Acceleration fields induced by hypervelocity impacts on spacecraft structures

This paper presents an overview of the hypervelocity impact test campaign ongoing in the frame of the ESA contract “spacecraft disturbances from hypervelocity impact”. The project aims at analyzing the propagation of shocks due to hypervelocity impacts from the external shell of a spacecraft to its internal components. The object of the study is the GOCE satellite, which has been recognized to be very sensitive to small disturbances because of its payload that has been designed to measure even very low acceleration levels. In the first step presented hereafter, the test campaign has been focused on the qualification of the background environment inside the impact chamber and on the determination of the vibration levels induced by perforating and non-perforating hypervelocity projectiles on simple aluminum plates. The results currently obtained and a preliminary data analysis will be presented in the following.     

Historical overview of hypervelocity impact diagnostic technology

The ability to understand hypervelocity impact phenomena and to validate predictive models of material behavior is largely dependent on the diagnostic tools available to the experimenter. These tools range from simple, post-impact examination of targets to extremely sophisticated and complex techniques, which simultaneously measure a myriad of impact parameters on a time scale of nanoseconds to milliseconds. This wide range of available techniques represents the challenge and opportunity if hypervelocity impact experimentation.

There has been a continual challenge to develop diagnostic techniques with ever-increasing resolution, as higher velocities and pressures are achieved. Today's techniques provide the experimenter the means of measuring most hypervelocity impact parameters, including velocity, displacement, temperature, radiation, volumetric change, impluse, stress, and strain of the materials involved. However, the prospective quantum leap in impact velocities to be produced by electromagnetic and electrothermal launchers will require corresponding advances in diagnostic systems.

This paper examines the capabilities and limitations of the major diagnostic techniques for hypervelocity impact experimentation and traces their evolvement as useful laboratory tools.     

Experimental evidence of triboluminescence induced by hypervelocity impact

The emission of light due to crystal fracture, or triboluminescence (TL), is a phenomenon that has been known for centuries. One of the most common examples of TL is the flash created from chewing wintergreen Lifesavers^®. For the last couple of years, the authors have been measuring fluorescence properties of phosphors like zinc sulfide doped with manganese (ZnS:Mn). Preliminary results indicate that impact energies greater than 16 mJ produced measurable TL from ZnS:Mn. Light was generated from the interaction of a dropped mass and a small number of luminescence centers in the ZnS:Mn powder. To extend this research, a two-stage hypervelocity light gas gun located at NASA's Marshall Space Flight Center (MSFC) was used to evaluate equipment and settings that show promise for hypervelocity TL detection. In these experiments, a projectile was accelerated to approximately 5–6 km/s before striking a ZnS:Mn phosphor-coated aluminum plate. This paper will provide an overview into the first experimental evidence of TL emission from ZnS:Mn due to hypervelocity impact. It is hoped that these results will generate interest in future hypervelocity research.     

Investigation and comparison between new satellite impact test results and NASA standard breakup model

This paper summarizes two new satellite impact tests conducted in order to investigate on the outcome of low- and hypervelocity impacts on two identical target satellites. The first experiment was performed at a low velocity of 1.5 km/s using a 40-g aluminum alloy sphere, whereas the second experiment was performed at a hypervelocity of 4.4 km/s using a 4-g aluminum alloy sphere, by a two-stage light gas gun. To date, approximately 1500 fragments from each impact test have been collected for detailed analysis. Each piece was analyzed based on the method used in the NASA standard breakup model 2000 revision. The detailed analysis will conclude (1) the similarity in mass distribution of fragments between low- and hypervelocity impacts encourages the development of a general-purpose mass-based distribution model applicable for a wide impact velocity range, and (2) the difference in area-to-mass ratio distribution between the impact experiments and the NASA standard breakup model suggests to describe the area-to-mass ratio by a bi-normal distribution.     

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 of small masses on large surfaces of piezoelectric ceramics

The hypervelocity impact of small masses on large surface piezoceramics was investigated to study the impact behavior of hypervelocity projectiles. From a linear elastic model obtained at lower velocities, solutions were found for the hypervelocity case which determine both the size and the momentum of impacting projectiles from the rising slope of the charge signal generated by the impact. The results lead to the development of a new generation of impact detectors for small masses at hypervelocities which consists only of a plate of piezoceramic material.     

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.     

The response of materials to dynamic loading

The response of materials to hypervelocity impact spans a wide region of material behavior, ranging from high impact pressures and temperatures, where thermodynamic effects prevail, to low pressures where mechanical properties are important. This paper discusses thermomechanical and physical processes important to hypervelocity impact events, presents a perspective of theoretical foundations and provides an overview of current equation-of-state and constitutive modeling capabilities.     

The production and evolution of impact-generated magnetic fields

The production of magnetic fields within impact-generated plasma may explain magnetic fields that have been observed during hypervelocity impact experiments at the NASA Ames Vertical Gun Range. The effect of impact angle on the production and subsequent evolution of impact-generated magnetic fields is assessed using magnetic field data obtained during macroscopic hypervelocity impacts conducted within two ambient magnetic field environments. The configuration and duration of spontaneous impact-generated magnetic fields are round to have a strong dependence on impact angle, exhibiting a smooth transition from a cylindrically symmetric field configuration at vertical incidence to a strong bilaterally anti-symmetric field configuration at high obliquity; hence, crater-related paleomagnetic fields may yield a diagnostic signature of impact angle where other clues (shape, ejecta pattern) are absent or ambiguous. As direct result of some surprising experimental results, a first-order model of field generation during the cavitation regime of high incidence angle hypervelocity impacts is explored. A possible consequence of this model is that magnetic fields produced during hypervelocity impacts (especially those that form large craters) may be an important component of planetary magnetism—especially lunar magnetism during the last 3.6 billion years.     

Further validation of a general approximation for impact penetration depth considering hypervelocity gouging data

A first-order approximation of penetration depth is developed for use in engineering design. A survey of available penetration data is used to construct a one-dimensional approach for estimating the geometry of a crater resulting from high-energy impact. The results are generalized to allow approximations to be made using existing experimental data without the requirement for laboratory testing. This approach for penetration depth approximation is validated using the hypervelocity gouging data from the Holloman High Speed Test Track (HHSTT) and hypervelocity gouging impact tests conducted by the authors.     

Material characterization and development of a constitutive relationship for hypervelocity impact of 1080 Steel and VascoMax 300

The area of hypervelocity impact and associated high energy is one of extreme interest in the research community. A specific example of this emphasis is the US Air Force test facility at Holloman Air Force Base which specializes in the field of hypervelocity impact testing. This Holloman AFB High Speed Test Track (HHSTT) is currently working to increase the speed of their test vehicle to above Mach 10. As the test sled's speed has increased into the Mach 8.5 range, a material interaction has developed which causes “gouging” in the rails or the sled's “shoes” and this starts a process that can result in catastrophic failure. In the tests that do not structurally fail, the rails and shoes are damaged. Previous efforts in investigating this event have resulted in a choice of the most suitable computer code (CTH), and a model of the shoe/rail interaction. However, the specific materials present in this impact problem were not available in CTH. In this work, the specific materials present at the HHSTT (VascoMax 300 and 1080 Steel) will be characterized using the Split Hopkinson Bar Test and a Johnson–Cook constitutive model will be developed. The model will then be validated by comparison to a series of Taylor impact tests. The coating materials utilized on the rails at the HHSTT will also be evaluated using a Taylor impact test.     

高速粒子撞击作用下LF6合金多层靶结构防护能力研究

针对总厚度为４ｍｍ的ＬＦ６合金双层靶和总厚度为２ｍｍ的三层靶进行了直径为２ｍｍ,速度分别为５．８和７．２ｋｍ／ｓ的ＧＣｒ１５粒子 撞击试验,并对双层靶进行了不同前靶厚度和靶间距的撞击试验,试验结果表明：与同样碰撞条件下半无限体靶上产生的破坏情况相比,多层靶被击穿的总厚度远淖于半无限体靶上形成的弹坑深度,采用多层靶结构可显著提高材料的抗高速粒子撞击能力,并大大降低航天器抗高速粒子撞击的防护结构的重量     

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.     

空间碎片高速撞击的数值模拟方法评述

计算机数值模拟是实现空间碎片撞击效应地面模拟的重要手段之一。撞击速度增加,撞击的物理机制和效应将发生改变,计算机数值模拟方法也应随之丰富和全面。介绍了基于有网格和无网格方法的高速撞击数值模拟发展历程,并针对数值模拟中常用的有限元法和SPH法进行了分析比较,阐述了高速撞击计算机模拟中无网格法的计算优势,并提出量子力学在未来无网格法数值模拟中的可能应用。为空间碎片高速撞击更加真实可靠的数值模拟提供参考。     

Hypervelocity impact in metals, glass and composites

This paper is a review of hypervelocity impact research carried out during the intense activity period leading up to the Apollo lunar missions. It is intended as a historical note on the research into hypervelocity impact phenomena in metallic, glass, and composite materials and the spacecraft applications of that research. The specific areas covered include cratering and spallation in thick, semi-infinite targets, perforation and hole formation in thin, single-thickness targets, spaced dual sheet armor, impact radiation, and impact ionization. Optimum and nonoptimum dual sheet combinations are treated in some detail because of the current interest in hypervelocity impact protection for the Space Station. On the other hand, the treatment of hypervelocity impacts on composites, phenolic resins and thermosetting epoxy systems reinforced with graphite or other high strength fibers, is limited because work in this area has just begun.     

Micrometeoroid impact on ceramic thin components for interplanetary probe

A new advanced ceramic thruster made of monolithic silicon nitride (Si₃N₄) is under development for the next interplanetary probe of PLANET-C Venus exploration mission in Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA). In order for secure operation of a spacecraft with a ceramic component onboard a real mission, the reliability against micrometeoroid impacts on the ceramic component has to be investigated in addition to the quasi-static mechanical and thermal analyses and verifications. First, the risk probability of the micrometeoroid impacts was evaluated by using an interplanetary flux model, and the risk evaluation in terms of impact energy was proposed by combining the velocity distribution with the flux model. The probability of impacts on the ceramic thruster during the mission was estimated with this model. Second, hypervelocity impact tests were performed with a two-stage light-gas gun. Three types of failure were observed: one was only a crater formed on the impact surface. Another type was crater formation on the front-face and spall fracture on the back-face and in the last type a perforation was formed in addition to cratering and spalling. The samples did not either shatter or breakdown for the impact energies tested in this study. The impact failure morphology observed in this study showed dependency on the plate thicknesses and the projectile kinetic energy. The energy-based risk evaluation together with the series of the hypervelocity impact tests indicated that the silicon nitride ceramic thruster onboard the interplanetary probe would have only a local damage and survive during the mission term.     

Triboluminescent properties of zinc sulfide phosphors due to hypervelocity impact

The emission of light due to crystal fracture, or triboluminescence (TL), is a phenomenon that has been known for centuries. One of the most common examples of TL is the flash created from chewing Wint-O-Green Lifesavers^®. From 2004 to 2006, research was completed using the two-stage light gas gun located at the NASA Marshall Space Flight Center (MSFC) in Huntsville, Alabama to measure the TL properties for zinc sulfide doped with both manganese (ZnS:Mn) and copper (ZnS:Cu). Results clearly show that hypervelocity impact-induced TL has been observed for both ZnS:Mn and ZnS:Cu. For ZnS:Mn, TL produced during 4.7 and 5.7 km/s impacts was statistically more luminous than was observed from similar data collected at 3.3 km/s. The TL decay time for ZnS:Mn was found to be 292 ± 58 μs, which is totally consistent with earlier measurements that did not use impact as an excitation source. Further, the emission of TL from ZnS:Mn undergoing hypervelocity impact has been demonstrated to have a significant component at the known peak emission wavelength of ZnS:Mn of 585 nm. Small TL emission generated as a result of hypervelocity impact was also observed from ZnS:Cu. The most intriguing conclusion from this research is that it may be possible to discriminate impact velocity by measuring the time-integrated luminosity of TL phosphors. An ability to measure the velocity of a hypervelocity impact is a significant indicator of the potential usefulness for this concept for use as an impact sensor in future spacecraft.     

Explosive simulation to investigate enhanced ablator removal

We have developed a method to simulate with explosives the impact and penetration of a recentry vehicle (RV) shell by a high-density hypervelocity fragment. Using a two-dimensional Lagrangian hydrocode, we modeled various hypervelocity fragment impact conditions and innovative explosive configurations that simulate the impact effects. The method is based on matching the damage inflicted on the heatshield by the impact and penetration of the fragment. Specifically, we set a simulation objective of matching the hole size, the time history of the stress environment, and the final effective plastic strain field for both the silica phenolic heatshield and aluminum layers while keeping the momentum imparted to the target the same. The calculations showed that the explosive jet from an explosive charge placed inside a short disposable steel barrel produced a hole that matched the simulation criteria reasonably well except that the aluminum substrate stretched excessively before failing. A much improved simulation was obtained when the target was penetrated with a fragment projected by an explosive charge. All the simulation criteria listed above were matched very well, indicating that explosive simulation can be used to simulate the impact of hypervelocity fragments with a high degree of fidelity.