Vision-Based Approach in Contact Modelling between the Footpad of the Lander and the Analogue Representing Surface of Phobos.

Marek Cała,Piotr Kohut,Daniel Wałach,Krzysztof Holak

doi:10.3390/s21217009

Abstract

Identifying solar system surface properties of celestial bodies requires the conducting of many tests and experiments in conditions similar to those found on various objects. One of the first tasks to be solved by engineers is determining the contact condition between the lander and the surface of a given celestial body during landing in a microgravity environment. This paper presents the results of experimental studies and numerical simulations of the contact phenomenon between the lander foot model and the Phobos analogue. The main goal of the experimental tests was to obtain measured deformation data of the studied analogues using 2D and 3D vision systems, which were employed to analyze the behavior of the lander foot and the surface of the studied analogue itself and to calibrate the numerical models. The analogue representing the Phobos surface was foam concrete. The variable parameters in the study were the analogue thickness and the lander foot velocity at the time of contact. Tests were conducted for three different contact velocities of 1.2 m/s, 3.0 m/s, and 3.5 m/s. Taking into account the mass of the lander foot model, kinetic energies of 30.28 J, 189.22 J, and 257.56 J were obtained. The results showed that at low contact velocities, and thus low kinetic energies, no significant differences in behavior of the material directly under the lander foot were observed, and similar values of forces in the lander foot were obtained. For higher contact velocities, the behavior of analogues with varying thicknesses was different, resulting in different values of analogue deformation and dynamics of increments and decrements of force in the lander foot itself. Although performed on a single material, the experiments revealed different behaviors depending on its thickness at the same impact energy. This is an essential guideline for engineers who need to take this fact into account when designing the lander itself.

Highlights

In recent years, advanced image processing methods and computer vision systems have found applications in many branches of science and industry
The obtained results of the strength and deformation parameters unequivocally indicated a significantly higher stiffness of the concrete base in relation to the applied foam-concrete analogue, which supported the assumed model of the research material, which was to be characterized by a stiff base and a surface material in the zone of direct contact with the lander footing with significantly lower stiffness
The results refer to the 30 cm and 10 cm thick analogues and the velocity of the lander’s foot in the moment of contact at the following values, namely 1.2 m/s, 3.0 m/s, and 3.5 m/s, which are assumed to be descriptive for this type of test

Summary

Introduction

In recent years, advanced image processing methods and computer vision systems have found applications in many branches of science and industry. The basic principle of visionbased methods is an analysis of information encoded in the light reflected from surfaces of objects and captured in the form of 2D images by a camera’s sensor, or in the form of video files, which contain temporal changes of the observed object’s image. This approach makes it suitable for a measurement in which a direct contact of a sensor with the measured structure is undesirable or impossible due to geometrical limitations.

Methods

Results

Conclusion