Mass sensitivity studies for an inductively driven railgun

Those areas which result in substantial system mass reductions for an HPG (homopolar generator) driven EML (electromagnetic launcher) are identified. Sensitivity studies are performed by varying launch mass, peak acceleration, launcher efficiency, inductance gradient (L'), injection velocity, barrel mass per unit length, fuel tankage and pump estimates, and component energy and power densities. Two major contributors to the system mass are the allowed number of shots per barrel versus the number required for the mission, and the barrel length. The effects of component performance parameters, such as friction coefficient, injection velocity, ablation coefficient, rail resistivity, armature voltage, peak acceleration, and inductance gradient on these two areas, are addressed     

Basic principles of coaxial launch technology

Coaxial launchers have received very much less attention than railguns because of their greater complexity, but they offer several significant advantages. They require no physical contact with the projectile, scale readily to very large diameter, can distribute thrust over the length of the projectile, have more adaptable energy supply and impedance requirements (being a multi-turn device), offer higher efficiency, positive control over the launch cycle, and permit component redundancy to achieve any desired degree of reliability. Thrust for a given current can be a hundred times higher than in a railgun, but the current must be synchronized with projectile motion. The voltage required to do so increases with velocity, and high voltage commutation capability represents the technological limit to launch velocity. Present research activity is concerned with commutation in the low and high velocity domains, position sensing techniques, dynamic stress containment in drive coils, and design of the first practical EM launcher: a Nimitz class aircraft catapult.     

Hypervelocity macroparticle accelerator experiments at CEM-UT

Several railgun experiments designed to accelerate projectile masses of 2 to 5 g to velocities greater than 6 km/s were performed. Two parallel rail-type accelerators with 12.7 mm square bores were used for the experiments. One gun is 2 m long, has molybdenum rails and alumina ceramic insulators. The other is 1 m long, has molybdenum rails and granite insulators. The greatest velocity achieved to date during the experiments was 5.1 km/s. During the test program, the following ideas to enhance launcher performance were tested: stiff-gun structures to reduce plasma leakage and rail movement, refactory bore materials to reduce ablation and frictional losses, and prefilling the gun bore with gases which will eliminate precursor arcs. After three experiments utilizing the 2 m long launcher, with peak currents ranging from 660 to 780 kA, a gun barrel comprised of 96% pure alumina ceramic insulators and 99.9% pure molybdenum rails has survived with minimal damage and no degradation of seals     

Electromagnetic coaxial railgun

Key design parameters of railguns are examined, namely, the inductance gradient, current distribution, electromagnetic pulses distribution and rail separation forces. A comparison of coaxial and parallel railguns indicates that the coaxial system has some advantages and should be considered during system design tradeoffs for an orbiting space probe launcher. It is suggested that an orbiting launcher could be used to send small and relatively inexpensive probes towards the planets and asteroid belt. A small, low-energy capacitor-powered coaxial railgun designed and built to demonstrate the armature acceleration and absence of the electromagnetic pulse forward of the armature is described     

Continuous measurements of in-bore projectile velocity

The application of velocity interferometry to the continuous measurement of in-bore projectile velocity in a small-bore three-stage railgun is described. These measurements are useful for determining projectile acceleration and for evaluating gun performance. The launcher used in these studies consists of a two-stage light gas gun used to inject projectiles into a railgun for additional acceleration. Results obtained for projectile velocities to 7.4 km/s with the two-stage injector are reported, and potential improvements for railgun applications are discussed     

Rail launchers to reach hypervelocity

In this paper we present a theoretical study of a 80 mm round bore railgun which allows us, by a current distribution along the projectile, to accelerate a long rod penetrator with a fineness ratio of 30 up to a muzzle velocity of 2500 m/s with an overall efficiency greater than 30%.

This study was started because an optimal impact velocity which allows a given depth of penetration to be reached with a minimum kinetic energy exists for all the targets (homogeneous, composite, structured or reactive). Two years ago we showed that this impact velocity is always greater than 2300 m/s for a heavy alloy penetrator with L/D = 30. For these velocities the electromagnetic rail launchers may have efficiencies over 35 % when classical powder guns have efficiencies about 20 %.     

The reconnection gun

An electromagnetic launcher called the reconnection gun is introduced. Its potential performance is shown to be superior to that of a modern railgun for projectiles with mass greater than a few hundred grams. It has a "characteristic velocity" which is an order of magnitude lower for much lower energy loss to ohmic heating. Also, it has several advantages for producing higher acceleration including; no barrel, no drop in acceleration with increase in projectile mass, higher peak pressure on the projectile and smaller differences between average and peak pressure. Experimental results and plans for high-performance, multi-stage designs are briefly discussed.     

Fast electromagnetic launchers

A general discussion of the form of the force equation for fast electromagnetic launchers, and of their energetics, is presented. It suggests that a class of launch devices whose total inductance decrease during the launch cycle has a number of attractive features, especially the potential for high electrical-to-mechanical energy conversion efficiency. Examples of specific launcher concepts in this class are given.     

Fabrication of ultralow-profile micromachined inductor with magnetic core material

We have fabricated a microinductor with an ultralow profile by a microelectromechanical systems (MEMS) technique. The fabrication process uses UV-LIGA, dry etching, fine polishing, and electroplating to achieve high performance. The dimensions of the inductor are 1500 /spl mu/m/spl times/900 /spl mu/m/spl times/100 /spl mu/m. It has 41 turns, with coil width of 20 /spl mu/m, space of 20 /spl mu/m, and a high aspect ratio of 5 : 1. The inductance is 0.424 /spl mu/H and the quality factor (Q factor) is about 1.7 at a frequency of 1 MHz. The stray capacitance is approximately zero over the frequency range measured.     

Hypervelocity impact testing using an electromagnetic railgun launcher

An electromagnetic (EM) railgun launcher facility has been developed to routinely conduct hypervelocity impact tests. Two types of completely reusable EM launchers have launched sabot/impactor packages between 2 and 43 grams to velocities between 1.5 and 8.5 km/s. The highly reliable railguns have conducted over 250 projectile launchings and have established a projectile/launcer data base covering interior as well as exterior ballistic considerations. A conventional type instrumented ballistics range is compatible with the EM launcher and can be used to conduct anti-armor and lethality experiments at hypervelocities.     

Railgun performance with a two-stage light-gas gun injector

Results obtained with the HELEOS (hypervelocity experimental launcher for equation of state) railgun, which uses a two-stage light-gas gun (2SLGG) as an injector, are presented. The high-velocity 2SLGG injector preaccelerates projectiles up to ~7 km/s. The high injection velocity reduces the exposure duration of the railgun barrel to the passing high temperature plasma armature, thereby reducing the ablation and subsequent armature growth. The 2SLGG also provides a column of cool, high-pressure hydrogen gas to insulate the rails behind the projectile, thereby eliminating restrike. A means to form an armature behind the injected projectile has been developed. In preliminary tests, the third-stage railgun has successfully increased the projectile velocity by 1.35 km/s. Extensive diagnostics have been used to determine the behavior of the armature and track the launcher's performance. Insome cases, velocity increases in the railgun section have been achieved, which are in close agreement with theoretical predictions, whereas in other experiments deviations from theoretical have been observed. The reasons for and implications of these results are addressed. Recent tests are reported     

Distributed-current-feed and distributed-energy-store railguns

Distributed-type railguns are combinations of power supplies and railguns designed to maintain a nearly constant current in the armature of a railgun and to overcome the accelerator length limitations of simple breech-fed railguns. This limitation arises from the increasing resistance and inductance of the rails with increasing railgun length. The energy efficiency of a railgun system from the primary energy store to the kinetic energy of the projectile can be improved as compared to the simple railgun in some applications. This is accomplished by a reduction of the stored magnetic field energy in the bore of the railgun at the end of a shot and reduction of the resistive losses in the rails. The improved system performance of the distributed railguns over the simple breech-fed railguns is achieved at the expense of greater system complexity. The only distributed-type railguns that have been built to date are distributed-energy-store (DES) railguns. These systems presently use capacitors as the primary energy store, which allows the use of closing switches to initiate current from each of the stores. In this paper a new type of railgun, the distributed-current-feed (DCF) railgun, is presented. The DCF railgun system is a compromise in system complexity and efficiency between the DES railguns and the simple breech-fed railguns. Also, the DCF railgun utilizes closing switches in such a manner as to allow the use of a variety of primary power supplies, including homopolar generators (HPGs), for such electromagnetic propulsion tasks as space launches.     

Isolated carbon nanotubes as high-impedance transmission lines for microwave through terahertz frequencies

A hybrid approach, combining quantum theory with classical distributed-element transmission-line models, is taken to study the transport of high-frequency energy in isolated metallic carbon nanotubes (CNTs). The characteristic impedance for these transmission lines would be approximately 40 k/spl Omega/, which is unusually high because of the kinetic inductance of the CNTs and the lack of capacitive shunting to a conducting ground plane or other objects. The propagation is by TM surface waves, instead of the TEM waves for propagation in nanotubes that are parallel to a planar conducting surface so the phase velocity is much less than the velocity of light in vacuum. The phase velocity would be approximately 3 /spl times/ 10/sup 6/ m/s, and both the characteristic impedance and phase velocity are essentially independent of the radius of the CNT. However, the numerical results must be regarded as being provisional because corrections have not been made for the effects of transport in multiple channels that are caused by the band structure and spin degeneracy. One application is considered for a new type of device that would generate radiation at microwave through terahertz frequencies by photomixing in laser-assisted field emission.     

High velocity linear induction launchers

Electromagnetic launchers (EMLs) have received great attention in the last decades because of their potential application to a variety of energy, transportation, space, and defense systems. Particularly, they can serve as kinetic weapons, such as ground-based and naval artillery, space-based anti-missile guns, Earth-to-Orbit launcher, and mass transportation. The main advantage is that EMLs can accelerate projectiles to hyper velocities, i.e. velocities greater than those achievable with conventional cannons. The Linear Induction Launcher (LIL) is an air-cored electromagnetic coil launcher operating on the principle of the induction motor. Polyphase excitation of the coils constituting the barrel is designed to create an electromagnetic wave packet, which travels with increasing velocity from the breech to the muzzle. The projectile is a hollow conducting cylinder (sleeve) carrying the payload within it. Relative motion (slip) of the wave packet with respect to the projectile induces azimuthal currents in the sleeve that interacts with the exciting magnetic field to produce both propulsive and centering forces. This paper deals with the design of a high velocity linear induction launcher with muzzle velocity up to 6000 m/s. It addresses the design specifications of the launcher and utilizing a projectile weighing 1 kg. In the paper, the design specifications with simulation results for the phase voltages, the currents, the velocity, and the temperature rise of the sleeve are presented.     

Dynamics of acceleration of millimeter-sized pellets in railgun accelerators with external magnetic field

A physical model of the acceleration of small (1–3 mm) solid pellets in a railgun with a plasma piston and an external pulsed magnetic field is proposed. For the typical operating parameters of the railgun, the effect of the erosion of electrodes, drag force, and dimensions of a body on its final velocity has been studied. It is shown that the saturation of velocity of 1- to 2-mm pellets occurs at short distances (15–20 cm) and is mainly governed by the capture of a portion of the erosion mass by the plasma piston.     

Analysis and design of a CMOS angular velocity- and direction-selective rotation sensor with a retinal Processing circuit

This paper implements and analyzes a CMOS angular velocity- and direction-selective rotation sensor with a retinal processing circuit. The proposed rotation sensor has a polar structure and is selective of the angular velocity and direction (clockwise and counterclockwise) of the rotation of images. The correlation-based algorithm is adopted and each pixel in the rotation sensor is correlated with the pixel that is 45/spl deg/ apart. The angular velocity selectivity is enhanced by placing more than one pixel between two correlated pixels. The angular velocity selectivity is related to both the number and the positions of the edges in an image. Detailed analysis characterizes angular velocity selectivity for different edges. An experimental chip consisting 104 pixels, which form five concentric circles, is fabricated. The single pixel has an area of 91/spl times/84/spl mu/m/sup 2/ and a fill factor of 20%, whereas the area of the chip is 1812/spl times/1825/spl mu/m/sup 2/. The experimental results concerning the fabricated chip successfully verified the analyzed characteristics of angular velocity and direction selectivity. They showed that the detectable angular velocity and range of illumination of this rotation sensor are from 2.5/spl times/10/sup -3/ /spl pi//s to 40 /spl pi//s and from 0.91 lux to 366 lux, respectively.     

The 10 KM/S, 10 KG railgun

The system design for a railgun powered by capacitor-based energy stores distributed along its length is presented. It is assumed that it is required to accelerate a mass of 10 kg to a velocity of 10 km/s. Parameters for the railgun and its energy stores are derived, and the performance of the system is computed with particular attention being paid to the efficiency with which store energy is converted to launch-package kinetic energy. It is shown that efficiencies of 90% can be expected from a properly designed system     

A second generation EMET railgun for secondary arc studies

Since 1985 GT-Devices has been operating a pair of railguns with lengths of 0.9 m and 3.6 m, respectively. A new second-generation railgun is now being constructed to improve straightness, stiffness, sealing, and diagnostic access. The basic design consists of a steel tube with a thin lengthwise slit forming two halves in cross section with bolt preloading. The internal structure consists of split tubular G-10 compression blocks with Glidcop AL-15 rails and polycarbonate insulators formed from 90 degree tube sections. A new 0.9 m launcher of the same design is now under construction, with a 3.6 m version to follow. An upgraded electrothermal injector has been developed using modified armature injection module (AIM) hardware. Injection velocities of 2500 m/s have been attained with 1.1 gram polycarbonate projectiles for stored bank energies of 65 kJ. Injection velocities of 3000 m/s may be possible. The design details of the new railgun, injector, and diagnostics are discussed, and some initial experimental results are presented     

Development of a scramaccelerator based hypervelocity launcher

The Scramaccelerator, a novel type of supersonic-combustion, tube-based launcher has been developed that can accelerate projectiles to velocities of 3 to over 7 km/sec. Extremely flexible in application, the Scramaccelerator could launch impact specimens, wind tunnel specimens, projectiles, satellites, or spacecraft. This paper describes the technology demonstration of the concept by firing 120 gram projectiles into a 38 mm barrel at 2.8 to 3.2 km/sec at the Titan/CRT Impact Research Laboratory in Albuquerque. This technology promises an upward scalability beyond that of any conventional ballistic guns and electromagnetic launchers for high mass hypervelocity applications. It is the objective of this program to demonstrate the practical application of detonation physics to hypervelocity launchers. Critical test issues discussed include sabot seperation, venting requirements, Scramaccelerator tube requirements, and test performance. The current data indicate projectile accelerations were achieved in excess of 5,000 g's. Hence, these tests finally demonstrate that oblique detonation/supersonic combustion can be harnessed as a useful mechanism for hypervelocity propulsion. In addition, these tests demonstrate hypersonic propulsion at Mach numbers above 9, acceleration at greater than 3 kilometers per second, and system integration technology sufficient to accomplish this success. Scalability of the device allows for the hypervelocity launch of large masses.     

A CMOS focal-plane motion sensor with BJT-based retinal smoothing network and modified correlation-based algorithm

This work presents and implements a CMOS real-time focal-plane motion sensor intended to detect the global motion, using the bipolar junction transistor (BJT)-based retinal smoothing network and the modified correlation-based algorithm. In the proposed design, the BJT-based retinal photoreceptor and smoothing network are adopted to acquire images and enhance the contrast of an image while the modified correlation-based algorithm is used in signal processing to determine the velocity and direction of the incident image. The deviations of the calculated velocity and direction for different image patterns are greatly reduced by averaging the correlated output over 16 frame-sampling periods. The proposed motion sensor includes a 32/spl times/32 pixel array with a pixel size of 100/spl times/100 /spl mu/m/sup 2/. The fill factor is 11.6% and the total chip area is 4200/spl times/4000 /spl mu/m/sup 2/. The DC power consumption is 120 mW at 5 V in the dark. Experimental results have successfully confirmed that the proposed motion sensor can work with different incident images and detect a velocity between 1 pixel/s and 140,000 pixels/s via controlling the frame-sampling period. The minimum detectable displacement in a frame-sampling period is 5 /spl mu/m. Consequently, the proposed high-performance new motion sensor can be applied to many real-time motion detection systems.