Oblique hypervelocity impacts: Implication for the analysis of material retrieved after exposure to space

In the past few years, a wide variety of surfaces have been brought back to Earth after being exposed to the space particulate environment. The impact features found on this material can give clues to the characteristics of the impacting man-made debris and meteoroids. Many investigations have been carried out to deduce projectile parameters (size, shape, and velocity vector) from the morphology of impact features and their origin from the analysis of projectile remnants inside craters formed. However, there are still ambiguities in the interpretation of these results. Recently, the post-flight analysis of solar arrays retrieved from the hubble space telescope (HST) showed the lack of data concerning the interpretation of many impact features. In the present study, we have examined especially the distinctive features of craters caused by particles at oblique incidence. These craters represent more than one third of impacts with a size between 5 μm and 1 mm observed on the European Retrievable Carrier (EuReCa) and HST solar arrays. Interpretation difficulties of this kind of impacts on solar cells led to hypervelocity impacts test onto pure silica targets performed with iron projectiles at different incidence angles and different velocity ranges. They were made in order to find a possible link between the incidence angle of a projectile, the impact velocity, and the parameters, which could be deduced from the analysis of the crater and projectile remnants. A detailed survey of impacts features formed was done for each couple angle velocity. High-resolution observations show an evolution of the crater morphology and circularity with the increasing angles of incidence and velocity, and some changes in the projectile remnants amount, appearance, and position are also noted.     

Acoustic response of aluminium and Duroid plates to hypervelocity impacts

The growing need for real-time impact sensors for deployment on both space vehicles and space habitats (in orbit or on the surface of atmosphere-less bodies such as the Moon) has stimulated sensor development programmes. The sensors should be low mass, low power, easily read-out electronically, cover large areas and be sensitive to impacts which can cause damage up to and including penetration. We propose that piezo-strain acoustic sensors can play an important role in this work. Accordingly we report on a series of hypervelocity impact tests of acoustic sensors mounted on thin plates (aluminium and Duroid plates). The acoustic sensors gave strong signals for impacts of sub mm-mm scale projectiles. We investigated dependences on impactor speed and size, angle of incidence and tested the difference between cratering and penetrating impacts.     

Cavity and crater depth in hypervelocity impact

We discuss the depth of cavities and craters caused by hypervelocity impacts as a function of impact parameters such as impact velocity, projectile and target densities, and projectile diameter, in two extreme cases: the penetration of intact projectiles at low impact pressure and the hemispherical excavation at very high impact pressure. The relations between the depth and the impact parameters are obtained. Then, previous experimental results are compiled; crater depth normalized by projectile diameter and the ratio of projectile and target densities is plotted for glass, plastic, and metal projectiles and metal, rock, ice, foam, sheet-stack, and aerogel targets. The trends of the data are consistent with the relations in the extreme cases.     

Seeking radio emissions from hypervelocity micrometeoroid impacts: Early experimental results from the ground

High-velocity impact experiments have been conducted to look for radio frequency (RF) emissions from impact-produced plasmas that could be used to identify micrometeoroid impacts to spacecraft in orbit. Launched by a three-stage light gas gun, 17 mm diameter by 0.9 mm thick Ti6Al-4V flyer plates impacted 0.75 mm thick indium (In) foil at more than 10 km s⁻¹. The resulting collision presumably ionized some fraction of the vaporized In cloud, which was accelerated to about 12 km s⁻¹. This weak In plasma then passed through a wide-band detection system that looked for RF emissions. Over the course of five shots during the experiment, no conclusive plasma emissions from the In were detected. However, strong evidence indicates that significant charge is accumulated on the flyer plate during acceleration and flight, possibly producing Paschen discharge to the chamber walls. Finally, plasma may be produced by the launcher secondary to launching the plate, leading to further contamination of the results. These effects have significant consequences for RF experiments attempted in launching systems of this type.     

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.     

Numerical modeling of hypervelocity impacts

This research presents a new “finite-size particle in cell” method developed for numerical modeling of processes at high energy density. It uses the Lagrangian–Eulerian representation of media which allows one to match contact and free surfaces and to calculate flows with strong deformations. Efficient models of thermodynamic properties, elastic–plastic deformation and fragmentation have been employed in the gas dynamic code adapted for parallel computations. 3D and 2D numerical modeling of plate penetration by impactors of different geometry has been done in a wide range of velocities. The influence of used materials properties models on numerical results has been investigated.     

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.     

On hypervelocity penetration of the mesh-bumper strings into a projectile

An elastic–plastic model describing hypervelocity penetration of a mesh-bumper string by an arriving projectile is presented. An analytical solution for the case of rigid penetration is derived whereby the dependence between penetration depth and impact velocity is established. A comparative analysis between rigid penetration and penetration with a spreading string is performed. The mesh strings interact between each other with the aid of flow arising during penetration. The model which is developed allows us to estimate destruction depth of the projectile during its interaction with the mesh strings.     

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.     

Numerical simulations of hypervelocity impact of asteroid/comet on the Earth

In this study, numerical simulations of asteroid/comet impact on the earth were carried out by using the hydrocode AUTODYN-2D (Century Dynamics Inc.). The ejected mass into the atmosphere originated from different sources was recorded at different altitudes as a function of time. It is claimed that the mass extinction at the Permian–Triassic (P/T) boundary was caused by an extraterrestrial impact and the following abrupt climate/environment change. The objective of this work is to substantiate the claim with numerical analysis. It is demonstrated that the materials from different origins are splashed into the atmosphere and that the crater size is a function of the diameter as well as the kinetic energy of the impactor. The effect of impact angle to the appearance of ejected materials is also investigated using two-dimensional plane strain model.