A Lagrangian model for debris cloud dynamics simulation

A new modeling approach has been developed for computer simulation of hypervelocity impacts on multi-plate orbital debris shields. This approach links an Eulerian finite difference code for shield perforation calculations to a Lagrangian finite element code for debris cloud evolution simulations. Mixture theory is used to account for the presence of void space in the debris cloud.     

Characterizing secondary debris impact ejecta

All spacecraft in low earth orbit are subject to high-speed impacts by meteoroids and orbital debris particles. These impacts can damage flight-critical systems, which can in turn lead to catastrophic failure of the spacecraft. In addition to threatening the operation of the spacecraft itself, on-orbit impacts also generate a significant amount of damaging ricochet ejecta particles. These high-speed particles can destroy critical external spacecraft subsystems, which also poses a threat to the spacecraft and its inhabitants. Since the majority of on-orbit debris impacts are expected to occur at oblique angles, the characterization of ricochet debris created in an orbital debris particle impact is an issue that must be addressed. This paper presents the results of a study performed to develop an empirical model that characterizes the secondary ejecta created by a high speed impact on a typical aerospace structural surface. Specifically, the model predicts the spread and trajectory of ricochet debris particles created in a hypervelocity impact as well as the size an velocity of the most damage particle in the ricochet debris cloud. Results obtained using the model are compared with experimental results and predictions obtained in a previous study.     

Hypervelocity impacts on gas filled pressure vessels

Space debris is a recognized threat for any Space Mission. Risk analyses have identified pressure vessels as the most critical items onboard spacecraft. Impacts of meteoroids or debris on pressure vessels can indeed lead to the catastrophic failure of the vessels and terminate prematurely spacecraft missions. In addition, pressure vessels bursts act as space debris generators. The aim of this work is to define experimentally the limit between simple perforation and catastrophic burst of pressure vessels under hypervelocity impacts. Targets have been selected according to the most immediate ESA needs : thin wall gas filled aluminium pressure vessels. Hypervelocity impact tests have been performed on aluminium vessels at a constant impact velocity (7 km/s) with aluminium projectiles, at a normal trajectory and, for most of the cases, on unshielded vessels. Projectile size and pressure in the vessels were varied to explore the conditions under which different damage mechanisms could be obtained. Results presented range from simple penetration holes and no visible damage on the internal wall opposite to the impact point to global burst of the vessel. While failure was thought to only occur from the side opposite to the impact point, certain combinations of pressure and projectile kinetic energy led to burst from the impact side.     

椭球弹丸超高速撞击防护屏碎片云数值模拟

低地球轨道的各类航天器易受到微流星体及空间碎片的超高速撞击.本文采用AUTODYN软件进行了椭球弹丸超高速正撞击及斜撞击防护屏碎片云的数值模拟.给出了三维模拟的结果.研究了在相同质量的条件下,不同长径比椭球弹丸以不同速度和入射角撞击防护屏所产生碎片云的特性,并与球形弹丸撞击所应产生的碎片云特性进行了比较.结果表明:在相同的速度下,不同长径比椭球弹丸撞击的碎片云形状、质量分布和破碎程度是不同的,随撞击入射角的增加弹丸的破碎程度增大,滑弹碎片云的数量增加;随撞击速度的增加,弹丸的破碎程度也增加.     

Hypervelocity impact damage to composites

This paper presents the results of hypervelocity impact tests conducted on graphite/PEEK laminates. Both flat plate and circular cylinders were tested using aluminum spheres of varying size, travelling at velocities from 2–7 km/s. The experiments were conducted at several facilities using light gas guns. Normal and oblique angle impacts were investigated to determine the effect of impact angle, particle energy and laminate configuration on the material damage and ejecta plumes. Correlations were established between an energy parameter and the impact crater size, spallation damage and debris cone angle. Secondary damage resulting from the debris plume on adjacent composite structures was studied using high-speed photography and witness plates. It was observed that for hypervelocity impacts, the debris plume particles have sufficient energy to penetrate adjacent structures and cause major structural damage as well.     

Development of a lightweight space debris shield using high strength fibers

In order to protect space structure against space debris impacts, it is indispensable to develop a shield with high strength materials. A high strength fiber is one of potential materials from a viewpoint of strength, lightweight, and flexibility. The purpose of this study was to develop a new lightweight shield composed of high strength fibers against medium size debris impacts. We developed four kinds of shields using Vectran fibers, and hypervelocity impact tests were carried out by a railgun accelerator. The experimental results showed that the developed shield could stop the polycarbonate projectile with 13 mm in diameter, 1 gram in weight, and 6.9 km/sec in velocity. Adoption of the high strength fiber in the bumper materials may reinforce the protection capability and reduce the weight drastically.     

Hypervelocity impacts on thin brittle targets: Experimental data and SPH simulations

The meteoroids and debris environment play an important role in the reduction of spacecraft lifetime. Ejecta or secondary debris, are produced when a debris or a meteoroid impact a spacecraft surface. Brittle materials are particularly sensitive to HVI in term of damages and amount of ejected matter: the ejected fragments total mass is in the order of 100 times bigger than the impacting mass. The French atomic energy commission (CEA) faces the same problem in the Laser MégaJoule project. The lasers optics will be bombarded by hypervelocity debris and shrapnel resulting from target disassembly. Two millimeter thick fused silica disposable debris shields (DDS) located in front of the main debris shields might be used to reduce very small shrapnel cratering on the main debris shields. The aim of this paper is to study the damaging and ejection processes that occur during HVI on thin brittle targets. A two-stage light-gas gun has been used to impact 2 mm DDS with 500 μm steel projectiles. Experimental characterization of ejected matter has also been performed: lightweight paperboards coated with adhesive have been used to collect ejected fragments including spalls. Numerical simulation using the smooth particle hydrodynamics (SPH) method of LS-DYNA and the Johnson Holmquist material model were performed. The results of these calculations are compared to experimental data which include the damage features in the targets (spalled zones and perforation hole) and the ejection clouds. Satisfying agreement between numerical and experimental simulations was obtained for damage characteristics and ejection phenomena.     

圆柱形长杆超高速正碰撞薄板结构破碎效应

超高速碰撞多层板结构破碎效应研究对空间碎片防护及动能武器毁伤效应研究有着重要意义。采用ANSYS/AUTODYN程序的SPH方法,对超高速碰撞碎片云的形成过程进行了数值模拟,某典型时刻一次及二次碎片云形貌的数值模拟结果与实验结果吻合较好,验证了计算方法和模型参数的正确性。在此基础上采用数值模拟方法,对钨合金、轧制均质装甲(Rolled Homogeneous Armor,RHA)及LY12铝三种材料的圆柱形弹体超高速碰撞薄板的破碎规律进行了研究,基于量纲分析方法得出了弹体破碎长度随弹靶材料特性、弹靶尺寸及初始撞击速度变化的关系式。并研究了钨合金及RHA两种材料的长杆弹对八层RHA板结构的超高速碰撞效应。     

Characterization of prompt flash signatures using high-speed broadband diode detectors

Impact flash is a brief, intense flash of light released when a target is impacted by a hypervelocity particle. It is caused by emissions from a jet of shocked material which is thrown from the impact site. Impact flash phenomenology has been known for decades, and is now being considered for applications where remote diagnostics are required to observe and diagnose impacts on satellites and space craft where micrometeoroid and orbital debris impacts are common. Additionally, this phenomena and remote diagnostics are under consideration for missile defense applications. Currently, optical signatures created from hypervelocity impact can be utilized as the basis for detectors (spectrometers, pyrometers), which characterize the material composition and temperature. More recent interest has focused on study of hypervelocity impact generated debris and the physics of the associated rapidly expanding and cooling multiphase debris cloud. To establish this capability technically in the laboratory, we have conducted a series of experiments on a two-stage light gas gun at impact velocities ranging from 6 to 19 km/s, which is representative for light emissions resulting from hypervelocity impacts in space. At these high impact velocities jetting is no longer the dominant mechanism for observed impact flash signatures. The focus of this work is to develop fast, inexpensive photo-diodes for use as a reliable prompt flash, and late time radiating debris cloud diagnostic to: (a) characterize material behavior in the shocked and expanding state when feasible; (b) ascertain scaling of luminosity with impact velocity; (c) determine the temperature of the impact flash resulting from radiating emissions when multiple silicon diodes are used in conjunction with narrow band pass filtering at specific wavelengths as a pyrometer. The results of these experiments are discussed in detail using both a metallic target, such as aluminum, and an organic material such as Composition-B explosive.     

Modified Cour-Palais/Christiansen damage equations for double-wall structures

Ballistic limit equations (BLEs) are used for the damage prediction of spacecraft in a meteoroid and space debris environment. For double-wall configurations, the Cour-Palais/Christiansen equations have been modified to yield a general approach including the influence of the shield thickness. The ratio of shield thickness to particle diameter is considered as additional parameter in the equations. These equations result in the single-wall equation when the shield thickness approaches zero. The modifications can also be applied to other BLEs. Impact tests have been performed in order to validate the modified equations. In this paper, the test results are compared to the modified BLEs. Especially in the hypervelocity region, the new equations are more suitable for configurations with very thin shields than the original ones.     

Response of woven ceramic bumpers to hypervelocity impacts

The multi-shock shield concept devised by Crews and Cour-Palais,¹ composed of multiple ceramic cloth bumper layers and an aluminum back sheet, was used to investigate the response of woven ceramic bumpers to a hypervelocity impact. Observations made on past hypervelocity impact test data show that areal density is the most important bumper characteristic for initially breaking up solid particles. Our research has shown that once the solid particle has been shocked into a cloud of liquid and vapor, the weave pattern of the cloth bumper can influence the ability of the shield to absorb and contain the energy of the debris cloud.

To design a weave that will absorb particle energy more efficiently, we need to understand the micromechanics of the interaction between the debris cloud and the cloth bumper. In this paper we discuss our observations on the response of a ceramic cloth bumper to a hypervelocity impact and the failure mode occurring at the individual strand level.     

Impact damage on sandwich panels and multi-layer insulation

Most spacecraft rely intensively on sandwich construction for external structures with multi layer thermal insulation where appropriate. Experience gained in ESA with various spacecraft (ROSETTA, METOP, ATV,…) covers a substantial range of materials and configurations. In this work, the applicability of simple damage equations (e.g. those presently used for single or Whipple shield ballistic limits) to more complex configurations (e.g. sandwich plates with and without MLI) is analyzed. The different sandwich configurations which were submitted to testing are reviewed, impact test results are presented and compared with impact reference data on single plates and Whipple shields. It has been found that sandwich panels have a better tolerance to hypervelocity impacts than monolithic structures. MLI placed in front of the sandwich panels contributes significantly to the overall protection performance in the range of the projectile diameters tested. The complexity of the sandwich structure is responsible for a considerable scatter in the test results. The predictors for Whipple shields applied to sandwich panels with and without MLI can only be considered on a case by case basis for risk assessment analysis.     

Effect of internal stress fields on the perforation response of dual-wall structures under hypervelocity impact

Traditional perforation-resistant wall design for long-duration spacecraft consists of a ‘bumper’ that is placed at a small distance away from the main ‘pressure wall’ of a spacecraft compartment or module. This concept has been studied extensively in the last four decades as a means of reducing the perforation threat of hypervelocity projectiles such as meteoroids and orbital debris. If a dual-wall systems is employed on an earth-orbiting spacecraft, then a biaxial stress field will be induced within the pressure wall of the dual-wall system due to the pressurization of the spacecraft. Unfortunately, little or no attempt has been made to include the effects of this low-level internal stress field in the study ofthe perforation resistance of dual-wall structural systems. This paper presents the results of an experimental study in which aluminum dual-wall structures were tested under a variety of high-speed impact conditions in an attempt to quantify the effect of an internal pressure wall stress field on perforation resistance. A test-by-test comparative analysis of the damage sustained by similar dual-wall systems with stressed and unstressed pressure wall plates under similar impact loading conditions revealed that the internal pressure wall stress field had a negligible effect on the ballistic limit of the dual-wall structures considered. However, the internal stress field did have a significant effect on the extent of the damage sustained by the pressure wall.     

Numerical simulation of non-perforating impacts on shielded gas-filled pressure vessels

In order to calibrate the output of hydrocode simulations of hypervelocity impacts on shielded gas-filled pressure vessels, Light Gas Gun impact experiments were performed. In a first step, tests were performed on so-called equivalent Whipple shield (EWS) configurations having basically the same set-up as the shielded pressure vessels (i.e. bumper thickness and - material, stand-off and backwall plate thickness and -material). Purpose was the determination of the impact conditions that lead to penetration into the backwall plate but not perforation of it or leakage through the impacted area. In a second step, impact tests on the corresponding shielded pressure vessels were performed with the same test conditions as the EWS. The purpose of the tests was the investigation whether leakage occurs when the vessel's front wall is not perforated, but just cratered. The test conditions lead to no leakage in all tests. The most important measured damage parameter was the crater depth of the deepest crater in the vessel's front wall/the backwall plate of the EWS, respectively. Hydrocode simulations were then performed to assess the capability of the numerical tool to correctly predict the damage on the impacted vessel surface. Normal impacts of aluminium spheres against shielded vessels were simulated using AUTODYN-2D, including and evaluating the effect of the static stress induced in the vessel walls by the inner pressure. Particular attention was focused on the exact determination of the maximum crater depth caused by the debris cloud impact on the vessel wall/the backwall plate of the EWS, respectively. Bumper and projectile were represented by SPH particles, the vessel shell was represented by a Lagrange grid. The results showed a very good agreement with the measured crater depths of the experiments.     

Response of space structures to orbital debris particle impact

All long-duration space and aerospace and transportation systems, such as the Space Station Freedom and the Space Shuttle, are susceptible to impacts by pieces of orbital debris. These impacts occur at high speeds and can damage the flight-critical systems of such spacecraft. Therefore, the design of a structure that will be exposed to a hazardous orbital debris environment must address the possibility of such hypervelocity impacts and their effect on the integrity of the entire structural system. A technique is developed for analyzing the response of dual-wall structures to oblique Hypervelocity projectile impact. Ballistic limit curves that predict the potential of an impacting projectiles to perform the main wall of a dual-wall strucutral system are obtained using the techniques and are compated against experimentally derived curves. Comparisons are performed for a variety of impact velocities, trajectory obliquities and projectile masses. It is shown that the results obtained using the technique developmed herein compare very well with experimetanl results.     

Selecting enhanced space debris shields for manned spacecraft

A research program was funded by the European space agency (ESA) to improve and optimize the shields used to protect the manned elements of the international space station (ISS) against impacts of micro-meteoroids and orbital debris. After a review of existing shielding systems and after a series of light gas gun (LGG) experiments to screen interesting new materials and configurations, the research focused on shields with a metallic outer bumper, an intermediate stuffing and an inner metallic wall (representing the pressure shell of a manned spacecraft). Additional LGG experiments were performed on several configurations, with bumpers containing aluminum foam or made from titanium and aluminum super-alloys and with several combinations of stuffing materials. The comparison of the test results showed that ceramic cloth (Nextel) plus aramid fabric (both 2D and 2.5D Kevlar weaving) used as intermediate bumper gave a good protection compared to the overall area density requested. Configurations with by-layered aluminum foam bumpers (sandwich panels with asymmetric Al face sheets and a core made from Al foam) and Kevlar stuffing showed excellent resistance to normal impacts at about 6.5 km/s. However, the influence of material properties varying from batch to batch and threshold phenomena made ranking among the tested options rather difficult. The test campaign showed that it was rather difficult to improve over the already good ballistic performances of the debris shields developed by Alenia Spazio for the ISS manned elements. The by-layered Al-foam bumper and Kevlar stuffing configuration was selected for additional tests, including low velocity and oblique impacts, to develop ballistic limit curves.     

一种改进的特征匹配算法在碎片云测量建模中的应用

为满足超高速撞击典型Whipple防护构型的损伤评估需求,利用图像处理技术对碎片云序列阴影图像进行深入研究.使用超高速序列激光阴影成像仪得到三组不同实验条件下碎片云发展过程的高清阴影图像,分别对每组最具代表性的2帧进行图像处理分析;根据碎片云图像特点以及碎片运动特性,提出了一种改进的碎片二次特征匹配算法,该方法包含碎片...     

Crater distribution on the rear wall of AL-Whipple shield by hypervelocity impacts of AL-spheres

All spacecraft in low orbit are subject to hypervelocity impact by meteoroids and space debris, which can in turn lead to significant damage and catastrophic failure. In order to simulate and study the hypervelocity impact of space debris on spacecraft through hypervelocity impact on AL-Whipple shield, a two-stage light gas gun was used to launch 2017-T4 aluminum alloy sphere projectiles. The projectile diameters ranged from 2.51 mm to 5.97 mm and impact velocities ranged from 0.69 km/s to 6.98 km/s. The modes of crater distribution on the rear wall of AL-Whipple shield by hypervelocity impact of AL-spheres in different impact velocity ranges were obtained. The characteristics of the crater distribution on the rear wall were analyzed. The forecast equations for crater distribution on the rear wall of AL-Whipple shield by normal hypervelocity impact were derived. The results show that the crater distribution on the rear wall is a circular area. As projectile diameter, impact velocity and shielding spacing increased, the area of crater distribution increased. The critical fragmentation velocity of impact projectile is an important factor affecting the characteristics of the crater distributions on the rear wall.     

Hypervelocity impact response of spaced composite material structures

The design of a spacecraft for a long-duration mission must take into account the possibility of high-speed impacts by meteoroids and orbiting space debris and the effects of such impacts on the spacecraft structure. With the advent of many new high-strength composite materials and their proliferation in aircraft applications, it has become necessary to evaluate their potential for use in long-duration space and aerospace structural systems. One aspect of this evaluation is the analysis of their response to hypervelocity projectile impact loadings. The analyses performed in this study indicate that the extent of damage to a dual-wall composite structure can be written as a function of the geometric and material properties of the projectile/structure system. A comparative analysis of impact damage in composite specimens and in geometrically similar aluminum specimens is also performed to determine the advantages and disadvantages of employing certain composite materials in the design of structural wall systems for long-duration spacecraft.     

Projectile density, impact angle and energy effects on hypervelocity impact damage to carbon fibre/peek composites

This paper explores the effects of projectile density, impact angle and energy on the damage produced by hypervelocity impacts on carbon fibre/PEEK composites. Tests were performed using the light gas gun facilities at the University of Kent at Canterbury, UK, and the NASA Johnson Space Center two-stage light gas gun facilities at Rice University in Houston, Texas. Various density spherical projectiles impacted AS4/PEEK composite laminates at velocities ranging from 2.71 to 7.14 km/s. In addition, a series of tests with constant size aluminum projectiles (1.5 mm in diameter) impacting composite targets at velocities of 3, 4, 5 and 6 km/s was undertaken at incident angles of 0, 30 and 45 degrees. Similar tests were also performed with 2 mm aluminum projectiles impacting at a velocity of approximately 6 km/s. The damage to the composite was shown to be independent of projectile density; however, debris cloud damage patterns varied with particle density. It was also found that the entry crater diameters were more dependent upon the impact velocity and the projectile diameter than the impact angle. The extent of the primary damage on the witness plates for the normal incidence impacts was shown to increase with impact velocity, hence energy. A series of tests exploring the shielding effect on the witness plate showed that a stand-off layer of Nextel fabric was very effective at breaking up the impacting debris cloud, with the level of protection increasing with a non-zero stand-off distance.