S.B. Pratap

Final design of an air core, compulsator driven, 60 caliber railgun system

The manufacturing phase of a laboratory-based small-caliber electromagnetic (EM) launcher and compulsator power supply is discussed. The objective of the 29-month program is to develop a compact, lightweight test bed capable of accelerating 32 g masses to 2 km/s at a rate of 10 Hz. Both the power supply and launcher feature significant component design advances which will allow the system to operate at considerably higher energy and power densities than previously demonstrated. The 750 kg compulsator will generate 2.2 kV and the silicon-controlled rectifier (SCR) switch will commutate 386 kA pulses into the 1.6-m long, 0.60 caliber augmented solid armature railgun. The final design and predicted operating characteristics of the compulsator system are described. Overall system performance parameters are reported, including results from the optimization code used to aid in the design of the compulsator system. A system design overview is presented, with emphasis on new materials and state-of-the-art machine components to be used for the first time in a compulsator. >

A field based, self-excited compulsator power supply for a 9 MJ railgun demonstrator

Fabrication efforts have begun on a field-based compulsator for firing 9 MJ projectiles from a railgun launcher. The machine is designed to store 200 MJ kinetic energy and fire a salvo of nine rounds in three minutes at velocities between 2.5 and 4.0 km/s. Prime power required to meet this firing schedule is 1.865 kW, and will be supplied by a gas turbine engine. It is also possible to fire a burst of two shots in rapid succession, if desired. Operating speed of the machine is 8250 r/min and it has design ratings of 3.2 MA peak current and 20 GW peak power into a 9 MJ railgun load. A two-pole configuration is used for pulse-length considerations, and selectivity passive compensation is used to produced a relatively flat pulse and limit peak projectile acceleration to about 980000 m/s/sup 2/. Other distinguishing features include an air core magnetic circuit, separate rotor armature windings for self-excitation and railgun firing, ambient temperature field coils, and excitation field magnetic energy recovery capability. A detailed description of the machine as designed, and its auxiliary and control systems, is provided. Fabrication and assembly methods are reviewed, and the current status of the project is discussed. >

Testing of a rapid-fire compensated pulsed alternator system

A compensated pulsed alternator (compulsator) has been designed and fabricated to drive a rapid-fire railgun system. Initial testing of the compulsator resulted in the failure of the compensation shield at full speed. An ambitious rebuild effort was undertaken, allowing testing to begin in August 1987. Since then, several rapid-fire shots have been performed, firing two 3 m guns at a 60-Hz repetition rate. A 65-g solid armature projectile was accelerated to 1.8 km/s during the initial tests with the compulsator operating at half-speed and reduced excitation. These preliminary results suggest a high probability that the compulsator rapid-fire system will meet and exceed the design goals. >

Design of a self-excited, air-core compulsator for a skid-mounted repetitive fire 9 MJ railgun system

The design of a lightweight, compulsator-driven 9-MJ electromagnetic (EM) launcher has been completed and is in the fabrication phase. Scheduled for initial field testing in early 1989, the system will be capable of firing a salvo of nine rounds in three minutes at muzzle velocities between 2.5 and 4.0 km/s. Prime power for the compulsator is supplied by a 5000-hp gas turbine engine through a gearbox and clutch arrangement, and auxiliary power is provided by a small 750-hp turbine. Electrical power generation and pulse conditioning for the launcher are performed by the compulsator, which features a self-excited, air-core magnetic circuit and selectively passive armature compensation designed to minimize peak projectile acceleration. Peak power from the machine is 27 GW, and a total of 30 MJ is extracted from the rotor during each firing of the gun. System mass, including gun, compulsator, prime power, and auxiliary systems, is less than 22 tons and will be mounted on a 36-ton concrete slab which simulates the mass of an armored vehicle on which the system will eventually be integrated. >

Discarding armature and barrel optimization for a cannon caliber electromagnetic launcher system

The authors detail the optimization and baseline design of the discarding metal armature and electromagnetic railgun developed for the US Army Armament Research Development and Engineering Center and US Marine Corps sponsored Cannon Caliber Electromagnetic Launcher program. The primary goals of this program have been to defeat specified targets at 1500 and 3000 m range utilizing an electromagnetic launcher system weighing less than 5000 lb. An optimization algorithm was developed to integrate the armor-penetrating subprojectile with a discarding armature/sabot forming an integrated launch package. This algorithm coupled integrated launch package electromagnetic and structural design requirements to launcher design parameters including rail resistance per unit length and inductance per unit length as a function of launcher rail geometric and structural configurations. Pulsed power supply size and mass requirements were subsequently estimated from launcher performance predictions. >

Salvo fire experiments using a 0.60 caliber electromagnetic launcher

A laboratory-based, small caliber electromagnetic launcher and compulsator power supply is being developed. The goal is to accelerate three 32 g masses to 2 km/s at a 10 Hz firing rate. A 0.60-caliber, series augmented, 1.6 m launcher has been fabricated and tested. The launcher testing utilized the iron core compulsator (ICC) power supply and the 400 kA small-caliber SCR switch. The extended pulse width of the ICC when firing the shorter small caliber launcher would ordinarily lead to a large muzzle arc. Using a muzzle shunt resistor on the augmented launcher can substantially reduce the muzzle arc. The launcher, SCR switch, muzzle shunt resistor, ICC power supply, and autoloader are described. The control apparatus used to synchronize the autoloader, SCR switch, and launcher is also described. Data from several double shots and one triple shot are presented. These data include launcher data, SCR switch data, muzzle shunt resistor current traces, and autoloader performance measurements for firing rates of up to 13.5 Hz. >

A rapid fire, compulsator-driven railgun system

It is becoming clear that compensated pulsed alternators (compulsators) are the preferred power supply for rapid-fire railgun systems. High efficiencies, inherently high repetition rates, and the elimination of high current opening switches are the primary advantages of compulsator-driven systems. The benefits and capabilities of these systems will be demonstrated in a project which is currently in the final stages of fabrication. The goals of this project are to accelerate a burst of ten, 80-g projectiles to 2 km/s at a 60 Hz rate of fire. Details of the compulsator design, the design, fabrication, and testing of system components, and proposed operation are presented.

The CEM-UT rapid-fire compulsator railgun system-recent performance and development milestones

Twenty-seven compulsator-powered railgun experiments have been performed, including a 1.0 MJ discharge at 3510 r/min. In this test, a 724 kA current pulse accelerated an 80 g, aluminum armature to 2.05 km/s, thus exceeding the projectile velocity goal at 73%-rated machine speed. Furthermore, operation with a single gun barrel has been achieved using a parallel path, solid-state closing switch to deliver 132 kA to the railgun injector. The latest data are presented from the rapid-fire compulsator railgun facility. Included is a discussion of the energy transfer, power output, and system efficiency during a 1.0 MJ discharge. Also shown are the injector current, voltage, and di/dt curves for this test which were used in the design of the solid-state closing switch. Results of railgun experiments using the solid-state switch are analyzed. >

9 MJ range gun compulsator stator design and fabrication

The authors provide a summary of the structural analysis of the compulsator stator as well as a detailed description of the major stator components. Fabrication and assembly techniques are also presented, along with the current status of the project. The range gun compulsator is a self-excited, air-cored alternator designed to provide pulsed power in a field portable electromagnetic launch system capable of accelerating a salvo of nine projectiles to a muzzle energy of 9 MJ at velocities ranging from 2.5 to 4.0 km/s. The compulsator is designed to deliver 3.2 MA current pulses to a railgun launcher at a peak power rating of 10 GW. The stator consists of a multiturn compensating winding with a laminated stainless steel support structure, an aluminum excitation field coil and support structure, a stainless steel stator casing and main end plates, hydrostatic bearings, seals, and support pedestals, and current collection mechanisms for the field excitation and main armature circuits. >