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The first goal of this work is to find a regression law for PVC (Polyvinyl Chloride) coupled to hydrogen peroxide on a 10-N-scale hybrid thruster, which appears to be suitable for small satellites when, for example, manoeuvres are required for orbital control purposes. Different techniques were initially analysed in order to reconstruct the ballistics inside the combustion chamber, starting from the experimental data. Subsequently, even if the different techniques lead to similar results, the one that takes into consideration the greatest number of the experimental measurements was chosen for the post-processing, and three different regression curves were obtained according to various criteria. The resulting regression laws coming from the selected method appear to be in agreement with the experimental results and constitute a powerful means for designing engines with this fuel. Finally, a performance analysis has been performed and in-space thrust and specific impulse have been estimated. PVC shows excellent performance and can be a good candidate for this type of applications, on a par with other more popular polymeric materials. [ABSTRACT FROM AUTHOR]

In this paper, we study the interior ballistic characteristics of rockets or missiles with acceleration less than 10 g during the compressed air ejection process. First, we designed and fabricated a full-size compressed air ejection system, and utilizing different missile mass and initial pressure variables. Then, we established the mathematical model of the interior ballistics of the ejection system using the fourth-order Runge-Kutta scheme to estimate the ejection performance and results of the system. In addition, we independently built a full-scale compressed air ejection system test platform and conducted multi-condition live ejection tests. The results show that the effective travel distance of the missile is greater than 2.5 m and the acceleration is basically less than 10 g. With a certain missile mass, the acceleration peak, velocity peak and displacement of the missile are positively correlated with the initial pressure, and the opposite variable is negatively correlated. The maximum acceleration and velocity values are 10.11 g and 13.5 m/s, respectively, and the minimum values are about 3.5 g and 4 m/s. The variables are the same, the pressure peak at each measuring point in the ejection barrel is bottom > middle > upper, and the amplitude of the pressure drop between middle and bottom gradually decreases. Depending on the appearance time of the pressure point, the maximum pressure attenuation time in the ejection barrel is determined to be 0.838 s, and the minimum is 0.343 s. Comparing the pressure peak points at the bottom, middle and upper with the calculated pressure curve, the attenuation trend of the two is basically the same. Therefore, the research results show that the full-scale compressed air ejection system is effective and practical, and the test results provide data reference for related launches. [ABSTRACT FROM AUTHOR]

Computational fluid dynamics is becoming a key tool for reducing the hybrid rocket operation uncertainties and development cost, but numerous challenges, due to the complexity of modeling the solid fuel consumption mechanism and the interaction with the reacting flowfield, have still to be addressed. These latter features are further complicated with paraffins for the melted-fuel entrainment phenomenon. This paper presents a computational thermo-fluid-dynamic model of the internal ballistics of hybrid rockets burning gaseous oxygen and paraffin-based fuel. With the purpose of predicting the local fuel regression rate, the model is coupled with an improved gas/fuel-surface interface treatment based on local mass, energy and mean mixture fraction balances, combined to an additional analytical equation for the calculation of the entrainment fraction of the fuel consumption rate. Parametric analyses are carried out to assess the effect of fuel properties on the regression rate. Several experimental test cases, obtained from static firing of a laboratory-scale rocket, are simulated. Calculated regression rates show an error with respect to the measured data around 10% in the worst case. Chamber pressure is predicted with lower accuracy, with errors less than 20%; the main factor of deviation is shown to be the estimation of the combustion efficiency. [ABSTRACT FROM AUTHOR]

Voronoi tessellation theory is applied to model the cells and ligaments in the open aluminum foam material. The cores of the cells are first generated by packing random spheres into the specified spatial domain. Weighted Voronoi tessellation is then applied to make the cellular structure of the foam material. For the open cell foam, the ligaments are created from the edges in the multiple polyhedron geometry. Hypervelocity impact simulation is conducted with the smoothed particle hydrodynamics method in LS-dyna. The finite element reconstruction technique is applied based on the particle output for the fragmentation analysis. The modeling and simulation techniques are verified by comparing the simulation results with testing results. The failure shown in the numerical prediction is consistent to the test result. The stress wave propagation in the foam material, which is extracted from the simulation output, is very different from that in the homogeneous material. The stress wave can only propagate inside the ligaments, and is diffused by the cellular structure. The important tensile failure pattern in the homogeneous material, which is generated by the reflection of the compressive wave on the free surface, is not observed in the foam material. The diffusion of the stress wave spreads the impact effect to a large area, leading to the enhanced dissipation of the impact energy, which increases the ballistic limit of the foam panel. [ABSTRACT FROM AUTHOR]

Sandwich structures usually are of particular importance in different industries including aerospace, marine and automotive due to their high performance and high energy absorption. In this research, the ballistic limit velocity of sandwich panels with wired core and aluminum face-sheets in normal impact with flat head cylindrical projectile has been investigated numerically and experimentally. It was also evaluated the effect of wire diameter and type of layout on the ballistic limit velocity of the panels. The diameter of wires was 4.44, 6, 8 and 10 mm and they were applied as core in 7 types of different layouts. Flat head steel projectiles with mass of 8.6 grams, diameter of 8 mm and length of 22 mm were impacted on the targets at velocities of 250–450 m/s. Results of this research showed that for the panels with the same mass, firstly, the ballistic limit was increased by reducing the wires diameter and increasing the number of their rows; secondly, reducing the distance between the wires also led to increase in ballistic limit and thirdly, the ballistic limit velocity of sandwich panel showed 45% increase with respect to a single-layer target with the same type and mass. [ABSTRACT FROM AUTHOR]

In this article, the ballistic impact response of square clamped fiber–metal laminates and monolithic plates consisting of different aluminum alloys is investigated using the ANSYS LS-DYNA explicit nonlinear analysis software. The panels are subjected to central normal high velocity ballistic impact by a cylindrical projectile. The implemented finite element models have been validated by comparison with published experimental data concerning GLARE 5 and monolithic 2024-T3 aluminum plates. Using the validated models, the influence of the mechanical properties of the constituent aluminum alloy on the ballistic resistance of the fiber–metal laminates and the monolithic plates is studied. Apart from 2024-T3, the aluminum alloys 2024-T351, 2024-O, 6061-T6, 7039 and 7075-T6 are considered. It is found that the ballistic limits of the panels can be substantially affected by the constituent aluminum alloy. The 7075-T6 aluminum alloy offers the highest ballistic resistance whereas 2024-O aluminum alloy offers the lowest ballistic resistance. [ABSTRACT FROM AUTHOR]

Numerical and non-linear internal ballistics analyses are conducted to investigate the performance characteristics of a pintle reciprocating in a nozzle. A conformal sliding mesh is successfully implemented to maintain smooth and continuous flow properties at the boundary of a moving pintle block. The proper mesh size is determined via a grid dependency test. The pintle nozzle operates under over-expansion conditions so that flow separation occurs at the nozzle wall at certain pintle stroke positions. Both the chamber pressure and thrust have hysteresis loci to allow for the reciprocation of the pintle's insertion and extraction motions, which have different trace-to-pintle speeds. The hysteresis loci reduce as the pintle speed increases. The thrust coefficient (rather than the thrust itself) is able to precisely determine the effects of the nozzle flow separation on overall performance. [ABSTRACT FROM AUTHOR]

A track-to-track fusion method to combine local estimates modeled with Gaussian mixture model is proposed for tracking a re-entry ballistic vehicle. An arbitrary power of a Gaussian mixture distribution is approximated with Gaussian mixture model using first order expansion approximation, which leads to an analytical fusion equation for approximate Chernoff fusion. In the end, we verify the effectiveness of the proposed fusion algorithm with a series of Monte Carlo simulations. [ABSTRACT FROM AUTHOR]

Electrodynamic tethers (EDT) represent one of the possible means to de-orbit defunct satellites from Low-Earth-Orbit at end-of-life. However, considering the large area exposed to the space environment and the consequent high number of debris impacts per unit time, a high tether survivability to orbital debris is of primary importance. This paper provides an estimation of the number of fatal impacts per unit time and per unit length on a tape tether, using for the first time an experimental ballistic limit equation that was derived for tapes and accounts for the effects of both the impact velocity and impact angle. It has recently been shown that, tape tethers, as opposite to round wires, are more resistant to space debris impacts. It is shown that considering a tape tether with cross section 45 mm × 50 μm , the number of critical events due to impact with non-trackable debris is always less than 0.01/yr/km, being maximum for orbit inclination of i = 90 ° . [ABSTRACT FROM AUTHOR]

The erosive burning of solid rocket propellant is an area of concern for high L/D rocket motors. Several explanations for the different causes for this phenomenon exist along with the modelling practices to predict the effects based on these causes. Universal nature of the erosive burning process was proposed by Mukunda and Paul irrespective of size, shape and type of the propellant. In the present work, the same model is applied for cylindrical port motors with high and moderate mass flux, as well as finocyl grain motors. It is observed that for cylindrical port motors, computed pressures with the burning time match very well experimental data. A modified form of the model (which becomes the original model for axisymmetric port) is used for finocyl geometries and a good prediction of pressures is observed. This study confirms the universality of the Mukunda and Paul model in its modified form which addresses non-axisymmetric port geometries also. The simplicity of the model makes it a useful tool for design and analysis of solid rocket motors of any size and port geometry. [ABSTRACT FROM AUTHOR]

This paper deals with interior ballistics of hydro-reactive motors. The propellant consists of water as the main oxidizer and the fuel rich pyrotechnic as a solid fuel. The effects of water on the propulsive characteristics of this propellant are investigated. It is shown that raising the amount of water increases the pressure and thrust as well as specific impulse. An experimental study has been conducted in order to approve the feature of the hydro-reactive propulsion systems. A binary mixture of magnesium and sodium nitrate powders with mass fractions of 0.75 and 0.25, respectively, is selected as a solid fuel. Three tests have been performed at different levels of water mass flow rates. The data were reduced from the tests and average values of characteristics were extracted. The results confirm the predicted trend of the effects of water on the behavior of propulsive characteristics. The specific impulse of about 400 s has been achieved at chamber pressure of about 22 bar and water mass ratio of 0.74. It is expected that introducing higher values of water mass fractions increases the specific impulse. The results show that the motor behaves with more stability at this condition. [ABSTRACT FROM AUTHOR]

The presence of large angles of attack at any stage of the flight path is a primary source of dispersion in free-flight motion of finned bodies. Nonlinear extensions of the aeroballistic theory are usually carried out with the addition of symmetry-preserving cubic terms to the linear aerodynamic coefficients. However, the roll-orientation dependence of the static yaw moment requires a better modeling. Based on the Maple–Synge expansion, a high order representation of the yaw moment is utilized to derive a simplified equation of the yawing motion, which shows good agreement with the exact solution, even with large angle-of-attack oscillations. The approximate equations can be useful to perform analytic studies on the coupled yawing and rolling motions, in particular, to determine their steady states based on nonlinear aerodynamic coefficients obtained from experimental data. [ABSTRACT FROM AUTHOR]