Small precision bomb program on fast track.

Seeking to meet growing demands for small precision-guided bombs, the U.S. Air Force is rushing to develop a new weapon that is more accurate but with less destructive power than current systems, such as the 2,000-pound joint direct attack munition (JDAM).

The smaller bomb ideally will help pilots hit specific targets in urban areas, for example, where traditional air strikes generally endanger civilians.

The 250-pound small-diameter bomb (SDB) also will make aircraft more productive by allowing them to carry more weapons and hit more targets per sortie. The F-15E Strike Eagle, which can load a single 2,000-pound JDAM, will be able to carry four SDBs.

"We basically quadruple load-out, and we're able to prosecute around 80 percent of the fixed targets," said Col. Jim McClendon, program director for the direct attack joint program office at the Air Force Air Armaments Center.

To achieve its accuracy, the SDB--officially called GBU-39/B--employs air advanced technology known as wide-area differential GPS (global positioning system) support infrastructure. It also introduces new mission planning software that will enable Air Force crews to program fixed targets via computer workstations on the ground or aboard aircraft in flight. The system wit tested on an F15E at Eglin Air Force Base in the first SDB guided flight April 22. All upgraded SDB with a moving target seeker will begin development in 2006.

Boeing, the system's prime contractor, demonstrated the technology in a series of Air Force Research Laboratory programs at Eglin from 1995 to 2000. It now leads an industry team providing the weapon, carriage system, GPS stations and other elements. "The real challenge was coming up with a system that was fieldable and could be supported in the Air Force infrastructure," explained Dan Jaspering, SDB program manager at Boeing Integrated Defense Systems.

The contract was awarded to Boeing in October 2003, and the Air Force chief of staff" ordered the weapon operational by the fourth quarter of 2006. "We are doing one of the most aggressive, if not the most aggressive, full-up weapons acquisitions that's ever been done," said McClendon. "Meeting the schedule is our top risk."

The abbreviated development schedule means that the development tests and operational tests will be combined. Operational testers will participate in the program far earlier than traditional programs. The upshot is that problems uncovered early in the program by operational aircrews and maintainers can be fixed more quickly, said McClendon.

After fielding on the F-15E, the small diameter bomb will be integrated with the F-16, B-2, F-22, F-35, unmanned aircraft and other strike platforms.

Unlike the JDAM kit applied to "dumb" bombs in the field, the SDB is stored, shipped and loaded as a complete weapon.

The cost per round in full-rate production is $64,000, calculated over 24,000 weapons and 2,000 carriage systems. Program officials said the goal is to bring the cost down to $41,000 per round, possibly as low as $30,000.

The decision to develop the SDB stemmed from a requirements view by the Air Combat Command. Based on a list of 14 common hard and soft target types, ACC officials decided they needed a mix of blast-fragmentation and penetrating bomb effects. "The war fighter looked at the target set and determined, of the fixed targets, about 80 percent could be covered by the warhead SDB brings to the fight, that is, a 250-pound class weapon," McClendon explained.

Improved energetics make the small diameter bomb an insensitive munition that is safer to store and handle. It is expected to penetrate more than 5 feet of reinforced concrete. The KDI Precision Products division of L3 Communications makes the reprogrammable electronic fuse that tailors the bomb to various targets.

The blast area, 26 feet, is considerably smaller than the 82-feet blast area of the 2,000-pound JDAM.

The JDAM, with its GPS/inertial guidance package, already betters its circular error probable (CEP) of 13 meters. The small diameter bomb with differential GPS and modest autopilot refinements promises a CEP of less than 4 meters. "Our requirement is four, but we expect to do better than that," noted McClendon.

SRI International provides the support infrastructure for the small diameter bomb. Wide area differential GPS ground stations correct errors in the satellite-based navigation system and transmit the corrections to authorized users. The ground stations can be located up to 1,500 miles apart. "We plan to have them delivered as part of the overall system capability," said McClendon. If, for any reason, the advanced support infrastructure is not available, the SDB will achieve JDAM accuracy with the GPS constellation alone.

This technology will be integrated into the joint direct attack munition with the next JDAM software drop, and it may find broader use. "It gets more weapons effectiveness for us, but it is not a closed system," said McClendon. "We're making this available to other Defense Department users."

The GBU-39 uses a Rockwell Collins GPS receiver with a Harris anti-jam module and a Honeywell inertial measurement unit to guide itself to the target. The tailfin actuators are made by HR Textron, and the bomb glides to the target on diamondback foldout wings made by missile maker MBDA. Free of the aircraft, the SDB deploys to glide over standoff ranges up to 60 nautical miles.

With wings folded, the small diameter bomb measures just 7.5 inches wide by 71 inches long and fits the internal weapons bays of the F-22 and F-35 Joint Strike Fighter. The current weight is 285 pounds, which still qualifies the SDB as a 250-pound class weapon. Initially, the F-15E will be cleared to carry 12 SDBs of, three BRU-61/A carriers--four weapons each on the centerline and two conformal tank stations. The Strike Eagle may acquire eight more bombs later in the integration program.

The SDB carriage system, made by Sargent Fletcher Inc., uses pneumatic ejectors instead of troublesome gunpowder cartridges. It contains its own stores management software and provides a mechanism to simplify integration with different aircraft. The F22, for example, will carry up to eight GBU-39s in its two internal weapons bays for attack missions. The B-2 could potentially deliver up to 216 SDBs in one load.

Air Force crews will program their bombs through a ground-based mission planning system. BAE Systems is providing PC-based mission planning software.

The software will assist aircrews planning to attack a series of target complexes, each containing several impact points. Boeing claims planning times can he less than one minute per mission. The Windows-style menus will allow users to generate and download mission data to drop the weapon from different aircraft.

A future upgrade of the small diameter bombs will introduce a seeker, data-link, and other enhancements intended to help strike moving targets. Those upgrades now are being studied and none yet has been funded.

The SDB is exactly what commanders need for 21st century conflicts, notes Air Force Maj. Dave Morgan of the SDB procurement office. "The world is changing. We have fewer aircraft. Targets are in sensitive locations," he told a conference of the Precision Strike Association. "Commanders need lower collateral damage."