Boeing GBU-39/B Small Diameter Bomb

During Operation ‘Allied Force’ in Kosovo and most recently during Operation ‘Iraqi Freedom’ F-15E aircrews had to strike military targets that were often located in a dense urban environment like Bagdad or Fallujah among the civilian population. The large concern for collateral demage among civilians once again validated the USAF’s push for a more accurate weapon that could take out the target more effectively with less collateral demage.

The solution to this need is the GBU-39/B Small Diameter Bomb, which is currently being tested on the F-15E Strike Eagle by the 40th Flight Test Squadron at Eglin AFB, Florida.

The GBU-39/B Small Diameter Bomb is a 250-lb-class all-weather precision weapon. With its weight of only 285 lb the GBU-39/B will improve the loadout effectiveness of the F-15E, since it has only half the weight of the GBU-12 Paveway II, the smallest precision guided bomb the F-15E uses today.

Four GBU-39/Bs can be carried on a single station by using the BRU-61/A four-store rack which is compatible with the MIL-STD 1760 aircraft electrical and digital interface.

Initially, operational aircraft will be cleared to carry the GBU-39/B in combination with the BRU-61/A rack on five weapon stations: underwing stations STA-2 and STA-8, centerline station STA-5 and lower inboard CFT-pylon stations RCT-2 and LCT-2. All these weapon stations, which are also cleared to carry JDAM, are already wired with the MIL-STD 1760 data bus allowing the transfer of guidance information to the weapon.

A future avionics update to the F-15E is expected to bring MIL-STD 1760 wiring to four more weapon stations: LCT-1, LCT-3 and RCT-1, RCT-3 will then be cleared to carry the GBU-39/B as well. F-15E test aircraft operated by the Air Armament Center at Eglin AFB and Boeing's St.Louis test facilities already carry the GBU-39/B on these additional stations.

GBU-39/B Components

The GBU-39/B is equipped with a 250-lb multi-purpose penetrating and blast-fragmentation warhead with a forged casing made by TAM Garland that contains a 50 pounds explosive charge. The lenght/diameter ratio and the nose shape of the GBU-39/B are designed to optimize penetration of more than 5 feet of steel-inforced concrete, a penetration comparable to the 2,000-lb BRU-109 penetrator warhead used with the GBU-15 or the AGM-130. The blast area of the GBU-39/B is only 26 ft (compared to 82 ft of a 2,000-lb JDAM), making the GBU-39/B a perfect weapon for urban warfare because the smaller warhead ideally will help pilots hit specific targets in urban areas where traditional air strikes generally endanger civilians.

The aircraft's MIL-STD 1760 data bus allows the aircrew to program the
GBU-39/Bs reprogramable, cockpit selectable electronic fuze (made by KDI Precision Products) and order the weapon to explode above ground, on contact or with a delay that will enable it to penetrate the target.

The guidance system of the GBU-39/B is located in the tail of the weapon and features an Advanced Anti-Jam GPS aided Inertial Navigation System (AJGPS/INS). Its Rockwell-Collins GPS receivers are paired with an anti-jam module made by Harris Corp. which makes the receivers resistant to unintentional or intentional RF interference or jamming. The inertial measurement unit (made by Honeywell) enables the GBU-39/B to guide itself to the target. Data from the guidance system is processed by the weapons Unisys flight computer and send to the control section which uses the tail fins (made by HR Textron) to guide the weapon to the target.

The accuracy of the GBU-39/B is 13 m CEP (Circular Error Probable) for a surveyed target, comparable to the accuracy of JDAM munitions. A GPS ground infrastructure currently under development by SRI International is expected to improve the accuracy of the GBU-39/B Small Diameter Bomb (and other GPS guided weapons) to only 3 m CEP. The new support infrastructure consists of wide area GPS ground stations that correct errors in the satellite-based navigation system and transmits the corrections to the weapon system resulting in an improved accuracy.

GBU-39/B Diamond Back Wing Kit

To increase the weapon's stand-off range, the GBU-39/B Small Diameter Bomb is equipped with the 'Diamond Back' precision attack gliding kit from MBDA Missile Systems. The tandem-wing design of the Diamond Back kit deploys from a compact storage position on the bottom of the GBU-39/B and integrates with the weapon's guidance system. The wing kit provides the
GBU-39/B with a low frontal area and compact form when the wings are stowed.

After the GBU-39/B has been released from the aircraft the weapon performs a 180 degrees roll. With the wing kit now on top of the weapon, a simple, robust and reliable extension mechanism extracts the wings within only 4 seconds to form a diamond shaped structure. The GBU-39/B benefits from the additional lift provided by the wings, which increases the weapon's stand-off range to more than 60 nm. The wings also improve the weapon's manoeuvrability and glide characteristics. If necessary, the wings can be discarded in midcourse to allow the weapon to build up velocity and kinetic energy before striking the target.

The Small Diameter Bomb evolved from a series of competitive weapons research programs conducted by the Air Force Research Laboratory (AFRL) at Eglin AFB and performed by Boeing from 1995-2000. The AFRL programs included Miniature Munition Technology (MMT), Small Smart Bomb (SSB), Smart Multiple Ejection Rack (SMER) and Small Smart Bomb-Range Extension (SSB-REX).

The Small Diameter Bomb competitive Component Advanced Development (CAD) program began in October 2001 when Lockheed Martin and Boeing were awarded contracts to begin developing a SDB program.

After this two-year concept demonstration competition with Lockheed Martin, Boeing was chosen to carry out development and production of the GBU-39/B on 28 August 2003. The new weapon system is expected to get Defence Acquisition Board (DAB) approval for low-rate production in spring 2005 and be operational with F-15E squadrons in fall 2006.

GBU-39/B Specifications

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