Projectile weapon (Classic Journeys Era)

Projectile weapons are apparatuses designed to project or throw an object of some design. Above all others, projectile weapons are the most abundant in the universe, having the distinction of being the most veteran and populated. Indeed, the most primitive of ranged weapons are projectiles.

The projectiles field is so numerous that there have been dozens of classification methods for its weapons. This section distinguishes the kinds of guns by the method that they throw the object.


 * Chemical refers to a weapon that uses pressure from a chemical reaction to push the slug toward the target. Called slugthrowers, conventional handguns operate on this principle. Slugthrowers enjoy the most popularity with the armed forces.
 * Electromagnetic weapons are only useful in highly specialized tasks. They use the power of magnets (usually superconducting) to deliver the firing energy to a highly aerodynamic slug. These weapons are often referred to as gauss rifles, rail guns, mass drivers, or coil guns.
 * Rocket-assisted include projectiles that are fired through the force of expanding gases. Unlike chemical weapons, rocket-assisted projectiles propel themselves autonomously. Rocket-assisted weapons are generally explosive and large, such as the missile.

Chemical
Chemical propulsion weapons use the gas pressure produced by a propellant to project a bullet or slug. These weapons are often referred to as slugthrowers. A slugthrower is fired by applying pressure to the trigger. The trigger releases a spring-driven hammer from a ready position. The hammer, or a firing pin hit by the hammer, strikes a primer in the loaded round. The primer explodes and ignites the round's propellant, which produces gases. It is this combined gas pressure that propels the bullet down the barrel of the gun.

In shoulder weapons, weapons designed to be fired by both hands, the hammer is replaced by a bolt, which is usually a metallic stick positioned within the breech, the part of the firearm behind the barrel. The firing pin is placed at the tip of the bolt.

Ammunition
Ammunition plays a factor in the firing process and overall effectiveness of the weapon. Currently, there are two distinct flavors of rounds: cased and caseless.

In cased ammunition, each round (or cartridge) houses the propellant and primer within its own round. This propellant is usually a composite smokeless powder, although antiquated cartridges may use black powder; it's relatively slow burning in order to prevent damage to the weapon. As the primer and propellant undergo a chemical reaction to produce gases, the bullet breaks through the tip of the case and is forced down the barrel of the gun. The leftover cartridge is then ejected and replaced with a new one. With the invention of caseless ammunition in the beginning of the XXIth century, cased ammunition became a rarity. Its viability is maintained for collection's sake.

In caseless ammunition, the propellant encloses the the bullet and essentially mimics a cartridge. The propellant, a solid explosive called composition L, produces gas when triggered by the primer, which is evenly mixed throughout the propellant. The bullet is ejected from the round when the propellant and primer burn away. Because the propellant completely combusts, there is nothing left in the chamber after the bullet is fired: there is no need to eject any casing. Not only does caseless ammunition completely eliminate the need for an extractor system (the mechanism for ejecting spent casings), it is also more powerful than cased ammunition--the propellant is rectangular and has more mass.

Bullets come in diverse designs and shapes. Certain rounds are longer and narrower to improve accuracy, some have special grooves that allow the bullet to expand when it hits (thereby causing more damage), and others are made of different materials to make it faster. As a rule, all bullets will cause damage when effectively fired. Certain bullets simply deliver this damage faster or in greater intensity.

Styles of slugthrowers
Slugthrowers can be further subdivided into five styles, destinguished by method of slug expulsion. This section of documentation assumes that cased ammunition is used; minor modifications are necessary for caseless compatibility.

A revolver is a handgun based on a revolving cylinder, with six breeches for six rounds. With each shot, the cylinder spins to the next loaded chamber. Some revolvers require the firer to pull back the hammer at each shot (single-action), while later designs used the pull on the trigger to force the hammer backward and then release it (double-action). The enduring popularity of the revolver is due to its reliability; it is simple, uses a small number of parts, and rarely jams.

A pistol is a handgun that operates on a magazine. Each magazine has a certain number of rounds stacked together. In each shot, the recoil energy is applied to push the next round into the breech. There are four primary methods for delivering the next round: electric blowback, gas blowback, gas non-blowback, and spring. The details of the individual methods are not within the scope of this document. The pistol is used by law enforcement officers, by guards or watchmen, and as an auxiliary or emergency weapon by members of the armed forces.

A gatling gun operates by crank or motor, which spins a circular bundle of barrels. A new round falls into each barrel as it passes under an ammunition hopper. As the barrel reaches the top of the cylinder, a firing pin inside the weapon snaps against the primer of the round, and the bullet is fired. The empty round casing falls through an extractor slot as the barrel reaches the bottom of the cylinder. The gatling gun is not a mobile weapon by any means. Most are found mounted or towed.

A rifle is a long shoulder weapon that requires the user to manipulate a bolt--a metallic stick inserted into the breech--after each shot. After shooting, the bolt is pulled back, causing the casing to be ejected free. A new round is loaded from a magazine as the bolt is pushed forward and locked. Because the ratio of moving parts to power is high, most rifles are accurate to a long distance. While rifles similar to the one pictured were used widely prior to the Earth industrial revolution, automatic rifles and submachineguns have since superceded it.

A machine gun uses the power of the cartridge explosion to force a new round into the breech and the power of a rear spring to push the firing pin against the primer, causing another cartridge explosion. Because of this system, continuous fire can be maintained if the trigger is depressed. There are three types of reloading mechanisms: recoil, blowback, and gas. Although this document will not discuss these mechanisms, the end result is identical. The machine gun is considered a powerful weapon because of its high caliber and rate of fire, but its sheer weight has prevented widespread use.

Concepts
The inside of the gun's barrel is called the bore. Most bores have spiral grooves etched into it called rifling. This pattern causes the bullet to spin when it leaves the barrel. The spin helps the bullet fly more accurately and aerodynamically.

The diameter of a firearm's bore is called the caliber. It is usually expressed in hundreths or thousandths of an inch. For example, a .45 caliber pistol fires bullets which are .45 inches across. Caliber may also be measured metrically. A 7x57mm firearm uses bullets that are 7mm in diameter. 57mm refers to the length of the bullet case.

The frequency at which a gun fires is called its rate of fire. Cyclic rate of fire means the theoretical frequency, while sustained rate of fire signifies the actual frequency. This distinction is made because slugthrowers produce an immense amount of heat as a byproduct of the burning propellant. The barrel of the weapon will actually melt if too many bullets are fired within a certain amount of time.

A common misconception is the source of the gunshot sound. The 'bang' that is heard is comprised of two elements: the bullet's sonic boom as it breaks the sound barrier, and the explosive release of pressure that was built up behind the bullet. A combination of silencers, or mechanisms designed to muffle the gunshot sound, can be employed to reduce the sound of both.

Recoil, or a backlash of the weapon after firing, is based on Newton's third law of motion; the bullet's rapid expulsion from the muzzle triggers an opposite push in the direction of the firer. As discussed, some of this recoil energy can be harnessed to reload and reprime the next round in the weapon.

Semiautomatic weapons require the user to squeeze the trigger for each shot, while automatic weapons allow sustained fire with only one squeeze. All machine guns are capable of automatic fire.

Many individuals distinguish a seventh genre of firearm: assault rifles. An assault rifle is essentially an automatic version of the bolt-action rifle with a smaller magazine and reduced propellant. The mechanism principle is identical to that of the machine gun. Therefore, this document considers assault rifles to be lightweight machine guns. The assault rifle has proliferated quickly because it strikes a successful compromise between the rifle and machine gun.

A submachine gun is a miniature machine gun that fires pistol rounds. Submachine guns trade stopping power for rate of fire and accuracy. It is balanced between the lethality of a machine gun and the weight of a pistol. The submachine gun has its niche in the special operations market: even though it is notoriously inaccurate at long ranges, it can hold its own in close-quarters combat because it fires faster than most other automatic weapons. Unlike assault rifles, submachine guns can be fully silenced.

Extension: Shotguns
A shotgun is a shoulder weapon designed to push small metal pellets, called shot, through a smoothbore barrel. A cartridge, or shell, holds the shot prior to shooting. Shotguns are made in both single-barrel (in single-shot or repeating types) and double-barrel models. The size of the bore of a shotgun barrel is stated as its gauge. The higher the gauge, the smaller the bore. For example, 12 gauge is 16.8mm (.725 inch) and 20 gauge is 15.7mm (.615 inch).

The mechanism for loading a shotgun cartridge is similar to conventional shoulder weapons. Its design, however, is slightly different. In a normal shotgun shell, the cartridge is cylindrical to accommodate more shot. A wad is present in order to separate the shot from the propellant (powder charge) because they can mix if allowed to intermingle. Because of the special composition of the cartridge, pellets leave the barrel in a narrow to moderate spread. This makes the shotgun immediately lethal at short ranges but almost innocuous at longer distances.

Shotguns are popular with armed forces conducting MOUT (military operations on urbanized terrain) because of their high stopping power and hit probability at close quarters.

Extension: Flechette pistols
The flechette pistol is an infamous weapon, drawing almost universal condemnation from gun authorities and governments. It operates like a shotgun but replaces the normal pellets with shards of aluminum. In terms of lethality versus a normal shotgun, the flechette pistol is not quite as powerful. Its sole purpose is to inflict mortal wounds but preserve the target's consciousness--to extend suffering, in layman's terms.

Because of this, the flechette pistol is banned by most worlds and governments. To the armed forces, it has neither purpose nor value.

Limitations and points to ponder
To the ordinary person, successful weapon handling is a skill that must be learned over the course of several months. Professional handling takes experience that accumulates in a lifetime; this means that no eighteen year old can have adept skills in firearms. Civilians, by large, have no knowledge of slugthrower use, and would not be able to fire one accurately without prior instruction.

An average slugthrower has over one hundred individual parts, each of which may break down. Members of the armed forces receive general instruction on how to clean and repair weapons, although this knowledge does not parallel to that of a professional gunsmith. An ordinary soldier cannot assemble a weapon from spare parts.

Recoil is a prevalent challenge to any user of slugthrowers. This means that with each successive shot on an automatic weapon the chances of hitting a distant target are less and less. Therefore, users of automatic weapons must learn to conservatively fire in either burst or semiautomatic mode. Rambo actions are impossible.

Assault rifles are designed to wound people. With less propellant in each bullet, assault rifles fire bullets with relatively moderate kinetic energy. These bullets are frequently "full metal jacket" rounds that tumble (bounce around inside the body), causing debilitating damage. The theory upheld by militaries is that if one enemy is wounded, then two or more are also put out of commission as the wounded person is cared for.

Bullets hurt. While the invincible hero propagated by movies and novels are entertaining, they are not accurate. The first direct wound suffered decreases the victim's combat effectiveness significantly. People can rarely survive past three bullet hits, and those that do are almost guarenteed to be afflicted with permanent disabilities. Even grazings cause burn damage. It is important to keep this consideration in mind when using slugthrowers.

Heavy weaponry
This document has so far only discussed small arms. Heavy weapons like the artillery gun or cannon are capable of dealing out swaths of damage with little regard for selectivity. The scope of this literature is insufficient to cover heavy weapons. Therefore, reviews of heavy weapons will contain a brief explanation of its mechanism.

Artillery weapons, excluding missile launchers, are weapons that fire projectiles larger than approximately 13 mm in diameter. These weapons normally fire high-explosive projectiles that can reach targets far beyond the range of small arms such as pistols, rifles, and machine gun. An artillery battery consists of two or more pieces (the general term used for individual weapons) of the same size and type that are usually controlled and fired together.

In artillery, the weapons are placed some distance behind the fighting front and the projectiles pass over the heads of friendly troops. The guns are used to inflict casualties and destroy or damage enemy defensive positions before an attack; to break up an enemy attack before the attackers come within range of infantry weapons; to harass and demoralize enemy troops; and to destroy enemy artillery, tanks, materiel, personnel, and ships.

Artillery fire is generally more accurate than aerial or spacial bombing, and can be kept up day and night in any weather. Accuracy comes from the use of various fire control instruments including telescopes, range finders, lasers, and sensors. Mathematical calculations based on data obtained with these instruments allow pinpoint precision. Forward observers, either on the ground, in the air, or in space, play an important role in directing artillery fire.

Parts of an artillery weapon
The typical artillery weapon has two main parts, the barrel and the carriage. The bore contains rifling that cause the projectile to spin in flight, increasing its accuracy. Like small arms, the rear of the barrel is called the breech. Most artillery weapons are loaded from the breech, either automatically through a slot or manually through a door called the breechblock.

The carriage consists of a recoil mechanism--a spring or hydraulic device that absorbs part of the backward-pushing force caused by the firing--and a mounting device that permits the gun or barrel to be traversed (pivoted) and the barrel to be pointed upward at varying angles. The carriage is generally mounted on hoverports or sometimes wheels. Some guns are protected by armor plating.

Artillery types
The size of an artillery weapon is usually expressed in terms of its caliber measured in millimeters or (rarely) inches and fractions of inches. In large guns, especially shipboard guns, the term caliber is also used as a measure of length. The size of the guns is occasionally expressed by the weight of the ammunition fired. Thus a "six pounder" fires a projectile weighing six pounds (2.7 kg).

Three kinds of artillery are recognized: guns, howitzers, and mortars. They are defined by the kind of trajectory (path) followed by their projectiles. Guns and howitzers not mounted on tanks, ships, or aircraft are called field pieces, or field artillery.

A gun is a weapon that has a low, or nearly flat, trajectory. It fires projectiles in a nearly straight or gently curving line. A gun's barrel is long in relation to its diameter. Guns are used against spaceships and tanks and as long-range bombardment weapons. The main weapon of a tank is usually a gun.

A howitzer, usually used as a field piece, has a higher trajectory than a gun--its projectiles follow a more pronounced curve. Guns have greater range than howitzers firing similar ammunition, but are less adaptable to firing over the heads of friendly troops or to reaching targets protected by hills. Most howitzer projectiles are self-propelled. That is, they are assisted by a rocket motor during flight.

A mortar has a very high trajectory; its shells are fired high into the air and plunge almost straight down. Most mortars, unlike guns and howitzers, are loaded from the muzzle (front end of the barrel) rather than from the breech. Since they have short, smoothbore barrels (barrels without rifling), they are short-range weapons of limited accuracy. The mortar consists of a tube resting on a heavy metal base. The shell is dropped down the muzzle. When it hits the bottom of the tube, an explosive charge that fires the shell is set off.

Electromagnetic
Electromagnetic weapons propel a small slug to a target through the use of magnets. These weapons trade off charging time for almost ludicrously high projectile speed and range. Electromagnetic weapons have many names, including gauss rifle and mass driver, but can be best distinguished by acceleration method: coil or rail.

Magnetism explained
A magnet is an object, usually in the shape of a rod or horseshoe, that attracts iron or steel. It has two poles of charge, positive and negative. When brought in the presence of another magnet, like poles repel each other and opposites attract. This makes magnets practical for a number of reasons. However, it wasn't until the early twenty-first century that weapons based primarily on magnets were created.

Electromagnets are alike to a regular magnet except its temporary nature. When electricity runs through a potential inductor, a field is created perpendicular to the flow. This occurs because the flowing electrons in electricity spin about their axis, creating an eddy that contributes to a powerful magnetic field. An electromagnet is considerably more powerful than a permanent magnet gram for gram due to its atomic activity.

Railgun
In a railgun, a current is run through two parallel plates that sandwich a slug--electrons go down one plate, jump through the slug, and return to the battery up the other plate. The current, in essence, transforms the entire rail gun into an electromagnet. It exhibits a Lorentz force that tries to maximize the size of the energy loop by pushing the slug away from the inductor and toward the target.

For a Lorentz force to be powerful enough to force a slug at appreciable speed down the barrel, an extremely high amount of voltage must be pumped through the weapon. The exact value for a desired muzzle velocity can be determined mathematically. In general, a lone powerpack cannot supply such a value. Capacitors, which store energy for immediate use, are necessary.

Railgun physics
In a railgun, the inductor is a single-turn coil consisting of the power source, rails, and slug (armature). The armature is free to slide along the rails, and it is the Lorentz force that causes it to speed down the barrel, away from the power source.

Qualitatively, the design is straightforward. The difficulty arises in trying to quantiatively determine the dynamics of the rail gun, the strength of the magnetic field, and so on. To do so, one must examine the relationship between the current, the field, the motion of the armature, and the geometry of the loop, all in relation of time.

This complex puzzle can be broken down and simplified in the following manner:


 * Determine the instantaneous induced magnetic field at any point as a function of loop geometry and current in the loop at a given time.
 * Take Faraday's Law and derive the equation for the induced EMF in the loop. Calculate this based on the magnetic field, determined above.
 * Solve Ohm's Law for an analytical formulation of current as a function of loop resistance, initial charge in the capacitor(s), capacitance of the power cap(s), and induced EMF. Take the derivative of this equation to get a first-order differential equation for I.
 * Now we need to replace I and its derivatives with something we know how to calculate. To do this, we'll first manipulate the Lorentz Force law like this:
 * Determine the instantaneous magnetic field at any point on the armature as a function of loop geometry and current in the loop at a given time.
 * Integrate the magnetic field over the length of the armature and multiply by the instantaneous current to reveal the magnitude of the Lorentz force on the armature at a given time.
 * Use Newton's equation of motion to relate the Lorentz force law to the mass and acceleration of the armature. Solve this equation for current and take its time derivative.
 * Now we have have two equations for the derivative of current which we can set equal to each other, leaving a differential equation for armature position on the rails. Solve this differential equation to reveal an analytical solution for the time evolution of armature position, velocity, acceleration, etc.

Coil gun
A strong electric field is created when electrons flow through a wire that is coiled many times. One side of the coil is positively charged, while the other is negative. A coil gun capitalizes on this phenomenon.

A series of coils are arranged along the barrel, with each progressive coil spaced closer together; the strongest magnets are installed on both ends of the firing line. The coils are magnetized in series with the aid of a timing circuit, pulling the slug faster and faster with each pulse until it leaves the chamber.

Considerations
Electromagnetic weapons experience a moderate amount of firing heat, which is dissipated gradually. Temperature is usually not a factor because of the long recharging times.

The sound produced by an electromagnetic weapon firing is caused by two factors: the sound of the slug as it breaks the sound barrier and the electrical discharge noise. When combined, a decent weapon can exceed ninety decibels.

Muzzle velocities for shoulder-fired weapons can reach ten kilometers per second in prime conditions, far exceeding that of conventional chemical-based weapons. This makes electromagnetic weapons ideal for extremely long-range sniping. However, the relative smallness of the slug makes it more prone to the elements, and can affect the trajectory of the projectile.

Rail guns experience stress fatigue over the course of its operating life. The Lorentz forces push the rails apart, eventually bending the base of the barrel and making the weapon inoperable.

The major disadvantage of electromagnetic weapons is its dependance on large amounts of energy. Because there is generally no "load" in the magnet current, there is a great waste of electricity. A way to recover the energy for reuse has since eluded scientists.

Recoil is very much a factor for users of electromagnetic weapons. Because of the sheer intensity of the aftereffects from the discharging slug, these weapons are designed to absorb the majority of the shock. Nevertheless, an improperly braced firer may lose grip of the weapon or be knocked down.

Rocket-assisted
Rocket-assisted projectiles are devices designed to travel in air or outer space, propelled by the force of expanding gases. These are called rockets or missiles. The word missile is a general term for all such devices. A rocket is a missile that carries its own supply of oxygen or other oxidizing agent, allowing it to operate beyond a planet's atmosphere.

A true missile is not supported in flight by wings, although it may have winglike fins to guide or stabilize it. Pilotless jet- or rocket- powered craft that have supporting wings are actually planes, though they are often called missiles.

A true missile, like a bullet or artillery shell, stays aloft only because of its momentum (movement). It differs from a bullet or shell in that it is self-propelled during at least part of its flight. However, once the engine ceases to operate (which happens in most cases a few minutes after launching), a missile behaves in exactly the same way as an artillery shell. Some missiles, however, have supplementary engines that can be turned on to make course corrections.

When equipped with a warhead (an explosive charge or nuclear bomb), a missile is a devastating weapon. A large missile travels at an enormous speed (more than 24000 km/hr is not uncommon), making it difficult to detect and destroy. Some missiles are designed to travel between planets. Small missiles, such as the bazooka rocket, can give a footsoldier the firepower of a tank. Some missiles can change course in flight and seek out and destroy moving targets. Some have more than one warhead, each capable of striking a different target. The multiple warhead system is called MIRV (multiple independently targeted reentry vehicle).

General
A missile's engine, either a rocket or jet engine, mixes fuel with an oxidizer (a substance, such as oxygen, in which the fuel can burn). The engine burns the fuel in a chamber, producing hot gases that expand and push against the chamber's walls. Since a jet engine requires oxygen from the air, a jet-powered missile cannot travel above the atmosphere. A rocket engine can travel above, as well as within, the atmosphere because it carries an oxidizer in addition to the fuel. The propellant (fuel plus oxidizer) may be in solid or liquid form.

The pressure of the gases in any direction tends to move the engine and missile in that direction. The pressure at a point on one side of the engine is balanced by an equal gas pressure on the opposite side. But the pressure on the front is not balanced because of a hole in the rear through which the gases escape. The result is that the engine and missile are pushed forward. This effect illustrates Newton's third law of motion: that for every action (here, the rearward escape of the gases) there is an equal and opposite reaction (the forward thrust).

Rocket performance
Thrust is the force that the rocket engine generates to move the rocket forward. Thrust is generally stated in newtons. The amount of thrust depends on the speed at which gases produced by the burning fuel are ejected from the rocket. This speed, called the exhaust velocity, varies with the burning characteristics of the fuel and with the design of the rocket nozzle. The most effective design in producing an extremely high exhaust velocity is one in which the nozzle is constricted just below the combustion chamber and then flares out below. The higher the exhaust velocity of a rocket, the greater its thrust.

The ability of a rocket to accelerate itself and its warhead depends on its thrust-to-weight ratio; that is, the ratio of the rocket's thrust to the weight of the rocket and its load. The thrust must be greater than the weight if the rocket is to lift off. The higher the thrust-to-weight ratio, the greater the rocket's acceleration. The thrust-to-weight ratio constantly changes during powered flight as the weight of the rocket is reduced through the consumption of fuel. Thus, under normal circumstances, a rocket's acceleration (and hence its speed) continues to increase until all its fuel is consumed. For a rocket being fired upward, the lessening of the planet's gravity also reduces the weight and increases acceleration.

Specific impulse is a description of the thrust produced by a particular fuel. It is the number of newtons of thrust produced by each kilogram of fuel burned during each second of engine firing. For example, if two kilograms of fuel burned in one second produces 4500 newtons of thrust, the fuel has a specific impulse of 2250 seconds. Most liquid propellants have specific impulses of 3000 seconds. THe specific impulses of solid fuels run somewhat lower, as do those of monopropellants. A monopropellant is a single liquid, such as hydrazine, that functions as both fuel and oxidizer.

Solid-fuel rockets
A solid-fuel rocket consists basically of a cylindrical shell containing a rubbery or plastic substance made up of fuel and oxidizer. When ignited, the fuel burns until it is used up. The same basic structure is used in a wide variety of devices from bazooka rockets to interplanetary ballistic missiles. Solid-fuel rockets can be fired with a minimum of preparation. They can be safety transported and stored fully fueld and ready to fire.

Whatever its size or shape, a single piece of solid fuel is called a grain, or charge. Most solid-fuel rockets contain a single grain, but a few have more than one. The shape of the grain influences the thrust produced. Some grains are shaped so that the thrust increases as the burning time passes; others are designed so that thrust either decreases or remains constant. Further built-in control of the thrust is created by the use of chemical inhibitors which slow down the rate of burning in specific areas of the grain.

Solid-fuel grains are made opaque to prevent possible explosion. In a translucent grain, electromagnetic radiation produced by the hot exhaust gases penetrates into the grain and produces hot spots that are hot enough to ignite the interior of the grain. These hot spots have no vent to release the gases produced and so can cause ane explosion.

Among the solid propellants in common use are ammonium nitrate composite, polysulphide-ammonium perchlorate composite, powdered aluminum, and polyurethane ammonium perchlorate composite.

Liquid-fuel rockets
Liquid-fuel rockets are mechanically much more complex than solid-fuel rockets. This complexity, however, is compensated for by their higher thrust and the fact that they can be turned off and then restarted. Most liquid-fuel rockets require that the fuel and oxidizers be kept at extremely low temperatures, and must therefore be fueled just prior to launching.

Much of the space inside a liquid-fuel rocket is occupied by fuel tanks and oxidizer tanks. In rockets designed for monopropellants, of course, only one type of tank is required. The fuel and oxidizer are carried to the combustion chamber through pipelines. Typically, the fuel is carried past the combustion chamber before entering it; this system both cools the chamber and preheats the fuel to improve its burning characteristics.

Most liquid fuels require an ignition system to ignite the fuel and oxidizer as they enter the combustion chamber. Some fuel-oxidizer combitions, however, are hypergolic; that is, they burst into flame spontaneously when they are brought into contact with each other. Hydrogen and fluorine is a hypergolic combination. A common liquid propellant is LOX (liquid oxygen) and liquid hydrogen.

Stages
The range and speed of a missile can be greatly increased by the use of multistage rockets. These consist of two or more seperate rockets, each called a stage, stacked end-to-end. At launching, only the bottom, or first, stage is in operation. When its fuel is used up the first stage drops away from the rest of the rocket and the next stage is ignited. The starting speed of the second stage is equal to the top speed of the first, and the weight of the rocket is greatly reduced.

Additional thrust at lift-off can be obtained by using booster engines in conjunction with the first stage. They are ignited at the same time as the first-stage engine and are jettisoned soon after launching, leaving the main engine in operation by itself.

Missiles that are designed to travel between planets are equipped with polydenum-powered OtherSpace drive boosters that are frequently larger than the missile itself. Like lift-off booster engines, OtherSpace drive boosters are jettisoned after use. Because they are expensive, OS boosters are usually equipped with beacons for retrieval.

Types of missiles
Missiles can be classified in several ways. The three common methods are (1) by target and launching positions, (2) by guidance, and (3) by range. Several special missiles are also outlined.

Classification by target and launching positions are based on the place from which a missile is launched and the position of its target. Combinations are fabricated from two terms. Valid terms are ground, air, surface, and space. For example, space-to-surface or surface-to-air.

The term guidance refers to the method used in steering a missile to its target. A ballistic missile is aimed during the first few minutes of its flight. After its rocket power is spent it coasts like a bullet in a curved path called a trajectory. The chief advantages of the ballistic missile are its great speed and its resistance to being thrown off course by hostile electronic "jamming." It can, however, be detected readily by radar and is thus vulnerable to attack by the enemy's defensive weapons. Guided missiles are designed so their courses can be corrected or altered at any time during the flight to the target. They can be guided remotely or by a preset internal guidance system. One type of internally guided weapon is called the cruise missile. It is not a true missile but a pilotless plane with a complex guidance system that allows it to fly close to a planet's surface even over hilly terrain.

Range classification is generally reserved for the more sophisticated and larger missiles. A short-range missile is any missile designed to travel less than 1000 km. An intermediate-range ballistic missile, or IRBM, can travel 1000 to 2400 km. A missile with range greater than 2400 km is an intercontinental ballistic missile, or ICBM. Finally, a missile used for space interdiction and for extreme long range planetary bombardment in excess of ten parsecs is called an interplanetary ballistic missile, or IPBM. IPBMs may be subjugated into short-, intermediate-, and long-range.

Rockets that carry certain payloads are not in essence true rockets. These usually have a narrow weight-to-thrust ratio or derive most of their momentum from other sources. Among them are artillery shells and grenades with rocket-assisted range boosting. In both cases, a chemical propellant is first utilized to fire the payload, and is considered the primary delivery method.

Folding fins
Missiles designed to be carried and fired in limited space are equipped with folding fins, which pop open automatically after launch. These missiles, which are launched from shoulder-fired bazookas, are called FFARs (folding fin aerial rockets).

Special thanks to Gadget for this information.