D.R. Peterson

Design and testing of large-bore, ultra-stiff railguns

As part of an EM (electromagnetic) gun technology demonstration program, a systematic design approach targeted at identifying critical gun design constraints affecting hypervelocity projectile performance has been pursued. Results of the study led to a laboratory-based EM gun design that provides bore straightness and tolerances characteristic of light-gas guns, dynamic bore deformations comparable to those of conventional guns, the ability to change and test rail/sidewall insulator materials quickly, and superior in-bore performance diagnostics. A high-stiffness, easily maintained, precision-bore 9-MJ EM launcher has been designed and fabrication is virtually complete. A half-scale prototype of this hydraulically prestressed EM gun design has been fabricated and successfully tested. The authors discuss the railgun design approach and performance parameters, the analytical and empirical railgun structured simulation techniques used to validate the full scale gun design, and the fabrication status and initial performance test results. >

9 MJ laboratory gun and range at The University of Texas at Austin

The authors describe a 9 MJ laboratory gun and range program. The goal of the program is to demonstrate a single-shot EM (electromagnetic) gun suitable for establishing gun parameters for repetitive EM gun systems and for supporting projectile development. A description is given of the activities of phase I of this program, wherein the power supply has been prepared, the range has been designed and constructed, a one-half-scale and a full-scale gun have been designed and constructed, and the one-half-scale gun has been assembled and undergone initial tests. Of significance is that within a six-shot test sequence on the one-half-scale gun the electric gun has matched the muzzle velocity of the conventional gun that is operated on the M1E1 battle tank. >

Wear of conductors in railguns: metallurgical aspects

The wear debris generated by an aluminum alloy armature sliding on copper rails was studied experimentally. The experimental parameters were set to maximize armature velocity. Preliminary rail and armature wear observations were documented as part of a database for solid armature development. A variety of debris collection and characterization approaches were used. Both in-bore debris and muzzle-exit debris were collected for size and chemical analysis. Debris constituents were copper-rich, and the compound Cu/sub 9/Al/sub 4/ was observed in the splat-quenched muzzle debris. The approach and method are detailed to indicate the potential of wear studies in defining the activity at the sliding interface. Some implications of rail surface roughening for zero wear measurements are also discussed, and the adoption of wear mechanism maps is proposed. >

Composite solid armature consolidation by pulse power processing: a novel homopolar generator application in EML technology

Graded electrical resistance and assured sliding contact are among the desirable characteristics for the solid armatures used in railguns attainable through the use of composite materials. Metal-metal, metal-ceramic, and metal-polymer composites are generic types of potential solid armature materials. The authors describe the production of these composites by a novel experimental approach that uses a homopolar generator in a pulse-powered materials consolidation system. The processing of copper-tungsten and aluminium-alumina composites is used to demonstrate versatility of the homopolar generator as a materials processing tool. Powder metallurgy and laminate bonding approaches have been utilized. Composite solid armature materials have been consolidated with subsecond high-temperature exposure. Densification in the solid state proceeds by a warm/hot forging mechanism, and fully dense composites are obtained by a combined application of pressure and a controlled energy input. >

Testing of a high performance, precision-bore railgun

This paper discusses the results of high-pressure (up to 350 MPa) railgun experiments. The gun is designed both to be capable of high-pressure operation without structural damage and to be readily disassembled for inspection, maintenance and component testing. Considerable effort has been invested to develop techniques to produce and measure smooth, extremely precise (>5µm of variation) bores. We have not deliberately varied bore precision to determine the effect of precision on performance, but our experience suggests that if two otherwise identical railguns, one with a polished, high-precision bore, were fired under identical conditions, the precisely finished gun would achieve a higher muzzle velocity. Very high accelerations have been achieved (>107m/s2). A 2-g projectile has been accelerated to 5 km/s in a 13 mm square-bore gun only 1 m long. Projectiles with an L/D as small as 0.65 have been successfully accelerated. Projectiles with smaller L/Ds have not yet been tested to determine the minimum L/D which can be successfully accelerated. A number of different insulator materials ranging from common float glass to fused quartz have been tested. The best results have been obtained with fused quartz, which shows promise of being reusable. In the course of testing, the importance of gasketing the rail-to-insulator seams to prevent loss of plasma has become apparent. We have made progress in gasket design, but more work is needed. Rail gouging has been a continuing problem. Gouging may be dependent on bore precision, projectile fit, rail mechanical properties, projectile L/D, structural stiffness, operating pressure, velocity, and shape of the current pulse.

Design and operation of a high-energy railgun facility

A high-energy railgun range has recently been put into operation. Projectiles are fired straight down into a target chamber 45-m underground. After discussing the design philosophy, the authors describe the railgun, the bore-finishing and gauging, the solid armatures, the buswork, and the breech access. It is concluded that the different components of the range are designed not just for safety and to function well but for operational convenience as well. >

Producing and gauging precision railgun bores

The authors discuss the use and results of a bore finishing and measuring system for obtaining and quantifying precision bores in railguns. The bore finishing system has been specially designed and installed to enable honing of round-bore railguns in situ. The honing tool is equipped with six metal-bonded diamond abrasive stones to minimize bore ovaling, and the honing machine has infinite and separate adjustment on rotation and reciprocation (0 to 180 r.p.m. and 0 to 20 m/p min, respectively) of the tool. Experience has shown that bore ovaling can be reduced to only 80 mu m difference between minimum and maximum diameters, and the bore diameter can be increased at the rate of about 0.1 m/hr. A tool for square-bore honing has been developed that greatly reduces the effort and time to finish bores, while improving bore accuracy. To quantify the round bores, diameter and straightness measuring tools have been developed. Using a calibrated dial bore gauge as reference, and accuracy of +or-0.01 m has been achieved for measuring bore diameter. >