since the reactive force of the initial impulse is largely absorbed by the launcher in conjunction with its recoil/counter-recoil system.
A gun barrel is normally thickest at the powder chamber where the greatest pressure effects occur. The gun barrel then tapers in thickness proportional to the pressures exerted by the propellant. To gain an appreciation of the basic principles involved in gun design, see figure 18-3.
Gun strength must exceed the powder pressure at every point by an amount that will provide a sufficient margin of safety. The pressure curves in figure 18-3 show pressure beginning at a value well above zero. This indicates the pressure build-up that occurs after the propelling charge begins to burn but before the projectile begins to move. (The x-axis in the figure represents projectile movement in the bore, not time or bore length.)
Note that the gun strength curve does not vary in parallel with the powder pressure curve. The reason is that the same pressure that the expanding gases exert against the base of the projectile is exerted equally against all interior surfaces of the gun behind the projectile. Hence, the breech part of the barrel must be designed for the maximum stress. After the projectile passes the point of maximum pressure, it continues to be accelerated by gas pressure until it leaves the muzzle. The total area under the curve, up to the point where the projectile leaves the gun, is a rough measure of initial velocity, and the pressure remaining at the muzzle is an indication of the muzzle loss. A high muzzle pressure increases muzzle flash. As can be seen in the figure, employment of a high explosive would exceed the strength of the gun almost instantaneously upon detonation. In fact, the release of energy would be so rapid that the greater portion would be expended in rupturing the gun rather than in translating the projectile through the barrel.
The gun barrel is subject to two principal stresses:
1. A tangential stress or tension, coupled with a radial stress, tending to split the gun open longitudinally.
2. A longitudinal stress tending to pull the gun apart in the direction of its axis.
The greatest stress is in a direction tangent to a radius of the barrel due to gas pressure, and thus the longitudinal stress can be neglected without significant error. Lames' Law states: "At any point in a cylinder under fluid pressure, the sum of the tangential tension and the radial pressure varies inversely as the square of the radius." This means that in a cylinder under internal pressure, points in the metal close to the bore experience a large proportion of the stress, while those at a greater radius experience progressively less stress. The result is that there is a limit beyond which any additional wall thickness will not add much in strength. Therefore, construction methods must be employed that will cause the outer layers of metal to absorb more stress.
All modern gun barrels are made of steel, and they are generally prestressed to make them more resistant to internal (bursting) pressures. The object of prestressing is to make the outer layers of metal in the barrel bear a greater proportion of the bursting load. The builtup method of prestressing is to heat steel ring-shaped jackets, or hoops, to high temperatures, then slip them over the gun tube and allow them to cool. As the hoops cool, they contract, until at the end of the process they squeeze the tube with a pressure of thousands of pounds per square inch.
Most modern gun barrels are of one-piece or monobloc construction. They are prestressed by a process of radial expansion. In this process, a gun tube with bore slightly smaller than the caliber desired is expanded by hydraulic pressure. When the pressure is released, the outer layers of the tube tend to return to their original dimensions, while the enlarged inner layers tend to maintain their enlargement. Thus, the inner layers of metal are severely compressed by the contraction of the outer layers, as if a hoop had been shrunk on them. The built-up and radially expanded methods may be incorporated in a single gun. The 8"/55-caliber gun, for example, has a jacket shrunk on a radially expanded tube. Smaller guns are made from a single steel forging with neither radial expansion nor hoops. The pressure per unit area may be higher in small guns than in large guns; however, the tube walls may be made thicker and more massive in small guns without resulting in an excessively large forging. This type of construction is limited to guns of 3-inch caliber and smaller.
18.5.1.2 Recoil/Counter-recoil Systems. Recoil is the rearward movement of the gun and connected parts during and after firing. It is caused by reaction to the forward motion of the projectile and propellant gases. After recoil, the gun and connected parts return to the in-battery, or firing position. This forward movement is called "counter recoil."
If the gun were mounted rigidly, without any recoil system, it would be practically impossible to build a carriage to withstand the loads imposed upon it, without rupturing, overturning, or displacing it. To bring the carriage stresses down to a reasonable value and to ensure stability, a recoil system is interposed between the gun and the carriage. The recoil mechanism absorbs the energy of the recoiling parts over a certain convenient length and returns the gun to battery for further firing. The recoiling parts are the gun and those parts of the recoil mechanism and carriage that move with the gun in recoil and counter recoil. A recoil mechanism usually consists of three components--a recoil brake, which controls the recoil and limits its length; a counter-recoil mechanism, which returns the recoiling parts to in battery position; and a counter-recoil buffer, which slows the end of counter-recoil motion and thereby prevents shock of the recoiling parts (figure 18-4).
In most naval guns the recoil brake is hydraulic and consists of four elements: a cylinder; a piston; a liquid, such as glycerin and water; and some form of orifice in the piston that allows the liquid to flow from one side of the piston to the other. The motion of the piston within the cylinder forces the liquid through the orifices, absorbing the energy of recoil and controlling the return of the gun to battery during counter recoil. The work required to force a liquid through a given orifice can be definitely determined from the laws of hydraulics and depends on the area of the orifice, the area of the piston, the velocity of the piston, and the weight of the liquid. It can be shown that the work absorbed by the hydraulic brake can be fully accounted for in the rise of temperature of the liquid. Under rapidfire conditions, the temperature rise is accumulative from shot to shot and results in a considerable rise in temperature, which must be taken into account in designing a recoil system.
18.5.1.3 Muzzle Brake. Another method of reducing the forces of recoil is the muzzle brake. A muzzle brake is a device consisting of one or more sets of baffles attached to the muzzle end of the gun barrel (figure 18-5). As the projectile leaves the muzzle, the high-velocity gases following the projectile through the tube strike the baffles of the brake and are deflected rearward and sideways into the atmosphere (figure 18-5). In striking the baffles, the gases exert a forward force that partially counteracts the force of recoil. The muzzle brake also acts as a blast deflector and reduces obscuration of the target, an important function in direct-fire weapons (tanks).
18.5.1.4 Soft Recoil Systems. In the development of gun launchers for aircraft, it was found that the high-velocity projectiles used caused excessive reaction forces at the gun trunnions. Consequently, additional structural strength had to be built into the airframe to absorb the stresses transmitted to the aircraft structure. To reduce these reactive forces, the principle of soft recoil was applied to these weapons. Another term for this principle is out-of-battery firing.
The soft recoil system differs from the conventional recoil system in that the recoiling parts are mechanically held against a gas spring force acting in the direction of firing. Upon release, the expanding gas accelerates the housing forward in the direction of fire; propellant ignition occurs automatically when proper velocity is attained. The firing impulse overcomes the forward momentum of the recoiling parts, reverses their direction, and forces them back against the gas spring until they are latched into the battery position. Figure 18-7 illustrates the difference between the conventional and soft recoil systems.
The advantages of the soft recoil system are that it greatly reduces the horizontal forces on the gun platform or trunnions and the total recoil cycle time is reduced, allowing for higher rates of fire. In addition to aircraft guns, this system is currently employed on the 105-mm light towed howitzer.
18.5.1.5 Recoilless Systems. Another solution to the recoil problem is the recoilless principle. The recoilless rifle operates on the basis that if the momentum of the propellant gases discharged to the rear is equal to the gases expelled forward, then the launcher will have no momentum imparted to it. Considering the four movable parts of the system to be the projectile, the gases forward, the gases rearward, and the gun itself, and representing the mass of each as m1, m2, m3, and m4, respectively, and the velocities of each as v1, v2, v3, and v4, then:
m1v1 + m2v2 + m3v3 + m4v4 = 0.
If the gun is recoilless, then v4 = 0, and the equation reduces to:
m1v1 + m2v2 + m3v3 = 0
or
m3v3 = - m1v1 - m2v2.
That is, the combined momentum of the projectile and the forward-moving gases is equal, but opposite in direction, to the momentum of the gases discharged through the breech. If this is true for all instants during the weapon's firing period, which is about a hundredth of a second, then the momentum of the weapon must equal zero at all times during firing, and the weapon can be considered perfectly recoilless. In practice, however, this is generally not the case. A recoilless weapon is usually recoilless in the mean; i.e., although the total momentum applied to it over the firing period is zero, the sum of the momentums at any instant is not necessarily zero. The weapon undergoes large unbalanced forces during some parts of the pressure interval, and oppositely directed forces during other parts of the pressure interval. Thus, its recoillessness is an average rather than an absolute value. Figure 18-8 illustrates the basic considerations associated with a recoilless rifle.
The main advantage of recoilless rifles over conventional guns of comparable caliber is their much lighter weight, which gives them greater mobility. The price paid for this advantage is a slight reduction in velocity and range, and a large (2.5 to 3 times as much) increase in the quantity of propellant required. The main drawback of recoilless launchers is the tremendous blast to the rear of the gun (back blast) caused by the escaping gas. The danger zone for a comparatively low caliber (57-mm) rifle is a conical section 17 meters long and 14 meters wide diverging rearward from the breech. Because of these disadvantages and the fact that techniques for achieving greater mobility of conventional guns have been developed, recoilless rifles are not as prevalent in the ground arsenal as in the past.
18.5.2 Ejector Launchers.
Impulse launchers for weapon ejection are employed for both free-fall and self-propelled weapons. Their main purpose is to ensure that the weapon safely clears the delivery vehicle. Ejection is usually accomplished by the expansion of high-pressure gases from a compressed air supply or from ignition of a propellant charge. Because it is used for ejection purposes only, the impulse is small, and the launcher can be built to withstand the shock of launching without the need for excessive structural strength or special devices. Thus, launchers of this type are fairly light and simple in design.
Self-propelled weapons, which are impulse launched, frequently are large and heavy, making transfer and loading a slow, laborious process. A launcher of this type usually has several launching tubes, and the weapons are stored within the tubes until needed. The most common launcher of this type is the torpedo tube. Torpedo tubes are installed in ships and submarines and may be of fixed or trainable design. Torpedo ejection is caused by expanding gas from a gas-generating chemical or from a compressed air supply. In earlier submarines, fixed torpedo tubes were installed in the bow and stern; in most U.S. Navy submarines, however, they are located only in the forward section. Fixed tubes are also found in certain surface combatants. These nontrainable tubes are mounted within enclosed spaces singly or in groups of two or more on each side of the ship. To preclude the launch vehicle having to maneuver radically to provide ideal orientation for the torpedo relative to the target at launch, torpedoes deployed from fixed tubes are equipped with guidance features to compensate for this restriction. The interior location permits all tubes to be located in a torpedo compartment where they may be readily maintained, regardless of weather or topside activities.
Trainable tubes are installed aboard surface ships in a clear deck area so that they may be oriented as required. The triple-tube launcher, illustrated in figure 18-9, is most commonly found on destroyer-type combatants.
To reduce space, the tubes are stacked one above the other. By fabricating the tubes of reinforced fiberglass, weight is reduced to a minimum, and maintenance due to topside exposure is less. In this figure, note the air flasks at the breech. Removable covers are provided at the muzzle when the launcher is in a stowed configuration.
One method in which missile-equipped submarines launch their missiles is by compressed-air ejection. Compressed air is stored in a launch flask until missile launch. At this time the compressed air is released into an eject pressure chamber beneath the missile where the pressure is built up at a programmed rate. This results in a smooth, rapid acceleration of the missile to the required ejection velocity.
Employing principles similar to that described above, ejection may be accomplished by burning a propellant grain. In this case, the hot gases generated by the propellant grain may be used to flash water to steam. The steam-gas mixture can then be introduced to the eject pressure chamber to accomplish missile ejection. This steam eject system is found aboard newer submarine classes. In either case, the result is a flameless launch, with rocket motor ignition of the missile occurring at a safe distance from the submarine.
In addition to ejecting large ballistic missiles from missile tubes, submarines can also ejection-launch smaller missiles from their torpedo tubes. Harpoon and Tomahawk can be launched in this manner.
Ejection launchers are also employed aboard aircraft. Nearly all free-fall and glide weapons carried by naval aircraft are ejection-launched. At the time of launch, an explosive cartridge(s) is detonated. This produces a high-pressure gas that acts on a piston, thus forcing the hooks holding the weapon to open, and simultaneously forcing a metal rod or ejection foot against the weapon. This action physically ejects the weapon away from the aircraft, ensuring that it is clear of the aerodynamic flow around the aircraft.
In addition to free-fall weapons, missiles are also ejection-launched to clear them from the aircraft prior to motor ignition. Phoenix and Sparrow are examples of this.
18.6 REACTION LAUNCHERS
This third general type of launcher is one in which the force separating the weapon from the launcher is contained within the weapon. These weapons are normally rockets or missiles. The propulsion system of the missile itself may be used to provide the necessary force. Thus, most self-propelled weapons, if not launched by ejection, are put into flight by reaction launchers.
Reaction launchers provide static support for the weapon and initial flight orientation. They are characteristically small and light since they are not required to sustain large moments of force upon weapon launch. Reaction-propelled weapons often depend upon wings or fins to provide lift, and must use rocket thrust to overcome gravity temporarily and to propel the weapon to desired flight speed. If, during the development of thrust, a weapon is free to move along the launcher, it might not have sufficient thrust or lift to overcome gravity at the time it leaves the launcher. Thus, the missile could fall to the deck of a launching ship or become completely disoriented before sufficient thrust or lift had been developed to sustain its flight. To prevent this from happening, the weapon is restrained on the launcher until sufficient thrust is generated. The restraining device may be simply a pin that is sheared when the weapon develops the required thrust, or it may be a more complicated, reusable device that releases the weapon when the required thrust is exerted.
The launcher must be protected from the blast and subsequent corrosive effects of the propellant exhaust stream. This is usually achieved by a protective covering of the launcher and by blast deflection plates or shields. The launcher structure must be able to resist the deteriorating effects of the propellant gases, and the structural design of the launcher should be such as to minimize loading or stresses due to propellant blast or recoil momentum. As with any launcher, the reaction launcher must be compatible not only with the space and weight limitations imposed by the delivery vehicle, but with the environment in which the vehicle operates as well. Launcher design is influenced by the degree of control and guidance required of the weapon system. An uncontrolled rocket may require a considerable amount of flight control by the launcher before it is released into free flight, while a guided missile does not require this initial control to the same degree. Consequently, reaction launchers are divided into four classes: rail, zero-length, platform, and canister.
18.6.1 Rail Launchers.
The term rail launcher may be applied to launchers making use of rails, tubes, long ramps, and even tall vertical towers. All provide, to a varying degree, constraint to the weapon while it is moving on the launcher, and they thus provide a considerable amount of flight control. For uncontrolled weapons, such as rockets, the rails must be fairly long so that the rocket is constrained for a longer portion of the rocket motor burning time to provide the necessary initial velocity vector control. If the missile is equipped with a guidance system, the rail length can usually be reduced. Long-range weapons, guided or unguided, normally require a longer rail since their initial acceleration is comparatively low relative to short-range weapons. A rocket booster may be employed, however, to provide sufficient acceleration to permit reduction of rail length. This is the case with the surface-launched Harpoon.
Thrust developed parallel to the axis of the rail or tube will propel the weapon along the rail and into a proper trajectory. Vertical components of the thrust will force the weapon against the rails or tube and thus against the launcher. The launcher must, therefore, be capable of withstanding a portion of the weapon thrust as well as of supporting the weapon. Lateral constraint of the weapon is necessary in order to prevent the weapon from lifting from the rails or wandering during its motion along the launcher rail. This is usually achieved by lugs on the weapon, which ride in slots on the launcher rail. In general, the longer the launcher rails, the better the initial flight control and the less the launching dispersion.
However, long rails, like long beams, can sag and bend. The longer the beam, the greater the possible deflection, unless the rail is well supported along its entire length. This kind of support is not practical in tactical launchers, so a certain amount of beam deflection or droop will occur at the end of long rail launchers. This droop and the effects of vibrations set up as the missile moves along the rail cause the rail to whip and produce unwanted deviations in the missile orientation. These effects can be minimized by reducing the length of the launcher rails. Thus, material and structural characteristics will limit the length of a rail launcher for tactical usage. This necessary restriction in rail length is not as serious as it might seem because the effectiveness of a rail launcher in constraining weapon travel to the direction of the rails varies as the ratio of time of rail travel to the total time of boosted uncontrolled flight. Since a weapon starts from rest on the launcher, the time of rail travel will vary as the square root of its length.
Since
S = 1at2 (18-1)
2
Then
t = 2S (18-2)
a
Where
S = rail length
a = missile acceleration
t = elapsed time of travel
Therefore, a relatively short rail will still provide considerable initial flight control to a weapon.
Rail launchers may be fixed or movable. They may serve as ready service storage for missiles and provide facilities for fueling and servicing. The simplicity of design of rail launchers also promotes reliability and ease of maintenance and repair. Airborne launcher rails, because of space and air flow-field problems, are usually very short. As a rule, the greater the speed the missile had achieved at separation from the launcher, the less the air-flow field effects will influence missile flight. Rail launchers are deployed aboard ships, submarines, aircraft, and in the field.
18.6.2 Zero-length Launcher.
Through common usage, the classification "zero-length launcher" has come to mean any rail launcher where the weapon travels less than eight centimeters before it is released from the rail. Since the weapon separates from the launcher shortly, or even immediately, after it begins to move, little or no effective flight control is provided by the launcher. Therefore, the launchers are used with weapons that can immediately assume stable flight. The chief advantages of zero-length launchers are their small size, light weight, comparative simplicity, and ease of maintenance and repair. Because of their small size and weight, the zero-length launchers require a minimum of deck space and are easily moved in train and elevation. Therefore, they are used extensively in shipboard, ground, and airborne installations for the launching of guided missiles. Figure 18-11 shows an aircraft version.
18.6.3 Platform Launcher.
A platform launcher is relatively simple in construction and is employed where the rocket or missile must achieve high altitude as soon as possible for most efficient operation. In the rarefied air of the upper atmosphere, velocity loss due to aerodynamic drag is minimized, resulting in greater final velocity and longer range. Long-range ballistic missiles are built as light as possible and are stressed primarily for longitudinal loads. ICBMs and similar missiles are normally launched vertically from a platform. At present, there are no platform launchers employed in Naval and Marine Corps weapon systems.
18.6.4 Canister Launchers.
With the advent of solid-state guidance, all-electric controls, and solid-fuel rocket motors with a long service life, guided missile storage requirements have been greatly simplified. These advances, combined with missile flight characteristics that allow the use of zero-length rail segments or by the surface of the container for lightweight weapons. The canister may be hand-held, as in the Stinger and Dragon employed by the Marines. For larger missiles such as Harpoon, the canister containing the weapon is installed on or within a support structure or launch tube that may be fixed or mobile. In either case the weapon remains within a sealed container until launch. This minimizes direct handling of the weapon and limits its exposure to adverse environments.
The Vertical Launch System (figure 18-15) employs a standard canister that may contain a variety of missile types, deployed in eight-cell modules aboard ship. The result is a net increase in weapon stowage as well as rate of fire. Each cell and canister acts as a separate launcher independent of the others, except for the exhaust-gas management system that is common to each eight-cell module. There is no launcher reload time, and thus a much higher rate of fire can be maintained.
The canister launcher, though advantageous in many ways, places additional stress on the weapon because of the interior ballistics of the system. The canister confines the weapon for a short period of time after rocket motor light off, subjecting if to shock waves due to the flow of high-velocity combustion products prior to the rupture of the canister end closures and
the weapon's emergence. Ignition of the rocket motor causes a shock wave to develop between the weapon and the inner wall of the canister. This shock wave is re-transmitted from the forward closure back to the missile radome. The net result is a pulsating axial load on the weapon due to dynamic gas phenomena in the canister during launch. The effects of these forces vary with the specific system, but have been known to reach 1,000 N in the VLS employing the Standard missile.
In the special case where the canister is stored and fired from within a ship hull, such as in VLS, exhaust-gas management is a significant problem. The exhaust stream typically has a temperature of 2,400 Kelvin and a velocity of over 2,500 meters per second. Additionally, it includes highly abrasive particles and active chemical agents. Whatever system is used to dissipate the missile exhaust, it must be able to withstand strong pressure waves, not only for the brief time between motor ignition and weapon departure, but it must also be able to handle the complete burn of the rocket motor with the weapon restrained in the canister in the event of accident. The ability to handle restrained rocket motor burn has been a missile-magazine design constraint since missiles were first placed aboard ship; the intent in VLS, however, was to make sure that not only would the ship survive, but that the remaining missiles were still operable as well. Steel surfaces are protected form melting or being weakened by a replaceable ablative coating that dissipates heat by vaporization during exposure to rocket-motor exhaust. The exhaust stream is routed to the atmosphere by a duct system that avoids impingement on unprotected surfaces.
18.6.5 Launcher Cutouts
Due to obstructions, guns and missile launchers aboard ship and ashore are subject to constraints in their coverage. Shore-based systems must deal with terrain features and man-made structures when a clear, flat emplacement area cannot be found. Shipboard weapons systems are subject to deckhouses, antennas, lifelines, boats, and other weapons in their firing arcs. All systems employ some type of mechanical linkage that inhibits the firing circuit at values of azimuth and elevation that would cause the weapon to damage structures or be damaged or deflected during launch. These firing cutout mechanisms can also be constructed so that the launcher or gun will automatically elevate to a safe firing elevation at azimuths where obstructions are located, while notifying the controlling weapon system of the circumstances.
18.7 STORAGE
To achieve and sustain optimum firing, the launching system selected for a given weapon system must include a storage subsystem capable of performing its allotted functions in a minimal period of time. The capacity of the subsystem must be adequate to sustain the desired firing operation and the facilities must be readily accessible. A magazine is a term used to denote a storage area needed to provide the space and the safety facilities for storage of large quantities of gravity, gun, or reaction-type weapons. Magazines are classified in three categories:
18.7.1 Primary Magazines.
This category is designed to stow the delivery vehicle's complete peacetime allowance of ammunition. Primary magazines are typically well-protected and equipped with thermal insulation, ventilation, and sprinkling systems designed to cool the weapons below a programmed upper temperature limit. A method of ensuring security, both physical and environmental, is associated with the primary magazine, such as locking devices and alarm systems, local and remote. In the case of reaction-type weapons, restraining equipment for the weapon is incorporated to prevent an ignited propulsion motor from moving the weapon. Vents are also provided to prevent disruptive pressures from developing within the magazine in the event of inadvertent propulsion motor ignition.
18.7.2 Ready Service Lockers.
This type of storage designates the ammunition storage facilities in the immediate vicinity of the launcher. This storage is used only when ammunition is required to immediately service the launcher. Under this classification scheme, certain gravity and reaction-type launching systems do not have primary magazines as such, and may be said to have only ready service magazines. However, the characteristics of primary magazines are normally incorporated in the design of these storage facilities.
18.7.3 Lockers.
These are compartments designed for storing sensitive or special types of ammunition such as fuzes, pyrotechnics, blasting caps, hand grenades, and explosive chemicals. Lockers are normally located above the damage control deck and on a weather deck if possible to localize and minimize the effects of fire or other adverse environment.
Most magazines are single-purpose. That is, they are designed for a homogeneous quantity of ammunition. Multipurpose magazines may be required because of space limitations in the delivery vehicle. In this case different types of ammunition will be stored. Such mixed storage will not include special types of ammunition designated for locker storage. Where mixed storage is employed in the multipurpose magazine, the various types of ammunition will be segregated for ease of identification and accessibility. Very specific requirements exist specifying ammunition types that may be stored in the same magazine or locker and those which are incompatible. These regulations are listed in OP5 for shore stations and in OP4 or OP3347 for ships.
18.8 TRANSFER EQUIPMENT
Weapon transfer equipment is designed to move weapons and associated components (fuzes, special payloads) from the primary magazine to ready-service lockers and then to the launcher. In addition, the transfer system is normally capable of returning the weapon to the magazine. To achieve rapid initial employment, the transfer system must be capable of moving the weapons at a rate commensurate with the launcher rate of fire. If a transfer line or channel has a transfer rate less than the required rate of fire, then two, or even three transfer lines may be necessary to feed the launcher. When transferring weapons to rotating launchers, it is necessary at some point along the line of shift from nonrotating transfer equipment to equipment rotating with the launcher. This becomes a problem of considerable magnitude for a high-rate-of-fire system where the weapon must be transferred while the launcher is rotating. This can be accomplished by a manual transfer, or by complex automatic equipment, as in high-rate-or-fire naval guns. When the weapons to be transferred are large, it is often necessary to have the rotating launcher return to a specified position before a weapon is transferred to it. Weapon flight preparation facilities are often found in the transfer system. En route to the launcher, operations such as weapon assembly, checkout, servicing, and even programming of the weapon may be performed. To prevent danger to operating personnel and damage to the delivery vehicle in the event of weapon explosion or ignition, the transfer system must be designed to localize and contain detonations, fires, propulsion-motor blast, etc. In addition to the lethal effects of the weapon itself, personnel can be injured by the moving and rotating machinery of the launching system. Thus, in the transfer system, as well as in every component of a launching system, careful attention must be given in the design of equipment to minimize the danger of accidents.
The transfer of gun ammunition and reaction ammunition can be as simple as moving an airborne missile on a dolly from the primary magazine, via elevators, to the launcher mounted on an aircraft, or it can be as complex as a system that provides for the automatic transfer to a dual-rail launcher of large guided missiles weighing in excess of one ton. In the more complex transfer systems, hydraulic, pneumatic, and electrical servo systems are employed to accomplish the task in such a manner that operating personnel must only monitor system functions from a local or remote-control panel.
18.9 LOADING EQUIPMENT
Weapon loading equipment is needed to place the weapon in firing position on the launcher in a rapid, reliable, and safe manner. The loading operation consists of moving the weapon from the transfer equipment to the launcher and positioning it on the launcher. This operation involves a transfer to the launcher and the moving or ramming of a weapon along rails or trays into firing position on the launcher. The transfer and ramming functions can be performed manually, mechanically with human operator control, or automatically with human monitoring. In some types of fixed launchers with low rates of tire, the ramming operation is not necessary. The weapon is simply hoisted or lowered into position on the launcher. However, loading high-rate-of-fire launchers requires a fast, precise ramming cycle. Some means must be provided for the unloading of unfired but usable weapons and for the jettisoning of unsafe and dud weapons. In most cases, the loading equipment is designed to accomplish these functions when it is not desirable that they be accomplished by hand. In some cases, special equipment must be provided to perform the jettisoning function. To achieve rapid weapon employment and to maintain a high rate of fire, the loading rate must be commensurate with the required launcher rate of fire. As with transfer equipment, this often requires the use of more than one loading unit per launching tube or rail, or more than one line or channel feeding weapons to the ramming equipment. The majority of automatic loading systems employ a catapulting device, a rail spade, or chain device.
18.9.1 Catapult Ramming.
This method is found in gun launchers employing fixed ammunition. A round is received form the transfer system and aligned with the gun bore. The tray in which the round is resting is then moved toward the breech rapidly, and abruptly stopped. At the end of the tray travel, the round is released and catapulted into the chamber, whereupon the breechblock seals the breech. Figure 18-18 portrays this loading method.
18.9.2 Rail-spade Ramming.
This method is frequently employed in the ramming of semi-fixed and separate loading ammunition, and in the loading of torpedoes and reaction weapons where the weapon is housed in a ready-service magazine (the launcher itself). Figure 18-19 depicts rail-spade loading of a torpedo/booster configuration.
The size of many reaction weapons require the use of manually controlled loading equipment. The weapon is supported by the loader, which may be fixed or portable, in the vicinity of the launcher and slowly rammed into position. This is a comparatively slow process and is suitable only for launchers that are not expected to engage a large number of targets between reloading.
18.9.3 Chain Ramming.
A flexible-link chain is frequently employed in the previous two categories of ramming, but in this category, the end of the chain is provided with a buffer pad that engages the base of the weapon. The chain is driven by a sprocket along a track, where it is free to move forward or retract, as required. In figure 18-20 notice that the chain can flex in only one direction. The buffer serves to protect the weapon from damage since velocities of more than three meters per second may be achieved by this ramming method in some designs.
18.10 CONTROL
Once the weapon has been loaded in the launcher, the final step of engaging a target may take place--the delivery of the weapon. For this to occur, the launcher must be positioned along a line that will ultimately result in the weapon intercepting the target. This line is, appropriately, the line-of-fire (LOF). In general, the launching system is subordinate in weapon-system dynamics in that is must respond to certain types of orders. Depending upon the weapon system employed, these orders are known as gun orders, launcher orders, torpedo orders, missile orders, etc. The specific nature of these orders will vary from system to system. For instance, a typical set of gun orders may be: gun train (Bdg'), elevation (Edg'), sight angle (Vs), sight deflection (Ls), parallax (pl), and fuze time (T5). The alphanumeric figures associated with each of the orders are known as fire control symbols. They are often employed as a shorthand device for describing information/data flow in weapon systems. Following is an example of a set of missile orders: seeker head orders, doppler predict, ship roll correction, channel select, gravity bias, and target select. Each of these orders will be transmitted from the computational system to the launching system and /or to the weapon itself continuously during the interval between launcher assignment and weapon launch or until the launcher has been taken out of the system electronically.
A launching system will often have several types of weapons stored within its confines, so it must receive orders regarding the type or types of weapons to be launched. For example, in a shipboard gunlaunching system, several types of projectiles are in the magazines. Control station personnel must select the type of projectile to be fired and notify the launching system of its choice. In a shipboard guided-missile launching system, both homing and beam-riding missiles may be available. The launching system must receive orders regarding which type of missile to launch. In addition to the type of missile, the launching system must know how many missiles to launch. For example, a submarine launching system may fire one, two, or a whole spread of torpedoes. A guided-missile launching system may fire a one- to two-round salvo, and a gun-launching system may fire continuously until a target is destroyed or out of range.
Basically, however, the most important function of the launcher is to provide initial flight orientation to the weapon. In cases where the launcher is fixed rigidly to the delivery vehicle, the whole vehicle must be maneuvered to provide this orientation. When a launching system is mounted in a vehicle that is not suitably maneuverable, a launcher that may be rotated about one or more axes is normally employed. As discussed in previous chapters, a sensor system will detect, classify, and locate a target such that present target position is continuously entered into the computational system. It is the output of the computational system that provides the orders that cause movement of the launcher to the LOF. As discussed in Chapter 5, once the line-of-sight (LOS) is defined by the tracking system, the weapon launch lead angle may be computed. The gross measure of this angle is between the LOS and the LOF. Movement of the launcher in azimuth (train), and elevation to the LOF is accomplished by respective analog signals in the form of DC error voltages representing magnitude and direction. The launcher is normally referenced to the delivery vehicle (reference frames will be discussed further in Chapter 19. The error signals are entered into the train and elevation servo systems of the launcher. The resulting drive signals cause the launcher to respond in train and elevation, while employing position and velocity feedback in a manner identical to that described in Chapter 3.
In order to carry out control of a launching system effectively, a scheme of communications must be incorporated. Physical movement of the launcher and transfer/loading functions may be directed by simple voice commands, followed by an appropriate action response. In more complex systems where multiple weapons are employed against various, simultaneous targets, communications are accomplished by information systems using electronic data-processing components. In the more extreme order of complexity like Aegis, communication and control may be initiated by the operator, whereafter the complete cycle of transfer, loading, positioning, and launching will occur without further human operator input.
18.11 LAUNCHING SYSTEMS
In the case of impulse and reaction systems, launching of the weapon is brought about by the activation of the propelling charge in such a manner that expanding gases result int eh expulsion of the weapon. Launching for gravity systems is brought about by the simple release of the weapon. Launching systems must provide for the safety of operating personnel and the vehicle in which the systems are installed. A great number of safety features are included in the various components that make up the entire system. Most launchers are equipped with mechanisms that prevent the launcher from pointing or firing at the delivery vehicle. Mechanical devices, such as firing cut-out cams and electrical circuitry programmed to cause arbitrary launcher movement upon approaching blind or non-firing zones, are employed to ensure that the line-of-fire never occurs within a danger zone without warning to operating personnel.
Methods to evacuate or re-direct propellant gases are a design feature of launchers to prevent physical harm to personnel and damage to components (gas ejectors in guns, blast deflectors and diffusers in reaction launchers). Generally, however, the delivery vehicle is protected from exhaust damage by the design and location of the launcher on the vehicle as well as by the maintenance of an unobstructed area around the launcher and the use of protective materials.
18.12 SUMMARY
The purpose of a launching system is to place a weapon into a flight path, the LOF, as rapidly as required. Launching systems must perform with speed and reliability, while displaying weapon system compatibility and safety. The basic functions of the launching system are weapon storage, transfer, loading, control, and launching. The three basic types of launchers are gravity, impulse, and reaction. The lightest and least complex type is the gravity launcher, while the impulse launcher is characteristically heavy and bulky. The requirement to contain the reactive propellant gases and to dissipate the reactive energy of the propellant through a recoil system contributes to the size requirement of impulse launchers. Reaction launchers have significantly minimized these disadvantages. Weapons employed with reaction launchers are characteristically more complex than weapons associated with gravity and impulse launchers. Launchers, once assigned to the weapon system, respond to error signals, called orders, from the computational system; these orders are derived from present target position as established by the sensor system.
18.13 REFERENCES/BIBLIOGRAPHY
Bureau of Naval Personnel. Navy Missile Systems. Washington, D.C.: GPO, 1971.
Commander, Naval Ordnance Systems Command. Weapons Systems Fundamentals. NAVORD OP 3000, vol. 2, 1st Rev. Washington, D.C.:GPO, 1971.
Naval Education and Training Command. Gunner's Mate G 3 2. Washington, D.C.: GPO, 1974.
Naval Education and Training Support Command. Principles of Naval Ordnance and Gunnery. Washington, D.C.: GPO, 1974.
Yagi, Jon J. "Internal Ballistics of Weapon Launching Systems." Naval Engineers Journal, Vol. 95, No. 3, May 1983, pp. 178-91.
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