PICATINNY ARSENAL, N.J. - The U.S. armed services, which aim to achieve widespread use of safer munitions less prone to accidental detonation, are closer to attaining that objective with the 500-pound bomb.

The term "insensitive munitions (IM)" is often used to describe munitions that are less likely to have a violent reaction when subjected to impact from bullets and fragments, heat from fire, and shock from nearby explosions.

The IMX-101 fill is intended to replace trinitrotoluene, commonly known as TNT, as the explosive material in some munitions.

While TNT does meet operational requirements, it does not meet IM requirements. This is the fundamental reason why the U.S. military has been moving slowly away from it.

The objective of the programs that led to the development of the 500-pound bomb replacement material, however, was not directly related to the replacement of TNT since the 500-pound bomb does not currently use TNT.

The sole purpose was to create a safer General Purpose (GP) 500-pound bomb. Both the Navy and Air Force have identified this munition as a priority for insensitive munitions technology for more than five years.

Using a common fill explosive across the board for all branches of the U.S. Armed Forces will lead to more efficiencies in procurement and provide an enhanced capability to the warfighter.

A common energetic approach to the GP bomb will increase efficiency during load, assemble and pack (LAP) by reducing the number of changeovers in completing bomb orders.

"Basically this means that if there is a common energetic solution for the BLU-111 series there would be less stoppages in the production line," said Anthony R. Di Stasio, Program Manager, Joint Insensitive Munitions Technology Program (JIMTP), under the Office of the Secretary of Defense for Acquisition Technology and Logistics.

The Armament Research, Development and Engineering Center at Picatinny Arsenal is involved in the project by virtue of a proposal regarding insensitive munitions that it submitted to the JIMTP. At the engineering center, the work is being conducted by the Explosives Technology and Prototyping Division, which is part of the Munitions Engineering Technology Center.

"Right now there are multiple versions of the 500-pound bomb, the A/B, the B/B and the C/B. By reducing the different variants, you can increase efficiency," Di Stasio added.

This will benefit the military's industrial base by allowing consolidation of multi-service requirements for bulk production of a common fill.

These efficiencies in LAP further the goal of getting this increased capability in the hands of the warfighter, allowing them to better execute their global mission.

"Over the course of the past five years the Joint Insensitive Munitions Technical Program (JIMTP) has been seeking insensitive munitions solutions for the (Bomb Live Unit) BLU-111 GP bomb to pass sympathetic detonation," said Di Stasio.

The most recent project involved an effort to select a new explosive fill for the BLU-111 500-pound bomb to meet the insensitive munitions requirement.

One of the first and biggest breakthroughs in IM technology came in the 1990s from the U.S. Navy with the development of PBXN-109 as the first step in creating a safer 500-pound bomb. A combined program with the Navy and Air Force more recently made substantial gains in developing and applying venting technology.

While these improvements did not pass all the IM tests, they were a tremendous improvement from the TNT based material, Di Stasio said. The U.S. Air Force and Navy have maintained the BLU-111 as a high priority munition, and as such it was heavily focused on by the Joint Insensitive Munitions Technology Program.

The BLU-111 munition is one of the highest ranked, most dangerous weapons in the Single Manager for Conventional Ammunition (SMCA) inventory. It is listed as a top priority for not only the Navy at Program Executive Office (PEO) Unmanned Aviation and Strike Weapons, but also the Air Force at PEO Weapons.

Due to the size of the munition, proximity in the logistical configuration and the sensitivity of the explosive fill, the current weapons mass detonate, creating a catastrophic effect on magazines, warfighters and platforms.

Under Munitions Area Technology Group III (MATG III), Blast Frag Warheads, there were three viable candidates: PBX-IH-140, Al-IMX-101, and AFX-770.  

<span style="font-weight: bold">HURDLES TO SURMOUNT </span>

According to the JIMTP Office, the hurdles facing IM technology for the BLU-111 are very similar to most other systems. Finding an extremely insensitive, thermally stable material that survives the difficult IM test series and maintains the level of effectiveness service members require is definitely the biggest hurdle, according to Di Stasio.

The joint service nature of the BLU-111 required unique considerations as well.

Multiple services meant multiple requirements, platforms, uses and life cycles. Meeting the requirements of various groups inevitably restricts design space and therefore makes the technology development and transition more difficult. It was necessary to consider every facet of the explosive candidates, including performance, sensitivity, producibility, load ability, initiability, cost, demilitarization, toxicity and environmental aspects.

IMX-101 is an effective material for U.S. Army artillery because it produces fragments that are required for artillery target elimination. General purpose bombs, however, require not only fragmentation but also high blast output.

Creating blast from an explosive material has often meant the addition of metal, typically aluminum. Years ago, bombs were filled with a combination of TNT and aluminum. It was quickly realized that if IMX-101 was a suitable replacement for TNT, the addition of aluminum might create a suitable main charge for general purpose bombs.

<span style="font-weight: bold">LOWERING DEVELOPMENT COSTS </span>

When developed, the IMX material was more costly than TNT. However, much has been done to lower the price. One of the benefits of developing IM solutions from materials that are readily available is the ability to leverage other efforts.

The current estimates for the raw explosive materials are less expensive than the PBXN-109 currently loaded in the BLU-111. The manufacturing process for the new material is different than that of the current material.

However, loading studies are being conducted to minimize the effects of any changes and ensure the manufacturing process is as efficient as possible.

The three explosive candidates developed by the JIMTP, of which Al-IMX-101 was selected as the first choice for the 500-pound bomb, are truly a breakthrough in the development of Insensitive Munitions and even more of a revolution for not only the GP-Bomb family, but also the entire family of large diameter munitions, according to Di Stasio.

The (Al) in Al-IMX stands for aluminum, a requirement Di Stasio said all bomb fills must have to add blast.

The second choice or risk mitigator is an explosive formulation developed by a team at Naval Surface Warfare Center, Indian Head Division.

Though slightly outscored by Al-IMX-101 in cost and performance, the PBX-IH140 material performed beautifully in the IM testing and will be evaluated should the first choice not be suitable.

"With that being said, it's my pleasure to inform you that the JIMTP, PMA-201, EBSN-AF, and PD-JP, in other words, the Navy, Air Force, OSD, and Army representatives for the family of General Purpose Bombs have all agreed that the first choice for the next generation IM fill for the BLU-111 Bomb should be Al-IMX-101," said Di Stasio.

The program includes IM evaluation for the final configuration, lethality testing, center of gravity and moment of inertia analysis as well as an initiation reliability study of the new detonation train that is compatible with legacy fuzes.

For the next three years, this will be the flagship program under MATG III, and arguably one of the most important program under the JIMTP, Di Stasio said. These formulations and the strides they represent for IM technology are some of the greatest successes in the history of the JIMTP, and will be presented as such to the Technical Advisory Committee (TAC) this year.

<span style="font-weight: bold">NEXT STEP TOWARD FIELDING </span>

According to the JIMTP, there is a still a lot of work to be done.

"The material must be produced in extremely large quantities to meet the needs of a bomb," Di Stasio said.

"The final design specifications must also be made to the detonation train along with substantiation that the effectiveness can be maintained. The loading procedure for the new material must be developed, tested and proved. The final system must then pass all the qualification tests to be ready for transition into the field. Having the support of the Navy and the Air Force however, goes a long way toward ensuring that each of these challenges can be faced one by one."