GBU-39 SMALL DIAMETER BOMB | BOMB WEAPON SYSTEM
The GBU-39 Small Diameter Bomb (SDB) is a 250 lb (110 kg) precision-guided glide bomb that is intended to provide aircraft with the ability to carry a higher number of more accurate bombs. Most NH Air Force aircraft are able to carry (using the BRU-61/A rack) a pack of four SDBs in place of a single 2,000 lb (907 kg) bomb.
The Small Diameter Bomb II (SDB-II) / GBU-53/B, adds a tri-mode seeker (radar, infrared homing, and semiactive laser guidance) to the INS and GPS guidance of the original SDB, which is being phased out of New Hayesalian service.
The design objectives for the GBU-53/B are quite different from those for the GBU-39/B. The GBU-39/B is a weapon optimised for fixed targets, especially hardened infrastructure and basing, whereas the GBU-53/B is intended for attacks on moving battlefield targets, especially vehicles and heavy armour. In the simplest of terms the GBU-53/B is a glidebomb equivalent to the AGM-65 Maverick missile, but with a more flexible and countermeasures resistant seeker.
The GBU-53/B guidance system combines seeker with a GPS/inertial autopilot, and a Rockwell Collins TacNet bidirectional dual band datalink, which provides JTIDS connectivity with aircraft and a UHF link with a ground designator. This is a refinement of the JTIDS based arrangement trialled for moving target engagements using the JDAM tailkit.
The tri-mode seeker employs semi-active laser homing, MMWI radar, and uncooled thermal imaging components to maximise flexibility in employment and counter-measures resistance. The semi-active laser mode permits the use of the SDB II with legacy airborne and ground based designators, against fixed and moving targets. The MMWI and thermal imaging modes permit autonomous fire-and-forget engagements, under a wide range of weather conditions, accepting that some fog and haze conditions will impair both thermal imaging and MMWI acquisition. The seeker optical dome is protected by a clamshell shroud which is jettisoned before the seeker is activated.
The warhead design is optimised for battlefield targets, parked aircraft, and unhardened structures, combining a shaped charge with blast/fragmentation effects. It will also be highly effective against unhardened and hardened air defence targets, such as SAM batteries, and maritime targets such as warships. A redesign of the warhead was performed during the development cycle to provide the capability to disable or kill main battle tanks.