| FGM-148 Javelin | |
|---|---|
| Type | Anti-tank guided missile launcher |
| Place of origin |  United States |
| Service history | |
| In service | 1996–present |
| Used by | See Users |
| Wars | Operation Enduring Freedom (2001–present) Operation Iraqi Freedom / Operation New Dawn (2003–present) |
| Production history | |
| Designer | Texas Instruments and Martin Marietta (now Raytheon and Lockheed Martin) |
| Designed | June 1989 |
| Manufacturer | Raytheon and Lockheed Martin |
| Unit cost | $40,000 (£20,000) (missile); $125,000 (reusable Command Launch Unit) |
| Produced | 1996–present |
| Specifications | |
| Weight | Missile: 11.8 kg (26 lb) CLU: 6.4 kg (14.1 lb) |
| Length | Missile: 1.1 m (43 in) Launch tube: 1.2 m (47 in) |
| Diameter | Missile: 127 mm (5.0 in) Launch tube: 142 mm (5.6 in) |
| Crew | 2 |
| | |
| Effective range | 75 to 2500 m |
| Warhead | Tandem shaped charge HEAT |
| Warhead weight | 8.4 kg (18.5 lb) |
| Detonation mechanism | Impact force |
| | |
| Engine | Solid fuel rocket |
| Guidance system | Imaging infrared (IIR) |
Missile
Warhead
The Javelin missile’s tandem warhead is a HEAT type. This round utilizes an explosive shaped charge to create a stream of superplastically deformed metal formed from trumpet-shaped metallic liners. The result is a narrow high velocity particle stream that can penetrate armor.
The Javelin counters the advent of ERA. ERA boxes or tiles lie over a vehicle’s main armor and explode when struck by a warhead. This explosion does not harm the vehicle’s main armor, but causes steel panels to fly across the path of the HEAT round’s particle steam, so that the warhead expends its most potent energy cutting through the panels, rather than through the main armor. The Javelin uses two shaped-charge warheads in tandem. The smaller diameter HEAT precursor charge sets off the ERA and clears it from the path of the much larger diameter HEAT warhead, which then penetrates the target’s primary armor.
A two-layered molybdenum liner is used for the precursor and a copper liner for the main warhead.
To protect the main charge from the explosive blast, shock, and debris caused by the impact of the missile's nose and the detonation of the precursor charge, a blast shield is used between the main and precursor charge. This was the first composite material blast shield and the first that had a hole through the middle to provide a jet that is less spread out.
A newer main charge liner produces a higher velocity jet. While making the warhead smaller, this change makes it more effective leaving more room for propellant for the main rocket motor, thus increase the missile's range.
Electronic arming and fusing, called Electronic Safe Arming and Fire (ESAF), is used. The ESAF system enables the firing and arming process to proceed, while imposing a series of safety checks on the missile. ESAF cues the launch motor after the trigger is pulled. When the missile reaches a key acceleration point (indicating that it has cleared the launch tube), the ESAF initiates a second arming signal to fire the flight motor. After another check on missile conditions (target lock check), ESAF initiates final arming to enable the warheads for detonation upon target impact. When the missile strikes the target, ESAF enables the tandem warhead function (provide appropriate time between the detonation of the precursor charge and the detonation of the main charge).
Propulsion
Most rocket launchers require a large clear area behind the gunner to prevent injury from backblast. To address this shortcoming without increasing recoil to an unacceptable level, the Javelin system uses a soft launch mechanism. A launch motor using conventional rocket propellant ejects the missile from the launcher, but stops burning before the missile clears the tube. The flight motor is ignited only after a delay to allow for sufficient clearance from the operator. To save weight, the two motors are integrated with a burst disc between them; it is designed to tolerate the pressure of the launch motor from one side, but to easily rupture from the other when the flight motor ignites. Both motors use a common nozzle, with the flight motor's exhaust flowing through the expended launch motor. Because the launch motor casing remains in place, an unusual annular (ring-shaped) igniter is used to start it; a normal igniter would be blown out the back of the missile when the flight motor ignited and could injure the operator.
In the event that the launch motor malfunctions and the launch tube is overpressurized—for example, if the rocket gets stuck—the Javelin missile includes a pressure release system to prevent the launcher from exploding. The launch motor is held in place by a set of shear pins, which fracture if the pressure rises too high and allow the motor to be pushed out the back of the tube.
Seeker
As a fire-and-forget missile, after launch the missile has to be able to track and destroy its target without the gunner. This is done by coupling an onboard imaging IR system (different from CLU imaging system) with an onboard tracking system.
The gunner uses the CLU’s IR system to find and identify the target then switches to the missile’s independent IR system to set a track box around the target and establish a lock. The gunner places brackets around the image for locking.
The seeker stays focused on the target’s image continuing to track it as the target moves or the missile’s flight path alters or as attack angles change. The seeker has three main components: focal plane array (FPA), cooling and calibration and stabilization.
Focal plane array (FPA)
The seeker assembly is encased in a dome which is transparent to long-wave infrared radiation. The IR radiation passes through the dome and then through lenses that focus the energy. The IR energy is reflected by mirrors on to the FPA. The seeker is a two-dimensional staring FPA of 64x64 MerCad (HgCdTe) detector elements. The FPA processes the signals from the detectors and relays a signal to the missile’s tracker.
The staring array is a photo-capacitive device where the incident photons stimulate electrons and are stored in the detector as an accumulated charge. The electrons are discharged, pixel by pixel, as currents to a readout integrated circuits attached at the rear of the detector.
Cooling/Calibration
The FPA must be cooled and calibrated. The CLU’s IR detectors are cooled using a Dewar flask and a closed-cycle Stirling engine. But there is insufficient space in the missile for a similar solution. So, prior to launch, a cooler mounted on the outside of the launch tube activates the electrical systems in the missile and supplies cold gas from a Joule-Thompson expander to the missile detector assembly while the missile is still in the launch tube. When the missile is fired this external connection is broken and coolant gas is supplied internally by an onboard argon gas bottle. The gas is held in a small bottle at high pressure and contains enough coolant for the duration of the flight of approximately 19 seconds.
The seeker is calibrated using a chopper wheel. This device is a fan of 6 blades: 5 black blades with very low IR emissivity and one semi-reflective blade. These blades spin in front of the seeker optics in a synchronized fashion such that the FPA is continually provided with points of reference in addition to viewing the scene. These reference points allow the FPA to reduce noise introduced by response variations in the detector elements.
Stabilization
The platform on which the seeker is mounted must be stabilized with respect to the motion of the missile body and the seeker must be moved to stay aligned with the target. The stabilization system must cope with rapid acceleration, up/down and lateral movements. This is done by a gimbal system, accelerometers, spinning-mass gyros (or MEMS), and motors to drive changes in position of the platform. The system is basically an autopilot. Information from the gyros is fed to the guidance electronics which drive a torque motor attached to the seeker platform to keep the seeker aligned with the target. The wires that connect the seeker with the rest of the missile have no friction to keep the seeker platform balanced.
Tracker
The tracker is key to guidance/control for an eventual hit. The signals from each of the 4,096 detector elements in the seeker are passed to the FPA readout integrated circuits which reads then creates a video frame that is sent to the tracker system for processing. By comparing the individual frames the tracker determines the need to correct so as to keep the missile on target. The tracker must be able to determine which portion of the image represents the target. The target is initially defined by the gunner who places a configurable frame around it. The tracker then uses algorithms to compare that region of the frame based on image, geometric, and movement data to the new image frames being sent from the seeker, similar to pattern recognition algorithms. At the end of each frame the reference is updated. The tracker is able to keep track of the target even though the seeker’s point of view can change radically in the course of flight.
To guide the missile the tracker locates the target in the current frame and compares this position with the aim point. If this position is off center the tracker computes a correction and passes it to the guidance system which makes the appropriate adjustments to the four movable tail fins, as well as six fixed wings at mid-body. This is an autopilot. To guide the missile the system has sensors that check that the fins are positioned as requested. If not, the deviation is sent back to the controller for further adjustment. This is a closed-loop controller.
There are three stages in the flight managed by the tracker: 1) an initial phase just after launch; 2) a mid-flight phase that lasts for most of the flight; and 3) a terminal phase in which the tracker selects the sweet spot for the point of impact. With guidance algorithms, the autopilot uses data from the seeker and tracker to determine when to transition the missile from one phase of flight to another. Depending on whether the missile is in top attack or direct attack mode, the profile of the flight can change significantly. The top attack mode requires the missile to climb sharply after launch and cruise at high altitude then dive on the top of the target (curveball). In direct attack mode (fastball), the missile cruises at a lower altitude directly at target. The exact flight path which takes into account the range to the target is calculated by the guidance unit.
Launch Tube Assembly
Both men carry a disposable tube called the Launch Tube Assembly which houses the missile and protects the missile from harsh environments. The tube also has built in electronics and a locking hinge system that makes attachment and detachment of the missile to and from the Command Launch Unit a very quick and simple process.
Command Launch Unit
The gunner carries a reusable Command Launch Unit (in addition to the Launch Tube Assembly) more commonly referred to as a CLU (pronounced "clue"). The CLU is the targeting component of the two part system. The CLU has three views which are used to find, target, and fire the missile. The CLU may also be used separately from the missile as a portable thermal sight. Infantry are no longer required to stay in constant contact with armored personnel carriers and tanks with thermal sights. This makes the troops more flexible and able to perceive threats they would not otherwise be able to detect. In 2006 a contract was awarded to Toyon Research Corporation to begin development of an upgrade to the CLU enabling the transmission of target image and GPS location data to other units.
Day Field of View
The first view is a 4× magnification day view. It is mainly used to scan areas for light during night operation because light is not visible in the thermal views. It is also used to scan during times following the sunrise and sunset when the thermal image is hard to focus due to the natural rapid heating and/or cooling of the Earth.
WFOV (Wide Field of View)
The second view is the 4x magnification night view, and shows the gunner a thermal representation of the area viewed. This is also the primary view used due to its ability to detect infrared radiation and find both troops and vehicles otherwise too well hidden to detect. The screen shows a "green scale" view which can be adjusted in both contrast and brightness. The inside of the CLU is cooled by a small refrigeration unit attached to the sight. This greatly increases the sensitivity of the thermal imaging capability since the temperature inside the sight is much lower than that of the objects it detects. Due to the sensitivity this causes, the gunner is able to "focus" the CLU to show a very detailed image of the area being viewed by showing temperature differences of only a few degrees. The gunner operates this view with the use of two hand stations similar to the control stick found in modern cockpits. It is from this view that the gunner focuses the image and determines the area that gives the best heat signature on which to lock the missile.
NFOV (Narrow Field of View)
The third field of view is a 9x thermal sight used to better identify the target vehicle. Once the CLU has been focused in WFOV, the gunner may switch to NFOV for target recognition before activating Seeker FOV.
Seeker Field of View
Once the best target area is chosen the gunner presses one of the two triggers and automatically is sent to the fourth view. The Seeker FOV is a 9x magnification thermal view. This process is similar to the automatic zoom feature on most modern cameras. This view is also available along with the previously mentioned views, all of which may be accessed with press of a button. It is not as popular however, because a high magnification view takes longer to scan a wide area. This view allows the gunner to further aim the missile and set the guidance system housed inside the actual missile. During this view is when information is passed from the CLU, through the connection electronics of the Launch Tube Assembly, and into the missile's guidance system. If the gunner feels uncomfortable with firing the missile, he can still cycle back to the other views without having to fire the missile. When the gunner is comfortable with the target picture he pulls the second trigger and establishes a "lock”. The missile launches after a short hesitation.
