Browsing by Author "Di Fraia, Marco Zaccaria"

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    Countermeasure Leveraging Optical Attractor Kits (CLOAK): interpretational disruption of a visual-based workflow
    (SPIE, 2020-09-20) Di Fraia, Marco Zaccaria; Chermak, Lounis
    Due to their negligible cost, small energy footprint, compact size and passive nature, cameras are emerging as one of the most appealing sensing approaches for the realization of fully autonomous intelligent mobile platforms. In defence contexts, passive sensors, such as cameras, represent an important asset due to the absence of a detectable external operational signature – with at most some radiation generated by their components. This characteristic, however, makes targeting them a quite daunting task, as their active neutralization requires pinning a small angular diameter moving at a high speed. In this paper we introduce an interpretational countermeasure acting against autonomous platforms relying on featurebased optical workflows. We classify our approach as an interpretational disruption because it exploits the heuristics of the model used by the on-board artificial intelligence to interpret the available data. To remove the struggle of accurately pinpointing such an imperceptible target, our approach consists in passively corrupting, from a perception point of view, the whole environment with a small, sparse set of physical observables. The concrete design of these systems is developed from the response of a feature detector of interest. We define an optical attractor as the collection of pixels inducing an exceptionally strong response for a target feature detector. We also define a physical object inducing these pixel structures for defense purposes as a CLOAK: Countermeasure Leveraging Optical Attractor Kits. Using optical attractors, any optical based algorithm relying on features extraction can potentially be disrupted, in a completely passive and nondestructive fashion.
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    NAV-Landmarks: deployable 3D infrastructures to enable CubeSats navigation near asteroids
    (IEEE, 2020-08-21) Di Fraia, Marco Zaccaria; Chermak, Lounis; Cuartielles, Joan-Pau; Felicetti, Leonard; Scannapieco, Antonio Fulvio
    Autonomous operations in the proximity of Near Earth Objects (NEO) are perhaps the most challenging and demanding type of mission operation currently being considered. The exceptional variability of geometric and illumination conditions, the scarcity of large scale surface features and the strong perturbations in their proximity require incredibly robust systems to be handled. Robustness is usually introduced by either increasing the number and/or the complexity of on-board sensors, or by employing algorithms capable of handling uncertainties, often computationally heavy. While for a large satellite this would be predominantly an economic issue, for small satellites these constraints might push the ability to accomplish challenging missions beyond the realm of technical possibility. The scope of this paper is to present an active approach that allows small satellites deployed by a mothership to perform robust navigation using only a monocular visible camera. In particular, the introduction of Non-cooperative Artificial Visual landmarks (NAVLandmarks) on the surface of the target object is proposed to augment the capabilities of small satellites. These external elements can be effectively regarded as an infrastructure forming an extension of the landing system. The quantitative efficiency estimation of this approach will be performed by comparing the outputs of a visual odometry algorithm, which operates on sequences of images representing ballistic descents around a small non-rotating asteroid. These sequences of virtual images will be obtained through the integration of two simulated models, both based on the Apollo asteroid 101955 Bennu. The first is a dynamical model, describing the landing trajectory, realized by integrating over time the gravitational potential around a three-axis ellipsoid. The second model is visual, generated by introducing in Unreal Engine 4 a CAD model of the asteroid (with a resolution of 75 cm) and scattering on its surface a number N of cubes with side length L. The effect of both N and L on the navigation accuracy will be reported. While defining an optimal shape for the NAV-Landmarks is out of the scope of this paper, prescriptions about the beacons geometry will be provided. In particular, in this work the objects will be represented as high-visibility cubes. This shape satisfies, albeit in a non-optimal way, most of the design goals.
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    Perception fields: analysing distributions of optical features as a proximity navigation tool for autonomous probes around asteroids
    (IEEE, 2021-08-19) Di Fraia, Marco Zaccaria; Feetham, Luke; Felicetti, Leonard; Sanchez, Joan-Pau; Chermak, Lounis
    This paper suggests a new way of interpreting visual information perceived by visible cameras in the proximity of small celestial bodies. At close ranges, camera-based perception processes generally rely on computational constructs known as features. Our hypothesis is that trends in the quantity of available optical features can be correlated to variations in the angular distance from the source of illumination. Indeed, the discussed approach is based on treating properties related to these detected optical features as readings of a field - the perception fields of the title, assumed induced by the coupling of the environmental conditions and the state of the sensing device. The extreme spectrum of shapes, surface properties and gravity fields of small celestial bodies heavily affects visual proximity operational procedures. Therefore, self-contained ancillary tools providing context and an evaluation of estimators' performance while using the least number of priors are extremely significant in these conditions. This preliminary study presents an analysis of the occurrences of optical feature observed around two asteroids, 101955 Bennu and (8567) 1996 HW1 in visual data simulated within Blender, a computer graphics engine. The comparison of three different feature detectors showed distinctive trends in the distribution of the detected optical features, directly correlated to the spacecraft-target-Sun angle, confirming our hypothesis.