David P. Bauer

High performance railgun barrels for laboratory use

High-performance low-cost laboratory railgun barrels have been developed. The barrel is composed of an inherently stiff containment structure, which surrounds the bore components machined from off-the-shelf materials. The shape of the containment structure was selected to make the barrel inherently stiff. The structure consists of stainless-steel laminations which do not compromise the electrical efficiency of the railgun. The modular design enhances the utility of the barrel, as it is easy to service between shots and can be recored to produce different configurations and sizes using the same structure. Barrels have been produced ranging from 15 mm to 90 mm square bore, a 30 mm round bore, and in lengths varying from 0.25 m to 10 m long. Successful tests with both plasma and solid metal armatures have demonstrated the versatility and performance of this design. The assembled barrel has a high inductance gradient (0.43 mu H/m) and has proven to be an effective tool for conducting railgun component research and development. >

Distributed energy store powered railguns for hypervelocity launch

It is noted that several deficiencies hamper full-scale railgun development for hypervelocity applications. Two key deficiencies are lack of hypervelocity performance (i.e., >6 km/s) and lack of compact power supplies. Highly distributed power supplies address these deficiencies. A railgun powered by highly distributed energy stores reduces the rail-to-rail voltage behind the main armature, reducing the tendency to secondary armature current formation. Secondary current elimination is necessary to overcome the velocity limit. Feasibility assessments of two distributed energy store schemes have been completed. A nested rail, distributed energy store (NESDES) system and an ultra distributed energy store system (UDESS) have been used to remove the rail-to-rail voltage. Analytical and experimental data are presented on both schemes. The results indicate that the aforementioned deficiencies are addressed. >

A maintainable large bore, high performance railgun barrel

This paper reviews the design features and performance characteristics for a large bore (90 mm) barrel system fabricated for the Defence Research Agency (DRA) to operate at the Kirkcudbright Electromagnetic Launch Facility. This 90 mm barrel was designed for testing developmental launch package designs. The barrel design permits the rapid refurbishment of bore insulators and rails that are commonly damaged by launch package failures during development testing. The barrel system is designed for operation with both plasma and metal armatures up to peak current levels of 3.5 MA. The results of initial performance testing including inductance gradient and bore deflection are presented. >

A multiple armature railgun launcher

The authors describe the theory and test results for multiarmature launch of high L/D (length-to-diameter ratio) projectiles. Railgun launchers with multiple armatures can distribute the accelerating force. Each armature is supplied gun current for acceleration through its own set of rails. This multirail, multiarmature concept has been tested at a railgun test facility. The results demonstrated feasibility. It was possible to control current distribution to multiple armatures. >

A novel railgun launch package concept

Low parasitic mass, high muzzle velocity railgun launch packages are required for railguns to compete with conventional guns. This paper describes a launch package concept for long rod penetrators which has the potential of achieving less than 50% parasitic mass and 3 km/s muzzle velocity. The launch package uses a new armature, a magnetic obturator design which does not require additional mass for contact loading and distributes the acceleration forces along the body of the projectile. This paper describes the launch package concept, summarizes the mechanical and magnetic analyses conducted, and presents subscale test results with velocities up to 3 km/s.

Diagnostics and hardware techniques for measuring in-bore pressures from transitioning metal armatures

For new tactical gun systems to have the potential be integrated into future lightweight combat vehicles, mass optimization is a key design feature. In an electromagnetic launcher during normal solid metal armature operation, the magnetic field pressure forces the conducting rails outward, applying an asymmetric load to the bore containment. This loading can be accounted for in the containment design. When a solid armature transitions, a gas pressure is developed, causing additional force to be applied to the insulator and the containment in the insulator direction. This force generates requirements for additional strength in the insulator and bore containment and creates an additional mass penalty. Quantification of transitioning armature pressure allows for optimization of the launcher design. In this paper, we describe the technique used in measuring these in-bore pressures. Detailed are the test setup, hardware, instrumentation, and data acquisition equipment used for the experiments. Additionally, initial testing results of measured pressure are presented here along with some comparisons to theoretical average pressures across the bore area.

Electromagnetic and thermal performance validation of finned rails for EM launch

The design of fieldable electromagnetic launchers must carefully balance structural, thermal and electromagnetic performance in conjunction with suitable life. IAP Research has been developing a novel launcher concept in which the barrel is constructed from mostly metal materials. Analysts has indicated that the design has relatively high inductance gradient, combined with high passive thermal performance. This enhanced performance derives from the use of transverse copper laminations on the nonbore surfaces of each rail. These laminations induce more current flow on the bore surfaces and thus reduce the apparent thickness of the rails, increasing the bore magnetic field. At the same time, the rail fins absorb and quickly distribute the heat generated in the rail to outer portions of the gun for ambient air cooling. Subsequent experiments have validated the concept. This paper describes the study conducted by IAP Research and IAT to validate the performance of finned rail technology.

Analysis of rotational forces in round bore railguns

Integrated launch packages in round bore railguns are designed to support acceleration forces based on a given current distribution in the armature/sabot. Deviation from this current distribution can lead to loads for which the launch package is not designed. One of the mechanisms which can cause current redistribution is in-bore rotation. In-bore rotation can alter the current and force distribution in a launch package leading to an early contact transition and possible launch package breakup. In a test series of the IAP/Loral SLEKE launch package at UTCEM, in-bore launch package rotation was observed. As a result, the amount of rotation was quantified, the possible causes of rotation were identified and possible solutions proposed. In this paper the authors describe the observed rotation, present the possible causes and discuss design modifications to prevent rotation. >

Multi-rail barrel design and performance

It is pointed out that railgun barrels containing multiple isolated rail pairs can be used to control armature current distribution and/or to obtain independent circuits for use with specialized power supplies. Armature current control can be used to effectively distribute acceleration forces for improved projectile launch. Independent rail load circuits are attractive for use with some power supplies such as a polyphase compulsator. A 30 mm barrel containing three distinct rail pairs has been built and tested. These three rail pairs were powered by separate power supplies. The authors describe issues associated with multirail barrel design and the present barrel design and performance. Rail alignment, isolation, and construction are described. The effect of multiple rail pairs on the effective inductance gradient of the barrel is described, and test results are provided. >

A novel railgun launcher design

Higher efficiency, and smaller power supplies are needed for most electromagnetic railgun applications. This paper describes the feasibility evaluation of a novel railgun barrel configuration that addresses these issues. The Hypervelocity High Efficiency (HYPE) railgun concept uses a distributed power feed railgun design, but eliminates the need for many separate distributed power supplies. Nested, segmented main rails are individually connected to a single pair of augmenting secondary rails. The augmenting secondary rails are powered from a single energy source. A 15 mm square bore, 300 mm long HYPE railgun was built and tested to evaluate concept feasibility. Analytical and experimental results show that the HYPE configuration is feasible, at least for low velocity. >