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Joint Direct Attack Munition (JDAM) Design

JDAM requires the MIL-STD-1553 data bus and MIL-STD-1760 digital interface. JDAM is compatible with the Navy Tactical Aircraft Mission Planning System (TAMPS) and is planned to be compatible with the Joint Mission Planning System (JMPS).

The JDAM variants are built-up by installing the Guidance Sets to MK 83, MK 84, BLU-109, BLU-110 or other bombs along with the required fuzing, sensors, initiators, and/or nose plugs/support cups. The Guidance Sets are functionally the same but are not interchangeable because the guidance software and physical interfaces are peculiar to each warhead type. Guidance Set physical differences correspond primarily to the different warhead interfaces.

Guidance Sets consists of a tail assembly, aerosurfaces, umbilical cover, and for the KMU-558 only, also contain a hardback, lug sleeves, suspension lugs, FZU Extender and SHOLS lugs.

Each tail assembly consist of a tail fairing, Tail Actuator Subsystem (TAS), wire harness, Guidance Control Unit (GCU), GPS antenna, three moveable control fins and one fixed control fin. The tail assembly has BIT capability which can be initiated both on and off the aircraft by both maintenance and aircrew personnel. The aircrew can perform BIT while the aircraft is in flight. BIT and reprogramming are accomplished using the AN/GYQ-79 Common Munitions Bit and Reprogramming Equipment (CMBRE).

The tail fairing is the forward structural member of the tail assembly. It mates to the TAS at a faying surface using a radial screw/nut plate configuration. The tail fairing has a fuze access door to facilitate assembly/disassembly operations.

The Tail Actuator Subsystem [TAS] consists of the aft tail assembly structure, three electromechanical actuators to power the three movable control fins, a Lithium Thermal Battery, and the associated controlling electronics. The aft structure provides a mounting surface for the GPS Antenna and mounting surfaces for the control fins. The actuators contain either electrically released motor brakes (used in KMU-55X/B Guidance Sets) or a fin lock device (FLD) (used in KMU-55XA/B Guidance Sets) that unlocks the tail control fins in flight. On Guidance Sets with the KMU-55X/B designation, markings are applied to the TAS to aid in determining proper fin positions. The TAS marking applies to electrically released motor brakes only. When the aft end of the fins are within the boundaries of the alignment marks, the fins are properly positioned for use. On Guidance Sets with the KMU-55XA/B designation, control fins are secured with the FLD that uses retractable locking pins designed to eliminate fin movement during high speed, low altitude captive flight. TAS with the FLD are not subject to captive carry flight restrictions. The controlling electronics process digital commands into independent fin control movements, provide fin position feedback, battery initiation, brake unlock commands, and BIT status. TAS for the KMU-556 and KMU-558 are physically identical; however, they are not interchangeable due to differences in the guidance software contained within the GCU.

The Wire Harness consists of the MIL-STD 1760 umbilical connector, the FMU-152/B fuze connector, GCU connectors, and a shielded wiring harness. A protective EMI cover is provided on the umbilical connector. The FMU-152/B fuze connector is connected to a stowage receptacle on the inside surface of the tail structure, when not in use.

The Guidance Control Unit [GCU] consists of an integrated electronics assembly that includes the Mission Computer, INS, GPS Receiver Module (GPSRM), and other power conditioning electronics integrated into a common chassis. The INS uses a Ring Laser Gyro (RLG) inertial measurement unit (IMU). The GCU is form factored to fit into the tail assembly of both the 2,000 lb. and 1,000 lb. guidance kits.

Mission computer software implements autopilot, guidance and navigation functions. Guidance software uses an adaptive optimal guidance law. The guidance law develops guidance commands based on weapon position and velocity state vector updates, target location, and desired impact parameters. The guidance law continually computes the optimal trajectory from the current position to the target to achieve an impact vector at the planned impact point, with the planned impact angle and impact azimuth, at the highest possible velocity. Different Operational Flight Programs (OFP) are utilized for the MK 84, BLU-109 and MK 83/BLU-110 variants to account for different mass properties and aerodynamic characteristics.

The GPS Receiver Module [RM] implements continuous P (Y) code tracking on L1 or L2 band for up to five satellites. A planned upgrade will incorporate a GPS receiver that can track all satellites in view. GPSRM software incorporates a fast acquisition mode that uses GPS position, velocity, time, and ephemeris data provided by the aircraft. Using this data, the GPS receiver can achieve full position and velocity acquisition within 27 seconds and full GPS navigation accuracy within 28 seconds after release. The GPS antenna is located on the aft end of the TAS. The antenna is connected to the GCU by a cable that runs along the exterior of the tail assembly and is protected by a cover.

Four control fins are attached to the Tail Actuator Subsystem [TAS]. Three of the control fins are moveable. The fourth control fin is fixed.

Aerosurfaces are fixed, mid body strakes that are attached to the warhead using steel bands and T-bolts, and in the case of the KMU-558, require a hardback.

KMU-556 Strake Aerosurfaces consist of three formed steel "strakes" that are strapped around the bomb body. The upper strake is positioned over the suspension lugs. Right and Left strakes attach to slots in the upper strake and are fastened around the bomb with three metal straps that are tensioned with T-Bolt adjusting nuts. The left and right strakes are fabricated in both stamped and riveted configurations that are interchangeable. The strakes provide aerodynamic lifting surfaces around the exterior of the bomb body to enhance weapon maneuverability and range.

KMU-558 Strakes/Hardback Aerosurfaces consist of right and left side formed steel "strakes" that attach to hooks on the hardback and strapped around the bomb body. The hardback is an aluminum casting that is positioned over a set of lug sleeves and attached with bolts. The strakes attach to hooks that are hung from the hardback and are fastened around the bomb with two metal straps (primary configuration) or three metal straps (alternate configuration). The straps are tensioned with T-Bolt adjusting nuts. The strakes provide aerodynamic lift, maneuverability and other needed flight characteristics. The hardback provides the necessary physical interface to the delivery aircraft.

KMU-559 Strake Aerosurfaces consist of three formed steel "strakes" that are strapped around the bomb body. The upper strake is positioned over the suspension lugs. Right and left strakes attach to buckles on the upper strake and are fastened around the bomb with two metal straps that are tensioned with T-Bolt adjusting nuts.

The hardback is used in the KMU-558 only. It provides the necessary physical interface to the delivery aircraft. It is an aluminum casting that is positioned over a set of lug sleeves and attached with bolts. Because it adds a significant amount of additional space between the bomb body and the interface to the delivery aircraft, additional lug sleeves and suspension lugs are provided. Additionally, a FZU Extender is provided for use when the FMU-143E/B and FZU-32B/B configuration is built. The FZU extender compensates for the height of the hardback and permits the FZU-32B/B initiator to physically interface with the bomb rack.

The umbilical cover is a formed steel part that attaches to the tail assembly by inserting the tab on the aft end of the cover into the harness exit hole. The forward end of the umbilical cover is positioned and captured by a slot in the upper strake. The umbilical cover positions the umbilical connector to mate correctly with the delivery aircraft MIL-STD 1760 interface and retains the umbilical connector during separation. The cover also provides protection for the wire harness during weapon handling operations. Different umbilical covers are provided in the KMU-556, KMU-558, and KMU-559 Guidance Sets to accommodate the physical differences in their respective warheads.

SHOLS lugs are used in the KMU-558 only. The SHOLS lugs are high strength steel parts that are installed under the hardback assembly and include the interfacing features to attach the SHOLS lifting trolleys with a single locking pin. SHOLS lugs provide the pin attach points for rapid attachment of the lift trolley assemblies to the weapon to facilitate weapon loading with the SHOLS loading equipment.

JDAM is compatible with the existing FMU-139 and FMU-143 fuzes. It is also compatible with the FMU-152/B JPF.

JDAM tail assemblies are compatible with the DSU-33B/B proximity sensor. The DSU-33B/B provides general-purpose warheads with an air-burst capability. The DSU-33B/B can be used in GBU-31(V)2/B, GBU-32(V)2/B, and GBU-35(V)1/B configurations to provide an accurate air burst capability against appropriate targets. The DSU-33B/B is not compatible with the GBU-31(V)4/B. When the DSU-33B/B is not used, a nose plug/support cup is used.

A MK 122 Mod 0 arming switch can be used in any configuration. It is used in lieu of an initiator and its corresponding cable. e. Initiators. When an arming switch is not used, either the FZU-32B/B or the FZU-48/B initiator and their corresponding cables can be used in the GBU-31(V)2/B or GBU-31( V)4/B configurations. Whenever the DSU-33B/B is not used, a nose plug/support cup is used, either the OGIVE or the MXU-735.

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