The shape effect of non-spherical projectiles in hypervelocity impacts

This paper provides qualitative and quantitative analyses of regular non-spherical projectile hypervelocity impacts on basic Whipple shields using test data obtained by light-gas guns, flat plate accelerators and shaped charge launchers. Surrogate cadmium and zinc test results are used to extend light-gas gun data beyond 8 km/s. Advanced Whipple shield derivatives are shown to be necessary to protect against non-spherical projectiles.     

Development of hypervelocity electromagnetic launchers

Interest has increased substantially during recent years in the application of electromagnetic launch (EML) technology for a variety of purposes. In part this increased interest is due to the recent availability of compact pulsed power supplies suitable for driving such launchers. Also, several successful EML experiments have provided encouraging results.

The history of electromagnetic launch is reviewed, the current status of the railgun is presented, and plans for the next generation of electromagnetic launchers are discussed.     

Elastic waves and solid armature contact pressure in electromagnetic launchers

Electromagnetic launchers suffer a phenomenon referred to as armature transitioning: when the armature and rails suddenly lose contact with each other, damage can occur to the armature and the rails of the launcher. In this paper, we explore transient elastic waves as a possible explanation for the transitioning of solid armatures in electromagnetic launchers. We use a finite-element code to model the transient dynamics of a typical electromagnetic launcher guide rail. We found that dynamic rail deflections caused by the movement of the armature are similar in magnitude to those caused by the magnetic field, and that the contact pressure between the armature and the rails changes dramatically when the speed of the armature reaches the critical velocity of the rails.     

EMET technology for rail launchers

The EMET concept is a marriage of electrothermal plasma jet technology with rail accelerators using plasma armatures. By injecting a structured plasma immediately behind a moving projectile prior to the current pulse, the plasma armature properties can be highly controlled. Parameters of interest are the armature mass and length, molecular weight, specific heat ratio gamma, and temperature. Proper control of these parameters leads to control of problems facing rail launchers such as wall ablation and viscous wall drag. In support of EMET, a Material Test Facility (MTF) has been developed for performing basic physics and materials research on hypervelocity launchers, by making direct measurements of the plasma pressure and jet velocity in a 1 cm bore. These measurements are then compared with theoretical models for various types of plasmas, in order to understand and eliminate barrel ablation. The paper discusses measurement techniques used on MTF, and the approaches being taken to develop EMET in the laboratory.     

Review of impact fusion concepts [EM launchers]

The authors review the main features of the impact fusion concept in which gram-sized metallic projectiles from electromagnetic launchers collide around heavy-hydrogen fusile gas to produce thermonuclear plasma whose pressure brings the projectiles to rest, providing a pulse of fusion power during the `turnaround' of the projectiles. They discuss the concepts of nonmagnetic as well as magnetically insulated, impact fusion, showing how its potential advantages as an inertial confinement system could be realized. Of particular interest is magnetically insulated impact fusion, where the decreased plasma heat loss may allow lower impact velocities, consistent with the nearer-term state of the art of electromagnetic launchers. Also considered is the concept of mechanical helicity injection that allows both convenience and flexibility in producing the final magnetic configuration     

The way ahead [EM launchers]

The author discusses the history and future of electromagnetic launchers, focusing on linear induction machines for producing standstill forces, for propelling high-speed vehicles, and as accelerators for producing kinetic energy. He refers to his own experience to illustrate the points made. Conclusions concerning fruitful directions for future research are drawn     

Analysis of helical brush commutation

Helical launchers are a logical candidate for launching large masses at intermediate velocities. Because of their simplicity and high efficiency it is worthwhile to consider their limitations in the higher velocity regime ( v > 1 km/sec) where the brush commutation process becomes of central importance. In an effort to establish these limits the physical principles of helical brush commutation are presented.     

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.     

从部队教学,训练实践谈测试中的几个问题

本文结合炮兵部队及炮兵院校在兵器弹药，射击指挥教学，训练和火炮实弹射击任务的实践中，提出有关测试方面的几个具体问题及建议。与专家和同仁共商。     

Ohmic heating losses in cryoresistive pulsed energy storage aluminium inductors for electromagnetic launchers

Analytic procedures are developed for calculating the ohmic heating loss for various cryoresistive magnetic energy storage coil configurations that are used to deliver periodic short huge bursts of energy to electromagnetic launchers (railguns). Simple geometries such as long solenoids, continuous winding toroids, low aspect ratio dipoles or straight wire are considered as examples. The effect of cabling on reducing eddy current losses is addressed in detail.     

Pulsed power requirements for electromagnetic launchers

Both linear (railgun) and coaxial (mass driver, etc.) electromagnetic launchers (EMLs) are treated as time-varying impedances to determine the relationships between acceleration force, payload velocity, and power supply voltage and current. These relationships are then examined in the light of electromagnetic parameters associated with each EML type to establish a basis for determining and comparing power supply requirements for various EMLs.     

A comparison of armature performance

All electromagnetic launchers require that the launch package have an armature. The armature is the component in which the electromagnetic forces are generated. In this paper we examine "armature efficiency" as one measure of armature performance which permits direct comparison of metal, plasma, and hybrid armatures. Efficiency also translates directly to energy and power requirements. In this paper we examine the efficiency of metal and plasma armatures for rail guns. The operating regimes in which each type performs best are identified.     

Influence of the critical velocity on deformation of launcher components

This paper is related to the dynamics of hypervelocity electromagnetic launchers. A projectile accelerating along launcher rails may cross a range of critical velocities and induce structural resonance. As a result, the rails and other components exhibit increased displacements and stress that may affect launcher performance and lead to premature launcher failure. This work is a continuation of our previous studies of the critical velocity and resulting transient resonance that was performed for a notional hypervelocity launcher [Nechitailo NV, Lewis KB. Critical velocity for rails in hypervelocity launchers. In: Proceedings of the 2005 hypervelocity impact symposium. International Journal of Impact Engineering Dec. 2006; 33: 485–495; Lewis KB, Nechitailo NV. Transient resonance in hypervelocity launchers at critical velocities [Selected papers from the 13th Electromagnetic Launch Technology (EML) Symposium, Potsdam, Germany, May 22–25, 2006]. IEEE Transactions on Magnetics Jan. 2007; 43 (No. 1, Part II): 157–162 [1,2]]. Analytical models including Bernoulli–Euler model of a beam resting on an elastic foundation and the Timoshenko and Flügge tube models as well as finite element tools helped to better understand the transient resonant regimes in launcher components and offered insight on how to alter the launching device materials and geometry to reduce the critical-velocity effects. Analysis showed that the various components of a launcher can have different critical velocities and there is a possibility of enhanced group resonance in the assemblies. The resonance in the launcher assembly can be reduced by controlling the bending stiffness of the individual components. Finite element models were used to illustrate the influence of variations in materials of launcher components on the resulting critical velocities, intensity of the group resonance, and resulting maximum displacements and stress.     

Transient magnetic field and temperature modeling in large magnetapplications

A coupled magnetic/thermal model for studying heat and magnetic field diffusion in conducting materials subject to time-varying external fields has been developed, using the General Dynamics Thermal Analyzer code. Applications include energy storage devices, pulsed power transformers, and electromagnetic launchers, and the time scales of interest range from a magnetic field pulse of a microsecond to hundreds of seconds. The results of this model, showing the time and spatial variation of the magnetic field and temperature, are discussed for the projectile of an electromagnetic launcher     

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.     

The use of hypervelocity launchers to explore previously inaccessible states of matter

The dynamic response of materials at very high pressure and temperature is important in a wide variety of scientific and programmatic applications. Thermodynamic regions of interest include the high-pressure response of condensed phases and the highly expanded states of materials. Since these regimes are normally studied with flat-plate impact techniques, it is necessary that projectile velocities achievable with highvelocity launchers be sufficient to access the desired thermodynamic regions. In this paper, we discuss the equation-of-state regions that would be accessible with a plate impact capability of 15 km/s and summarize the status of a hypervelocity launcher under development which will provide the required velocity capability.     

Comparison of two post-calibration correction methods for complex permittivity measurement of biological tissues up to 50 GHz

Two correction methods are discussed in this paper to remove residual errors due to the lack of repeatability of coaxial-to-microstrip launchers as part of the TRL calibration procedure. These methods are applied for accurate insertion loss measurement of biological tissues embedded in a two-port microstrip test fixture, from which the tissues' complex permittivity values are extracted for frequencies between 15 and 50 GHz. In the first method, distilled water is used as a calibration standard as part of a two-port calibration procedure. The second method identifies an error transfer function using the difference between simulated and measured insertion loss for distilled water, and then applies it as a correction factor to the measurement results for biological tissues. Both methods are compared in terms of extracting the accurate complex permittivity of brain matter.     

A review of explosive accelerators for hypervelocity impact

A technical overview of experimental methods using high explosive techniques for conducting hypervelocity impact studies is presented. The explosive techniques use the explosive detonation fronts as means of accelerating the projectile, or as means of compressing a light gas which is then used to launch the projectile.

The explosive launchers are in six subdivisions: high explosive pellet accelerators, flyer plate accelerators, shaped charges, explosive-formed projectiles, fragment and microparticle accelerators, and explosive gas guns. Each one of the subdivisions presents the various techniques, their advantages and disadvantages, the range of mass and velocity capable of being accelerated, and whether the technique can be scaled for larger or smaller masses.     

Integrated design approach for advanced aerospace vehicles

Advanced aerospace vehicle design requires special design features that should meet the mission requirements of high payload to weight ratio in the case of space launchers and low radar cross-section for specific missiles/aircraft. The conventional design packages used are discussed in relation to their constraints. An interactive integrated design approach to eliminate the constraints imposed by individual design modules through interface design modules is discussed. Typical examples of such interface design modules are given. Also, a computer network necessary for an interactive integrated design approach interfacing the mainframe with a computer-aided design and drafting system and parallel processing is presented. This note has been prepared based on detailed discussions with designers in various areas of technology.     

Buckling analysis and design of anisogrid composite lattice conical shells

Composite lattice anisogrid shells have now become a popular choice in many aerospace applications. Their use in various structural components, such as rocket interstages, payload adapters for spacecraft launchers, fuselage components for aerial vehicles, and parts of the deployable space antennas requires the development of more advanced finite-element models and analysis techniques capable of predicting buckling behaviour of these structures under variety of loadings. A specialised finite-element model generation procedure (design modeller) is developed and applied to the buckling analysis of the composite anisogrid conical shells treated as three-dimensional frames composed of the curvilinear ribs made of unidirectional composite material. Featuring a dedicated control procedure for positioning the beam elements, the design modeller enables a close approximation of the original twisted geometry of the curvilinear ribs. The parametric finite-element buckling analyses of the anisogrid conical shells subjected to axial compression, transverse bending, pure bending, and torsion showed the robustness and potential of the modelling approach. It was demonstrated that the buckling resistance can be significantly enhanced by either increasing the stiffness of a few hoop ribs located in the close proximity to the section with the larger diameter, or by introducing the additional hoop ribs in the same part of the conical shell. The effectiveness of the design analyses is demonstrated using particular examples. It has been shown that the resultant optimised designs can produce up to 22% mass savings in comparison with the non-optimised lattice shells.