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This work presents the results of an experimental study of ice particle impacts on a flat glass plate. The experiment was conducted at the Ballistics Impact Laboratory of NASA Glenn Research Center. The main objective of the experiment was to gain understanding about the modifications needed to the experimental configuration for a future parametric study at a larger range of values for particle diameters and other parameters. This was achieved by studying the effect of the velocity of an impacting ice particle on the post-impact fragment size and distribution for a reduced range of impacting particle diameters. Pre-impact particle diameter and velocity data were captured with a high-speed side camera. Post-impact fragment data were captured in a single frame with a 29-megapixel camera located above and normal to the target. Repeat runs were conducted for ice particles with diameters ranging from 1.7 to 2.9 millimeters, impacting at velocities between 39 and 98 meters per second. The fragment areas were measured, and the corresponding equivalent diameters and histogram distributions were calculated. Analysis of the data showed that the average equivalent diameter for the fragments in a run was an order of magnitude smaller than the diameter of the impacting ice particle. The histograms for equivalent diameter distribution were nonnormal with long tails, with most of the fragments having equivalent diameters concentrated toward the minimum value of the fragment size that could be resolved. Factors affecting the accuracy of the data during the digital imaging analysis were identified. Needed modifications to the setup to handle small size ice particles and other testing conditions were also identified.

Proof-of-principle experiments of in-tube propulsion in which the propellant was supplied from the launch tube wall were conducted. The launch tube had a 25 mm × 25 mm square inner cross-section. A pair of opposing launch tube walls were made of polyacetal (POM), which was ablated using repetitive Transeversely-Excited Atmospheric (TEA) CO2 laser pulses. The laser beam was sent through a ZnSe window at the tube bottom to the symmetric parabolic surfaces of the projectile, and focused onto the ablator surfaces. The momentum coupling coefficient was measured from a vertical launch trajectory. When the breech of the launch tube was plugged, a momentum coupling coefficient of 4 mN-s/J at least was obtained. Even when the breech was connected to a vacuum chamber at a pressure lower than 20 Pa, the projectile could be vertically launched with a constant momentum coupling coefficient of 0.14 mN-s/J, the value of which was the same order as that obtained by directly irradiating a laser pulse onto a POM ablator.

Detailed theoretical studies have been carried out to examine the variation of ignition transient on identical motors with different ignition delay. Igniter ballistics and propellant properties are varied for getting different ignition delay. We observed that the altered variation of ignition delay will alter the flame spread and thereby the overall ignition transient history of identical solid rockets. Significant peak pressure variation is observed in the case of solid motors with non-uniform ports. We concluded that, after maintaining the constant igniter ballistics, the designer can reduce the peak pressure by altering the surface condition by pasting high conducting material over the surface of the propellant. Such a change in thermal conductivity can be easily achieved by slightly altering the metal loading in the propellant. This ratiocinative approach will help the designer in reducing the peak pressure by altering the propellant ignition properties and the igniter characteristics without sacrificing the basic grain configuration or the volume loading.

The Army Research Laboratory has developed a scaleable, 3D, multiphase, computational fluid dynamics (CFD) code with application to gun propulsion (interior ballistics) modeling. The NGEN3 code, which incorporates general continuum equations along with auxiliary relations into a modular code structure, is readily transportable between computer architectures and is applicable to a wide variety of gun propulsion systems. Two such systems are the Army's Modular Artillery Charge System (MACS) and the Future Combat System (FCS). The MACS is being developed for indirect fire cannon on both current and developing (e.g., Crusader) systems. The efficiency of the MACS charge is dependent on proper flamespreading through the propellant modules; a process that has been repeatedly demonstrated in gun firings, successfully photographed using the ARL ballistics simulator, and numerically modeled using the NGEN3 code. The FCS requires weapons systems exhibiting increased range and accuracy. One of the technologies under investigation to achieve these goals is the electrothermal-chemical (ETC) propulsion concept, in which electrically generated plasma is injected into the gun chamber igniting the high-loadingdensity (HLD) solid propellant charge. NGEN3 code development and application to the MACS and FCS is currently a DoD HPC Challenge Project (No. 112) and is being greatly advanced by access to the DoD high performance computers (HPCs). Associate Fellow AIAA. Propulsion Physics Team Leader, Ballistics and Weapons Concepts Division, Weapons and Materials Research Directorate. Mechanical Engineer, Propulsion Physics Team, Ballistics and Weapons Concepts Division, Weapons and Materials Research Directorate. This paper is declared a work of the U.S. Government and is not subject to copyright protection in the United States. INTRODUCTION A solid propellant gun system consists of a reaction chamber connected to a gun tube through which a projectile is guided once propelled by pressurization of the chamber. Chamber pressurization is accomplished by placing a solid propellant (SP) charge in the chamber and igniting it by various means. Current SP charges are generally complex structures consisting of hundreds or even thousands of distinct regularly formed (e.g., spherical, cylindrical) grains, which may be loaded in either regular or random arrangements. In addition to small-scale voidage between grains (i.e., porosity) many charges also contain large-scale voidage (i.e., ullage), which surrounds the entire charge (such as when the charge does not fill the entire chamber volume) or separates distinct subcharges (i.e., increments or modules) that together comprise the whole charge. The addition of energy to the chamber, usually near the gun breech, or rearmost end of the chamber, and in some cases through a tube extending along the centerline of the chamber, ignites the SP. In general, all of the grains are not ignited simultaneously, but an ignition flame spreads from the breech to the projectile base. The burning of the SP transforms chemical energy into heat as hot gases evolve from the surface of each grain of propellant. Initially the projectile resists movement allowing the pressure in the chamber to climb rapidly. Since the burn rate of the propellant is proportional to the pressure, hot gases are produced at an accelerated rate until peak pressure is reached in the chamber. Movement of the projectile down the gun tube, usually slight before peak pressure and much more significant afterwards, causes the chamber volume to increase, and generates rarefaction waves, which lower the pressure and thus the burn rate of the propellant. Upon ignition and burning, the gas dynamic flowfield in the gun chamber takes on a highly complex structure that includes the dynamics of propellant motion and combustion and various gas dynamic flow phenomena such as turbulent mixing, highly transient pressure waves, steep gradients in porosity and temperature, nonideal thermodynamics, and gas generation.

Thefundamentalsoftheinternalballisticsofsolid-propellantnozzlelessrocketmotorshavebeenstudiedtheoreticallyandexperimentally.Aimedatthemajorbasicaspects,thetheoreticalanalysisconsistedofaquasi-steady-state one-dimensionale ow ofa perfect gas in a constant-area port, assuming a uniform burning rate along the grain asa resultofthecompensating effectsoferosiveand pressure-dependentburning contributions.Thesimplie edanalysis has beenfound to be an excellent tool to exhibit fundamental characteristics. Itrevealed that thetheoreticalachievable specie c impulse in a nozzleless rocket cannot exceed approximately 86% of its value in an adapted-nozzle rocket operating at the same average chamber pressure. An experimental parametric study using cylindrical propellant grains has demonstrated good agreement with the major parameters addressed in the theoretical analysis, indicating that the assumption of a uniform burning rate is a realistic approximation.

The ignition transients and penetrative burning characteristics of confined granular propellant beds in a cylindrical tube (loading densities up to 1.03 g cm3 and pressures up to 4000 bar) were investigated to test the 1-D pressure-wave propagation profiles predicted by the 1971 Kuo-Vichnevetsky-Summerfield analytical model. Thus, it was found that following the initial pressure rise along the bed, the position of peak pressure occurs within the bed and progresses downstream at an accelerating rate. The ignition time of the granular bed increases sharply with decreasing loading density. Wall friction acting on the unburned propellant along the tube attenuates downstream transmission of solid phase pressure generated by the upstream burning processes. This work has applications to the internal ballistics of guns, deflagration to detonation transition, and fast-burning rocket charges.

The intense radiation from the arc in a railgun may cause vaporization and partial ionization of rail and insulator material. The mass of material added to the arc can have a significant adverse effect on projectile velocity. A numerical model has been developed to predict the change in mass of the arc as a function of several parameters. That model has been incorporated in the Los Alamos Railgun Estimator (LARGE) code and simulations have been run to assess the accuracy of the model. Analytical predictions were found to be in good agreement with experimental data for railgun tests run at Los Alamos. Ablation appears to have a significant effect on railgun performance.

The internal ballistic effects of combined radial and circumferential grain temperature gradients are evaluated theoretically for the Space Shuttle solid rocket motors (SRMs). A simplified approach is devised for representing with closed-form mathematical expressions the temperature distribution resulting from the anticipated thermal history prior to launch. The internal ballistic effects of the gradients are established by use of a mathematical model which permits the propellant burning rate to vary circumferentially. Comparative results are presented for uniform and axisymmetric temperature distributions and the anticipated gradients based on an earlier two-dimensional analysis of the center SRM segment. The thrust imbalance potential of the booster stage is also assessed based on the difference in the thermal loading of the individual SRMs of the motor pair which may be encountered in both summer and winter environments at the launch site. Results indicate that grain temperature gradients could cause the thrust imbalance to be approximately 10% higher in the Space Shuttle than the imbalance caused by SRM manufacturing and propellant physical property variability alone.

A transient ballistics and combustion model is derived to represent the closed vessel experiment that is widely used to characterize the high pressure burning rates of solid propellants. The model is applied to explain why burning rates deduced from the closed vessel are in basic agreement with those measured from an equilibrium strand burner in the case of homogeneous propellants, but differ significantly in the case of nitramine composite propellants. Thermal profile time lag effects become small at high pressure because the burning rates become high. However, the development of the burning surface structure of those nitramine propellants which exhibit shifts in pressure exponent causes the mass burning rate to lag and then exceed the equilibrium value. It is necessary to consider this mechanism in applications dealing with high pressures and pressurization rates.

on results that illustrate the importance of wall ablation. Section 111 develops a simple model of a plasma armature incorporating wall ablation. The model is applied first to the analysis of a constant current railgun to show how ablation affects railgun behavior and then to the experimental data of Section 11. Section IV develops an extension to the simple ablation model that includes viscous drag on the arc plasma. Again comparisons with the data of Section I1 support the inclusion of viscous drag as an important process in railguns. Finally, in Section V the future of plasma armature railguns is examined with particular emphasis on scaling to large devices and techniques to eliminate Parametric measurements have been performed on a plasma armature railgun at Las Alamos. The railgun is extensively instrumented for studies of the projectile motion and its interaction with the plasma armature. The most important parameter, driving current, was varied from 100 kA to 400 kA. Additional parameters investigated include current waveform, injection velocity, injection gas, wall insulation material, and initial pressure. For all combinations of parameters investigated, the measured performance was substantially below theoretical or control the ablation process. predictions. A strong correlation was found between performance loss and abnormal plasma armature features such as multiple arc formation, or separation of the armature from the projectile. In extreme cases, the plasma armature was observed to come to rest inside the railgun. A plasma armature model has been developed which successfully accounts for the measured performance loss and for many of the abnormal plasma armature features. By incorporating the ablation of wall material into the armature plasma thismodel predictstwo parasitic forces that dominate the motion of the armature at high velocity. One force is the inertial drag term mav. The other is frictional drag between the hot, turbulent plasma and the walls, which increases as m,v2. Simple scaling relations, which incorporate the plasma I. Experimental Apparatus The experimental results reported below were obtained with the HYVAX Phase I (HYVAX-I) railgun. The HYVAX railgun is a high performance modular device designed for distributed operation. It has a design length of 13 m and a theoretical velocity capability of 25 km/s at a design current of 500 kA. HYVAX-I consists of two 1.22 m long barrel modules and three 0.30 m long current connection modules from the H W A X device. The modules are assembled as a single stage railgun with an effective lenmh of2.5 m. A cross section ofthe barrel is shown ~ armature model, rho; that velocities >IO km/s wil l he ex. tremely dificult to achieve with plasma armature railguns unless the effects ofablation are eliminated or carefull, controlled.

vibration and gives information on the relative importance of various elements to system stability. To eliminate the vibration, hydraulic accumulators were placed in the propellant suction lines near the pump inlets. This is shown schematically in the left fuel line in Fig. 2. The accumulator is a spring mass device that alters the dynamic characteristics of the suction line. By proper choice of accumulator constants, the propulsion system can effectively be decoupled from the structure. Mathematically, the accumulator is included in the model through the equation

Range, wind tunnel, and instrumented free-flight tests have shown that a subcaliber boom at the base of a spin-stabilized projectile will produce significant changes at both small and large yaws. Almost all properties, but in particular the static and magnus moments, are affected. These aerodynamic changes, together with the inertial properties of the shell, are shown to affect both the static and the dynamic stability adversely.