A special design condition to increase the performance of two-stage light-gas guns

This paper reports a theoretical and numerical study aimed at increasing the operating efficiency of two-stage light-gas guns by appropriately changing their working conditions. In particular, a method is presented for increasing the projectile speed without any rise of the maximum breech pressure. The classic design theory of two-stage guns starts from the assumption that the highest velocity is reached in a gun which constantly maintains the maximum acceptable pressure at the base of the projectile during the full launching time. The main drawback of this working condition is that it may require an unfeasible rise of the gun maximum pressure, especially when very high muzzle speed is requested. To overcome this limitation, a new reference case different from the constant-base-pressure one is presented, based on a novel gas-dynamics solution that can be expressed in exact form if losses are not accounted for. According to such an approach, it is theoretically shown that the projectile base-pressure can be appropriately shaped (i) to improve the final speed without increasing the breech pressure or, in other terms, (ii) to achieve a given muzzle velocity with reduced maximum gas pressure. The analytical application of the new gas-dynamics condition showed the capability of obtaining a 1 km/s velocity improvement with no increase of the breech pressure or, alternatively, a pressure reduction up to 30% with no penalty on the model final speed. A numerical verification of the calculations was performed through the CISAS light-gas gun full numerical model, which includes real effects such as friction losses and heat transfer. Finally, an experimental verification of the numerical test case was attempted and a speed augmentation of 0.8 km/s with no increase in the breech pressure was confirmed in laboratory, highlighting the agreement with numerical predictions.     

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.     

Micrometeorite impact simulation at EMI — a review

Activities at EMI in the field of hypervelocity impact techniques are reported. Optimization experiments have been carried out with a light gas gun in order to achieve projectile velocities up to 10 km/s. Different methods for measuring the projectile velocities have been developed and adapted according to respective velocity and mass ranges of projectiles. Experimental efforts have been undertaken to accelerate also microgram particles in light gas guns. Masses as small as 37 μg can be accelerated as individual particles. As examples, several contributions to recent space projects are described.     

Development of a three-stage, light-gas gun at the University of Dayton Research Institute

An elusive goal of the hypervelocity impact community has been the evaluation of the ballistic response of space hardware to impact velocities ranging from 8 to 11 km/s using projectiles with known properties. The design, development, and use, during the 1960s, of a three-stage, light-gas gun at McGill University is reviewed. The developers of this gun claim that they were able to launch cylindrical, 12.7-mm-diameter Lexan disks with masses of 1.5 and 1.1 g to velocities of 9.6 and 10.5 km/s, respectively. This paper presents the results of an internally funded program at the University of Dayton Research Institute (UDRI) to duplicate the published performance of the McGill University launcher. A support structure and various components of a third stage which used an 8.1-mm-diameter launch tube were added to the UDRI 75/30-mm, two-stage, light-gas gun, making the arrangement of the components similar to the one used by McGill University. Work on the development of the UDRI three-stage, light-gas gun is a continuing effort, with the goal of successfully launching small diameter (3 mm or less) aluminum spheres to velocities in excess of 9 km/s. To date, the highest projectile velocity achieved with the UDRI three-stage, light-gas gun has been 8.65 km/s.     

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.     

Hugoniot measurement by hyper-velocity impact at velocities up to 9 km/s using a two-stage light-gas gun under optimized shot conditions

The optimization for acceleration of a projectile was performed by varying piston mass in consideration with the correlation with projectile mass and the engineering limits of the two-stage light-gas gun, and the projectile velocity has been achieved 9.2 km/s using the optimum acceleration conditions. Moreover, the Hugoniot measurements of oxygen-free copper were performed using the line reflection method at pressures up to 380 GPa by symmetric impact. The tilt and curvature of shock front were investigated according to the impact velocity, and it is proved to be important that the continuous spatial profile of shock front would be recorded.     

Reverse impact experiments against tungsten rods and results for aluminum penetration between 1.5 and 4.2 km/s

Reverse impact experiments against 0.76 mm diameter L/D = 20 tungsten rods have been conducted with a 38 mm diameter launch tube, two-stage light-gas gun using four 450 kV flash X-rays to measure penetration rates. Techniques for projectile construction, sample placement, alignment, and radiography are described. Data for penetration rate, consumption velocity, and total penetration were obtained for 28 mm diameter 6061-T651 aluminum cylinders at impact velocities between 1.5 and 4.2 km/s. It was found that penetration velocity was a linear function of impact velocity over this velocity range. Above 2 km/s impact velocity, penetration was completely hydrodynamic. There was substantial secondary penetration, and the total penetration increased linearly with impact velocity over the range 1.5 to 2.5 km/s.     

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     

Aeroballistic and impact physics research at EMI an historical overview

On the occasion of the Distinguished Scientist Award presentation at HVIS 1992, the technical and scientific promotion of the Impact Physics Division at EMI in the field of aeroballistics, free flight dynamics, terminal ballistics and impact physics is described. This development is closely related to the work of the recipients.

The activities began in the late fifties when a small pressurized ballistic range with a gas gun was built. The problems to construct a well working facility with observation stations are reported that arose, at those early times, from the lack of experience, money and suitable locations. In the mid-sixties, the experimental possibilities were extended by building a two-stage light gas gun that could also be used as a gun tunnel. These facilities have been the foundation for research in the field of free flight aerodynamics, such as the study of near and far wakes behind a blunt hypersonic body or the study of shock wave boundary layer interactions. In 1972, the division took the first step into terminal ballistics and, because of increasing interest, impact physics became the main research area. The division grew and with it the instrumentation. Today, diverse gas guns, powder guns and two-stage light gas guns are in operation. One topic of main interest during the years has been the penetration of rod shaped projectiles. Here the best-known result may be mentioned, the so-called ‘Hohler-Stilp S-shaped penetration curves’. In addition to this, many other topics have been investigated that can be summarized under the title “penetration mechanics and impact physics”. Based on a well developed launching technique and instrumentation, problems were investigated at low velocities of a few hundred m/s, at ordnance velocities and especially at hypervelocities up to 10 km/s. It has been recognized that dynamic material behavior and microstructural effects play an important role in understanding the interaction of projectiles with targets. Therefore, a VISAR, an electronic raster microscope, a Hopkinson bar and further equipment have been installed. Basing on the work of a period of more than 20 years, EMI has come into contact with national and foreign institutions and has become a partner for many cooperations.     

Design limitations on ultra-high velocity projectile launchers

The maximum velocity attainable in a gasdynamic gun is limited by the maximum sound speed in the driver gas. For a conventional 2-stage light gas gun, the limit is 10 km/s. Higher velocities are possible, but probably not without the destruction of the gun barrel. As long as this occurs on a time scale longer than the residence time of the projectile, a useful system may still result. Using a newly developed computer code called IGUN, we have evaluated the performance of several multistage designs capable of achieving ultra-high projectile velocities. The main problem is in maintaining the integrity of the projectile. Our calculations indicate that 20 km/s should be achievable without fracturing the projectile. If it is only required to retain near original areal density, velocities in excess of 30 km/s appear feasible.     

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     

Programmed input of energy into the discharge chamber of a light-gas electric-discharge accelerator of bodies

The effect is investigated of the duration of electrical energy input into working gas and of discharge power profile on the launching velocity and efficiency of acceleration of bodies using a light-gas electric-discharge accelerator with a caliber of 30 mm. It is found that, for the same energy input to the arc or for the same pulsed pressure of working gas in the discharge chamber of the accelerator, the projectile velocity in the mode being programmed is 7–10% higher, and the efficiency of conversion of internal energy of working gas to kinetic energy of projectile is 2 or 3% higher, than those in the synchronous mode.     

Preliminary study of counter impact with two-stage light gas gun using electrothermal–chemical gun technology

Recently, hypervelocity impacts between space structures and space debris have been brought to attention with the advance of space development. The impact velocity at low earth orbit (LEO) is up to 15 km/s. Such impact velocity cannot be attained by the current two-stage light gas gun (TSLGG). Therefore we have a plan of counter impacts that used two sets of TSLGGs in order to raise impact velocity. There are three problems in order to realize the counter impacts. They are launch timing, recovery of target and alignment of gun axis. In this research, we considered launch timing of TSLGG among them. It is important to control variation of delay time from propellant ignition to projectile launch in the counter impacts. In a conventional TSLGG, combustion rate changes every time and impact position will vary widely. In order to stabilize combustion rate, we developed a new TSLGG that used the technology of electrothermal–chemical (ETC) gun for its 1st stage. In a conventional TSLGG, the variation of delay time is 20–30 ms. On the other hand, in a new TSLGG, we have succeeded in suppressing the delay time variation less than 200 μs. It is concluded that the TSLGG based on the technology of ETC gun is effective to control the delay time in this paper.     

Equation of state measurements of materials using a three-stage gun to impact velocities of 11 km/s

Results of an experimental series performed utilizing a three-stage gun to obtain precise material property equation of state (EOS) data for a titanium alloy (Ti6-Al-4V) at extreme pressure states that are not currently attainable using conventional two-stage light-gas gun technology is reported herein. What is new is the technique being implemented for use at engagement velocities exceeding 11 km/s. Shock-velocity in the target is being determined using 100 μm diameter fiber-optic pins and measuring shock transit times over a known distance between two parallel planes. These fiber-optic pins also indicate that the flyer-plate bow and tilt is comparable to two-stage light-gas gun technology. The thermodynamic state of the flyer plate prior to impact has also been determined both experimentally and calculationally. In particular, the temperature, and hence the density of the flyer-plate is also well known prior to impact. Results of these studies indicate that accurate Hugoniot information can be obtained using the three-stage light gas gun. This new test-methodology has extended the EOS of Ti6-Al-4V titanium alloy to stresses up to approximately 250 GPa.     

Computational design of hypervelocity launchers

The andia ypervelocity 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 (10⁹ 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.     

复合射孔技术综述

文章综合分析了复合射孔现有方法和技术,以及各种方法、技术的优点和不足.STIMGUN系统装药量大,作业效果好,避免了炸枪,可使用常规射孔枪;但有时不得不使用小直径射孔器.分体式复合射孔技术药量调整范围较大,不会炸枪,可使用常规射孔枪;不足之处是由于火药装药与射孔段不在同一层,气体利用效率较低.一体式复合射孔技术火药装药与射孔段在同一层位,火药产生的高压气体正对射孔孔道做功,效率高,作业效果好;缺点是装药量少,产气量较低,需使用带泄压孔的特制射孔枪,有时发生炸枪事故.双复射孔器可以适当扩大枪径,提高了射孔枪的承载能力,具有避免炸枪、环空峰压减缓、作用时间加长等特点.     

RDX和NGU对叠氮硝胺发射药动态燃烧稳定性的影响

以30 mm高压模拟炮为试验平台,以单基发射药为参照,研究了3种典型叠氮硝胺(DIANP)发射药的动态燃烧稳定性,分析了配方组成对DIANP发射药起始燃烧特征、膛内压力上升过程及膛内压力波动的影响,探讨了DIANP发射药配方组成与其起始燃烧特征、膛内压力上升特点和压力波强度的相互关系。结果表明,在DIANP发射药配方中添加质量分数30%的固体组分黑索今(RDX)或硝基胍(NGU),发射药膛内动态燃烧稳定性增加,膛压-时间曲线波动减小,膛压从30 MPa增至50 MPa所需的时间分别增加了92%和78%,起始负压差从－40.7 MPa降低至－4.44 MPa和－10.66 MPa。在DIANP发射药体系引入高含量的固体组分RDX或NGU,由于低压下RDX分解前熔融吸热,而NGU火药燃烧表面存在坚实熔融层,均可有效减小DIANP发射药起始燃气的生成速率,降低发射装药起始燃气生成猛度,缓减起始阶段膛内压力的上升,提高药床起始燃烧一致性,减小膛内压力波强度。     

Mechanical design aspects of the HYVAX railgun

The hypervelocity experiment (HYVAX) railgun (Fig. 1) is designed to produce projectile velocities greater than 15 km/s in a 13-m-long, round bore gun. The HYVAX gun incorporates a modular design enabling it to operate in either a distributed energy-storage mode or a single-stage mode. The gun is composed of seven O.3-m-long power input modules and nine 1.2-m-long accelerating modules. The gun is designed for a 100-shot life. To accommodate this, the bore may be enlarged from an initial diameter of 10.8 mm to a final diameter of 12.7 mm. This will allow the bore to be refinished several times during the life of the gun. To minimize mechanical and arc damage to the gun between bore refinishing operations, the gun will incorporate a low pressure helium projectile injector. Projectiles will be injected under vacuum at 350 m/s. The gun will be operated at a peak current and voltage of 600 kA and 6 kV respectively. The gun will undergo three phases of testing. The first phase will be the characterization of the gun's performance using a 3.0-m-long section of the gun comprising two power modules and two accelerating modules. This testing will be accomplished using two of the seven capacitor bank modules shown in Fig. 1. The second test phase will use a distributed power configuration and seven capacitor bank modules, as shown in Fig. 1, to demonstrate a velocity of 15 km/s with a 1-g projectile. The predicted performance of the gun for this test phase is illustrated in Fig. 2. In the third phase of testing we will use a magnetic flux compression generator (MFCG) to power the gun with a goal of demonstrating a velocity of 25 km/s.     

The electromagnetic θ gun and tubular projectiles

Unlike the better known rail gun, the θ gun applies the propelling force along the length of its projectile. This is shown to allow much greater acceleration of high fineness ratio projectiles for a given barrel pressure, allowing much shorter barrels for military applications. A computer code which simulates performance of the θ gun is described and experimental results from a few simple, low energy experiments show close agreement with code predictions. Trajectories and aerodynamic heating for three candidate military projectiles are calculated for vertical and horizontal atmospheric launches where initial velocity is as high as 3 km/s. The calculations indicate that in some cases a thin layer of heatshield (ablator) will be required to control projectile heating.     

High-velocity solid ejecta fragments from hypervelocity impacts

The recent discovery of meteorites from the moon and the strong probability that the 8 SNC (Shergottite, Nakhlite and Chassignite) meteorites originated on Mars indicate that large hypervelocity impacts eject some solid debris at very high speed (more than 2.5 and 5 km/sec in the above cases). The standard Hugoniot relation between particle velocity and shock pressure predicts that lunar ejecta should be very heavily shocked (40–50 GPa) and Martian ejecta should be vaporized (100–200 GPa). However, the lunar meteorite ALHA 81005 was in fact subjected to less than 15 GPa, while the most highly shocked SNC meteorite was exposed to ca. 50 GPa, while others showing no detectable shock damage at all.

Theoretical work shows that the normal Hugoniot relation doesn't apply in the vicinity of a free surface. The free surface is, by definition, a pressure-free boundary, so shock pressures on it must be identically zero. On the other hand, the acceleration of debris is proportional to the pressure gradient, so that near-surface material may be accelerated to high speed and still escape compression to correspondingly high pressure. This process occurs only in a restricted zone near the free surface. The thickness of this zone is proportional to the rise time of the stress-wave pulse generated by the impact.

The rise time of the stress wave generated by a large impact is typically a/v_i, where a is the projectile radius and v_i its impact velocity. The near-surface zone in this case is comparable in thickness to a fraction of the projectile radius. Since the cratering event itself displaces many thousands of times the projectile mass, the quantity of lightly-shocked, high speed ejecta is small, amounting to only a few percent of the projectile's mass (for ejecta speed>few km/sec). The fastest solid ejecta leave at about 1/2 the impact velocity.

Although the total quantity of high speed solid ejecta is thus small in comparison to the total crater ejecta, it is significant because no other process yields such high velocity fragments. Many meteorites appear to be near-surface samples of their parent bodies (many are regolith samples and one is a vesicular lava) and so may have been ejected by this process.