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How missiles work

By Sakhal

Frequently, the most refined procedures of military technology have been developed for the effective operation of missiles. The investigation of increasingly effective systems for control, launching, propulsion and guidance often gave as result important scientific progress.

Control systems

Many of the missiles fitted with wings are controlled by aerodynamic surfaces actuated by electric motors, hydraulic systems, pressure gas, regulation of the engine power or any other mean of achieving the same functionality. Future hypersonic models should be capable of aiming in the desired direction, without requiring wings or fins. Besides, any missile can be steered by controlling the thrust vector, according to the desired trajectory. In some cases, a combination of several control systems is used. To achieve greater precision, some missiles have also an additional correction system - a rocket that is activated when the main engine is detached - and some old models incorporated air brakes.

How missiles work

A4: This pioneer of the ballistic missiles had a fixed combustion chamber, with graphite control blades in the exhaust and small aerodynamic controls in the four large stabilizer fins. Modern ballistic missiles rarely need fins. Bloodhound: This anti-aircraft missile of the cruise type could have had cross-plan wings and fins - which are the most common type -, but instead it was directed by an original system that makes the missile to rotate in place. The horizontal wings firstly - with different movement each - stabilize the missile and then they move in unison to place the missile in the desired course. Thor: The first generation of North American mid-range intercontinental ballistic missiles had propulsion engines fed by liquid fuel Rocketdyne, with hanging combustion chambers. Large pistons moved the full body of the chamber and the feeding ducts were of flexible section. Polaris A1: This pioneer of the ballistic missiles launched from submarine had in its first phase an engine with a gas evacuator in each of the four fixed nozzles, and each of these with its own thrust vector control. This method could be used in missiles propelled by either liquid or solid fuel. The last versions of the Polaris discarded this system. Polaris or Minuteman, phase 2: A thrust vector control, of liquid injection, regulated the exhaust by injecting a volatile fluid, such as the refrigerant Freon, through selected nozzles placed around the chamber. Swingfire: This system was not fully used in any missile, but variants of it were used in some missiles launched from aircraft manufactured by French company Aerospatiale. The thrust vector control uses a sheet that vibrates accross the nozzle. The required power control is lesser that in missiles with aerodynamic fins. Advanced missile: It was unknown which missiles could include the North American system Techroll or similar methods that include sealed spheric surfaces. Some older missiles - such as the French SSBS and MSBS - had rotatory nozzles of inclined axes. Tomahawk: The Tomahawk is a type of modern cruise missile, with deployable wings of large wingspan and efficient aerodynamics. The missile is controlled by the rear cross-plan fins, managed in vertical or horizontal pairs, to correct azimut and elevation respectively.

Launching systems

The first long-range ballistic missile - the German A4 - was a weapon of the Army used as artillery and deployed by mobile systems. But when the United States Air Force took control of all the North American strategic weapons, it was abandoned the development started by the Army of a missile of mobile deployment - the Jupiter - and the efforts concentrated in weapons emplaced in fixed emplacements, such as the Atlas and Thor. When it became patent the vulnerability of these facilities against a hypothetical attack from enemy missiles, the Air Force decided to protect the emplacements, eventually placing the missiles in underground silos. But soon these silos would be vulnerable as well due to the extreme precision of the newer intercontinental missiles. The only answer to the future of these missiles seemed to return to their deployment in mobile installations, be it by land, sea or air.

How missiles work

A4: The German Army did not even think of setting up fixed bases or protected emplacements for such a distinguished weapon. This way, they achieved to make it almost invulnerable against the Allied air force, which despite its supremacy could only hit the missiles when these were being transported by railway. Some decades later the circle closed itself, and mobility and hidden emplacements seemed about to return, albeit the decision took in December 1982 by the United States Congress to install the new MX missiles in fixed emplacements - because of economical reasons - supposed a certain regression. Atlas I: This pioneer of the intercontinental ballistic missiles was installed in unprotected emplacements in the surface. The roof opened and the missile was placed in vertical position to load the liquid fuel. Half a hour later it was ready to be launched. Titan I: This intercontinental ballistic missile was stored in semi-protected silos, but it had to be raised to the surface for loading the fuel (however faster than in the Atlas) and then be fired. Minimum reaction time was about twelve minutes. Titan II: This missile representad an intermediate step in the search for an ideal launching system. The rocket engines used storable liquid fuel so the missile was ready to be fired and it could be fired from the bottom of the silo, which was provided with exhaust ducts for the efflux of the engines. Minuteman: In the 1960s, United States had perfected which seemed to be the ideal method for the indefinite storage of land-based intercontinental ballistic missiles: propulsion by solid fuel, instant reaction time and fully protected silos, from which the missiles could be launched without requiring any exhaust duct for the efflux of the engines. Soviet ICBM: Several modern Soviet land-based weapons, including the impressive SS-18, were ready for an instant reaction in protected silos from which they were "launched in cold". The missile is activated with a high acceleration by means of a powerful gas generator, and the propulsor of its first phase is ignited only when the missile is already over the surface. This system prevents the destruction of the silo, allowing the same emplacement to be available - in a relatively short time - for launching another missile. Despite the SALT (Strategic Arms Limitation Talks) treaties forbid the possibility of recharging the emplacements of strategic missiles, the development of this modern technique - then only in possession of the Soviet Union - meant to leave an open door to the launching of more than one missile from a same emplacement, which in the practice meant a serious alteration of the concept of nuclear balance between the two superpowers.

Propulsion systems

The very concept of ballistic missile rests in the concept of rocket. But today it could be interesting to consider a ballistic weapon propelled by air, flying at hypersonic speed in the stratosphere, with its trajectory controlled by an aerodynamic design in its structure, and with a range that probably would surpass the one of ballistic rockets of similar size. This is actually more similar to long-range artillery, but with the differences that propulsion could continue during longer time and that trajectory could be corrected by cuts in the propulsion. Also, a certain number of warheads could be distributed along different targets. The use of this system would require however at least two decades of investigation from the 1980s.

How missiles work

A4: Albeit, during the Second World War, Von Braun and his team in Peenemunde knew everything about the system of multiple-phase rockets, they decided due to prudence that their first missile of large dimensions would have a single phase. With the technology that they had then, the mass ratio (mass in the moment of the launching divided by the mass that remains when all the fuel has been consumed) did not exceed 3.2. With propulsion based in liquid oxygen and alcohol, maximum range was limited to about 370 kilometers. Modern single-phase rockets are much better. They can carry a greater load or having more range. But despite of that the A4 remains as the greatest individual progress in the history of missiles. Atlas: During the design of this pioneer of the intercontinental ballistic missiles - from 1954 to 1956 -, it was found impossible to obtain the required range with a single phase. Also, it was not considered feasible the ignition of a second phase once in the space. The answer to the problem was a configuration of "phase and half". One phase carried the main tanks and a central lift engine, while the other phase had a double chamber with two impulse engines, which detached in the middle of the combustion. The mass ratio increased to 13.5. Titan II: The Titan was one of the first two-phase missiles. The first phase detached itself and the ignition of the second phase was produced when the missile was already above the atmosphere. Its design dates back from 1955-57, when the technical risk of a two-phase intercontinental ballistic missile was deemed as acceptable. Trident C4: This missile had a propulsion system with two phases that occupied the whole diameter of the missile and solid-fuel engines of great lift power. There was also a third much narrower phase and a system of control and propulsion of the eight atmosphere-reentry vehicles which with was fitted the explosive charge, each of them carrying a nuclear warhead that could be directed towards a predetermined target.

Guidance systems

This vital function was invariably the weak point - which even could cause the disappearance - of the first missiles. The designers struggled then to achieve systems allowing to remotely control the missiles by means of radio emissions or electric signals transmitted by wire. In those years it was very difficult to develop any method of auto-navigation or search capability built in the very missile, but few decades later a wide variety of these systems already existed. In return, appeared as well countermeasures - more or less effective - against all of those guidance systems. A first and clear distinction between the different guidance systems is the one separating those intended to hit a static target - the case of strategic missiles - from those intended to hit a moving target. The graphic depicts the main systems achieved after some lustrums or decades of investigation.

How missiles work

Guidance by wire with automatic remote control (A): The first guidance systems by wire forced the operator to direct the course of the missile during the whole travel towards the target. Thanks to the automatic remote control - of French invention -, the operator only had to keep the optical viewfinder aimed towards the target. The viewfinder perceives the flash produced by the exhaust of the rocket that propels the missile, keeping this one in the correct trajectory towards the target. Semi-active laser (B): This method allows for an extreme precision when attacking tanks or any other target that can reflect the laser beam. The laser designator can be used either by a soldier or by the attacking aircraft. Inertial (C): This is the ideal system for intercontinental ballistic missiles and ballistic missiles launched from submarine. The whole system is included in the missile, which this way does not require assistance of any kind - and hence cannot be interfered by electronic countermeasures -. Precision depends on the exactness with which the geographical position of the launching point is known, and it decreases in proportion to the duration of the travel, but modern ballistic missiles are very fast. The system determines a trajectory from some exact coordinates to other coordinates in the planet and the error introduced by the temporal variation is due to the rotation of the Earth. Radar command (D): This was one of the first systems used in anti-aircraft missiles but in the 1980s it started to be considered as obsolete. It consists of a radar which tracks the target and another radar which tracks the missile. A computer directs this latter so its data about orientation, altitude and distance eventually matches the corresponding data of the target. Hence, when the data of both radars matches, the explosive charge of the missile is activated. Active radar seeker (E): It is the case of the missile that carries its own radar capable of localizing the target (such as the German anti-ship missile Kormoran depicted in the graphic). Certainly the system can be interfered by electronic countermeasures and many ships emit so many types of signals that this guidance system should not be necessary and a passive radar system - immune to interferences - could be used instead. Semi-active radar seeker (F): This system became fundamental for every kind of anti-aircraft or air-to-air missile (such as the Sparrow or the Sky Flash depicted in the graphic). The missile is guided by the projection of the radar on the launching aircraft, that reflects in the target. The attacking aircraft has to fly towards the target until the missile hits it, which constitutes a serious drawback. Astronomical (G): The first cruise intercontinental missiles complemented their inertial guide with astral navigation. Setting the course according to the position of some stars previously selected, the missile could measure with exactitude the data of elevation and azimut. Reference on the terrain (H): Cruise missiles are invariably fitted with an inertial guidance system, but they can complement said system with the denominated TERCOM (Terrain Contour Matching) to achieve an almost perfect precision. The missile is equipped with very sensitive altimeters that measure the profile of the terrain immediately beneath the course of the missile and contrast their measurements with the information stored in the memory banks. Each scan is unique for each terrain strip. Infrared (I): This system which directs the missile towards heat sources is very attractive for any missile whose purpose is to shoot down an aircraft. One of these like the Soviet MiG-25 which appears in the graphic with the afterburners at full power, could be one million of times easier to destroy than a small turboprop aircraft or a helicopter, due to the very intense heat source that its exhausts represent. Radio command (J): This was the first method used by German missiles during the Second World War, but in more recent times it achieved great perfectioning. Some missiles require that the operator keep them in their trajectory towards the target, but others, such as the Martel depicted in the graphic (launched from a British aircraft Buccaneer), have a television camera incorporated in the nose to transmit what is in front of the missile to a screen monitored by the operator, allowing to direct the missile with precision.

The different missions of missiles

The following diagrams illustrate about the missions that missiles would perform in a modern conflict, in which every possible weapon were used. To ease a better comprehension, the scale and nationality of the distinct systems depicted are not rigurous at all.

How missiles work

A: Warned about the presence of an enemy armored force, a self-propelled artillery piece fires Copperhead missiles upon the general area where the enemy forces are, usually beyond visual range. B: An infantry soldier sights the enemy tanks, checks the safety of his emplacement and fires a series of missiles, directing the course along the entire travel by means of a wire. C: An infantry soldier is warned about his own forces firing Copperhead missiles against the enemy tanks and directs his laser designator against one of the tanks. The missile catches the reflection of the beam and impacts against the tank. D: In close air support missions, the pilot detects visually the target, activates the missile, focuses the television viewfinder of the missile on the target, by means of a screen in the cockpit, and then fires the missile. E: The radar of the fighter aircraft, controlled by a computer, delivers to the pilot the data about the enemy target. The pilot fires against the target an air-to-air missile fitted with a semi-active radar search head. F: A two-phase intercontinental ballistic missile is launched from its silo and the first phase detaches after completing its combustion. Then it starts the ignition of the second phase and the missile starts to direct itself, forming a wide arc, towards the target.

How missiles work

G: In a submerged submarine is prepared a ballistic missile, supplying to it the precise data of the position where it currently is, and then fired against a target previously determined in the memory of the computer that guides the missile. H: A surface warship detects an enemy ship in her radar, fires an anti-ship missile against her and, in some cases, assists the missile during its travel - which passes slightly above water level - towards the target. I: A surface warship of large size, who still has not detected the missile approaching her in contour flight, launches an anti-submarine missile when her sonar system detects an enemy submarine. The missile transports a torpedo - which in a certain moment detaches from the carrier missile - fitted with its own search system. J: A bomber fitted with electronic countermeasures, both offensive and defensive, launches a cruise missile from a distance considered as safe.

How missiles work

K: The atmosphere-reentry vehicle of the ballistic missile launched by the submarine falls directly upon enemy targets, albeit many of these missiles are prepared to disseminate a cloud of small explosive charges. L: An anti-aircraft missile is launched against a combat aircraft, which manages to divert the missile by ejecting lures that originate sources of more intense heat than the one generated by the engines of the aircraft, attracting towards them the infrared search system fitted in the missile. M: Reentry vehicles of an intercontinental ballistic missile return to the atmosphere and disperse a cloud of explosive charges, which after few seconds after the reentry make impact in separated targets. N: An F-14 fighter aircraft armed with air- to-air Phoenix missiles detects and tracks six different targets and fires simultaneously against them with its charge of six missiles. O: A cruise missile advances accross enemy territory, controlling and readjusting its path by means of successive TERCOM (Terrain Contour Matching) measurements that the missile effectuates in selected parts of its course.

Categories: Missiles - Electronic War - 20th Century - [General] - [General]


Website: Military History

Article submitted: 2015-05-12

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