FRAGMENTATION MISSILE WARHEADS: DEVELOPMENT POTENTIALS

Fragmentation warheads are currently defined as munitions that defeat targets by a high velocity spray of a great number of homogeneous inert lethal elements, propelled by the explosion of a high explosive charge. Lethal elements are represented by splinters of uncontrolled fragmentation, preformed fragments, and prefabricated fragments. Consequently, the term "fragmentation" in the broad sense of the word is surely outdated, and the notion "splinter" can only refer to the products of uncontrolled fragmentation. 

High explosive fragmentation warheads differ from fragmentation warheads by their ability to penetrate before explosion into soil or any obstacle as part of the missile or separately. In the strict sense of the word, the term HEF warheads can be applied only to ground attack, antiship and similar missiles. 

Sometimes, wishing to stress that an air target can be destroyed by a blast wave and explosion products at near misses, specialists make an error when they apply the term "HEF" to SAM warheads outfitted with proximity fuzes. In this case, it would have been more correct to use the term "blast fragmentation warhead" that corresponds to the English term "high explosive blast fragmentation warhead." 

As to target type, we distinguish multipurpose (versatile) HEF warheads (for example, HEF warheads with uncontrolled fragmentation intended for MLRS) and specialized fragmentation warheads intended to defeat specific targets. The latter warheads include antipersonnel warheads intended to inflict damage upon unsheltered and lightly protected personnel (with conventional weight "w" of splinters ranging from 0.1 to 1 g), antivehicle warheads intended to defeat ground and air soft-skinned materiel (w = 1 to 10 g), and antiarmor warheads intended to defeat lightly armored targets featuring a steel equivalent of up to 20 mm and other hard-to-hit targets like battlefield missiles (w = 10 to 100 g). 
    
In terms of fragmentation pattern, the following three types of warheads are distinguished: 
– warheads with circular patterns; 
– warheads with axial patterns; 
– warheads with radially directed patterns. 

Circular pattern fragmentation warheads are most commonly used. Their main advantages are the highest efficiency factor of explosive charge energy, arrangement of the warhead in any part of the missile, and engagement of targets at any side misses. 

Narrow and wide fragmentation patterns are distinguished in terms of the magnitude of a meridian angle. The angle of dispersion is mainly determined by the form of the envelope and the scheme of initiation. Small angles of dispersion (fragmentation patterns of the "cutting disc" type) are formed by the envelope with concave generatrix, two-point initiation on the explosive charge end faces, and multipoint synchronous initiation along the axis of the explosive charge that generates a diverging detonation wave of a nearly cylindrical shape. Large angles of dispersion are generally formed by explosion of barrel-shaped or at least spherical-shaped warheads. 

The warheads of missiles and rockets featuring high g-loads at launch usually employ controlled fragmentation envelopes created by grooving, using winded grooved strips, embrittled lattices produced, for example, by electron beam or laser treatment and the like. Warheads featuring relatively low g-loads at launch (n < 100), mainly SAM warheads, are fitted with assembled and bonded envelopes with prefabricated fragments in the form of cubes and cylinders made from steel or heavy alloys on the basis of tungsten with a 16 to 
18 g/cm3 density. Work is underway to increase the incendiary effect of prefabricated fragments by adding magnesium, zirconium, and beryllium. Missile warheads are filled with mixtures of trotyl and hexogen of the TG 40 and TG 50 types or trotyl with hexogen and aluminum powder of the TGA, TGF, and other types. The use of more powerful explosives, mainly octogen (density 1.9 g/cm3 and detonating velocity 9,100 m/s), is limited by their cost. The volumetric efficiency (ratio of explosive charge weight to warhead weight) for SAM warheads is usually within 0.4 and 0.6, and the speed of fragments is 1,800 to 2,500 m/s. 

The development of blast action warheads filled with air-fuel explosive mixtures is of particular interest. 

The source of effectiveness of ground attack fragmentation warheads is an air burst. The air burst at an optimum altitude considerably increases the fragmentation effect on ground targets compared to a ground burst during which the entire lower hemisphere of the spray is intercepted by the soil, thereby creating a dead space. 

The following main methods are used to perform fragmentation warhead air bursts: 
– use of time or proximity fuzes; 
– use of stems and leaders (cable extenders); 
– arrangement of the fragmentation warhead in the missile base; 
– bouncing of the fragmentation warhead from the ground after missile impact. 

One method of obtaining circular fragmentation patterns is the employment of so-called turning warheads. A turn allows the use of fragmentation warheads with a small meridian angle and high pattern density. The main type of turn for the circular-pattern ground-attack fragmentation warheads is the turn about its axis to a vertical position before explosion to create a circular kill zone on the terrain. The in-flight turn of the separating fragmentation warhead to a vertical position with the aid of the brake parachute is effected in the 122mm Prima MLRS. A very promising method of guiding flat trajectory missiles is the active method of turn through the use of jet engines or ballast weights ejected by powder charges. 

Rod warheads intended to defeat aircraft panels constitute a separate type of fragmentation warheads with prefabricated fragments. The main element of the rod warhead is a set of square or round rods arranged on the surface of the explosive charge, as a rule, at a small angle to its generatrix. The rods can be connected (welded) alternately at their upper and lower ends or devoid of connection. During the explosion, the rods are projected forming an unbroken ring if they are connected or an overlapping broken ring if they are loose. The rods outperform conventional prefabricated fragments because they rip the skin and framework, thereby destroying the airframe structure, that is defeating the air target by causing the instantaneous breakdown of the air target in the air. 

In a rod warhead, a layer of compact prefabricated fragments is placed over the set of rods. This configuration of the warhead is used in the 9M311 SAM that is operational with the 2K22M Tunguska field AD missile-gun system and the 3M87 Kashtan shipborne system. This warhead weighs 9 kg, its rod length is about 600 mm, the rod diameter ranges from 4 to 9 mm, and the diameter of the rod ring is about 5 m. A layer of cubic-shaped prefabricated fragments weighing 2 to 3 g is arranged over the rods. 

The R-27R, R-27T, and R-73 aircraft missiles are fitted with rod warheads. The rod warheads are designated in foreign publications as HECR (High Explosive Continuous Rod). 

Relative weights of circular fragmentation warheads (ratio of the warhead to the launch weight of the SAM) vary from 0.075 to 0.1. 
The main drawback of circular fragmentation warheads featuring more or less wide patterns required for reliable target coverage is the low density of the fragmentation pattern (low density of kinetic energy of fragments per unit of the spatial angle of the pattern)...