泡沫铝防护屏的Whipple防护结构弹道极限数值模拟研究

为研究泡沫铝板作为防护屏的Whipple防护结构抵御空间碎片超高速撞击的特性,模仿泡沫金属的生产原理建立了泡沫金属细观结构几何模型,结合自编的光滑质点流体动力学程序进行了超高速撞击数值仿真,通过与实验对比验证了模型的有效性.分别对相对密度为23.2%的理想均匀和非均匀开孔泡沫铝板作为防护屏的Whipple防护结构进行了数值仿真,得到了它们的弹道极限曲线,并与实心铝板作为防护屏的Whipple防护结构进行了对比分析.结果表明,相同面密度的泡沫铝板相对于实心铝板能够在更低的速度上将弹丸粉碎、液化及气化.泡沫铝板作为防护屏,在总体上拥有更好的防护性能;相同面密度的理想均匀泡沫铝板的防护性能总体上优于非均匀泡沫铝板.     

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.     

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.     

Advanced all-metal orbital debris shield performance at 7 to 17 km/s

Increasing demands on orbital debris shielding systems have spurred efforts to develop shields that are more efficient than the standard single-bumper system. For example, for a given total bumper mass, experiments at velocities near 7 km/s have shown that a multiple-bumper system is more efficient than a single bumper in preventing wall perforation. However, the performance of multiple bumper systems at velocities above 7 km/s is unknown. To address this problem, the cadmium surrogate-material technique described by Schmidt et al. [1] has been extended to two dual bumper systems. A complete dimensional analysis is developed to include similarity requirements for the intermediate layers. Results of experiments, for impact angles of 0° and 45°, are presented and compared to those for single bumpers, along with limited results for an equal-mass four-bumper shield. Surprisingly, for scaled velocities near 16 km/s at normal incidence, a single bumper defeats impactors approximately 30% larger in diameter than multiple bumpers of the same total areal density.     

Hypervelocity impact tests and simulations of single whipple bumper shield concepts at 10km/s

A series of experiments has been performed to evaluate the effectiveness of a Whipple bumper shield to orbital space debris at impact velocities of 10 km/s. Upon impact by a 19 mm (0.87 mm thick, L/D 0.5) flier plate, the thin aluminum bumper shield disintegrates into a debris cloud. The debris cloud front propagates axially at velocities of 14 km/s and expands radially at a velocity of 7 km/s. Subsequent loading by the debris on a 3.2 mm thick aluminum substructure placed 114 mm from the bumper penetrates the substructure completely. However, when the diameter of the flier plate is reduced to 12.7 mm, the substructure, although damaged is not perforated. Numerical simulations performed using the multi-dimensional hydrodynamics code CTH also predict complete perforation of the substructure by the subsequent debris cloud for the larger flier plate. The numerical simulation for a 12.7 mm flier plate, however, shows a strong dependence on assumed impact geometry, i. e., a spherical projectile impact geometry does not result in perforation of the substructure by the debris cloud, while the flat plate impact geometry results in perforation.     

近地轨道航天器微流星及空间碎片风险度分析研究

以单防护屏防护结构为例,根据描述其防护性能的撞击极限方程,微流量及空间碎片环境数学模型,建立了航天器结构的有限元分析模型,进行了航天器在微流星及空间碎片环境下风险度的初步分析,其结论可供工程实践参考。     

Shielding against space debris. A comparison between different shields: The effect of materials on their performances

The space environment requires the Space Station to be shielded against orbital debris. A technological programme undertaken by the European Space Agency has led to a preliminary definition of the shield configuration for the European Attached Pressurized Module. The envisaged shield is a modified Whipple shield. A second bumper is located midway between the first bumper and the backwall.

The work described has been initiated to quantify experimentally the merits of different shields compatible with the APM system requirements. For this technological investigation, two requirements had to be satisfied. The spacing between the front bumper and the backwall had to be limited to 120 mm. The backwall thickness could not be reduced to technological limits as it has structural functions as well. In addition, the long life requirements of the Space Station precludes the use of unproved materials for the external parts of the shield.

Different materials have been tried as second bumper. The effect of the first bumper thickness on the projectile fragmentation has been explored as well. Shields based on Aluminium, Kevlar and Glare have been investigated. Kevlar 29 fabrics impregnated with epoxy resin were used for this work. Glare is a material developed to improve the fatigue strength of metal structures. It is primarily intended for aircraft skin applications. Glare consists of a 60 percent fibre volume adhesive prepreg with high-strength unidirectional or cross-ply R-glass fibres. A variety of lay-up sequences is available ranging from 2/1 (two layers of aluminium alloy sheet bonded by one layer of prepeg) to any number of layers. The 2/1 layers version of the Glare material has been used for this work.

The tests results indicate the performances of materials can change significantly with the impact conditions. Glare shows the best performances in the low velocity regime while Kevlar is very promising in the high velocity regime. It is concluded the use of Kevlar can improve substantially the performances of the APM shield.     

Simulation of hollow shaped charge jet impacts onto aluminium whipple bumpers at 11 km/s

The computational technique of Smoothed Particle Hydrodynamics (as implemented in the hydrocodes AUTODYN-2D and AUTODYN-3D) has been used to simulate the impact of hollow shaped charge jet projectiles onto stuffed Whipple bumper shielding. Due to limited availability of material models, the interim Nextel/Kevlar-Epoxy bumper was modelled as an equivalent thickness of aluminium. Stuffed Whipple bumper shields are used for meteoroid and debris impact protection of the European module of the International Space Station (the Columbus APM). A total of 56 simulations were carried out to investigate the impact processes occurring for shaped charge jet impact. Sensitivity studies were carried out on the influence of projectile shape, pitch, yaw and strength at 11 km/s to determine the range of debris cloud morphologies. The debris cloud structure was shown to be highly dispersed, and no projectile remnant was observed at the centre of the cloud. The mass of an aluminium sphere producing equivalent damage to a shaped charge jet projectile was in the range 1.5 to 1.75 times greater than the mass of the shaped charge jet projectile. Upon loading by the dispersed debris cloud, the interim bumper failed by spallation, producing fragments moving at 2 km/s or less. The fragments distorted the rear wall (pressure wall) of the shield but did not perforate it. The experimental data show rear wall deformation but to a lesser degree. Perforation of the rear wall, observed for one test, was not reproduced by the simulation. Nextel/Kevlar-epoxy material models are required to reproduce correctly the interim bumper failure under debris cloud loading.     

微流星及空间碎片高速撞击航天器风险度分析

给出了微流星及空间碎片高速撞击航天器风险分析的方法 ,并采用风险分析软件 ,以柱状近地轨道航天器为例 ,对不同防护结构方案、航天器的飞行姿态、防护屏的厚度以及航天器的运行时间等因素对航天器不发生穿孔损伤的影响进行了分析 ,给出了分析的结果     

Debris clouds produced by the hypervelocity impact of nonspherical projectiles

The significant features of debris clouds produced by the normal impact of spheres are described and compared with the features of debris clouds produced by the normal impact of nonspherical projectiles. Projectile shape and orientation at impact are shown to have a significant effect on the ability of a single-sheet bumper shield to promote the breakup of the projectile and the dispersion of the projectile fragments. The debris clouds produced by the normal impact of spheres are “relatively benign” in terms of their potential for damage to the rear wall of a spacecraft. Debris clouds produced by nonspherical projectiles contain one or more very large fragments at their leading edge that significantly threaten rear wall integrity.     

Micrometeorite and space debris simulation for columbus hull components

An experimental impact simulation program is currently performed with respect to Columbus hull components. The main objectives are to establish a data base for an optimum design of meteoroid/debris protection shields (MDPS) as well as viewport components, and to obtain input data for numerical models which describe the penetration and perforation processes of meteoroid bumper and viewport systems.

As expected, it has been experimentally demonstrated that protection against particles in the order of 1 cm, at relatively low impact velocities (around 3 km/s), is extremely problematic.

Applying usual dual-plate Al bumper techniques would require unrealistically thick and heavy systems in order to safety stop such particles, which are expected to occur within the low earth orbit space debris complex.

Preliminary results obtained with multiplate Al targets as well as hybrid target systems (Al-ceramics, Al-Kevlar) indicate that the situation can be considerably improved with respect to the shielding efficiency at a given areal material density.

These investigations are still in progress. Results of the test series performed with Al dual-plate systems and with laminated glass targets as viewport components are reported and discussed.     

铝双层板结构撞击损伤的板间距效应实验研究

为了研究空间碎片对航天器防护结构的超高速撞击损伤特性,采用二级轻气炮发射球形弹丸,对铝双层板结构进行了超高速撞击实验研究.弹丸直径为3.97 mm,撞击速度分别为(2.58±0.08)km/s、(3.54±0.25)km/s和(4.35±0.11)km/s,板间距为10~100 mm.实验得到了铝双层板结构在不同撞击速度区间的后板损伤模式.结果表明,弹丸撞击速度一定时,后板弹坑分布随前后板间距的不同而不同.前板背面返溅影响区和后板弹坑分布区随板间距的增大而增大,各弹坑分布区扩散角随板间距的增大而减小.     

A simple defense conservative model for mass requirements of hypervelocity projectile impact shields for reentry vehicles

Simple analytical modeling of the physics of interaction of hypervelocity (50–100 km/s) projectiles with a bumper shield countermeasure is given. The interaction of projectile and bumper is discussed briefly. Expansion of bumper/projectile debris in the region between bumper and underlying vehicle and interaction of bumper/projectile debris cloud with vehicle are examined. Expansion of debris is treated as an expansion superimposed upon a translation with partition derived from a simple inelastic collision model. The effect of nonunity aspect ratio of compressed debris is included. Debris colliding elastically with the vehicle will impart momentum equal to twice the incident normal component. A steady-state diffusion model is used to estimate the effect of stagnation radiative loss on collision elasticity. Impulse may be reduced up to a factor of 2 by stagnation radiative losses for small projectiles and large bumper/vehicle stand-off. Stagnation radiation loss is small for larger projectiles and smaller stand-off. Impulse can be enhanced by vehicle ablation from radiative coupling, shock heating (inadequate stand-off), or liquid droplet microcratering (inadequate bumper thickness). Estimates of required bumper mass are given for a specific example.     

Development and optimization of a multibumper design model for spacecraft protective structures

The development and optimization of a design model for multibumper spacecraft protective structures to defeat orbital space debris is presented. The Marshall Space Flight Center (MSFC) Materials and Processes (M&P) Laboratory Hypervelocity Impact Database is first filtered to experiments comprising metallic configurations without multilayered insulation present and for projectile velocities exceeding 2.5 km/sec. This filtering results in 337 single, double, and triple bumper hypervelocity impact experiments. Regression variables of interest include projectile diameter, density, velocity, and impact angle, bumper standoff distances, bumper densities and thicknesses, wall density and thickness, and number of bumpers. The dependent regression variable is the total number of plate penetrations, beginning with the wall and continuing through the witness plates. A unique intrinsically linear regression form, which accounts for the number of bumpers employed and invokes a posynomial (polynomial with positive coefficients, positive valued independent variables, and real valued exponents) form, is chosen based on a comparison of various regression forms using correlation coefficient and F-statistic as measures of effectiveness. The least squares regression is performed followed by an ANOVA, tests of the correlation and F value, and graphical examination of residuals. Regression results indicate that statistically significant least squares is possible using the chosen form on the MSFC M&P database with small residual effects. Generic nonlinear regression forms are also investigated.

The resulting regression model is next used in the formulation of a nonlinear optimization program. This program is devised to minimize the protective structures areal density subject to a limitation on total standoff distance between the first bumper and the wall. The decision variables of interest are the optimal values of the areal densities of the bumpers and wall, as well as the optimal individual standoff distances. The problem is solved using the dual transformation of geometric programming. The optimal independent variables and minimum system areal density are solved for analytically in terms of the systemic parameters. A sensitivity analysis to these parameters is then performed. Additionally, the optimal number of bumpers is evaluated in this sensitivity study. The most significant results from a hypervelocity impact standpoint are that additional hypervelocity impact tests and analyses should be performed to support understanding of multiple bumper, large particle diameter, large separation, large particle mass density, various particle impact angles, and spallation phenomenologies. Additionally, more emphasis should be placed on understanding the transition regions between particle shatter, melt, and vaporization, while less emphasis should be placed on small velocity differences within these regions. Major protective structures design results indicate that for Space Station Freedom impact scenarios of interest, and within the limitations of the regressed hypervelocity impact database, at most four metallic bumpers are optimal. In particular, a transition region from optimal number of bumpers of 2 to 3 (and 3 to 4) has been identified for particle diameters in the 0.25–0.5 cm (and 1 to 1.25 cm) range. An interesting transition region from 3 to 4 optimal number of bumpers has been discovered for standoff distances between 10 and 15 cm. Furthermore, the optimal protective structures design sensitivity to impact angle is very low. Finally, the results of this investigation indicate that this combination of regression form and resulting optimization approach is useful in identifying protective structures design trends for spacecraft subject to hypervelocity impact environments.     

5A06铝合金单层板超高速撞击弹道极限分析

日益增长的空间碎片对在轨航天器的安全运行构成了严重威胁,毫米级空间碎片的防护已成为航天器结构设计必须考虑的问题之一.航天器的蒙皮是抵御空间碎片超高速撞击的最基本防护结构.采用数值仿真并结合试验验证的方法,对5 mm厚5A06铝合金单层板承受2A12铝合金球形弹丸正撞击下的弹道极限进行了研究.研究表明,在验证实验速度范围内,数值仿真结果与实验结果吻合良好;使用数值仿真对实验速度以上的区间进行拓展研究,获得了其弹道极限曲线和弹道极限方程;数值仿真和实验结果与已有经验方程对比表明,经验方程与具体材料的弹道极限有较大偏差,因此,应具体问题具体分析.     

Debris clouds generated by hypervelocity impact of cylindrical projectiles with thin aluminum plates

Orthogonal, flash x rays were used to observe the debris clouds produced by the hypervelocity impact of cylindrical aluminum projectiles with thin aluminum sheets or bumpers. Three major structural features were observed in the debris clouds--a front cone, a bulbous main debris cloud, and an inner cone. Inclination of the projectile at impact changed the orientation of these features and the severity of damage to the rear wall of a double-sheet structure; projectiles with the greatest inclination produced the most damage. Two experiments, using aluminum and copper as projectile and target or target and projectile, respectively, were performed to determine the source of material in each of the three structural features of the debris clouds. The front cone and main cloud were shown to consist of bumper debris while the inner cone was composed of projectile fragments.     

Impact experiments on low-temperature bumpers

This paper presents the results of hypervelocity impact experiments that were carried out at CISAS Impact Facility onto aluminum bumpers cooled down to −120 °C with liquid nitrogen and to −60 °C with solid carbon dioxide. The thickness of the targets was 0.8, 1, 2 and 3.17 mm, the diameter of the spherical projectiles was 1.5, 1.9, 2.3 and 2.9 mm and the impact velocity did span between 4 and 5 km/s. To establish if any temperature dependence exists in the bumpers’ impact response, two different features were analyzed: the hole size and the bumper protection capabilities. The latter property, that is related to the bumper capacity of producing debris cloud composed of fragments as fine and slow as possible, was assessed through observation of the damage patterns on witness plates and through measurements of the debris cloud tip velocity. Moreover, qualitative analyses of high-speed shadowgraphs representing the debris cloud evolution were performed. On one hand, it was found that low temperature has only minor influence on the hole diameter. On the other hand, the examination of shadowgraphs showed that the debris cloud structure varies with bumper temperature, even though it was not proved that such differences correspond to significant dissimilarities between damage patterns recorded onto witness plates.     

Hypervelocity testing of advanced shielding concepts for spacecraft against impacts to 10 km/s

Experiments have been performed on NASA state-of-the-art hypervelocity impact shields using the Sandia Hypervelocity Launcher (HVL) to obtain test velocities greater than those achievable using conventional two stage light-gas sun technology. The objective of the tests was to provide the first experimental data on the advanced shielding concepts for evaluation of the analytical equations (shield performance predictors) at velocities previously unattainable in the laboratory, and for comparison to single Whipple Bumper Shileds (WBS) under similar loading conditions. The results indicate that significantly more mass is required on the back sheet of the WBS to stop an approximately flat-plate particle impacting at 7 km/sec and at 10 km/sec that the analytical equations (derived from spherical particle impact data) predicted. The Multi-Shock Shield (MSS) consists of four ceramic fabric bumpers, and is lighter in terms of areal density by up to 33%, but is as effective as the heavier WBS under similar impact conditions at about 10 km/s. The Mesh Double Bumper shield (MDB) consists of an aluminum wire mesh bumper, followed by a sheet of solid aluminum and a layer of Kevlar^® fabric. It provides a weight savings in terms of areal density of up to 35% compared to the WBS for impacts of around 10 km/s.     

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.     

Micrometeroid and debris impact test on space station bumper

To design the micrometeoroid and debris protection bumper of the outboard structure space station module, we made a two-stage helium light gas gun and carried out hypervelocity impact tests which simulated micrometeroid and debris impacts on space station. Fundamental characteristics of hypervelocity impact phenomena was investigated, for a projectile mass 0.45gr to 1.5gr, impact velocity about 4km/sec and aluminum-alloy bumpers. When the bumper is of double-sheet type, there exists an optimal front sheet thickness that causes melting of the front sheet. However, for thin front sheets, penetration occurs, and for thick front sheets, spall fracture occurs. In addition to the impact tests, the computational simulation of the typical test result was carried out using the PISCES code with the Tillotson constitut ive equation of aluminum-alloy. The computational sumulation result had a good agreement with the test result.