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Moon to mars: Challenges and strategic frameworks for space traffic management in cislunar and cismartian environments
No full textInternational audienceThis chapter comprehensively explores the unique challenges, risks, and gaps associated with managing space traffic in cislunar and cismartian environments, focusing on the complexities introduced by the Moon-to-Mars mission trajectory. It examines the technical hurdles, such as astrodynamics, communication, and Positioning, Navigation, and Timing (PNT) systems, which are critical for safe and effective space traffic management (STM) in regions beyond geostationary orbit (xGEO). The report also addresses the escalating issue of space debris in these areas, which poses significant threats to future lunar and Martian missions, underscoring the urgent need for innovative debris mitigation strategies.The chapter emphasizes the necessity of developing a robust international policy and legal framework to govern space activities in the increasingly congested cislunar and cismartian regions. It highlights the current gaps in existing treaties and regulations, particularly concerning planetary protection and space traffic coordination around the Moon and Mars. The report calls for international cooperation and enhanced data sharing as essential components of a sustainable and secure space environment, recommending establishing an international civil agency to lead space traffic coordination and the development of an open architecture database for space object monitoring.Concluding with actionable recommendations, the chapter proposes leveraging lessons learned from aviation, maritime, and Antarctic governance to inform space traffic management practices in cislunar and cismartian contexts. It advocates for ongoing international dialogue and collaboration through established organizations and new initiatives to ensure the safe, responsible, and efficient use of space for the benefit of all humankind. This chapter serves as a call to action for stakeholders to address the immediate and long-term challenges of space traffic management in cislunar and cismartian environments, paving the way for successful and sustainable Moon-to-Mars missions
Microstructure Evolutions in Ni-Based Superalloys Under Complex Creep Loadings
No full textInternational audienceThe phase field method has emerged as the most powerful method for modelling microstructure evolutions during phase transformations, particularly when elastic coherency stresses are generated in solids. However, in many materials, microstructural changes are coupled with plasticity. This is particularly the case for high temperature creep in nickel based superalloys.In this work, a three dimensional phase field model is coupled to a crystal plasticity model based on dislocation densities. This model includes both the anisotropy and the size dependence of the plasticity, which is expected when the plasticity is confined to a region smaller than a few microns. Several creep conditions are considered, such as tensile loadings along the [001], [011] and [111] directions, as well as shear loadings. The anisotropy of the rafting and its sensitivity to small misorientations is discussed, and the relative importance of elastic and plastic driving forces is analyzed
A probabilistic model to consider scale and gradient effects in the prediction of the fatigue life of Inconel 718 for turbine disk application.
No full textInternational audienceThe aim of this paper is to implement and compare different fatigue post-processing approaches for fatigue life assessment of complex parts. Inconel 718 is taken as an example, as it can exhibit several factors influencing fatigue life, such as mean stress, stress gradient and scale effects. Tests on different specimen geometries to exacerbate these effects were carried out at 550°C. The range of service operating life is between 103 and 106 cycles. A modelling chain was then set up. A structural calculation was performed using an elasto-visco-plastic behavior law to obtain the mechanical fields at cycle stabilize. These values were finally exploited by applying a post-processing treatment approach to predict the fatigue life of the structure. Two main types of post-processing approach were investigated: standard and probabilistic. The way in which the different factors influencing fatigue life are considered, depending on the approach used, was discussed. Finally, the probabilistic volume approach yields better results, thanks to its ability to consider mean stress, stress gradient and scale effects in the proposed formulation
Synthèse de Poly(diméthylsiloxane) autocicatrisants et leurs stabilités aux irradiations protons
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Isoler des hologrammes à particules uniques d'un hologramme à particules multiples Hologramme numérique
No full textInternational audienceA method is developed to isolate the interference-fringe pattern associated with an individual particle from a single digital in-line hologram containing overlapping patterns from multiple particles. The method is illustrated with a measured hologram of road-dust aerosol particles nominally 20-50 µm in size. It is further tested for 2.5-3.0 µm particles by simulation with the discrete dipole approximation. By incrementally degrading a hologram’s resolution, the method is shown to perform well for particles that are poorly resolved, at least for the first few central fringes in the pattern. The method may be useful in cases where particle characterization is done directly from a hologram, i.e., instead of from the reconstructed images.Une méthode est développée pour isoler le motif de franges d'interférence associé à une particule individuelle à partir d'un seul hologramme numérique en ligne contenant plusieurs motifs superposés de plusieurs particules. La méthode est illustrée par un hologramme mesuré de particules d'aérosol de poussière de route du Kansas d'une taille nominale de 20 à 50 μm. Elle est ensuite testée pour des particules de 1,5 à 3,0 μm par simulation avec l'approximation du dipôle discret. En dégradant progressivement la résolution de l'hologramme, la méthode s'avère efficace pour les particules qui sont mal résolues dans la reconstruction d'image, au moins pour les premières franges centrales du motif. La méthode peut être utile dans les cas où la caractérisation des particules est effectuée directement à partir d'un hologramme, c'est-à-dire au lieu des images reconstruites
Faisabilité de la détection des déversements d'hydrocarbures dans les environnements portuaires à partir de l'imagerie UV
No full textInternational audienceOil spills in ports are particular cases of oil pollution in water environments that call for specific monitoring measures. Apart from the ecological threats that they pose, their proximity to human activities and the financial losses induced by disturbed port activities add to the need for immediate action. However, in ports, established methods based on short-wave infrared sensors might not be applicable due to the relatively low thickness of the oil layer, and satellite images suffer from insufficient spatial resolution, given the agglomeration of objects in ports. In this study, a lightweight ultraviolet (UV) camera was exploited in both controlled experiments and a real port environment to estimate the potential and limitations of UV imagery in detecting oil spills, in comparison to RGB images. Specifically, motivated by the scarce research literature on this topic, we set up experiments simulating oil spills with various oil types, different viewing angles, and under different weather conditions, such that the separability between oil and background (water) could be better understood and objectively assessed. The UV camera was also used to detect real-world oil spills in a port environment after installing it on a vessel for continuous monitoring. Various separability metrics between water and oil, computed in both scenarios (controlled experiments and port environment), show that the UV cameras have better potential than RGB in detecting oil spills in port environments.Les marées noires dans les ports sont des cas particuliers de pollution pétrolière dans les milieux aquatiques qui nécessitent des mesures de surveillance spécifiques. Outre les menaces écologiques qu'elles représentent, la proximité des activités humaines et les pertes financières induites par les activités portuaires perturbées ajoutent à la nécessité d'une action immédiate. Cependant, dans les ports, les méthodes établies basées sur des capteurs infrarouges à ondes courtes peuvent ne pas être applicables en raison de l'épaisseur relativement faible de la couche de pétrole, et les images satellites souffrent d'une résolution spatiale insuffisante, compte tenu de l'agglomération d'objets dans les ports. Dans cet article, une caméra ultraviolette (UV) légère est exploitée à la fois dans des expériences contrôlées et dans un environnement portuaire réel pour estimer le potentiel et les limites de l'imagerie UV dans la détection des marées noires, par comparaison avec les images RVB. Plus précisément, motivés par la rareté de la littérature de recherche sur ce sujet, nous avons mis en place des expériences simulant des marées noires avec différents types de pétrole, différents angles de vue et dans différentes conditions météorologiques de sorte que la séparabilité entre le pétrole et le fond (eau) puisse être mieux comprise et évaluée objectivement. La caméra UV est également utilisée pour détecter les marées noires réelles dans un environnement portuaire après l'avoir installée sur un navire pour une surveillance continue. Différentes mesures de séparabilité entre l'eau et le pétrole, calculées dans les deux scénarios (expériences contrôlées et environnement portuaire), montrent que les caméras UV ont un meilleur potentiel que le RVB pour détecter les déversements de pétrole dans les environnements portuaires
Extending InSAR2InSAR to Sentinel-1 Data
No full textInternational audienceInterferometric SAR parameters estimation is a very important and challenging problem. The InSAR2InSAR method previously proposed is one of the few self-supervised methods that aims to estimate InSAR parameters. This method has proven to outperform state-of-the-art methods on simulated synthetic data. However, it has to be extended on real data. In this letter, we demonstrate that Sentinel-1 images acquired in the Interferometric Wide Swath mode possess the necessary properties to train and apply InSAR2InSAR effectively. In this paper, we demonstrate the ability of InSAR2InSAR to process across-track Sentinel-1 interferometric images with state-of-theart performances
Clustered Active Subspaces for Aerodynamic Shape Optimization
No full textInternational audienceWe present the Clustered Active Subspaces (CAS) method for global, constrained, surrogate-based aerodynamic shape optimization in high-dimensional design spaces. We start by clustering the design space based on function topology, before computing local Active Subspaces (AS) inside these clusters to capture local trends in the quantity of interest. Surrogate models are trained in these locally reduced spaces, where the lower number of hyperparameters allows for more precise construction and lower cost. We introduce a novel way to extend the local surrogate model training sets in order to improve surrogate model accuracy at the boundaries between clusters without requiring additional training points. Finally, the local experts are recombined into a smooth global surrogate model using a Mixture of Experts (MoE) formulation. This surrogate model is then iteratively enriched to perform constrained Surrogate-Based Optimization (SBO) of the quantity of interest. The well-known Efficient Global Optimization (EGO) framework is adapted to handle constrained EGO in the objective function’s reduced space, when the constraint lives in a separate Active Subspace. To further increase efficiency, an intelligent stopping criterion estimates convergence, stopping the EGO loop when the basin of attraction of the global minimum is discovered, enabling the switch to gradient descent to efficiently finish the optimization. The method's ability is demonstrated on the constrained aerodynamic shape optimization of a NACA0012 airfoil in transonic viscous flow.Nous présentons la méthode des Clustered Active Subspaces (CAS) pour l'optimisation aérodynamique de forme globale, sous contraintes, dans des espaces de conception à grande dimension. Nous commençons par partitionner l'espace de conception en fonction de la topologie de la fonction objectif, avant de calculer des Active Subspaces (AS) locaux au sein de ces clusters afin de capter les tendances locales de la grandeur d'intérêt. Des modèles de substitution sont entraînés dans ces espaces localement réduits, où le nombre réduit d'hyperparamètres permet une construction plus précise et à moindre coût. Les experts locaux sont recombinés en un modèle de substitution global lisse via un mélange d'experts (Mixture of Experts, MoE). Ce modèle de substitution global est ensuite enrichi de manière itérative pour réaliser l'optimisation Bayésienne sous contraintes de la grandeur d'intérêt. Le formalisme Efficient Global Optimisation (EGO) est adapté pour gérer d'optimisation Bayésienne sous contraintes dans l'espace réduit de la fonction objectif, lorsque la contrainte réside dans un sous-espace actif distinct. Pour accroître encore l'efficacité, un critère d'arrêt intelligent estime la convergence, interrompant la boucle EGO dès que le bassin d'attraction du minimum global est découvert, permettant d'embrayer sur un algorithme de descente de gradients et efficacement terminer l'optimisation. La méthode est testée par une optimisation aérodynamique d'un profil NACA0012 en écoulement visqueux transsonique, sous contrainte de portance
Simulation of a GaInP 2 -GaAs -GaInAsN -Ge photovoltaic cell for space applications
No full textInternational audienceWe use an open-source simulation software to design III-V multi-junction solar cells containing a dilute nitride subcell. We discuss the different modeling techniques in terms of physical models and numerical methods, and provide an educated guess for a GaInP2 -GaAs -GaInAsN -Ge lattice-matched 4-junction solar cell performance assessment. We suggest a way to ensure an effective computation of the main output values of an opensource Poisson-Drift-Diffusion solver for multi-junction solar cell analysis. An optimization of a multi-junction cell including a n-i-p subcell is performed, starting from basic theoretical considerations, to the use of a double-layer anti-reflective coating to target the most limiting subcell, and then with an optimization of the n-i-p architecture in the 1eV subcell with respect to the GaInAsN layer properties. We show that the detrimental effects of low diffusion lengths in the GaInAsN layer can be alleviated by taking advantage of field-assisted collection