Proceedings of the 2019 Hypervelocity Impact Symposium
April 14 – 19, 2019, Destin, FL, USA
Markus Graswald *, Raphael Gutser, Jakob Breiner, Florian Grabner, Timo Lehmann,
and Andrea Oelerich **
TDW GmbH, Hagenauer Forst 27, 86529 Schrobenhausen, Germany
** WTD 91, Schießplatz 1, 49716 Meppen, Germany
An open source research and vulnerability study of main battle tanks and their protections systems revealed that current anti-tank weapons may not be suited to defeat modern threats. One example is the novel T-14 tank being developed and tested in the Russian army with its combined hard-kill and soft-kill active protection system AFGANIT / SHTORA, its new reactive armor MALACHIT as well as improved multi-component passive armor. Additionally, modern active protection systems currently developed in, e.g., Israel, the United States, and Germany feature also multi-sensor and multi-effector systems with drastically improved detection and intercept ranges, short system reaction times as well as protection against multiple threats attacking simultaneously and / or from similar directions. While known effectors and concepts may overcome fielded active protections systems, they are probably not suited in defeating such modern and even future systems. Countermeasures relying on high engagement velocities through improved kinetic energy projectiles or hypervelocity penetrators may provide a potential solution. Another promising concept generates directed, far-distance electromagnetic effects defeating sensors and communications systems of modern main battle tanks.
After such a mission kill, a following salvo attack through an anti-tank or modern multi-role weapon will eventually lead to a catastrophic kill. Feasibility studies of these mobile electromagnetic effectors have already shown their high potential.
The enduring competition between weapon effectiveness and platform protection has already entered a new act. The threat on main battle tanks imposed by various effectors such as anti-tank missiles (anti-tank (guided) missile, ATM / ATGM) or shoulder-launched rockets (rocket propelled grenade, RPG) with tandem-shaped charge warheads (e.g., TOW 2A, PARS3 LR), kinetic energy (KE) projectiles (e.g., M829 or DM 63), and top-attack munition with explosively formed projectile (EFP) warheads (e.g., TOW 2B or SMArt) has been drastically increased over the last decades . This lead to recent developments with T-14 tanks (built on the standardized ARMATA track vehicle platform) in Russia using novel and / or improved active protection systems (APS), explosive reactive armor (ERA), and passive protection. Table 1 compares Israeli main battle tank MERKAVA 4 with Russian tanks T-90 and T-14 showing significant improvements in terms of both
fire power and protection systems of the latter. It needs to be noted that data refers to 2013 sources and may be dependent also upon environmental conditions, i.e., weather, day vs. night time. The greatest challenge, however, is offered through the new generation of active protection system being developed.
This paper presents major results of a comprehensive survey on trends in developments on new main battle tanks and their protection systems.
Focussing on active protection systems, a classification scheme is provided and countermeasures
assessed. Two promising concepts, a combined kinetic energy effector and a mobile high power electromagnetic effector, are introduced in detail along with simulation and experimental results of subsystems.
2 Technological trends in the field of main battle tank protection
The novel T-14 main battle tank currently tested in the Russian army was first fully shown at a parade in Moscow on May 9th, 2015. After this initial rate, an ambitious series production of 2000+ units shall be completed in the early 2020s.
Although not all details on its capabilities are known, it uses a comprehensive protection concept with indirect and direct measures: [1, 3]
- Reducing or changing signatures through stealth technologies in infrared and radar spectrum such as special coatings, improved heat isolation, absorbing materials, cooling of exhaust gases, as well as an active, electromagnetic mine protection system
- Avoiding hits by soft kill active protection systems like SHTORA-1
- Avoiding both hits and penetration by hard kill active protection systems like ARENA, DROZD, or novel AFGANIT
- Reducing the effectiveness through explosive reactive armor like KONTAKT-5, RELIKT, or novel MALACHIT
- Reducing the system impact through passive, multi-component ballistic protection based on novel high-strength steels such as 44S-SW combined with non-metallic materials like ceramics, aramid fabrics, and plastics, e.g., PU (polyurethane) or PE (polyethylene), providing an RHA (rolled homogeneous armor) equivalent of more than 900 mm in the front section
Active protective systems of main battle tanks and armored vehicles are typically classified into soft or hard kill systems. Their functionality is visualized in Figure 1. Based on a threat detected by sensors, a fire control solution will be determined dependent upon threat analysis, its predicted trajectory, and the counter measure. A soft kill system distracts the incoming threat either trough infrared (IR) emitters, jammer, or decoy/flares, or interrupts the line-of-sight by smoke shells, while a hard kill system is designed to destroy the threat in a distinct and safe distance to the tank through deployed or distributed blast/fragmentation projectiles, shaped charges or (multi) EFP, or directed high explosive (HE) charges. 
In a comprehensive literature and online search, a total of 26 active protection systems have been found and categorized [3, 5]. Besides various Russian systems named earlier, SASLON/ZASLON as active and NOZH and DUPLET as reactive, Ukrainian made protection systems are supposed to be highly effective. Israeli Trophy APS installed on MERKAVA MK4 tanks are known as combat proven in several armed conflicts. In NATO countries like the United States and Germany, a number of both soft kill and hard kill active protection systems are developed and mounted onto main battle tanks or armored vehicles such as PUMA and STRYKER. Turkey and South Korea develop their own systems called AKKOR and KAPC for future integration on their main battle tanks ALTAY and K2, respectively.
Table 2 shows a classification scheme of APS with their protection against threat types, their sensor and effect or principle, and system aspects along with typical examples and essential data of Russian, Israeli, and American systems.
It differentiates between classical state-of-the-art systems like DROZD or SHTORA and modern or future systems like AFGANIT or TROPHY since engagement concepts and weapon systems overcoming them may differ significantly. It reveals that modern and potential future developments
- use a combination of sensors with different physical principles, long detection ranges, virtually no dead zones, and capabilities to track multiple threats simultaneously
- rely on (a combination of) hard kill effectors with increased engagement ranges, and
- provide drastically reduced system reaction times from threat detection to countermeasure interaction
This allows the defeat of multiple – also high velocity – threats attacking simultaneously or successively from the same or different directions. Further development trends concentrate on both sensors and countermeasures and indicate to use active protection systems through cooperative engagements for other or even unprotected vehicles as well. Besides new and modern tanks, classical tanks like T-72 or T-90 may also be upgraded with modern APS.
Various approaches have been identified to overcome active protection systems as visualized through an onion model adapted for single or salvo engagements of effectors in Figure 2. These opportunities can also be combined for being more effective and sustainable. The analysis revealed that existing anti-tank weapons and engagements principles exploiting sensor-dead zones and using saturation attacks may still be suited against classical tanks, while they might be outdated for current and future developments of active protection systems. Potential solutions meeting these challenges are, therefore, provided through a combined kinetic energy effector relying on super or hyper velocities and a mobile high power electromagnetic effector aimed at defeating APS sensors. They are introduced in the following subsections.
In addition, anti-tank or multi-role missiles with tandem or new multi-effect warheads may still be effective against explosive reactive and passive armor. They can also be used against a wider target set consisting of personnel, unarmored vehicles, and light infrastructures.
3 Combined penetrator effector
Besides high explosive anti-tank missiles, kinetic energy projectiles like DM 63 or M829 provide a high threat potential against classical main battle tanks. They are typically fired from 120 mm caliber guns and reach high velocities > 1000 m/s
∗Acronyms not introduced earlier: active electronically scanned array (AESA), electro-optical (EO), infrared (IR), electronic warfare (EW), azimuth (Az), elevation (El), machine gun (MG).
to penetrate both reactive and passive armor. Modern tanks with active protection systems, improved reactive and passive armor may, however, drastically decrease their performance.
Supplementing a kinetic energy penetrator with a precursor shaped charge provides an incredible excess velocity so that the EFP may be fired well outside the APS engagement range hitting unrecognized the explosive reactive armor and initiating it. The concept is visualized in Figure 3. An EFP charge may also serve as a deception device for APS, so that the KE penetrator survives and eventually engages the main target effectively. The precursor charge consists of a high strength metal such as tantal, a
high-performance octogene-based high explosive charge like a KS33 or P31 with a reactive detonation
wave shaper and a shock-hardened inline (electronic safe-and-arm device, ESAD) fuze system embedded into light weight titanium structure. A sub-caliber, high L/D tungsten penetrator is located behind and may be further improved through reactive materials. This cost-efficient and robust lethal package can be integrated into various systems like a hyper-velocity missile or an armor piercing fin-stabilized discarding sabot (APFSDS) munition.
The EFP precursor charge was designed meeting desired velocities of >800 m/s, L/D ratios of 5, and fin-stabilization measures with the hydrocode SPEED . Its effectiveness against various targets was modeled using a 3D Eulerian mesh as well. Results of a representative explosive reactive armor module consisting of Comp B (RDX/TNT) applying the History Variable Reactive Burn (HVRB) initiation model are shown in Figure 4. They indicate that the EFP can penetrate inert flyer plates and initiate the explosive layer at least with a deflagration or low-order detonation reaction. Assuming a sufficient timely stand-off, the ERA target should be cleared for the succeeding penetrator killing the main target with its remaining passive armor.
4 High power electromagnetic effector
A mobile high power electromagnetic (HPEM) effector integrated into an anti-tank missile as displayed in Figure 5 seems interesting for defeating active protection systems sensors and communication devices of main battle tanks. Early studies generating electromagnetic effects through explosive devices date back several decades, e.g., [7, 8, 9] and recent feasibility studies of have already shown their high potential [10, 11]. The concept consists of an explosively driven flux compression generator (FCG), an electrical opening switch and the subsequent shaping of the electrical pulse into an high frequency (HF) radio signal (e.g., by applying a magnetron) that is radiated through an antenna system. This enables a compact design for
integration into mobile applications such as missiles, shoulder-launched munitions, or artillery shells. The following section describes the design of an FCG and several proof-of-principle firing tests as well as a HF generator and directed antenna investigating the vulnerability of electronic components.
4.1 Proof-of-principle tests on prototype FCGs
The working principle of a flux compression generator can be explained by using the transient Maxwell equations. Its main purpose is generating a short-time high level electric power peak by converting chemical energy into kinetic energy – released by detonating a high explosive charge – and eventually into electrical power. This changes the magnetic field and induces an Eddy current similar to an electrical motor. The high-explosive driven magnetic flux compression generator shown in Figure 6 consists of a capacitor bank, a stator coil (solenoid), an armature filled with a HE charge, and a load switch.
This system operates through these three major steps:
- Seeding current: An initial magnetic flux density is required to start the process which can then be compressed by the system. This flux density has to be provided conventionally by an appropriate high power source such as a Marx Generator or a capacitor bank that generates the seeding current.
- Flux compression: After charging the solenoid with the seeding current and establishing a high magnetic flux density within the system, the conventional power generator is removed from the system and the detonation process starts.
The expansion of the armature creates an electric contact with the coil/solenoid compressing the magnetic flux in a very short time. This results in an instantaneous increase of the magnetic energy density within the system allowing the generation of currents of several 100 kA.
- Power conversion: The generated power needs to be transmitted to a load such as a HF generator with an antenna structure. For the flux compression process, the load switch needs to be closed in order to enable a high current for flux compression. This short circuit switch needs to be opened in a short time transmitting the power to the load.
An explosive electric opening switch is a possible option to realize fast switching.
Prototypes of high explosive driven generators, a test setup and diagnostics including a Rogowski probe for current measurements were developed for proof-of-principle trials at Schrobenhausen site. Circuits for the flux compression generator and detonator initiation were galvanically separated. Test setups with FCG prototypes are displayed in Figure 7 (with capacitor bank not shown). Figure 8 shows a successfully measured output current from the FCG (red line) prototype and shunt (blue line) during detonation. The detonation of the FCG was timed to the positive peak of the pulse generator resulting in an output current of several hundreds of kA in the microsecond regime. This complies to a current amplification
with a factor of approx. 30 that was basically predicted through the system simulation.
FCGs can be further optimized through increasing the seeding current, the forming of the magnetic field and the subsequent timely trigger for initiating the high explosive charge. An appropriate design of the armature and solenoid, the type of high explosive charge, and a precise manufacturing and assembly process are also important. Another development step is the interface design between the current power output and HF generator to fulfil the radiation characteristic requirements. This current to HF signal transformation depends also on the targets of interest and operational endgame settings.
4.2 Vulnerability tests of representative components
Since microcontrollers and FPGAs serve as subsystem controllers in a variety of applications such as sensoring, navigation, and other data processing, a malfunction of these devices lead usually to a critical system state and may cause overall system failures as well. Their damage levels are typically classified as follows:
- Level 1: disturbance of core functionalities of electronic components while the interference signal is active
- Level 2: temporary disturbance of core components until system reboot
- Level 3: permanent damages of components – their exchange is required for proper operations
Besides these electronic components, transmission lines such micro strip lines and coaxial lines are considered as well since they are used in integrated circuits and for connecting all electronic devices transmitting signals in the high frequency domain. These lines are modeled in COMSOL Multiphysics  and eventually exposed to electrical fields.
- Figure 9a shows a coaxial line modeled through three concentric circles, a di-electricum between conductor lines, and ports at conductor ends:
electrical field lines pointing from the inner to the outer line, magnetic field lines passing in concentric circles parallel to both lines, and a pointing vector pointing into the plane. The model implementation is initially simulated using a test signal and without outer influences for verifying typical line characteristics such as damping depending upon signal frequency or impedance with analytical calculations and experimental data. Figure 9b shows a good correlation of simulation results with analytical and literature data except in the lower frequency domain.
Shielding electronics against electromagnetic fields was also investigated through simulations.
Figure 10a displays a copper Faraday cage that provides a perfect shielding. Openings such as slits and grits are mostly required for practical reasons. They are also used in radar sensor systems and communication devices and allow a transmission of electromagnetic signals as exemplified in Figures 10b and 10c.
A representative microcontroller (LPC2103FBD48) is also modeled in a COMSOL Multiphysics simulation  and its response on externally generated electromagnetic fields evaluated. The induced current into the component is simulated and the resulting damage evaluated through the given CMTI (Common mode Transient Immunity) value.
Figure 11 shows the microcontroller model and the simulated induced current at a given field strength. If the component dependent CMTI value measured through means of surge protection measurement (SPM) is exceeded, the system will usually shutdown.
Permanent component damages can be assumed by exceeding this value by a factor of 5.
In an experimental setup for subcomponent tests, a continuous and a pulsed magnetron were used for generating HF signals that were transmitted through a horn antenna. Figure 12 shows a simulated far field and gain of a typical horn antenna with CST Microwave Studio . The electrical field strength is measured robustly with D dot sensors.
The effectiveness of the emitted signal is eventually evaluated against commonly used FPGAs such as an Altera MAX10 and Xilinx Spartan6 as well as microcontrollers like an Intel PIC18.
Development boards with these two embedded FPGAs and a microchip were used for vulnerability tests at the anechoic chamber located at Schrobenhausen site. The test setup is shown in detail in Figure 13. Each board uses a different set of input and output devices, e.g., LEDs, switches, VGA port, GPIO pins. Hundreds of tests of these board were performed.
During each test campaign, the variation on supply voltages besides a logic signal in the domain of kilohertz have been measured. Parameters varied include the distance and direction of the antenna to the component relating to the field strength as well as pulse and idle times of the interference signal.
The experimental investigation shows a variety of results. The transmitted wave form of the signal, e.g., either a continuous RF signal or a pulsed rectangular wave signal, remains the same in the measured signal of the boards.
While a dependency of the results on pulse power periods and their power-to-idle ratio could not be observed, the electrical field strength and angle of attack are significant parameters. Changing this angle of attack of the antenna to the component, it was proven that individual angles exist where sudden increases or decreases of the signal voltage measured occur. Parameter settings for best and worst signal deflections were eventually identified. Damage levels observed vary widely between all
three components investigated.
While a level 1 damage was mostly observed, a level 2 was only noticed infrequently and a level 3 not at all. This might be changed through applying higher field strengths or through shorter wave lengths providing more efficient disturbances at a given field strength. These experimental results will be used for verifying a simulation of the electronic components modeled in LT Spice.
The ongoing development of a new generation of main battle tanks with its improved protection systems provides a challenge for existing anti-tank effectors. The study identified vulnerabilities of modern and future active protection systems.
Several potential counter measures were assessed and two promising concepts down selected, i.e., a combined penetrator effector relying on excess velocities and a high power electromagnetic effector for defeating sensor and communication devices.
The theoretical and experimental investigations performed enable detailed concept designs for different system applications. In future, it is planned to build prototypes of complete effector systems for performing experimental tests against relevant military targets based on operational scenarios and associated endgame settings.
The authors gratefully acknowledge the financial support by Meppen proving ground WTD 91, GF-440, and BAAINBw K1.5.