Optical Fragment Tracking in Hypervelocity Impact Experiments

Paper number

IAC-17,A6,3,7,x40359

Author

Mr. Erkai Watson, Fraunhofer - Institut für Kurzzeitdynamik, Ernst-Mach-Institut (EMI), Germany

Coauthor

Dr. Max Gulde, Fraunhofer EMI, Germany

Coauthor

Mr. Lukas Kortmann, Fraunhofer - Institut für Kurzzeitdynamik, Ernst-Mach-Institut (EMI), Germany

Coauthor

Dr. Frank Schäfer, Fraunhofer EMI, Germany

Coauthor

Dr. Stefan Hiermaier, Fraunhofer - Institut für Kurzzeitdynamik, Ernst-Mach-Institut (EMI), Germany

Year

2017

Abstract

In-orbit collisions between spacecraft and space debris are increasingly likely due to the growing number of satellites in orbit. In order to model and predict the future debris environment, detailed information about the fragmentation process is needed. Spatially and temporally resolved fragmentation information is however limited due to the high-speed nature of the phenomena. In this paper, we propose a technique for tracking debris cloud fragments, capable of resolving mass and velocity information in hypervelocity impact (HVI) experiments. 

In order to measure spatio-temporal fragmentation information, we make use of established techniques such as Particle Tracking Velocimetry (PTV) and Particle Image Velocimetry (PIV), originally developed for fluid dynamics, and adapt them to HVI experiments. The experimental setup involves using a high-power continuous wave laser to create a thin laser plane placed parallel to and within the expanding post-impact fragment cloud. Perpendicular to this plane is a high-speed video camera, which records an image sequence of the fragments as they move along the laser sheet. In this way, we record a series of images containing only the particles illuminated by the laser plane.

We process the image sequence by identifying individual fragments in each image and stacking them into a 3D position-time space (XYT). Individual trajectories are then identified as straight lines in the XYT space with the Random Sample Consensus (RANSAC) algorithm, thereby creating a Lagrangian description of the fragments. We estimate the fragment mass with an algorithm that determines each fragment’s area and averages this result over the entire recorded trajectory of the fragment.  This reduces errors caused by tumbling, or partially obscured fragments.

In this paper, we demonstrate the capabilities of this method by presenting a study of HVIs on aluminum bumper plates where we use our fragment-tracking algorithm to extract detailed information about the mass and velocity of the debris cloud fragments. We use data gathered from this experiment to calculate information about each tracked fragment, such as its trajectory, momentum, and point and time of ejection.  

Our fragment tracking technique applied to HVI experiments has been shown to yield spatio-temporal fragmentation information that could be extremely useful for validating HVI numerical simulations and space debris environment models.  Continued developments planned include algorithm robustness improvements, measuring three-dimensional trajectory information with multiple cameras, and correlating the mass distribution with post-impact collected debris fragments.

Abstract document

IAC-17,A6,3,7,x40359.brief.pdf

Manuscript document

IAC-17,A6,3,7,x40359.pdf (🔒 authorized access only).

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