Cannon Caliber Electromagnetic Gun Research Articles

Single shot switch performance on the cannon caliber electromagnetic gun program

The Cannon Caliber Electromagnetic Gun (CCEMG) program at The University of Texas at Austin Center for Electromechanics incorporates two solid state switch modules. The 95 MW rectifier/inverter bridge (RIB) generates the field inside of the compulsator (CPA) and the 825 kA gun switch module (GSM) is the main closing switch between the CPA and the launcher. Since commissioning the CCEMG system, nearly 400 discharges have been performed using these switches. These tests produced a significant amount of information which will be very useful for the design of future solid-state switching systems on other electromagnetic launch programs. This paper presents the basic design, testing and lessons learned from the commissioning of the CCEMG system switches.

Continued testing of the cannon caliber electromagnetic gun system (CCEMG)

The cannon caliber electromagnetic gun system is based upon a compulsator driven 30 mm rapid fire railgun system. The objective of the program was to develop a compact, lightweight test bed capable of launching three, five round salvoes of 185 g integrated launch packages to 1.85 km/s at a firing rate of 5 Hz. Per contractual requirements, the pulse power system is also size compatible with the amphibious assault vehicle. The pulse power system was developed around a fourth generation air-core, 4-pole rotating armature, self-excited, compulsator design. Although the contract for this effort has expired, the system continues to be used in part to demonstrate compulsator driven railgun technology. This system has performed seven single shots using identical control settings for each shot, which is the first such experience using a compulsator driven railgun system. This paper describes the experimental set-up for the demonstrations and compares the generator, converter, gun switch, and launcher performances for each shot.

Observation and simulation of armature contact performance in the cannon-caliber electromagnetic gun

Major components developed under the Cannon-Caliber Electromagnetic Gun (CCEMG) Program are presently undergoing tests at the U.S. Army Research Laboratorg (ARL) located at Aberdeen Proving Ground (APG), MD. The CCEMG launcher is a series-augmented barrel 2.25 m in length and has a rectangular bore cross section of 17.3 mm/spl times/37.3 mm. The system is designed to operate with a peak current of 835 kA, a launch package mass of 185 g, and an exit velocity of 1,850 m/s. CCEMG is a multishot system demonstrator. The test results we discuss here are for single-shot operation. The muzzle voltage in an augmented launcher contains contributions from the fields due to the augmenting turn. These imposed voltage terms tend to mask the transition of the armature contact, thereby making the transition event less discernable than in a simple railgun. The Army Railgun Modular Simulator (ARMS) computer code has been modified to provide a one-dimensional (1-D), lumped parameter model of the launcher and contact wear at the armature-to-rail interface. The CCEMG launcher data are used to further validate the ARMS code and contact wear model. Additionally, a two-dimensional, transient finite difference (2-D TFD) model is used to assess heating in the armature. In this paper we present photographic and electrical data from two shots in which armature performance is simulated.

Metallurgical analysis of an aluminum sabot fired in the cannon caliber electromagnetic gun (CCEMG)

An aluminum 7475 alloy sabot fired from the Cannon Caliber Electromagnetic Gun (CCEMG) was metallurgically characterized. More melting was seen on the rear contact surface than the front and bubbles and cracks due to high-temperature oxidation (HTO) were observed. The hardness profile showed a decrease in hardness along the outer surfaces of the sabot, particularly the contact surfaces. The softening and the HTO suggest that the material was pushed past its melting point (477-635/spl deg/C). Cracks caused by overaging were found at the roots of the contact surfaces. Black residue found in the launcher was analyzed and found to be various compounds and nonstoichiometric compounds of aluminum and copper. These compounds did not oxidize.

Metallurgical post-mortem analysis of the cannon caliber electromagnetic gun: rails and insulating sidewalls

A post-mortem tear down analysis was performed on the chromium-copper rails (alloy C18200) and alumina insulating sidewalls (AD-96) of the Cannon Caliber Electromagnetic Gun (CCEMG) after it had launched forty-nine aluminum alloy 7475 slugs or sabots with projectiles. The rails did not exhibit signs of gouging, however, a layer of aluminum from the armatures, approximately 13 microns thick, was deposited on them. The hardness and conductivity values of the rail material remained consistent along the length of the rails. The alumina sidewalls were cracked at the breech end of the gun from the start of the gun to a distance of 61 cm. Most of the cracks were due to the armatures cutting notches in the ceramic and exceeding the critical crack size of the material. Molten aluminum was found in the cracks suggesting that the cracks had formed in service and not due to the tear down procedure. Aluminum had deposited on and adhered to the alumina sidewalls as well as the rails. Despite sustaining some damage to the sidewalls and a buildup of aluminum on the rails and sidewalls the gun functioned until its decommissioning.

Cannon-caliber electromagnetic launcher

The University of Texas at Austin, Center for Electromechanics (UT-CEM) designed and fabricated a rapid-fire railgun launcher. Three, five-round salvos of 185-g launch packages are to be accelerated to 1,850 m/s at a rate of 5 Hz. The 2.25-m-long series-augmented launcher has a 30-mm round-bore equivalent rectangular geometry and is water-glycol cooled. Rapid-fire operation is achieved by driving the launcher with multiple 835-kA peak pulses provided by the Cannon-Caliber Electromagnetic Gun (CCEMG) compulsator. A single-shot launcher prototype was tested for the CCEMG system at UT-CEM and at the US Army Research Laboratory (ARL). The launcher has demonstrated an efficiency over 50%. A high CCFEMG system efficiency is in part due to the use of a solid armature and is enhanced by having a structurally stiff railgun. Historically, a railgun's stiffness was proportional to its weight. Laboratory-based railguns that have respectable mechanical properties have required massive structures that are nowhere near meeting the requirements of future vehicle integration and weaponization. The CCEMG railgun design incorporates a directional preloading mechanism, ceramic sidewalls, and a composite overwrap, which together give it a structural stiffness dominated by a high-modulus ceramic. The overall mass of the launcher is 273 kg. These characteristics make the cannon-caliber launcher one of the most fieldable railguns built to date.

Testing of the cannon caliber rapid fire railgun

A rapid fire launcher has been designed, built, and tested in single-shot mode for the Cannon Caliber Electromagnetic Gun (CCEMG) System. The 2.25-m long railgun has a rectangular cross-section (30 mm round bore equivalent) and has a series, two-turn augmented rail configuration. The gun is designed for rapid fire operation; three, five round salvos of 185 g integrated launch packages (ILPs) accelerated to 1,850 m/s with a minimum time between salvos of 2.5 s. Launch packages will be autoloaded at a repetition rate of 5 Hz via a hydraulic mechanism capable of up to 3,000 lb insertion forces. The railgun support structure and flexible buswork permit the railgun to recoil approximately 2 cm to mitigate the electromagnetic repulsion loads. Multiple 830 kA pulses provided from the CCEMG compulsator power supply require the gun to be liquid cooled for thermal management. Diagnostics for the single-shot tests include B-dots, flux rulers, voltage, and current measuring sensors. Other launcher diagnostics include rail conductor temperatures, coolant temperatures, and railgun preload mechanism (flatjacks) dynamic pressures. This paper presents the test results and general gun performance observations for single-shot, compulsator powered experiments.

Integrated launch package performance in the cannon-caliber launcher

The Cannon-Caliber Electromagnetic Gun (CCEMG) Program is a major effort toward proving the viability of electromagnetic weapons for future use by the Armed Forces. The effort is focused on the successful, system-designed integration of several major components. Crucial to the success of the program are the operational characteristics of the launcher and the integrated launch package (ILP). This paper addresses the launch and flight characteristics, accuracy, and terminal performance of the ILP and subprojectile. The results presented here represent the first known experimental assessment of these parameters obtained from electric gun firings of a tactical flight body over realistic ranges. To date, 39 shots have been fired using a 1.6-MJ capacitor bank located at the U.S. Army Research Laboratory (ARL). A wide variety of instrumentation was incorporated to survey transitional, free-flight, and terminal ballistic regimes from the gun muzzle to target impact 222 m downrange. Free-flight aerodynamic data indicated that the round has adequate in-flight stability. Round-to-round dispersion was computed over a wide range of launch velocities based on downrange impact locations and was used to provide estimates of the dispersion at the design launch velocity of 1,850 m/s. A detailed analysis of the transitional ballistic process has been performed to quantify the various contributors to the total launch disturbance. The results indicated that the sabot/armature discard contributes equally with the aerodynamic jump toward target impact dispersion and increases with launch velocity. For the current launcher configuration, the variability of the discard process Is oriented in the vertical direction. Finally, impact data on armor were limited but nonetheless indicate the round is capable of meeting the CCEMG system requirements.

Laboratory testing of the pulse power system for the cannon caliber electromagnetic gun system (CCEMG)

The team of (prime contractor) United Defense LP (UDLP) and The University of Texas at Austin Center for Electromechanics (UT-CEM) has completed a significant portion of the testing phase of a trailer mounted compulsator driven 35 mm (round bore equivalent) rapid fire railgun system. The objective of the program is to develop a compact, lightweight pulse power test bed capable of launching 3, 5 round salvos of 185-g integrated launch packages to 1.85 km/s at a firing rate of 5 Hz. Per contractual requirements, the pulse power system is also size compatible with the Amphibious Assault Vehicle (AAV). The pulse power system is developed around a second generation air-core, 4-pole rotating armature, self-excited, compulsator design. The 40 MJ at 12,000 rpm composite rotor stores all 15 shots inertially and is capable of 2.5 GW performance into the 2.21 m long series augmented railgun. This paper describes the CCEMG pulse power supply configuration and highlights important features of the commissioning test plan. The paper then presents test results from mechanical runs, stand alone compulsator (CPA) rectifier tests, short circuit tests, and single shot live fire tests. Finally, CPA performance is compared with predictions for the single shot tests presented.

Design and testing of the power electronics for the cannon caliber electromagnetic gun system

The University of Texas Center for Electromechanics (UT-CEM) is in the final fabrication and testing phase of a power electronics system required to operate a skid mounted compulsator-driven railgun. Design goals for the self-excited air core compulsator include a 95 MW rectifier/inverter bridge for field coil self-excitation. Initial field coil seed energy is supplied by a 50 kJ capacitive discharge from the field initiation module. The field coil is passively protected from voltage transients by an array of metal oxide varistors. Other system power modules include the gun closing switch and explosive opening switch. This paper presents a brief system overview and detailed design of the rectifier/inverter bridge module with performance data from shots up to 6.