The validation of hydrocodes for orbital debris impact simulation

Orbital debris pose a danger for spacecraft in orbit. Protection against this threat is obtained by shielding. One or more shields placed at some distance from the structure to be protected can minimize the damage inflicted by projectiles at high velocity. The range of velocity between 0 and 8 km/s is well covered by tests. Unfortunately, the average velocity of debris in low earth orbit is above 10 km/s with a maximum velocity around 15 km/s. The methodology presented in this paper aims to validate the numerical approach. It will predict and extrapolate the behavior of multishock shields in the velocity range between 8 and 15km/s. The formation and propagation of the debris cloud, after perforation of the shields and the generation of damage in the backwall, are key factors. These phenomena are examined, discussed and illustrated with correlation between numerical simulation with EFHYD^TM analytical formulae and test results.     

Laboratory simulation of hypervelocity debris

A series of hypervelocity damage experiments were performed on spacecraft materials in order to simulate micro-size space debris traveling at 3 to 8 km/s. Two types of impact simulations were investigated: high-power pulsed laser and laser-launched micro-flyer plate. In the first case a laser was used to generate a high-pressure shock wave which propagated into the target by means of rapid ablation of the target surface. The second case used the same laser to accelerate micro-flyer plates at a target. The laser-ablation technique and the apparatus used to propel the micro-flyer plates were compatible with a space environmental chamber equipped with instrumentation capable of analyzing the vapor ejected from the sample. Data obtained from two separate damage effects were of interest in this study: the vapor blow-off produced by the impact and the mechanical damage to the target. The value of the data obtained from both simulation methods was evaluated in terms of likeness to actual space debris damage.

Data for this work were obtained from polysulfone resin and a graphite polysulfone composite. Polysulfone was selected because it was flown on the Long Duration Exposure Facility (LDEF) satellite which spent several years in low earth orbit and experienced many space debris impacts.

The chemistry of the vapor produced by the two simulation techniques was analyzed with a time of flight mass spectrometer (TOFMS) which measured changes in the vapor chemistry as a function of time after impact, obtained a velocity measurement of the vapor, and estimated surface temperature immediately after impact using dynamic gas equations. Samples of the vapor plume were also captured and examined by transmission electron microscopy (TEM).

The mechanical damage effects caused by the simulation methods on a graphit polysulfone composite and a polysulfone resin were studied. Impact craters were examined under optical and scanning electron microscopes (SEM). Based on the two damage effect criteria the micro-flyer method proved to be a useful way to simulate hypervelocity impact of space debris. The laser-ablation method however, had shortcomings and required drastic compromises in the set criteria.     

Characteristics of hypervelocity impact debris clouds

This paper describes an experimental investigation of hypervelocity impact debris clouds produced by impacting metal rods with Kapton flyers in an electric gun facility. Soft copper witness plates placed in the path of the debris were cratered and coated with rod material. From the sizes of the craters on the witness plates we could obtain values for a cratering parameter containing the ,asses and velocities of the debris fragments that formed the craters. By combining the cratering parameter with rough estimates of the fragment masses, we then estimated the fragment velocities. By measuring the thickness and extent of the coating on the witness plates, we obtained a bound on the amount of material vaporized by the impact.     

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.     

An investigation of metal matrix composites as shields for hypervelocity orbital debris impacts

The improvement of space vehicle shield designs to resist penetration by hypervelocity impacts of meteoroids or man-made orbital debris can lengthen mission life and increase mission efficiency. One option to improve shields is to create new bumper materials which can be tailored to meet the requirements for effective shielding. Metal matrix composites are one such material. Fiber content, type, and orientation could be varied to tailor the material to the specific properties needed for weight efficient shielding. In this study, two varieties of aluminum matrix composites were investigated, one with continuous graphite fibers and one with silicon carbide particulates. The objectives of the study were: to compare the penetration resistance of the composite with the known resistance of aluminum; to study the penetration mechanics by comparing the condition of the composite after the impact test with the pre-test condition; to study the effects of fiber content and fiber orientation on penetration resistance; and to recommend a material “design” for metal matrix composites which would best protect a space vehicle from orbital debris. The composite bumpers did not perform significantly better than aluminum bumpers. The particulate composites are more effective bumpers than the continuous fiber composites for the conditions tested. The differences in the measured hole diameters resulting from the impact tests as compared to predicted hole diameters for the particulate composite bumpers, are within the expected differences for metallics. However, the continuous fiber composites had much larger holes than predicted.     

A simple model for debris clouds produced by hypervelocity particle impact

A simple debris cloud model is developed by considering the one dimensional shock wave motion in the material together with the catastrophic fragmentation theory by Grady. The model provides a simple method for calculating the velocities at the outer perimeter of the cloud and the average particle size in the cloud.     

Behind-armor debris from the impact of hypervelocity tungsten penetrators

Behind-armor debris is the main mechanism by which targets are destroyed by projectile impact. The behind-armor debris generated from the impact of tungsten heavy alloy (THA) penetrators with a length-to-diameter ratio (L/D) of 20 against 6061-T6 aluminum targets was characterized. Behind-armor debris characteristics described were the number of debris particles, their positions, and their size distribution. Experiments were performed against two nominal target thicknesses, 100 and 150 mm, and covered a velocity range from 1.7 to 2.6 km/s. Two methods of obtaining data were used—radiographs were taken of the behind-armor debris, and perforation patterns were generated on steel witness packs placed behind the aluminum target. Debris particles recovered from the witness packs were also studied. Results are discussed for the effect of changes in target thickness and impact velocity on behind-armor debris particle characteristics.     

Computer characterization of debris clouds resulting from hypervelocity impact

A computational study to examine the effects of parameter variation on debris cloud formation and perforation behavior in a simple sphere-plate impact situation is described. The parameters varied were impact velocity, thickness: diameter ratio, projectile-target material combination and number of plates. In particular, effects associated with changes from strength-dominated to hydrodynamic behavior were considered.     

Advanced algorithms for computer simulation of hypervelocity impact

Presented are several algorithms that allow a Lagrangian hydrodynamic computer code to simulate hypervelocity impact. Such impacts typically involve very large material deformations and ordinarily can be handled only by Eulerian codes, in which the materials flow through a stationary grid. In Lagrangian codes, the mesh is attached to the material and deforms with it; in problems involving severe distortions, the mesh can become tangled, resulting in loss of accuracy or even a breakdown of the computational scheme. However, Lagrangian codes present several advantages in economy, ease of programming and use, and interpretation of results.

This paper describes several modifications of the DEFEL code (Flis, Miller, and Clark, 1984). This code, a descendant of EPIC-2 (Johnson, 1976), was originally developed to simulate low- to medium-velocity impact and explosive-metal interaction. Modifications include automatic rezoning, a surface-erosion model, and treatment of fracture (cracking) by automatic introduction of sliding lines between elements. These fractures allow DEFEL to handle a variety of problems in the hypervelocity regime. Included are discussions of several example problems.     

An improved hybrid particle-element method for hypervelocity impact simulation

An improved hybrid particle-finite element method has been developed for hypervelocity impact simulation. The method combines the general contact-impact capabilities of particle codes with the true Lagrangian kinematics of large strain finite element formulations. Unlike some alternative schemes which couple Lagrangian finite element models with smooth particle hydrodynamics, the present formulation makes no use of slidelines or penalty forces.     

Numerical simulation method for elastic-plastic dynamic response for hypervelocity impact phenomena

This study presents a time-dependent numerical method for impact in planar or cylindrical symmetry. We use Eulerian finite-difference scheme, Tilloston's Metallic Equation of state, von Mises Yield criterion, for calculating the large deformation of elastic-plastic high velocity impact. Failure, cavitation and melting of solids are accounted for. The present model treats the formation and evolution of a crater, the deformation of the projectile and the deformation and dynamical response of the target. A two-stage gas gun was employed to experimentally study the phenomena of hypervelocity impact. Good agreement is obtained between the present computational results and craters obtained in experiments of polyethylene/aluminium impacts. The relation of crater shape and penetration depth to dynamic parameters of the projectile and the target is discussed. The Multi Purpose Graphics System (MPGS) is used to describe the calculation results with color graphics.     

Mesh double-bumper shield: A low-weight alternative for spacecraft meteoroid and orbital debris protection

A number of new, innovative, low-weight shielding concepts have resulted from a decade of research at the NASA Johnson Space Center (JSC) Hypervelocity Impact Test Facility (HIT-F). One such concept, the mesh double-bumper (MDB) shield is a highly efficient method to provide protection from meteoroid and orbital debris impacts. Hypervelocity impact (HVI) testing of the MDB shield at the HIT-F and other facilities have demonstrated weight savings of approximately 30% to 50% at light gas gun velocities compared with conventional dual-sheet aluminum Whipple shields at normal impact angles. Even larger weight savings, approximately 70%, have been achieved at 45 degree oblique angles. The MDB shield was developed to demonstrate that a Whipple shield could be “augmented” or modified to substantially improve protection by adding a mesh a short distance in front of the Whipple bumper and inserting a layer of high strength fabric between the second bumper and rear wall. From the test results, formulas have been developed that allow the design engineer to size MDB shield elements for spacecraft applications.     

Space shuttle meteoroid and orbital debris impact damage

Post-flight surveys of meteoroid and orbital debris (M&OD) impacts on the Space Shuttle Orbiter are conducted to identify damage caused by hypervelocity impacts from M&OD and to identify the source (i.e., whether meteoroid or orbital debris) of the projectiles responsible [1,2] This report provides data on Orbiter M&OD impacts for a five-year period and describes in detail the 39 most significant impacts. For the period 6/92 through 12/99 there were 49 Shuttle Transportation System (STS) missions (STS-50 through STS-103) of which 38 had post-flight inspections to identify M&OD impacts. Approximately 10% of the vehicle is surveyed in the M/OD inspections. The data for the 39 most significant impacts based on size found during the inspections are summarized in Table 1. This work contains estimates of impactor size which were determined using appropriate impact damage penetration equations that were derived by hypervelocity impact (HVI) test and analysis on relevant Orbiter materials. Although predictions for numbers of impacts are produced for each STS mission, we do not compare those predictions to the actual damage reported here as further efforts must be made to analyze the as-flown attitude timeline and adjust the predicted damage accordingly.     

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.     

Space station JEM design implementation and testing for orbital debris protection

The Japanese Experiment Module (JEM) is the Japanese contribution to the International Space Station (ISS) Program. The core part of JEM is a Pressurized Module where the crew conducts space experiments in a microgravity environment in space. The development of a shield design to protect against micrometeoroids and orbital debris (MM/OD) has been a key issue for the permanent manned space station which is expected to have an operational life exceeding 10 years. Many technical approaches for MM/OD protection have been studied. As the launch of the space station elements draws near, the shield design has become mature, and the technical test data for the MM/OD shielding obtained has increased confidence in its performance. NASDA, which is responsible for JEM design and development, has conducted a series of tests and simulations to define the MM/OD shield configuration and design. The structural failure due to MM/OD strikes has also been assessed for the combined shield and pressure shell configuration.     

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.     

弹丸超高速撞击半无限厚铝板数值模拟

微流星体及空间碎片的超高速撞击威胁着长寿命、大尺寸航天器的安全运行,导致其严重的损伤和灾难性的失效.撞击损伤特性研究是航天器防护设计的一个重要问题.本文采用AUTODYN软件的Lagrange法对半无限铝板的超高速斜撞击和与其具有相同法向速度的正撞击进行了模拟,给出了不同撞击角和不同法向速度下半无限厚铝板弹坑深度、宽度、长度的变化规律及多弹坑的形成过程,并与经验方程进行了比较分析.结果发现:随撞击角的增加,弹坑的深度和宽度减小,而弹坑的长度增加;随撞击速度的增加弹坑的直径和深度增加;在撞击角大于70度时出现多弹坑.     

Application of schemes on moving grids for numerical simulation of hypervelocity impact problems

We describe a numerical technique for solving hypervelocity impact problems. Computational method is based on Godunov scheme on moving grid. To describe flows with strong deformations a technique of decomposition of numerical region into subregions is developed. The boundaries of subregions can be moved both in Eulerian and Lagrangian fashion. Using the method developed several multimaterial problems with strong deformations have been solved.

To apply Godunov method for elastic-plastic flow conservative form of governing equations is used, which allows one to obtain jump conditions in the case of discontinuous flow.