Spherical warhead

A spherical warhead is disclosed which yields a greater than 120.degree. ped charge of preformed fragments and which further permits non-destructive cook-off of explosives to prevent undesirable detonation.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention lies in the realm of mechanics and ballistics. More 
particularly, the invention discloses a shaped charge explosive yielding a 
120.degree. shaped charge, particle dispersion, radially from the point of 
detonation, and further discloses an improved warhead cook-off capability 
to prevent an undesirable explosion/detonation of the warhead. 
2. Description of the Prior Art 
Anti-Radiation Missile (ARM) warhead designs are premised on the assumption 
that the missile they are employed in will not impact on a vulnerable 
region of the target. This is essentially the case as the aimpoint is on 
the transmitter antenna; however, an impact on the antenna usually will 
only degrade the performance of the radar. As a result such warheads are 
designed to produce significant levels of damage without actually 
impacting on the target. This is accomplished through the explosive 
dispersion of a large number of metallic fragments. In the design of ARM 
warheads, two basic factors must be taken into account. These factors are 
the probability of hitting the target, PH, and the probability of killing 
the target, PKH, given a hit by the fragmentation. The overall probability 
of killing the target, PK, is the product of these two factors. 
EQU PK=PH.times.PKH 
Since no probability value can ever exceed 1, the system PK can never 
exceed either PH or PKH. Theses two factors, PH and PKH, are interrelated 
through the warhead design. The probability of a hit (PH) is a function of 
the miss distance which is controlled by the guidance system, the burst 
point location which is controlled by the fuze, and the number of 
fragments and their impact densities on intercepting the target which is 
controlled by the warhead design. The probability of kill (PKH), given a 
hit, is controlled by the placement and shielding of the components, i.e. 
the target, size of the fragments, and impact densities on intercepting 
the target. As can be seen, the impact densities are an important element 
in determining a target kill. This, however, results in conflicting 
requirements being placed on the warhead design, the need for high impact 
densities, for high PKH's, but large dispersion angles, for high PH's, 
which leads to low impact densities. Past warhead designs for ARM 
applications have usually employed a cylindrical shape with an ogival 
front end. When looked at in cross section, the warhead design appears as 
a series of stepped layers of fragmentation along the length with an 
explosive fill in the center. When the warhead is detonated in a static 
environment, the fragmentation, except for the ogive, is projected 
radially outward, the sections with the larger number of fragments being 
projected at a lower velocity than the sections with fewer fragments. When 
a missile with a sufficiently high terminal velocity is used with the 
warhead in that missile, this fragment pattern turns into an expanding 
cone of fragmentation due to the vector addition of missile and fragment 
ejection velocity. This design approach has certain limitations. First, it 
requires relatively high terminal missile velocities to achieve proper 
fragment dispersion. Second, because it is an expanding cone, it relies 
upon proper burst point control by the fuze so that the warhead does not 
detonate after it has passed the target. This requires a sophisticated 
fuze and/or a relatively small miss distance which requires more 
sophisticated guidance. More specifically, it requires that target 
location along the trajectory be known with respect to fuze and guidance 
systems. As a result very simple fuzing, such as fixed height of burst 
fuzes, cannot be readily used with this type of warhead. 
Therefore, there exists a continuing need for a more effective warhead that 
can yield a greater probability of kill in near miss situations with less 
sophisticated fuze and guidance equipment, less missile terminal 
velocities, and a radially shaped charge having an expanding cone of 
projectiles to the rear (aft) as well as to the leading edge (fore) of the 
fly by missile. 
SUMMARY OF THE INVENTION 
The invention is a spherical shaped warhead which yields a greater than a 
120.degree. shaped charge. The warhead consists of two closely spaced 
concentric spheres truncated with flat bulkhead/cover plates on a fore and 
aft end of the spheres. A plurality of preformed fragmentation cubes is 
interspersed and potted between the two concentric spheres above and below 
a central porous annular ring which circumvents between and couples the 
concentric spheres together. The interior of the central sphere is filled 
with a high explosive (main charge) surrounding a cylindrical channel 
extending between the two cover plates for holding a fuze and a detonator 
(booster charge). Cookoff holes/vents are provided in a booster charge 
loading port disc, said disc being threaded into said fore cover plate, to 
permit release of expanding gases of fuel decomposition to prevent 
pressure buildup which might cause undesirable detonation. 
OBJECTS OF THE INVENTION 
It is therefor a primary object of the invention to provide a shaped charge 
warhead having a large polar dispersion angle, greater than a 120.degree. 
fragmentation spread, radially from the point of detonation. 
Another object is to utilize preformed fragments disposed between an inner 
and an outer shells of a spherical warhead. 
Yet another object is to provide a warhead which permits, but does not 
require, low missile terminal velocities and further requires less 
sophisticated fuze and guidance systems while still achieving high kill 
probabilities. 
A further primary, object of the invention is to incorporate in a missile 
warhead a cook-off/fuel fire protection device, that does not require 
traditional booster safe/arm ejection devices. 
Another object of the invention is to allow pressure buildup inside the 
warhead, which includes the booster and main charge explosives, to pass 
through a loading port cover thereby exposing the main charge explosive 
and the booster to flame and free to burn in a nondestructive manner. 
These and further more advantageous benefits and features of the invention 
will become more readily apparent to the reader on consideration of the 
attached drawing, together with the following description of a preferred 
embodiment in the light of the appended claims.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The invention warhead, illustrated in cross section (cut in half) in the 
Figure, is basically a spherical design. It consists of an inner 12 and an 
outer 14 metal spheres attached to a first 16 and a second 18 metal 
bulkhead/cover plates. Half way down the warhead, between inner 12 and 
outer 14 spheres, is a permeable/porous metal ring 22, see FIG. 2. 
Preformed tungsten cubes 24 are poured first from one end while the 
assembly is vibrated and, when full, poured from the other end until the 
opposite side of the warhead is full of cubes. Center ring 22 serves two 
purposes, first as a spacer during assembly to keep proper space between 
inner 12 and outer 14 spheres, and second as a stacking surface so that 
stacking of cubes 24 can be started at the center and largest diameter of 
the warhead. When all cubes have been placed into the warhead, cubes 24 
are then potted in place with a potting compound 26 by setting the warhead 
on end and drawing a vacuum from the top side, allowing the vacuum to pull 
the potting material up through the cubes and out the top. When the 
potting material has set up, the warhead is then lined with an inert 
material 28 (e.g. polyethylene) compatible with the main charge explosive 
32. The warhead is then loaded with an explosive 32, e.g. PBX 116 (M) an 
RDX military explosive. Outer metal sphere 14 serves to hold cubes 24 and 
potting material 26 in place during fabrication, provides a limited amount 
of structural strength, and serves as protection for the completed warhead 
for minor scratches and abrasions. Inner liner 28 provides separation 
between inner sphere 12 and main charge explosive 32. The inner sphere 12 
carries the main structural loads, and serves as a gas check to improve 
the fragment 24 accelerational capability of the explosive. Without inner 
sphere 12, fragment velocity losses of up to 40% will occur. 
The warhead further contains a tube 34 running from the forward bulkhead, 
first plate 16, aft to the rear bulkhead, second plate 18. This tube 
provides the cavity for a safe/arm (S/A) fuze device to be inserted at a 
later time and is separate from the warhead. At one end of S/A tube 34 is 
a booster well 36, which will contain a booster explosive (e.g. CH-6). The 
booster explosive will be inserted, first into a thin plastic sleeve, and 
then into booster well 36 through a loading port 38 threaded into first 
plate (foreplate) 16. Through the design of the loading port cover and 
booster explosive location, a high degree of cook-off or fuel fire 
resistance is obtained. Pressure buildup due to the increase in 
temperature of the explosives, booster charge 36 or main charge 32, pass 
through vent holes 40 in loading port cover 38 allowing the explosive to 
burn rather than build up pressure to a detonation. Mounting holes 42 
permit use of a spanner wrench to screw on loading port cover 38. 
The warhead is currently designed to achieve at least 120.degree. of polar 
angle radial dispersion. This angle is measured from the nose to the tail 
of the missile system. Static tests with this warhead indicated that the 
current design produces fragmentation starting between 25.degree. to 
30.degree. off the nose and has fragmentation back to 150.degree. to 
155.degree. from the nose of the missile. In the actual design and 
fabrication of the warhead a number of alternatives exist. First, all 
metal parts except for the fragments are aluminum. However, any other 
easily formed metal alloy may also be used for this application. The 
preformed metal cubes in this warhead are of tungsten. Again, most other 
metal alloys could be used in this application. Also, the use of cubical 
shaped fragments is not a requirement. Spheres, although less efficient in 
use of the volume, are possible candidate fragment shapes as well. An 
electrical potting compund is used in this warhead to pot the cubes in 
place. However, any low viscosity material capable of being poured into 
place and cured into a rigid matrix is acceptable. A polyethylene liner 
was selected because of known compatibility with the PBXC-116 (M) main 
charge explosive. The main charge explosive need not be PBXC-116 (M). The 
liner need not be polyethylene. The only requirement is that the materials 
be chemically compatible. The plastic sleeve around the CH-6 booster 
explosive is polycarbonate. Again, compatibility is the main issue and 
none of the above materials are unique. 
Although there has been described herein above a particular design and 
arrangement of components thereof for the purpose of illustrating the 
manner in which the invention may be used to advantage, it will be 
appreciated that the invention is not limited thereto. Accordingly, any 
and all modifications, variations, or equivalent arrangements which may 
occur to those skilled in the art should be considered to be within the 
scope of the invention as defined in the appended claims.