The ATGM operator Javelin looks at the command and launching unit
Homing Head (GOS)
Just like Stinger, the Javelin rocket belongs to the “shot-forget” system. Once launched, it must be able to track and destroy its target without further intervention by an operator or other external source. The decision on the need for a “shot-and-forget” system was made jointly by the army and the Marine Corps and was implemented through an IR detector and the most modern on-board tracking system.
As described above, the operator uses the IR PBC system to detect and identify the target. Then he switches to an independent infrared missile system to set a mark on the target and "fix" it. The operator sets the frames around the target image, “fixes” them, placing them so that the target fills the space between the frames as much as possible. The task of the GOS is essentially to remain focused on the target image, continuing to recognize it even when the target is in motion, when the trajectory of a rocket flying at a speed of more than 150 m / s changes the viewpoint of the GOS when the angles of attack and when you change the image size of the target as the rocket approaches it. All the many details of the GOS should function properly, but three components are particularly worth mentioning: the detector, the cooling and calibration system, and the stabilization system.
The GOS is located under a hemispherical cap made of zinc sulfide, which is transparent to long-wave infrared radiation used in the detector. Infrared radiation penetrates through the cap, and then through a focusing transparent lens made of germanium and zinc sulfide. IR energy by means of polished aluminum mirrors is reflected to the detector. The GOS of the Javelin rocket is equipped with a two-dimensional matrix in the focal plane the size of 64 on the 64 element. The detectors are made of an alloy of cadmium-telluride and mercury-telluride (called cadmium-mercury telluride, or HgCdTe). It should be noted that, unlike the PBC detector IR, which is a scanning linear array, the GOS detector processes the signals from the sensors and transmits the signals to the rocket tracking system.
The development of a two-dimensional matrix in the focal plane proved to be very difficult. Texas Instruments has developed focal-plane arrays for PBC and GOS using photo-capacitive devices in which incoming photons stimulate electrons that are initially in the detector in the form of an accumulated charge. Electrons are discharged pixel by pixel as the currents of the readout integrated circuit pass into the back of the detector. Despite the fact that such an approach has proven itself in the PBC matrix, it has proved very difficult for the missile seeker to create a working two-dimensional matrix in the focal plane. Texas Instruments could not get the HgCdTe quality required for acceptable photo-capacitive process, and the two-dimensional matrix did not have enough electron capacity. Texas Instruments was able to make enough two-dimensional matrices in order to win the competition, but the process of their mass production did not meet the quality and marriage standards. Only from 0,5% to 2% of the produced matrixes fully met the requirements. Production problems threatened to double development costs and generally jeopardize the very existence of the Javelin program.
The urgency of this problem manifested itself in 1991-92. The United States Department of Defense Office, Department of Ground Forces, and MICOM have created a special team to address this issue. Relying on her own technical experience, she concluded that Texas Instruments was simply not able to produce its development in the required quantities. The army acknowledged that the program’s success depended on GOS technology and found an alternative source for matrix production. They became the corporation LORAL, which also encountered difficulties in the production of matrices. Fortunately, the solution was at hand: the Hughes' Santa Barbara Research Center, SBRC Research Center, under an agreement with DARPA, developed another matrix design in the focal plane that could be made more efficiently. Hughes' design used a photoelectric mechanism in which the voltage signal was generated directly from the effects of photons and charge accumulation occurred in the readout integrated circuit itself, and not in the detector material. Program management refused Texas Instruments services as the lead contractor, and also refused LORAL services as an alternative source and selected SBRC as a matrix provider in the focal plane of the GPS. As a result, the development of SBRC met the required specifications, volumes of supplies and the number of scrap. Texas Instruments continued to manufacture scanners for CPB.
For optimal functioning of the GOS, the matrix in the focal plane should be cooled and calibrated. The PBC IR detector is cooled using a Dewar vessel and a closed-loop Stirling engine. There is not enough space in the rocket to use this design. Before starting, the power and cooling unit is installed on the outside of the launch canister. It feeds the rocket’s electrical systems and provides the cooling gas through the Joule-Thomson throttle to the rocket's GOS - while the rocket itself is still in the launch canister. When a rocket is launched, this external connection is broken and the cooling gas is supplied from the gas cylinder with argon embedded in the rocket. The gas is contained in a small cylinder at a pressure of about 420 kg per square centimeter. This is enough to cool the GOS during the entire flight of the rocket - about 19-seconds. The external power supply and cooling unit must be replaced in case the homing unit was activated and the rocket for some reason was not launched within four minutes.
This cooling system also serves the integrated circuit. Initially, the integrated circuit was placed outside the cooled area and therefore a large number of wires were used for large arrays. The manufacturer managed to place the microprocessor in the cooled area on the back side of the detector. Thus, only the wires from the microprocessor go to the outer side of the cooled area. Thus, the number of wires has dropped significantly: from 200 to 25.
GOS Javelina is calibrated using the so-called "helicopter" wheel. This device is essentially a fan with 6 blades: 5 black blades with very low IR radiation and one semi-reflective blade. These blades rotate in front of the optics of the GOS in a synchronized order, so that the matrix in the focal plane is constantly provided with landmarks (reference points) in addition to the observed target. These guidelines serve as a matrix to reduce the constant noise introduced by different degrees of sensitivity of individual elements of the detector.
Besides the fact that the GOS must be continuously cooled and calibrated, the platform on which the GOS is located must be stabilized with respect to the movement of the rocket body and the GOS must always remain on target. Although, unlike Stinger, the Javelina hull does not rotate in flight, the stabilization system must be able to cope with sharp accelerations, up / down movements and lateral movements and other requirements of the rocket’s trajectory, such as a sharp climb and a steep dive. This is achieved by a two-axis cardan system, accelerometers, gyroscopes, and motors for controlling changes in the position of the platform. The information received from the gyroscopes is fed to the electronics of the guidance system, which in turn controls the engines mounted on the GOS platform so that the GOS remains on the target. The wires connecting the GPS to the rest of the rocket were specifically designed to not cause any friction, so that the GPS platform could remain exactly balanced. GOS Javelina deviates only 10-20 microradians by one G, which indicates an excellent level of isolation.
Guidance and control system
The tracking device Javelina is an essential element of the guidance and control system. The signals from each of the more than 4000 elements of the GOS detector are transmitted to a readout integrated circuit that creates a single-channel video signal transmitted to the tracking device for further processing. The tracking device compares individual frames and calculates the necessary adjustment to hold the rocket on the target. To accomplish this task, the tracking device must be able to determine which part of the overall image represents the target itself. Initially, the target is designated by the operator, who places an aiming mark on it. After that, the tracking device uses algorithms to compare this part of the frame (the comparison is based on the image, geometric data, data on the movement of the target) with the image coming from the GPS. At the end of each frame, the link is updated. The tracking device is capable of holding the rocket on the target, even when the point of view of the GOS changes radically during the flight.
For missile guidance, the tracking device determines the position of the target in the current frame and compares it with the aiming point. If the target's position is not in the center, the tracking device calculates the corrections and transmits them to the missile guidance system, which, in turn, transmits the corresponding corrections to the control surfaces (Javelin has four moving tail flaps, as well as six fixed wings in the middle part of the hull ). This part of the system is called autopilot. It uses a feedback control system to guide the missile, that is, the system uses sensors to determine the position of the control surfaces. If they are rejected, the controller receives a signal for their further adjustment.
There are three main three stages of rocket control throughout the entire flight trajectory: the initial phase immediately after the launch of the cruise engine, the main part of the flight and the final phase in which the tracking device selects a "pleasant place" on the target for its defeat. The autopilot uses guidance algorithms and data from the GOS to determine when the rocket moves from one stage of flight to another. The flight profile can vary significantly depending on the chosen attack mode: straight or top (the default mode). When the attack mode is on top of the rocket, after launch, it sharply gains altitude, makes a cruise flight at an altitude of about 150 meters, and then swoops into the upper part of the target. In direct attack mode, the rocket makes a sustained flight at an altitude of about 45 meters. The exact flight path taking into account the distance to the target is calculated by the pointing unit.
The development of the Javelina tracking device was produced both by the industry itself and by the Redstone arsenal. Texas Instruments designed and manufactured prototypes, and Redstone upgraded and independently evaluated the capabilities of the tracking device. Enhanced static tests of the GOS and the tracking device allowed the developers of the tracking device to test, refine and update the algorithms before the start of the flight tests themselves. The static test program also provided invaluable data for integrated flight simulation developers. The tracking design program is still not complete.
Propulsion system and warhead
Like the Stinger, the Javelin uses a soft start system. In other words, the starting engine is launched in the launch container and stops its operation before the rocket leaves the container, thus protecting the operator from the effects of hot gases. A soft start provides poor recoil when shooting from the shoulder and allows you to launch anti-tank systems from buildings or covered platforms. After the rocket leaves the launch canister and is removed to a safe distance, the rocket's main engine starts, and the wings and flaps open. The rocket moves to the target at subsonic speed. Due to the soft start requirements, operator safety and low weight, the most modern achievements of that time were used to develop the unique Javelin ATGM engine. The engineers of the Javelin program have made significant technological progress, which, combined with the achievements of the industry, has allowed the company to develop an engine that meets all stringent requirements. The ATGM Javelin engine was developed by Atlantic Research Company (ARC), now Aerojet. ARC adapted the design developed by Alliant Technology. Like the Stinger, the Javelin has built-in starting and mid-flight engines. Among other benefits, this integrated design ensures low system weight.
The engine works as follows. The ignition device of the starting engine initiates a flammable charge, which, in turn, drives the starting engine itself. The solid propellant charge of the starting engine burns out from the inside and outside, as well as from both its ends. Combustion products exit through the nozzle of the starting engine. After some time, a signal arrives at the firing device of the main engine, initiating a igniting charge, which activates the solid fuel charge of the main engine. When a sufficient gas pressure is created in its combustion chamber, the membrane separating the starting and sustainer engines is broken, and the gases of the sustainer engine throw down the combustion chamber and the nozzles of the starting engine. Operator safety was one of the key factors of the Javelin program. The missile is equipped with a pressure relief system so that in the event of an unauthorized start of the starting engine, this does not lead to an explosion. The starting engine is equipped with shear pins developed jointly by the government and the industry, collapsing in the event of overpressure of the starting engine and allowing the engine to fall out of the rear of the launch canister.
ARC has also developed a flammable starter charge. Its ring-shaped design has become a key part of the system and serves to integrate the starting and main engines. The igniting charge of the starting engine had to be placed in the nozzle, but it could simply be thrown away by a jet of gas from there, which is unacceptable from the point of view of operator safety. The use of a ring igniter solved this problem as the gases pass through the ring. It also ensures the passage of hot gases into the solid fuel charge 360 degrees and provides a more reliable ignition. Another important element in the design of the engine is a rupture disk, separating the starting and sustainer engines. This component, developed by the ARC, has a higher threshold limit to pressure from the starting engine and lower from the main engine. This allows the membrane to protect the main engine from the effects of the starter engine, but on the other hand, when creating sufficient overpressure by the main engine, break the membrane and direct the gases of the main engine past it and down through the starting engine chamber.
Javelina engine is based on technologies previously developed for other missiles. The solid propellant charge of the starting engine is identical to that used on other missiles. The solid propellant charge of the main engine was borrowed from TOW and Hellfire missiles and was adapted for Javelin by the joint efforts of the US government and industry.
As with the engine development, joint efforts were crucial to the successful development of the Javelin ATGM warhead. Collaboration between the program leadership, the army, the Marine Corps and industry has proven particularly successful in optimizing the characteristics of a tandem warhead. The tandem combat unit Javelina is a cumulative anti-tank ammunition. This munition uses a shaped charge to create a jet of superplastic deformed metal formed from a funnel-shaped metal coating. The result is a high-speed jet (10 km / s at the tip and 2-5 km / s in the tail), which is able to dynamically penetrate solid armor.
The basic concept of a cumulative charge has been known since 1880's, but the laboratories of the US Army have done significant work to improve this technology and its application in weapon systems. The laboratory of ballistic studies contributed to basic research, especially in the field of modeling, and Picatinny Arsenal was responsible for design and demonstration performance tests. Physics International, working under a Redstone contract, created the main cumulative charge of the Javelina warhead. Advances in cumulative charge efficiency have led to the emergence of dynamic protection. Dynamic protection is located on the main armor of the vehicle and detonates when it gets ammunition. The explosion does not harm the vehicle’s main armor, but at the same time the fired metal plate destroys the cumulative jet of ammunition. To overcome the dynamic protection Javelin uses a tandem-shaped cumulative warhead. Leading charge triggers dynamic protection, and the main charge does not lose its destructive power. This concept was first applied to the TOW rocket and was based on the work done by the Ballistic Research Laboratory and Picatinny Arsenal.
Developers Javelina initially tried to make the tandem warhead function. Although the main charge developed by Physics International, which used a copper coating to form a penetrating jet, showed good results, the leading charge with a copper coating hardly overcomes the dynamic protection. The competitor in the development of the warhead was the company Conventional Munitions Systems Inc. (CMS), which acquired a company called Orlando Technology Inc. This company had its own computer models and developed a successful leading charge design using a two-layer molybdenum coating. As a result, the leading charge design of CMS and the main charge of Physics International was used on Javelina.
Another problem in the development of the Javelina tandem warhead was to protect the main charge as much as possible from the possible consequences of a missile strike on a target or a detonation of a leading charge (concussion, shock wave, missile fragments). Fragments of the rocket and the shock wave can adversely affect the formation of a jet of the main charge. To limit the interference between the leading and the main charge, a protective screen designed by Redstone Arsenal was placed. It was the first composite explosion-proof screen and the first through which a hole was made through the middle providing protection for the cumulative jet.
The next stage of upgrading the Javelina warhead included changing the coating of the main charge in order to get a jet of higher speed. These changes will make the warhead more efficient in terms of penetrability and thus will reduce the size of the charge and use the vacant space to increase the size of the solid-fuel engine and, accordingly, increase the range of the missile. Technical work at this stage was carried out at Picatinny Arsenal and General Dynamics Ordnance and Tactical Systems, which took over part of the work of Physics International.
During the development of the Javelin ATGM system, major improvements were implemented in the area of fuses and the deployment of a warhead to a combat platoon. Before Javelina, fuses were mainly mechanical consisting of gears, rotors, checks, etc. However, with the advent of several warheads in one rocket, variable time delays, restrictions on weight and volume, as well as stricter safety requirements, installing mechanical fuses on Javelin and other missiles has become unacceptable. As a result, an electronic system of fuses and placing the warheads on a combat platoon was used on these missiles. This concept is based on the results of the nuclear warheads carried out at Sandria and Los Alamos and was implemented by engineers at Redstone Arsenal in the middle of the 1980's. It received the name ESAF (Electronic Safe Arming and Firpe, electronic protection system, arming warheads and firing). The first ESAF systems turned out to be too cumbersome, but the development of microelectronics allowed them to be used not only on Javelin, but on other systems, such as Hellfire missiles.
The ESAF system allows the deployment of a warhead to a combat platoon and firing, subject to certain conditions regarding the safety of the missile. After the operator pulls the trigger, the ESAF commands the engine to start. When the rocket reaches a certain acceleration (it signals the system that the rocket left the launch container and retired to a safe distance from the operator) and in combination with other factors, the ESAF produces a "second warhead set on a combat platoon" necessary to launch the sustainer. After another verification of the relevant conditions (for example, the presence of a captured target), the ESAF initiates a "final combat platoon", which allows the warhead to detonate when it hits the target. So, when a rocket hits the target, the ESAF initiates the function of a tandem warhead, providing the necessary time interval between the detonation of the leading and main charges.