Hard targets pose a near-term problem as USAF explores weapon and fuze options
Despite a grim fiscal environment, the U.S. Air Force still has ambitions to acquire a new generation of air-launched weapons that will take advantage of the stealthy in its fleet and the that will be introduced late this decade. But the service is being forced to prioritize its needs, putting a near-term emphasis on attacking hard and deeply buried targets such as nuclear weapons or command-and-control facilities in North Korea or Iran.
The Air Force is also exploring concepts for a Long-Range Standoff Weapon that would eventually replace the Air-Launched Cruise Missiles (ALCMs) in the fleet today. An analysis of alternatives should be completed by year-end to prepare for a fiscal 2014 program start.
However, a longtime goal of combining the AIM-120 Advanced Medium-Range Air-to-Air Missile (Amraam) mission with that of an air-defense killer—once called the Joint Dual-Role Air Dominance Missile, or the Next-Generation Missile—has been put on hold in the near term.
One factor driving requirements for improved weapons stems from the limitations of the service's decision decades ago to shift to an all-stealthy fighter force. TheF-22 and eventually the F-35 will provide the operational flexibility of stealthy missions in enemy airspace, but this attribute comes at a price. The internal weapons bay, used for stealthy operations, has only two positions. So the service is pushing weapon manufacturers to mature technologies to make future munitions smaller and more flexible. This, in turn, is reinforcing a need for more sophisticated explosive fills—perhaps halving the size of a warhead without compromising its explosive effects. Additionally, a decades-old hope remains for fuzes that facilitate variable explosive effects or shaped blast-fragmentation effects.
Air Combat Command (ACC) is conducting an analysis of alternatives to explore options for a future Hard Target Munition (HTM) that could be employed by legacy fighters as well as the F-22 and F-35. “Next-gen weapons need to be more flexible in terms of the types of targets they can address and, in some cases, may need to be smaller without sacrificing intended weapons' effects,” says Col. Sam Hinote, director of requirements at ACC. “This will allow our fifth-gen fighters to have a deeper magazine [increased load-out] and more flexible targeting options.”
The Air Force hopes to field a 1,000-lb. penetrator suitable for use in stealthy weapons bays in the next decade, with a program starting potentially as early as 2014, says Maj. Gen. Kenneth Merchant, Air Force program executive officer for weapons. Though the service has not yet refined requirements, options include a boosted 1,000-lb. version that would make use of a rocket motor for speed and momentum and, possibly, a 5,000-lb. follow-on without the motor. The goal with the 1,000-lb. version is to maintain the effects of a 2,000-lb. BLU-109 with a smaller weapon.
Although the Air Force is still able to employ the BLU-109, a weapon used heavily during the 1991 Persian Gulf war for hard-target missions, it hopes to shift to a smarter fuze capable of both burrowing and counting the layers through which it travels before detonating. To do so, better casings capable of withstanding layers of concrete and other materials also are needed.
Alliant Techsystems (ATK) is under contract to develop the new Hard-Target Void-Sensing Fuze and plans to begin demonstrations in fiscal 2013. Production is slated to start in the middle of fiscal 2014.
A void-sensing fuze is the “Holy Grail” of fuzing, says Merchant. “Fuzes and hard targets don't work well together,” largely because of the lateral and vertical loads placed on a weapon penetrating concrete at high speed.
The service has manufactured developmental versions of the Massive Ordnance Penetrator (MOP). At 30,000 lb. and carrying 5,000 lb. of explosive fill, MOP is the largest conventional munition in the U.S. arsenal, and it is ready for use on the B-52 and B-2 bombers. But MOP currently lacks a void-sensing capability.
Because of MOP, however, improved processes have been devised for pinning internal equipment onto the electronics boards so that they stay intact through a violent penetration, says Merchant. He also notes that the Air Force was able to incorporate more “observing features” into the MOP design, meaning that the weapon can provide more data to commanders about how it executed its mission, potentially giving key details for a bomb-damage assessment. Self-assessing capabilities are another feature sought for future weapons, says Hinote.
In the meantime, the Air Force will begin incorporating electronic safe and arming devices on its fuzes. These will lack the less reliable mechanical parts of their predecessors. Merchant says funding available, and the Air Force will phase this capability into the FMU-152A/B Joint Programmable Fuze, which has already demonstrated a reliability of more than 98%, as these devices replace the FMU-139s in service. Merchant says that with a $50-75 million investment, the new electronic safe and arm capability can be qualified within two years.
Overall, however, the fuze industrial base continues to be fragile, owing to the exacting nature of the work and notoriously low financial return. Manufacturers such as, ATK and Kaman receive far more orders for electronics for commercial items such as mobile phones. Thus, the Pentagon has a hard time keeping up with the current generation of electronics in production owing to a lag in qualifying them for weapons use. And it is not financially viable for manufacturers to continue building older Pentagon designs without certainty regarding projected orders.
Merchant says he is pushing in the forthcoming fiscal 2014 budget request to “refill the bucket” of funding. Fuze reliability will become even more crucial as the F-35 is introduced into service. With 2-8 weapons carried internally for stealthy use, the drawback to encountering a dud on a mission is even worse than with today's fighters that have a larger loadout.
The portfolio of existing weapons is largely healthy, Merchant says. It includes the once-troubled Lockheed Martin Joint-Air-to-Surface Standoff Missile, or(a stealthy cruise missile), 's 250-lb. Small-Diameter Bomb and various (JDAM) kits, as well as the short-range, air-to-air missile. Jassm, which is now being fielded, is expected to have a 15-year service life. JDAM and SDB are expected to be in service at least 20 years. The BRU-61 bomb rack is designed to carry four SDBs in each JDAM position on the F-22, quadrupling the number of ground targets it will eventually be able to attack in a single sortie.
In contrast,'s Amraam has suffered setbacks. Despite years of development and $2 billion spent to incorporate improved kinematic software, a new data link and better electronic-protection capabilities to the internationally available AIM-120C7, the U.S.-only D continues to slip further behind schedule.
The current problem is faulty rocket motors provided by ATK, prompting the Air Force to halt motor production and to withhold $621 million in payments to Raytheon pending delivery of all-up rounds. At issue was firing the motor at the extreme edge of its design parameters, about 165 deg., said Harry Schulte, Raytheon's vice president of air warfare systems, who spoke with Aviation Week at the Farnborough air show this summer.
Merchant says improvements have been incorporated into ATK's propellant and assembly process, and they are being incorporated into the next batch of production motors. Meanwhile, the Air Force is working to qualify Norway's Nammo as a second source. Nammo is building a limited-production configuration incorporating the company's propellant and blast tube with the existing casing from ATK. Nammo plans eventually to incorporate its own casing into a production design.
Both ATK's and Nammo's designs must still be tested and qualified before production of all-up rounds can restart. Results from tests on ATK's design are expected this month.
Also plaguing the Amraam D is a software/hardware integration problem that prompted operators to have to “reboot” the system in order to dispatch a missile from the wing of a fighter. Thus far, releases from thehave proven easier than those from the Navy's . Root-cause analyses have been discovered for a fix, says Merchant.
The Amraam D entered operational testing in June and is slated for service in fiscal 2014. Payments will resume once all-up rounds begin arriving in sufficient numbers, he says.
Experts at Merchant's Air Armament Center are also closely monitoring Raytheon's work on the Small-Diameter Bomb II, a 250-lb. weapon designed with a trimode seeker to destroy moving surface objects, day or night or in bad weather (see p. 61).
The uncertainty surrounding the fiscal 2013 budget is “nerve-wracking,” says Merchant. Because lawmakers have failed to pass a budget for fiscal 2013, the government will be forced to operate at funding levels approved in fiscal 2012. Because the production programs are “buy-to-budget,” Merchant says he will not be able to increase purchase rates. This will reduce the economies of scale available when buying higher quantities, increasing per-unit pricing.