USAF: Next bomber will be manned with no exotic technology

Conventional Bunker Busters
During the 1991 Gulf war, allied forces knew of several underground military bunkers in Iraq that were so well reinforced and so deeply buried that they were out of reach of existing munitions. The U.S. Air Force started an intense research and development process to create a new bunker-busting bomb to reach and destroy these bunkers. In just a few weeks, a prototype was created. This new bomb had the following features:

* Its casing consists of an approximately 16-foot (5-meter) section of artillery barrel that is 14.5 inches (37 cm) in diameter. Artillery barrels are made of extremely strong hardened steel so that they can withstand the repeated blasts of artillery shells when they are fired.

* Inside this steel casing is nearly 650 pounds (295 kg) of tritonal explosive. Tritonal is a mixture of TNT (80 percent) and aluminum powder (20 percent). The aluminum improves the brisance of the TNT -- the speed at which the explosive develops its maximum pressure. The addition of aluminum makes tritonal about 18 percent more powerful than TNT alone.

* Attached to the front of the barrel is a laser-guidance assembly. Either a spotter on the ground or in the bomber illuminates the target with a laser, and the bomb homes in on the illuminated spot. The guidance assembly steers the bomb with fins that are part of the assembly.

* Attached to the end of the barrel are stationary fins that provide stability during flight.

The new EGBU-28 (the “E” being for enhanced) replaces the GBU-37. This latest version of the “bunker buster” uses the Global Positioning System for guidance so that it can be dropped with accuracy at higher altitudes in foul weather. The amount of rock and concrete that the EGBU-28 can penetrate is classified, but Major Dick Wright, who was the weapon’s test manager in 1991, said that the older version “went through 20 feet of concrete like butter” and when dropped onto hard ground, penetrated down to 100 feet.

New production would be for about 350 weapons. Development is slated to begin this fiscal year with a single contractor team. Production is expected to start in 2005. The B-2 and F-15E will remain the only launch platforms for the weapon. The Air Force has developed a new steel that is available for bidders to use. Called Eglin Steel (ES-1), it is a collaboration between the Air Force and National Forge, which builds the casing for the BLU-113. The largest ingots that can be made, current producer are 69 inch diameter. Current size ingots being made, current producer are 39 inch diameter. ES-1 alloy is weldable, as it is a "low carbon alloy" Penetrator wall thickness of 2 inches has been heat treated. Test Sections 4 inches thick have been evaluated, with excellent and consistent hardenability through wall. Among the candidate explosive fills is the AFX-757 used in the warhead of the Joint Air-to-Surface Standoff Missile. The Air Force-developed fill produces more blast energy and is less likely to be set off in a fire than Tritonal. The current BLU-113/B contains about 600 lb. of Tritonal.

The BLU-118/B is a penetrating warhead filled with an advanced thermobaric explosive that, when detonated, generates higher sustained blast pressures in confined spaces such as tunnels and underground facilities. The BLU-118/B uses the same penetrator body as the standard BLU-109 weapon. The significant difference is the replacement of the high explosive fill with a new thermobaric explosive that provides increased lethality in confined spaces.

The BLU-118/B warhead uses a Fuze Munition Unit (FMU)-143J/B to initiate the explosive. The FMU-143 fuze has been modified with a new booster and a 120-millisecond delay. All weapon guidance systems and employment options currently used with the BLU-109 warhead are compatible with the new BLU-118/B warhead.

BLU-118/B payload candidates included PBXIH-135 [one of the Navy's new insensitive polymer bonded explosives], HAS-13, or SFAE [solid fuel air explosive] loaded into existing BLU-109 Weapon Bodies. Conventional high explosives (CHE) are characterized by a sensitivity to mechanical or thermal energy. Insensitive high explosives (IHE), on the other hand, require extraordinarily high stimuli before violent reaction occurs. Insensitive explosives reliably fulfil their performance, readiness and operational requirements on demand, but the violence of response to unplanned hazardous stimuli is restricted to an acceptable level. This means that when a munition is in a fire, hit by a fragment, bullet or high velocity projectile or subject to some other hazard the result will not be a detonation or a violent reaction of the explosive and propellant; no more than severe burning will ocur [such a deflagration is an exothermic reaction that occurs particle to particle at subsonic speed]. Some insensitive explosives are known to react in a different way to conventional explosives. For instance, detonation reactions are slower but more energy is released in a way that has the potential to produce a lot more damage.

One of the newest weapons in the Air Force's arsenal of hard target penetrating bombs is the AFRL Munitions Directorate-developed Advanced Unitary Penetrator (AUP) shrouded aerial bomb, equipped with the Hard Target Smart Fuze (HTSF). The bomb and its smart fuze were a big hit during Operation Allied Force. The AUP mimics, in appearance and dimensions, the already combat-proven BLU-109 (Bomb Live Unit) warhead, a 2,000-pound hard target penetrating warhead used by the Air Force and Navy. The AUP is designated the BLU-116 and boasts twice the penetration capability of the BLU-109.

The Advanced Unitary Penetrator (AUP) is the next-generation, hard target penetrator munition that provides a lethal capability to penetrate and defeat extremely hard multilayer underground facilities. Sharing an external appearance and flight characteristics with the 2000 lb BLU-109, the AUP has an advanced heavy steel penetrator warhead filled with high-energy explosives that can penetrate more than twice as much reinforced concrete as the BLU-109. Performance is enhanced by a void-sensing Hard Target Smart Fuze that detonates the AUP at the optimum point in a target to inflict maximum damage.

A bomb typically includes a hard casing having an interior hollow space for containing an explosive material. The physical characteristics of the bomb, including the weight, center of gravity, moments or inertia, and the aerodynamic shape, all affect the free-fall response of the bomb, whether or not a guidance package is included with the bomb. Bombs delivered from aircraft, including free-fall guided or unguided bombs, glide bombs, and boosted bombs, must pass rigorous field testing which includes the safe release from a deploying aircraft and accuracy of delivery to the target. These tests must be conducted for each type of aircraft that will carry the bomb. The development of new weapons, therefore, is subject to significant delay and expense before the weapon is qualified for use.

The ability of a bomb, or other projectile, to penetrate a target is proportional to the mass and the velocity of impact of the projectile and inversely proportional to the cross-sectional area of the bomb. That is, the greater the kinetic energy and the smaller the cross-sectional area, the greater the penetration that can be expected. To adapt an existing bomb for greater penetration by reducing the external diameter of the bomb can also result, however, in changes in the mass properties such as weight, center of gravity, moment of inertia, and in the aerodynamic properties, all of which can affect the flight characteristics of the bomb. These changes also require that the adapted bomb be qualified for use.