Hypervelocity Launchers Research Articles

Hypervelocity launchers for satellite structures orbital debris characterization

Orbital debris poses increasing threats to the space environment because of increasing space activities, therefore on-orbit hypervelocity impact should be simulated using the experiment by launch projectile into the target. Generally, ground-based experiments include three major sectors: projectile launch, impact monitoring including shock wave and debris cloud formation imaging, and finally result processing. For ground-based hypervelocity impact tests, various acceleration techniques such as light two and three-stage gas guns, plasma accelerators, electrostatic accelerators, and shaped charge accelerators have been used. This paper will primarily focus on those that are most relevant to current research on hypervelocity tests and would improve current research in the field of hypervelocity impact tests on composite material for primary satellite structures.

Hypervelocity launchers for satellite structures orbital debris characterization

Orbital debris poses increasing threats to the space environment because of increasing space activities, therefore on-orbit hypervelocity impact should be simulated using the experiment by launch projectile into the target. Generally, ground-based experiments include three major sectors: projectile launch, impact monitoring including shock wave and debris cloud formation imaging, and finally result processing. For ground-based hypervelocity impact tests, various acceleration techniques such as light two and three-stage gas guns, plasma accelerators, electrostatic accelerators, and shaped charge accelerators have been used. This paper will primarily focus on those that are most relevant to current research on hypervelocity tests and would improve current research in the field of hypervelocity impact tests on composite material for primary satellite structures.

Down-Bore Velocimetry of an Explosively Driven Light-Gas Gun

Hypervelocity launchers are used in a number science and engineering applications. The ability of the two-stage light-gas gun to launch relatively large and well characterized projectiles to hypervelocity has made it the launcher of choice for a wide range of hypervelocity impact research fields. However, practical concerns typically limit launcher operation to 8km/s. This work will present the development of an explosively driven light-gas gun in which the linear implosion of a thin walled steel tube is used to dynamically compress helium gas, which subsequently expands to propel a projectile. Despite modest development efforts, the implosion-driven launcher has demonstrated the ability to launch a 0.36-g projectile to 10.4km/s. This study will focus on a down-bore velocimetry experiment of an implosion-driven launcher using a photonic Doppler velocimetry system which was able to track the projectile velocity up to 7.8km/s. The observed projectile acceleration is significantly higher than internal ballistic model predictions. It is proposed that mixing of ablated wall material with the light gas in the launcher driver is responsible for the anomalously high projectile acceleration.

A Potential Approach to Launch Hypervelocity Projectiles up to 10 km/s Based on Two-stage Gas Gun Facilities

On the basis of Sandia's third-stage launcher, a new scheme of hypervelocity launchers is brought forward for purpose of propelling a one-gram-weight projectile in the shape of sphere or cylinder upwards of 10km/s. It includes an assembly of a sabot, a projectile and a steel impactor, and a hypervelocity launcher (HVL) that is attached to the muzzle end of two-stage light gas gun (LGG). With a specially designed sabot for LGG, the projectile together with the ring-shaped impactor being fixed on the sabot is first driven by LGG to a speed of 6-7km/s. The projectile will gain the secondary acceleration in the HVL synchronously controlled by the high-speed impactor.Three kinds of designs are put forth for a HVL with propelling media of explosive, epoxy resin, or hydrogen respectively. To accomplish the sabot/projectile separation and secondary driven of the projectile, enormous computations have been performed to attain an optimized configuration of the sabot and the HVL. For the launcher using explosive, the projectile is driven by gas productions resulted from strong detonation. It is illustrated by simulations that a 1.03g spherical projectile of 2024 alloy can be accelerated from an injection velocity of 6km/s (LGG launching speed) to 9.6km/s without extremely large deformation and spall damage. To launch a cylindrical projectile with constrained deformation, an improved design for HVL is achieved with adoption of a secondary impactor and an epoxy resin ring in place of explosive. It is capable of propelling a cylindrical projectile from 6km/s towards 8km/s by converging gas production of decomposition of epoxy. In the third design for a HVL, a pressure container with hydrogen is embedded in the tube of a HVL in an attempt to drive a projectile with hydrogen. Preliminary simulations reveal that a projectile (chunk plate) is possible to be accelerated towards 10.6km/s at initial hydrogen pressure of 7MPa, and towards 12km/s at an increased pressure of 20MPa. Enormous efforts are still required, however, to put this scheme into practice.

Enhanced Performance of Electrothermal Plasma Sources as Fusion Pellet Injection Drivers and Space Based Mini-Thrusters via Extension of a Flattop Discharge Current

Electrothermal plasma sources have been introduced as a method to propel frozen hydrogenic pellets for fueling of future magnetic fusion reactors. These sources are also useful as mini-thrusters in space shuttles, pre-injectors in hypervelocity launchers and igniters in electrothermal-chemical Guns. The source is a capillary discharge that generates the plasma from the ablation of a liner in an ablation-dominated regime, or from the flow of gas into the capillary in an ablation-free regime. Most electrothermal plasma sources uses pulse power delivery system with a pulse length in the range of 100 μs with FWHM of 50 μs. This research is a computational study on the effect of extending the top of the discharge current pulse to the range of 1,000 μs on the source exit parameter to achieve higher pressures and better exit velocities. Calculations using 0.4 cm diameter, 9.0 cm length Lexan polycarbonate capillary source, using ideal and nonideal plasma models, show that extended flattop pulses at fixed amplitude produce more ablated mass which scales linearly with increased pulse length, however, other plasma parameters remain almost constant. Results suggest that quasi-steady state operation of an electrothermal plasma source may provide constant exit pressure and velocity for pellet injectors for future magnetic fusion reactors deep fueling.

An Algorithm for the Hypervelocity Launcher Simulation of High-Low Density Flyer Plates

In this paper, we present a numerical method to simulate the hypervelocity launcher (HVL) experiment in which the two-stage light-gas gun impact launches flyers to hypervelocity. HVL is a complex process in numerical simulation, which includes multi-materials, multi-interfaces, huge distortion, high densities and severe shock wave problems, etc. A two-step Euler high-resolution finite volume scheme is used to solve the multi-fluid hydrodynamic equations. The first step is the Lagrange step in which the computation cells are distorted to follow the material motion, and the second step is the Remap step where the distorted cells are mapped back to the Euler meshes. Based on the Volume of Fluids model (VOF) and parabolic piecewise method (PPM), a shock wave physics code named multi-fluid parabolic piecewise method (MFPPM) is developed to simulate the experimental configuration of the hypervelocity launchers and the resolution of the algorithm is also tested. We emphasize the distinguished features of the code that aid in understanding the sensitivity of hypervelocity launcher calculations to the numerical methodology. The MFPPM code is verified and validated by simulating a series of hypervelocity launcher experiments implemented in Sandia National Laboratories. Good agreements are shown when comparing the numerical results with experimental data. Besides, in our National Key Laboratory for Shock Wave and Detonation Physics Research, two new models of the high/low density (Tantalum/Titanium) flyer plates HVL experiment are simulated by the code. Again, the numerical results and experimental data agree well with each other.

Influence of the critical velocity on deformation of launcher components

Abstract 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 Flugge 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 Resonance in Hypervelocity Launchers at Critical Velocities

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> A projectile accelerating along launcher rails may cross a range of critical velocities and induce resonance. As a result, the rails and other components exhibit increased displacements and stress that may cause launcher failure. This work is focused on the computation of the critical velocity and investigation of the transient resonance in the assembly of a notional electromagnetic hypervelocity launcher. Several analytical and finite-element models were employed. Different models yielded a good correlation and aided in better understanding of the launcher dynamics. Analysis shows that various components of a launcher can have different critical velocities. The results of this work will further be used to develop a novel design approach based on the idea of controlling the intervals between the critical velocities to minimize the enhanced occurrence of induced resonance regimes in launcher assemblies. </para>

Critical velocity for rails in hypervelocity launchers

This paper is related to the dynamic and strength analysis and optimized design of hypervelocity electromagnetic launchers. Projectile motion along the rails at critical velocity is associated with damaging resonant regimes. These regimes reveal increased displacements and stress that can lead to failure of a launcher. To calculate critical velocity and to visualize dynamic deformations of the launcher we have developed two alternative approaches utilizing analytical and finite element models. The first approach employs a closed form analytical solution for critical velocity that is based on the Bernoulli–Euler model of a beam resting on an elastic foundation and subjected to a moving load. The critical velocity is expressed as a function of geometric and material parameters of the rail and equivalent stiffness of the supporting structure. The stiffness of the supporting structure is found from a 2D finite element model. In the second approach, we employed beam finite element and 3D solid finite element models to visualize and measure the “natural” and “forced” bending waves traveling along the rails. These approaches helped to better understand the transient resonant dynamic processes and offered insight on how to alter the launching device materials and geometry to reduce the critical-velocity effects.

Ram-accelerator: A new hypervelocity launcher for ballistic studies

Summary Investigations are conducted at ISL on new hypervelocity launchers to fulfill requirements in different fields of ballistics such as launching dynamics, aeroballistics, terminal ballistics, aerothermodynamics, and supersonic combustion studies. One objective considered is to determine the operational conditions to accelerate a 90mm-caliber projectile with a mass of ~1.5kg to a velocity of 3km/s while keeping the acceleration level below 40,000g. This moderate level of acceleration is required to investigate at high velocities models that are fragile because of their design and/or their onboard opto-electronical equipments. A means to fulfill these velocity and acceleration requirements is ram-accelerator technology. This paper presents research conducted at ISL with smooth-bore ram-accelerators in the thermally choked propulsion mode. Therefore, two accelerators in calibers 30 and 90mm respectively, operated within the launch room of the aeroballistic range facility are described. Experimental results are presented describing the two-fold strategy followed to achieve the maximum performance, i.e., optimization of the projectile configuration and optimization of the combustible gas mixtures. To date a maximum velocity of about 1985m/s has been achieved with the 90mm accelerator (projectile mass = 1.34kg, ram-section length 16.2m, injection velocity in the ram-section 1330m/s) and 2380m/s with the 30mm accelerator (projectile mass 68.6g, ram-section length 9m, injection velocity in the ram-section = 1380m/s). Potential applications of ram-accelerators for ballistic studies are discussed and performances compared to those of conventional launchers that are currently used at ISL for ballistic studies. Finally, very first preliminary experiments are presented describing the acceleration of high l/d rods using a ram-accelerator.

Computational design of hypervelocity launchers

The S andia H ypervelocity L auncher ( HVL ) uses two-stage light-gas gun impact techniques to launch flier plates to velocities in excess of 10 km/s. An important requirement in designing successful third stage techniques for impact launching fliers to such velocities is detailed understanding of the interior ballistic performance of the third stage. This is crucial for preventing melt and fracture of the flier plates during the extraordinary accelerations that they undergo (10 9 g). We seek to optimize HVL launch conditions in order to achieve two major goals: first, to maximize the potential launch velocity for a given flier, and second, to allow different flier configurations. One tool that we have applied in studying HVL performance are multi-dimensional wave propagation codes, particularly the Sandia Eulerian code CTH. Recently this work has culminated in a major contribution to HVL design, namely the capability to launch “chunk” fliers. The initial phases of design development were solely devoted to CTH computations that studied potential designs, identified problems, and posed possible solutions for launching chunk fliers on the HVL. Our computations sufficiently narrowed the design space to the point that systematic experimental progress was possible. Our first experiment resulted in the successful launch of an intact 0.33 gram titanium alloy chunk flier to a velocity of 10.2 km/s. The thickness to diameter ratio of this flier was approximately 0.5.

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.

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.

Testing of a homopolar generator, energy storage inductor, opening-switch railgun system

The first homopolar-fired railgun system was operated in Canberra in 1972 [1,2]. Since that time two additional systems have been tested, the EMACK homopolar generator (HPG) built by Westinghouse and operated by Army Research and Development Center (ARDC) [3] and the joint effort by The Center for Electromechanics of The University of Texas (CEM-UT) and General Dynamics in 1982 [4]. This paper describes the homopolar railgun system operated by CEM-UT in 1985. The aspect that makes this system different from the previous experiments is the design of a fast opening switch (10 to 20 µs) that will allow operation of the HPG into hypervelocity launchers.

The 1986 hypervelocity impact symposium: October 21–24, 1986 municipal auditorium host hotel: St. Anthony inter-continental hotel San Antonio, Texas

A critical appraisal is made of the design, research, development, and operation of the novel UTIAS implosion-driven hypervelocity launchers and shock tubes. Explosively driven (PbN6-leadazide, PETN-pentaerythritetetranitrate) implosions in detonating stoichiometric hydrogen-oxygen mixtures have been successfully developed as drivers for hypervelocity launchers and shock tubes in a safe and reusable facility. Intense loadings at very high calculated pressures (almost megabar range), densities (g/cm3) and temperatures (thousands °K), at the implosion centre, cause severe problems with projectile integrity. Misalignment of the focal point can occur and add to the difficulty in using small calibre (6–8 mm dia.) projectiles. In addition, the extreme driving conditions cause barrel expansion, erosion, and possible gas leakage from the base to the head of the projectile which cut the predicted muzzle velocities to half or a third of the lossless calculated values. However, in the case of a shock-tube operation these difficulties are minimized or eliminated and the possibilities of approaching Jovian re-entry velocities are encouraging. In a recent run using about 100 g of explosive PETN and 400 psi 2H2 + O2 a shock Mach number Ms ≈ 60 was obtained in air at an initial pressure of 1 torr in a 1.0-in.-dia. shock-tube channel. In addition, the use of focused, explosive-driven implosion waves may have many other physical and technological applications.

Appraisal of UTIAS implosion-driven hypervelocity launchers and shock tubes

A critical appraisal is made of the design, research, development, and operation of the novel UTIAS implosion-driven hypervelocity launchers and shock tubes. Explosively driven (PbN 6-leadazide, PETN-pentaerythritetetranitrate) implosions in detonating stoichiometric hydrogen-oxygen mixtures have been successfully developed as drivers for hypervelocity launchers and shock tubes in a safe and reusable facility. Intense loadings at very high calculated pressures (almost megabar range), densities (g/cm 3) and temperatures (thousands °K), at the implosion centre, cause severe problems with projectile integrity. Misalignment of the focal point can occur and add to the difficulty in using small calibre (6–8 mm dia.) projectiles. In addition, the extreme driving conditions cause barrel expansion, erosion, and possible gas leakage from the base to the head of the projectile which cut the predicted muzzle velocities to half or a third of the lossless calculated values. However, in the case of a shock-tube operation these difficulties are minimized or eliminated and the possibilities of approaching Jovian re-entry velocities are encouraging. In a recent run using about 100 g of explosive PETN and 400 psi 2H 2 + O 2 a shock Mach number M s ≈ 60 was obtained in air at an initial pressure of 1 torr in a 1.0-in.-dia. shock-tube channel. In addition, the use of focused, explosive-driven implosion waves may have many other physical and technological applications.