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Formation Control of Flying Spacecraft over Signed Networks with Inter-Satellite Constraints
No full textInternational audienceThis paper addresses the distributed formation control problem of networked satellites operating in cooperative and competitive settings. We propose a distributed bipartite formation controller that guarantees connectivity maintenance among cooperative satellites while preventing collisions between interconnected satellites. We design a gradient-based control law using barrier-Lyapunov functions to ensure that the constraints on the inter-satellite distances are satisfied. Moreover, we establish asymptotic stability of the bipartite formation manifold for almost all initial conditions satisfying the required constraints. Finally, the proposed approach is illustrated through a numerical simulation.</div
Solving Approaches for High Multiplicity RCPSP with Learning Effect and Compound Activities
No full textInternational audienceThis paper addresses the High Multiplicity Resource-Constrained Project Scheduling Problem (HM-RCPSP), in which multiple projects are performed iteratively while sharing limited resources. We extend this problem by integrating the learning effect, which makes the duration of some activities decrease when they are repeated. Learning effect can be represented by any decreasing function, allowing us to get flexibility in modeling various scenarios. Additionally, we take composition of activities into consideration for reasoning about precedence and resources in a more abstract way. A Constraint Programming model is proposed for this richer problem, including a symmetry-breaking technique applied to some activities. We also present a heuristic-based search strategy. The effectiveness of these solving approaches is evaluated through an experimentation conducted on data concerning real-world satellite assembly lines, as well as on some adapted literature benchmarks. Obtained results demonstrate that our methods serve as robust baselines for addressing this novel problem (denoted by HM-RCPSP/L-C).Cet article traite du problème d'ordonnancement de projet avec ressources limitées et haute multiplicité (HM-RCPSP), dans lequel plusieurs projets sont exécutés de manière itérative tout en partageant des ressources limitées. Nous étendons ce problème en intégrant l'effet d'apprentissage, qui réduit la durée de certaines activités lorsqu'elles sont répétées. L'effet d'apprentissage peut être représenté par n'importe quelle fonction décroissante, ce qui nous permet une grande flexibilité pour modéliser divers scénarios. De plus, nous prenons en compte la composition des activités afin de raisonner de manière plus abstraite sur les dépendances de précédence et les ressources. Un modèle de Programmation par Contraintes est proposé pour ce problème enrichi, incluant une technique de réduction de symétrie appliquée à certaines activités. Nous présentons également une stratégie de recherche heuristique. L'efficacité de ces approches de résolution est évaluée à travers une expérimentation menée sur des données issues de lignes d'assemblage de satellites dans le monde réel, ainsi que sur des benchmarks adaptés de la littérature. Les résultats obtenus démontrent que nos méthodes constituent des bases solides pour aborder ce nouveau problème (désigné par HM-RCPSP/L-C)
Hybridizing machine learning and optimization for planning satellite observations
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Towards Scalable Collision Avoidance in Dense Airspaces with Deep Multi-Agent Reinforcement Learning
No full textInternational audienceIncreasing airspace congestion requires the development of robust collision avoidance systems to mitigate the risk of near mid-air collisions between aircraft. The Airborne Collision Avoidance System-X (ACAS-X) is a next-generation solution that provides both better conflict resolution maneuvers and fewer unnecessary actions compared to the conventional equipment (TCAS-II) currently used in most commercial and general aviation aircraft. ACAS-X is achieved through dynamic programming for one-to-one aircraft encounters. However, this solution still faces significant limitations, in particular the restriction to single intruder scenarios and the reliance on discretized state and action spaces. In this paper, we show that the naive application of ACAS-X to multi-threat scenarios leads to suboptimal and even catastrophic results. To address these issues, we formalize the multi-agent aircraft collision problem and argue for the adoption of deep multi-agent reinforcement learning (MARL) techniques, which have the potential to compute optimal maneuvers in complex multi-aircraft scenarios. Finally, we identify key challenges and open research questions for the multi-agent aircraft collision avoidance problem
Essais en soufflerie sur la géométrie BOLT à Mach 7 : comparaison entre installations et analyses de stabilités
No full textA subtask of this working group is focused on transition due to the interaction of multiple instability modes, and for this subtask, the Air Force Office of Scientific Research (AFOSR) Boundary Layer Transition (BOLT-1) geometry has been selected as a focus geometry. The BOLT-1 geometry has previously been shown to produce a complex flow field in which multiple boundary-layer instability modes are expected to occur simultaneously on the low-curvature concave surface of the geometry [1].Within the working group, new ground-testing campaigns were recently conducted by the German Aerospace Center (DLR) and the French Aerospace Lab (ONERA) with the French Alternative Energies and Atomic Energy Commission (CEA) on subscale models of the BOLT-1 flight experiment geometry. This chapter presents a comparison of transition measurements obtained in the two facilities at Mach 7. These measurements include global characterization of the transition front, as well as direct measurement of boundary-layer instabilities.The ground test results will be compared to stability analyses performed using different methods. Two experi-mental conditions at Mach 7 were identified for further computational study to be conducted collaboratively by the Johns Hopkins University Applied Physics Laboratory (APL), the NASA Langley Research Center (LaRC), the University of Kentucky, and the University of Maryland. The present analysis shall employ transition-prediction tools that are suited to the study of flowfields with strong variation in multiple dimensions, as en-countered on BOLT. The first analysis technique to be considered is a combination of 2D eigenvalue analysis and planar-marching PSE (PMPSE) methodologies, which allow for disturbances to vary strongly in a plane, as opposed to just the wall-normal direction [2–4]. The PMPSE will be performed using two different tools: the Sandia LSTPACK code and the NASA LaRC MAtrix Forming Instability Analysis (MAFIA) code. The second technique used to study the BOLT flowfield stability is referred to as Adaptive Mesh Refinement Wavepacket tracking (AMR-WPT). Comparison of the PMPSE and AMR-WPT results will be made to legacy Linear Sta-bility Theory (LST) methods using the NASA LaRC Stability and Transition Analysis Code (LASTRAC) and line-marching PSE (LMPSE) results from MAFIA, which assume spanwise homogenous flow
Les accéléromètres de l’ONERA pour la mission NGGM et les futures missions de gravité
No full textInternational audienceThe 2017-2027 Decadal Survey for Earth Science and Applications from Space has identified the Targeted Mass Change Observable as one of 5 Designated Mission. In Europe, the development of the ESA Next Generation Gravity Mission is on progress, with the start of the Phase B in 2024.These missions will continue the observation provided by GRACE and GRACE-FO. In these missions and the future concepts, the accelerometer provides either the gravity signal in a gradiometer configuration (GOCE type mission), or the non-gravitational acceleration to be suppressed to the ranging measurement between two satellites (GRACE-type mission).In the frame of NGGM activities with ESA, Onera is developing the new accelerometer MicroSTAR, a high accuracy accelerometer with 3 sensitive linear acceleration measurements as well as 3 angular acceleration measurements for the attitude control or reconstruction. PDR of the accelerometer chain has been done at the end of year 2024 and CDR of the accelerometer sensor head will be held in May 2025.ONERA have procured the accelerometer for all the previous gravity missions (GRACE, GOCE, GRACE-FO). In parallel, ONERA work to improve the scientific return of the instruments for the future missions:a miniaturized version of MicroSTAR, the CubeSTAR accelerometer, is developed with internal funding. CubeSTAR is adapted for constellation or nanosat, An other way is to improve the low-frequency noise of the accelerometer, by hybridization of electrostatic accelerometer with cold atom interferometer. The presentation will present the status of the MicroSTAR development, and will detail the development of future instruments
EASA Helicopter Vortex-Ring-State Experimental Research Project
No full textInternational audienceThe vortex ring state (VRS) is an aerodynamic condition for helicopters that develops at low airspeeds and moderate descent rates. The result is an unsteady turbulent flow over a large area of the disk with a toroidal shape, called vortex ring. The VRS is characterized by high vibration, uncommanded pitch and roll oscillation, and limited control power of the flight controls, while high descent rate may be developed up to 4 000 fpm. Although known and largely studied, this phenomenon remains the cause of numerous accidents every year and many questions are still open, regarding the flight conditions at which it starts to develop for example, the main parameters influencing and contributing to its symptoms and effects, or the effectiveness of the recovery techniques currently applied.In order to better understand the VRS phenomenon on different types of helicopters and to evaluate the effectiveness of recovery maneuvers such as the one proposed by Capt. Vuichard, the European Union Aviation Safety Agency (EASA) launched the Helicopter Vortex-Ring-State Experimental Research project (EASA.2022.C11) in November 2022. This project was conducted under a contract between the EASA and ONERA/DGA-EV (French Flight Test Center) and was funded from the European Union's Horizon Europe research and innovation programme.The main objectives of this experimental research project were to determine the flight conditions at which the VRS starts to develop for two different helicopters, to support and evaluate the correctness of theoretical methods for prediction of the vortex boundaries and to evaluate the effectiveness of the classical and Vuichard recovery techniques for the considered helicopters.The project outcome will be a key element for the EASA in the assessment of the need for possible changes to the certification specifications, pilot training regulations and associated guidance material
Correcting Differential Reynolds Stress Models Using Data-Assimilation
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Qualification des modèles de microclimat et des outils de simulation : une intercomparaison académique
No full textInternational audienceIn recent decades, numerous urban microclimate models have been developed to address various applications, such as diagnosing urban overheating and evaluating heat mitigation strategies using green or grey solutions. These models account for complex physical interactions; however, their qualification and validation remain significant challenges due to their complexity and the lack of a standardized framework and comprehensive reference datasets.This paper presents the first step of a comprehensive qualification and validation methodology through the definition of an academic benchmark and its application to four urban microclimate models. The proposed methodology follows an incremental phenomenological approach, systematically analysing heat transfer processes within an idealized street canyon with well-defined conditions across four cases: shortwave radiation, longwave radiation, aeraulics, and their coupling with heat conduction and storage in walls and ground. The benchmark aims to analyse the behaviour of different microclimate models, quantify deviations between simulation results, and identify their underlying sources within the physical models. This is achieved through the intercomparison of simulation results, incorporating reference data with a known standard deviation where available.The results show good agreement between models for solar radiation, infrared radiation, and heat conduction but reveal significant deviations in surface convection, stressing the need for further research into convection modelling and its influence on coupled processes. Additionally, the results confirm the suitability of the proposed methodology in identifying the sources of deviations between models. This benchmark provides a robust framework for model qualification and is expected to be widely adopted in future studies.Au cours des dernières décennies, plusieurs modèles de microclimat urbain ont été développés et utilisés pour diverses applications. Ces modèles permettent de diagnostiquer les surchauffes urbaines ou d'évaluer différentes stratégies d'atténuation de la chaleur, basées par exemple sur des solutions vertes ou grises, en tenant compte de toutes les interactions physiques. Cependant, leur validation reste un défi pour la recherche, en raison de leur complexité et de l'absence d'un cadre de qualification commun. Cet article propose et met en œuvre la première étape d'une méthodologie de qualification commune progressive par le biais d'un benchmark sur une étude de cas académique idéale, correspondant à un canyon de rue. La méthodologie proposée vise à analyser d'abord, de manière aussi indépendante que possible, les différents phénomènes physiques simulés, tels que le rayonnement solaire, le rayonnement infrarouge, l'aéraulique et la conduction thermique, puis leur couplage. Cette méthodologie a été appliquée à quatre modèles de microclimat urbain : MATHIS, SOLENE-Microclimat, SOLENE-SUSHI et TRABOULE-ProLB, mettant en évidence leurs capacités respectives, leurs similitudes et leurs différences. Dans l'ensemble, les résultats montrent une bonne correspondance pour le rayonnement solaire, le rayonnement infrarouge et la conduction thermique, mais des écarts significatifs pour la convection à la surface. Ces résultats soulignent l'importance de poursuivre les travaux de recherche sur la modélisation de la convection. Ils montrent également la pertinence de la méthodologie développée afin d'évaluer l'origine des divergences entre les modèles. Par conséquent, cette méthodologie devrait être appliquée plus largement à l'avenir