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USAF Devises Ideas To Kill Underground Targets
Aviation Week & Space Technology
05/17/2004, page 49
Robert Wall and Douglas Barrie
Eglin AFB, Fla.
Experience gained from MOAB effort shapes design for massive penetrator
Bunker 'Plinking'
The U.S. Air Force has sketched preliminary designs for a huge bunker-busting bomb, but questions remain about how best to attack those hard-to-defeat targets.
The concept builds on experience the Air Force Research Laboratory (AFRL) gained last year with the 21,000-lb. GBU-43/B Massive Ordnance Air Burst bomb. The MOAB project was aimed at quickly fielding the Pentagon's largest guided bomb for combat operations in Iraq.
MOAB never was employed, and production ceased after a small inventory was built. However, the design work is proving useful in devising the Massive Ordnance Penetrator (MOP), says Fred Davis, a technical director at the Air Force Research Laboratory's munitions directorate.
U.S. Air Force researchers expect to draw on experience gained building the Massive Ordnance Air Burst weapon as they design a huge penetrator bomb.
The huge lattice fins used to control MOAB could be exploited for the penetrator, notes Lt. Stephen Kitay, who oversaw the weapon's development. Like MOAB, MOP would be GPS-guided. But there would be major differences between the two munitions. For instance, at roughly 30,000 lb., MOP would weigh more and its steel casing would be much thicker than MOAB's to achieve the desired penetration, while at the same time being filled with smaller amount of explosive.
Moreover, MOP would be smaller than MOAB and fit inside a B-2A bomber; MOAB is C-130-delivered. Operational employment altitudes also would differ: MOP is expected to be dropped from 40,000 ft.; MOAB is released at about 20,000 ft.
MOP would feature four fins along its airframe to provide stability during flight. Because the weapon is supposed to penetrate, the bomb has to impact near-vertically. The controls have to be tightly managed to ensure a steep angle-of-attack; the margin is much smaller than in the case of the air burst bomb, Davis notes.
Developers are exploring various design "trades" to determine the optimum material for the casing and how to create a bomb that would still be affordable.
Cost has already become a concern for some USAF officials as they mull pursuing MOP, which is often referred to as "Big-BLU" outside the laboratory. Integrating the weapon on the B-2A bombers could be extremely expensive, so other options might have to be looked at, suggests one USAF representative.
There's little doubt among Air Force weapon experts that enhanced target-penetration capabilities must be developed. Several officials at USAF's Air Armament Center here point out that engineering companies are offering structures advertised to be impervious to the service's 5,000-lb.-class penetrators now used to attack hardened targets.
Still, there might be alternatives to a huge penetrator. USAF's Jassm stealthy cruise missile has a 1,000-lb.-class warhead with penetration capability. To bolster that feature, mission planners could arrange for two missiles to strike the same spot in quick succession, with one weapon flying down the hole created by a preceding one, notes Gerry L. Freishler, USAF program director for long-range attack. Tests have demonstrated Jassm's ability to meet the tight accuracy requirements, he notes.
One technical problem any penetrator weapon would have to address is fuzing. After years of research, the Air Force has scrapped work on the Alliant Techsystems Hard-Target Smart Fuze, arguing that production problems that bedeviled the system could not be overcome. HTSF was being designed to count layers and voids to detonate a weapon at a preselected point within a target.
However, military officials assert that the need for such a fuze hasn't gone away. The Pentagon--including representatives from the Navy and Defense Threat Reduction Agency, which is chiefly responsible for defeating underground weapons of mass destruction storage facilities--is now studying its options.
Several proposals are emerging for a new program. One would be to try to make HTSF work. Another would involve adapting the multi-event hard-target fuze designed by Thales Missile Electronics in Basingstoke, England. The Pentagon probably would insist on a U.S. partner, USAF officials note. Furthermore, the service might opt for a new development project, suggests Steve Butler, director of engineering at the Air Armament Center. The HTSF design is based on 10-year-old technology, he says, so new options may exist.
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