Insensitive High Explosives [IHE]
In an effort to improve munitions survivability and safety, the Department of Defense (through the Joint Requirements Oversight Council) established a policy requiring all new munitions be capable of withstanding accidents, fires, or enemy attack. One method of addressing this requirement, the use of "Insensitive Munitions" (IM), including propellants and explosives, was mandated. Thus a new class of IM explosives was developed over the following decade. Because these IM formulations differ somewhat from each other in a variety of ways (physical properties, explosive output, manufacturing process and cost, sensitivity and toxicity, etc.,) the explosive selection process for a given munition has become more complex. They must meet MIL-STD-2105, Hazard Assessment Tests, Non-Nuclear Munitions.
The US Air Force developed an insensitive explosive fill for its general use bombs using a mixture of trinitrotoluene (TNT) and aluminum. Since the insensitive fill is not ready to be used in tactical bombs, and there is no available TNT in the stockpile, Joint Munitions Command (JMC) Bombs/Energetics Division awarded an indefinite delivery/indefinite quantity (IDIQ) contract for supply of TNT over a 5-year period to Alliant Ammunition and Powder Co. (AAPC).
Virgin TNT would be supplied from a National Technology Industrial Base source, reclaimed and OCONUS TNT. The facility that produced the virgin TNT can be easily modified to produce other energetic materials, notably insensitive explosives. The IDIQ is delivering sufficient quantities of TNT to meet increased requirements. Partnering with major contractors has proved beneficial for current program execution. New partnerships are now being established with AAPC for TNT and General Dynamics Tactical and Ordnance Systems for bombs. Through these partnerships, communications would be improved, expectations would be better understood, common goals can be set, delivery times improved and problems identified so they can be resolved early on.
There are several reasons that make the development of new explosives for hard target penetrators and related systems important. First, there are a variety of new energetic molecules that offer real promise in terms of energy and processibility. The targets of precision guided warheads are high value, making the performance of the warhead more important than that required by mass-use systems. Furthermore, prior to precision guided warheads, improvements in explosive energy density added little to the probability of a kill if the miss distance was large. Now that weapons routinely hit the intended targets, small improvements in the lethality of the warheads can have a significant impact on target damage.
The development of high explosives for hard target munitions has historically been difficult due to the expense of full-scale penetration trials. Since high explosives development has been an iterative process between formulation and testing, new materials for hard target penetrators were effectively eliminated. New computational approaches and diagnostics for explosives characterization have made the development of a “designer” main charge feasible.
The Air Force Science Advisory Board has reviewed concepts for decreasing the volume of weapons without decreasing lethality. It was concluded that it is possible to significantly reduce the volume of Air Force weapon systems without compromising lethality. Performance improvements that are realistically attainable in the near-term in high explosives would make a significant contribution to this goal. There are significant differences in terms of the energy available for accelerating fragments as well as the energy available for blast. There can be major differences in the energy density relative to the baseline explosive depending on whether a fragment or a blast metric is used. Hence, explosive selection depends strongly on the target.
Power is an indication of an explosive’s ability to accelerate metal, whereas energy is typically proportional to blast and heave performance. The inverse relationship between power and energy density is the conundrum of how to optimize between fragmentation and blast performance.
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