Scramjets have been identified as a potential long-term replacement for rocket and ramjet propulsion systems due to their enhanced performance at high Mach numbers. The introduction of solid fuels in these scramjet systems allows for shaping of the solid fuel cavity by additive manufacturing and introduces the possibility of enhancing combustion rates and stability. The present investigation aims to develop a coupled, high-order computational model to study the combustion of solid fuel scramjets. The primary objectives are to identify the effects of changing geometry on combustion and to better characterize the combustion process and flow patterns within a solid fuel scramjet engine. The high-Mach number of the air inflow over a scramjet cavity introduces a strong coupling between fluid dynamics, combustion, and regression time scales. Existing models often use simplified treatments of melt-layer conditions and combustion models that over-predict experimental rates, along with highly dissipative numerical schemes that inhibit the study of thermo-acoustic interactions between coherent pressure waves and the burning walls of the cavity. These limitations in current models suggest the need for a Navier-Stokes solver based on a high-order, discontinuous Galerkin method, incorporating melt layer equations and enhanced combustion manifolds. These manifolds should account for the effects of pressure and high oxidizer temperatures on flamelet dynamics. The focus is on modeling the flow field with accurate chemical heat release and residence time, to better study the effects of heat flux on the solid surface and the resulting coupling. An investigation of solid fuel scramjets was performed, and the numerical methodology with which the problem was tackled is described. A novel combustion mechanism was developed using a counterflow burner to study the combustion and regression of solid model fuel polymethyl methacrylate (PMMA). The diffusion flame between the fuel and oxidizer was studied numerically using a solid fuel decomposition and melt layer model to simulate convection and pyrolysis of the material. This model was validated using new experimental data as well as previously published works. The foam layer parameters are critical to the success of the validation. Results showed that the increased residence time of the gas in the bubbles facilitates the fuel breakdown. Fully coupled fuel injection and solid fuel surface monitoring was implemented based on this counterflow model and was a function of heat flux. Fuel regression was handled using adaptive control points for a B-Spline basis that updates based on surface movement. This methodology was used due to its resilience against the creation of surface discontinuities likely to result from large temperature gradients during combustion. Fourth-order computational simulations of ramjet combustion without regressing fuel walls using an in-house Discontinuous Galerkin approach were performed with a fully conjugate solution for the thermal wave in the solid. Results in ramjet geometries showed the turbulent combustion strongly affects the heat feedback to the walls and thus increases both the regression and fuel injection rates. Scramjet geometries were also simulated using the flamelet-progress variable approach in two different oxidizer conditions. All of these simulations showed strong agreement with experimental data and helped to uncover flame holding characteristics of the scramjet cavities and the strong coupling between the recirculation region and pyrolysis of fuel. The analysis has led to a better understanding of the effects of solid fuel scramjet geometries on mixing, enhanced modeling of acoustic instabilities in solid fuel air-breathing propulsion, and improved fuel chemistry modeling. It has been shown that cavity design significantly influences heat transfer to the solid fuel in both ramjet and scramjet conditions. The presence and thickness of the melt layer will guide designs that aim to reduce or enhance mechanical removal of fuel. Additionally, ramjet results indicate that longer cavities can couple with acoustics to induce self-excited conditions, leading to increased heat transfer to the solid. The importance of self-sustained instability and its coupling with melt layer fuel injection will contribute to improved acoustic stability. Developing pressure/temperature-dependent manifolds and melt layer models will advance our understanding of solid fuel supersonic combustion and its effects on phenomena such as blowout, fuel residence time, and solid fuel dual-mode transition. / Doctor of Philosophy / Scramjets, a type of high-speed jet engine, could one day replace rockets due to their efficiency at very high speeds. By introducing solid fuels into these engines, researchers can use advanced manufacturing techniques to shape fuel cavities, potentially enhancing the engine's performance. This study focuses on developing a sophisticated computational model to understand how changes in engine geometry affect the combustion process in solid fuel scramjets. The research aims to better understand the complex interactions between airflow, combustion, and fuel consumption, with the ultimate goal of improving engine design. The findings from this research provide valuable insights into how different scramjet designs impact fuel combustion. For instance, the design of the fuel cavity can significantly affect heat transfer, influencing the efficiency and stability of the engine. The study also highlights the importance of understanding the interaction between airflow and fuel injection, which is critical for optimizing engine performance and ensuring reliable operation at high speeds. Overall, this research advances our understanding of solid fuel scramjets and contributes to the development of more efficient and stable high-speed propulsion systems. By improving our ability to model and predict the behavior of these engines, the findings will guide future designs, potentially leading to more effective and reliable scramjets for various applications, including space exploration and high-speed flight.

<p dir="ltr">The dynamics and characteristics of a high-speed compressible turbulent boundary layer or shear layer have significant effects on separation, heating, shockwave boundary layer interactions, effectiveness of control surfaces, and ultimately the performance of supersonic / hypersonic vehicles. Experimental data with high spatiotemporal resolution and low uncertainty is necessary for understanding complex flow physics and validating computational models. </p><p dir="ltr">Background oriented schlieren (BOS) is a technique derived from traditional schlieren imaging to provide whole-field, quantitative density gradient measurements with a simplistic setup at the expense of reduced spatial resolution and increased uncertainty. The majority of BOS applications focus on low-speed flows with an entocentric optical setup which causes low depth-of-field, wall-blurring, and perspective error issues, making conventional BOS not suitable for high-speed compressible turbulent flow settings. Additionally, despite the widespread adoption of BOS, it has primarily been used as an alternative visualization technique to traditional schlieren imaging and thus the quantitative capabilities of BOS are left under-exploited.</p><p dir="ltr">The workflow of BOS consists of image acquisition, displacement estimation, and integration of the density gradient field. The work presented in this thesis improves the image acquisition and displacement estimation of the BOS workflow by implementing a telecentric optical system and conducting a comprehensive comparison and optimization of several state-of-the-art displacement estimation techniques. Experimental results for a Mach 2 turbulent boundary layer exhibit high spatiotemporal resolution and low uncertainties and are compared against high-fidelity computational results for validation. This work also focuses on the development of BOS velocimetry capabilities, by leveraging ray tracing simulations of an LES turbulent shear layer. Overall this dissertation advances the accuracy, precision, spatial resolution, and capabilities of BOS for fluid dynamic applications relevant to defense and propulsion.</p>

As the world moves towards environmental sustainability, the civil aviation enterprise has responded by setting challenging goals for significantly increased energy efficiency and reduced harmful emissions into the atmosphere as codified by National Aeronautics and Space Administration (NASA) and Advisory Council for Aircraft Innovation and Research in Europe (ACARE). The airline industry supports these goals because of their positive impact on operational cost and the environment. Achieving such goals requires introduction of novel technologies and aircraft concepts. Previous studies have shown that electrified aircraft can be effective in meeting these challenges.While there are several mechanisms to incorporate novel technologies for electrified aircraft, two such technologies: turbo-electric propulsion and distributed propulsion, are used in this research. Integration of these two technologies with the airframe leverages the well-known favorable interference between the wing and the tractor propeller wake to provide increased lift during takeoff.In the present research, the advantages and disadvantages of integrating a turbo-electric distributed propulsion (TEDiP) system are assessed for a regional transport aircraft (RTA). With near term motor technology, an improvement in trip fuel burn was observed on the four and six propeller variants of the TEDiP aircraft. The takeoff field length(TOFL) also improved in all three design variants which is a direct result of the working of distributed propulsion leading to better aerodynamic performance at takeoff conditions.The approach and findings for this research are reported in this thesis. / Master of Science / While air transportation system is considered the fastest means to travel, the avi-ation industry is responsible for 2.1% of all human-induced CO2 emissions, whichputs a renewed emphasis on environmental sustainability. There is heightenedinterest in exploring alternative propulsion technologies for aviation to mitigatethe effects of ever increasing demand for air travel coupled with fossil fuel pricevolatility.Ambitious plans have been outlined by leading aerospace organizations to reduceharmful emissions into the atmosphere. Achieving these ambitious goals requiresdevelopment and introduction of game changing technologies and aircraft con-cepts. Few such concepts include novel propulsion systems like all electric andhybrid-electric propulsion, distributed propulsion, and boundary layer ingestion.The X-57 is a novel all-electric aircraft being developed by NASA as a technologydemonstrator and makes use of multiple electric motors and propellers placedon the wing.Owing to battery technology limitations, all-electric and hybrid-electric propul-sion are not considered as viable options. In the near term, incorporatingdistributed propulsion alongside turbo-electric propulsion, for a Turbo-ElectricDistributed Propulsion(TEDiP) system may be a promising option in the near--to-mid-term. The overall goal of the present study is to investigate potentialbenefits and penalties of TEDiP systems for regional transport aircraft (RTA).To perform this study, the aerodynamics module of Pacelab Aircraft PreliminaryDesign (APD) Multi-Disciplinary Optimization (MDAO) framework is alteredto account for changes in wing-propeller aerodynamics due to the interactionof wing and multiple propellers. This required selection of a cost-effective toolthat captures aerodynamic data for multiple propellers and wing. VSPAEROis the aerodynamic tool of choice for this research. Aerodynamic data fromVSPAERO is coupled to APD and three TEDiP design variants with four, sixand eight propeller are designed with the ATR 72-500 as the baseline. Thebenefits and penalties of integrating the TEDiP system onto these variants isinvestigatedThe results show that a performance comparable to the baseline can be achievedin the near term with the four propeller variant even with current electricalsystems technology trends with a small weight penalty, and in the medium termon a six propeller variant. A decrease in trip fuel burn and improved takeofffield length(TOFL) performance justifies the usage of TEDiP systems.

Conventional airliners use two to four engines in a Cayley-type arrangement to provide thrust, and the thrust from these engines is typically concentrated right behind the engine. Distributed propulsion is the idea of redistributing the thrust across most, or all, of the wingspan of an aircraft. This can be accomplished by using several large engines and using a duct to spread out the exhaust flow to form a jet-wing or by using many small engines spaced along the span of the wing. Jet-wing distributed propulsion was originally suggested by Kuchemann as a way to improve propulsive efficiency. In addition, one can envision a jet-wing with deflected jets replacing flaps and slats and the associated noise. The purpose of this study was to assess the performance benefits of jet-wing distributed propulsion. The Reynolds-averaged, finite-volume, Navier-Stokes code GASP was used to perform parametric computational fluid dynamics (CFD) analyses on two-dimensional jet-wing models. The jet-wing was modeled by applying velocity and density boundary conditions on the trailing edges of blunt trailing edge airfoils such that the vehicle was self-propelled. As this work was part of a Blended-Wing-Body (BWB) distributed propulsion multidisciplinary optimization (MDO) study, two airfoils of different thickness were modeled at BWB cruise conditions. One airfoil, representative of an outboard BWB wing section, was 11% thick. The other airfoil, representative of an inboard BWB wing section, was 18% thick. Furthermore, in an attempt to increase the propulsive efficiency, the trailing edge thickness of the 11% thick airfoil was doubled in size. The studies show that jet-wing distributed propulsion can be used to obtain propulsive efficiencies on the order of turbofan engine aircraft. If the trailing edge thickness is expanded, then jet-wing distributed propulsion can give improved propulsive efficiency. However, expanding the trailing edge must be done with care, as there is a drag penalty. Jet-wing studies were also performed at lower Reynolds numbers, typical of UAV-sized aircraft, and they showed reduced propulsive efficiency performance. At the lower Reynolds number, it was found that the lift, drag, and pitching moment coefficients varied nearly linearly for small jet-flap deflection angles. / Master of Science

To combat the effects of climate change, more industries are beginning to move away from fossil fuels and towards green energy via electrification. This process is currently underway in the aerospace industry. The demand for more power-dense machines grows as manufacturers look to increase the capabilities of electric machines for use in propulsion applications within all-electric aircraft. Recent advances and research into aerospace electrification show that high-speed radial flux permanent magnet synchronous machines have the potential to power small electric aircraft and air taxis. However, issues arise when considering the high-speed nature of this type of motor topology. The immense centrifugal force that acts upon the rotating assembly, which is compounded with thermal expansion and interference fits, substantially increases the rotor components' stress, strain, and deformation. It is also prone to vibrational failure as a result of shaft whirling and resonance. This thesis will first review the structure and operation of electric machines. Electric machine topologies and architectures are briefly explained. A review of the current state of-the-art electric machines used in aerospace applications will also be discussed to provide background on what trends exist in terms of the power density and speed of high-power motors. This thesis details the design process of two high-speed, high-power radial flux permanent magnet propulsion machines. The first motor is a 20,000 RPM 150 kW motor. The features and mechanical design considerations of Motor A will be thoroughly explored. The second motor is a 20,000 RPM 1 MW motor introduced in this thesis. The second motor will only consider the rotating assembly in its analysis due to its significance in determining the power density and safety from multiple failure modes, such as magnet retention failure and vibrational failure. Optimization is not the express goal of this motor, but rather a detailed explanation of how to iterate and improve upon the mechanical design using various results, such as critical speed, eigenfrequencies, strain energy density, stress, strain, deformation, nodal forces, and force reactions. Evaluation of the rotating assembly design and possible improvements are summarized in the conclusions. / Thesis / Master of Applied Science (MASc)

Les orthèses de propulsion mandibulaire sont fréquemment utilisées en orthopédie-dento-faciale pour stimuler le développement de ce maxillaire. Le déplacement antérieur de son centre de gravité et les tensions musculaires et viscérales (appareil aéro-digestif) qui apparaissent alors sont susceptibles d’influer sur la posture du sujet debout. Pour le déterminer, une étude stabilométrique a été menée. Elle permet de mettre en évidence les variations de position de la projection au sol du centre de gravité du corps (PGv). Les effets du port de trois orthèses imposant une quantité de propulsion différente ont été analysés, comparés entre eux et à la situation sans orthèse portée. Ces résultats ont été complétés par ceux issus d’une étude électromyographique, menée pour détecter les muscles mis en jeu dans le contrôle de l'équilibre. L’ensemble de ces expérimentations montre principalement une perte du contrôle postural (augmentation des oscillations de PGv) et un repositionnement plus postérieur du centre de gravité corporel lors d’avancement mandibulaire important, et ce d’autant plus que l’orthèse portée provoque peu de désocclusion inter-maxillaire. Une activité accrue des muscles fléchisseurs dorsaux du pied, de la hanche, du cou et extenseurs du rachis lombaire accompagne ces variations de position de PGv. Une hypothèse d'adaptation posturale en réaction à l'avancement de la mandibule est formulée ainsi qu’une critique et une évolution du protocole d’étude. / Mandibular propulsion splints are frequently used in dento-facial orthopedics so as to stimulate the development of this maxilla. Consequently, we can notice that its centre of gravity moves forward but also that visceral (the aerodigestive apparatus) and muscle tensions appear. These elements are likely to have an influence on the position of a person standing. A stabilometric study was carried out to highlight the changes in the projection onto the ground of the body centre of gravity (PGv). We analysed and compared the effects of the wearing of three different splints (each of which required a different level of propulsion). But a comparison between these results and the normal situation (no splint worn) was also drawn. Moreover, an electromyographic study was carried out to find out which muscles were stimulated in the balance control. Its results were then added to those of the stabilometric study. These experiments mainly show that we lose control of the postural equilibrium (increase of the PGv oscillations). It also shows that when the mandible is significantly moved forward, the body center of gravity goes back into a more posterior position. This is all the more true as the splint worn does not cause much inter-maxillar disocclusion. The back flexor muscle of the foot, of the hip, of the neck and the extensor muscle of the lumbar rachis are greatly stimulated in the variations of the PGv. A postural adaptation to the mandibular advancement is hypothetically expressed, together with a criticism and an evolution of the study procedure.

En propulsion solide, l'ajout de particules d'aluminium dans le propergol améliore de façon significative les performances du moteur grâce à une augmentation sensible de la température de chambre. La présence de gouttes d'aluminium et de résidus d'alumine de différentes tailles et en quantité importante a un impact notoire sur le fonctionnement du moteur. Dans cette optique, nous souhaitons obtenir une meilleure prévision de la stabilité de fonctionnement en cas de déclenchement d'instabilités d'origine aéroacoustique ou thermoacoustique. Nous visons des calculs plus précis de l'étendue de la zone de combustion, de la chaleur dégagée par la combustion distribuée des gouttes et de la distribution en taille des résidus. Nos efforts ont porté sur la modélisation des échanges entre la phase gazeuse et cette phase dispersée composée de gouttes de nature et de taille très diverses. Le paramètre taille pilotant la dynamique du spray et le couplage avec le gaz, le suivi précis des changements de taille est un enjeu majeur.Dans cette contribution, nous avons choisi une approche cinétique pour la description des sprays polydisperses. L'équation cinétique de Williams-Boltzmann utilisée pour suivre l'évolution des propriétés du spray est résolue par une approche eulérienne. Les méthodes Multi-Fluide (MF) traitent naturellement les changements de taille tels que l'évaporation et la coalescence. Ces méthodes reposent sur une intégration continue de la variable taille sur des intervalles fixes appelés sections sur lesquels nous pouvons dériver des systèmes d'équations de conservation. Chaque système est vu comme un fluide qui est en couplage fort avec la phase gazeuse via des termes sources.Nous avons travaillé sur une méthode MF à deux moments en taille basée sur une famille de fonctions de forme polynomiale pour reconstruire la distribution en taille au sein des sections. Cette approche d'ordre deux en temps et en espace s'avère performante car elle décrit avec précision l'évolution de la distribution avec un nombre modéré de sections. Un travail original a été mené afin d'étendre l'approche MF à des gouttes bicomposants. Cette méthode ouvre la voie à des modèles de combustion des gouttes d'aluminium plus représentatifs. Dans le contexte des simulations instationnaires, nous avons porté une attention particulière à l'emploi d'une stratégie numérique robuste et précise pour le couplage entre les phases modélisées par une approche Euler-Euler. Nous montrons qu'une méthode de splitting séparant le traitement du transport des phases gazeuse/dispersée de celui des termes sources est particulièrement adaptée pour la résolution d'un problème multi-échelle spatial et temporel. Dans la mesure où les conditions de réalisabilité sur les moments en taille des méthodes MF ne sont pas garanties avec des méthodes d'intégration traditionnelles, nous avons développé des schémas innovants pour l'intégration des termes sources. Les travaux proposés dans cette contribution répond à deux exigences : 1- un ratio coût/précision attractif pour des simulations industrielles 2- une facilité d'implémentation des méthodes et une modularité assurant la pérennisation des codes industriels. Ces développements ont d'abord été vérifiés à l'aide d'un code ad hoc ; des cas test d'étude d'acoustique diphasique linéaire ont notamment souligné la pertinence de la technique de splitting pour restituer avec précision les interactions spray-acoustique. Les nouvelles méthodes ont ensuite été implémentées et validées au sein du code multi-physique CEDRE développé à l'ONERA. Des calculs de propulsion solide sur des configurations moteur réalistes ont finalement mis en évidence le niveau de maturité atteint par les méthodes eulériennes pour décrire avec fidélité la dynamique des sprays polydisperses. Les résultats de ces simulations ont mis en avant la sensibilité des niveaux d'instabilités en fonction de la distribution en taille des gouttes d'aluminium et des résidus. / The addition of a significant mass fraction of aluminum particle in the propellant of Solid Rocket Motors improves performance through an increase of the temperature in the combustion chamber. The distributed combustion of aluminum droplets in a portion of the chamber yields a massive amount of disperse aluminum oxide residues with a large size spectrum, called a polydisperse spray, in the entire volume. The spray can have a significant impact on the motor behavior and in particular on the onset/damping of instability. When dealing with aeroacoustical and thermoacoustical instabilities, the faithful prediction of the interactions between the gaseous phase and the spray is a determining step for understanding the physical mechanisms and for future solid rocket motor optimization. In such a harsh environment, experimental measurements have a hard time providing detailed explanation of the physical mechanisms and one has to resort to numerical simulation. For such a purpose, the distributed combustion zone and thermal profile therein, the heat generated by the combustion of the dispersed droplets and the large size distribution of the aluminum oxide residues and its coupling with he gaseous phase hydrodynamic and acoustic fields have to be accurately reproduced through a proper level of modeling and a high fidelity simulation including a precise resolution of size polydispersity, which is a key parameter.In this contribution, we choose a kinetic approach for the description of polydisperse sprays. The Williams-Boltzmann Equation is used to model the disperse phase and we derive a fully Eulerian approach through moment methods. The Multi-Fluid (MF) methods naturally treat droplet size evolution through phenomena such as evaporation and coalescence. These methods rely on the conservation of size moments on fixed intervals called sections and yield systems of conservation laws for a set of "fluids" of droplet of various sizes, which is strongly coupled with the gas phase via source terms. We derive a new optimal and flexible Two Size Moment MF method based on a family of polynomial reconstruction functions to describe the size distribution in the sections, which is second order accurate and particularly efficient at describing accurately the evolution of the size distribution with a moderate number of sections. An original work is also conducted in order to extend this approach to two-component droplets. For size moment MF methods, realizability of the moments is a crucial issue. Thus, we have developed innovative schemes for integrating source terms in moment conservation equations describing transport in phase space. This method enables the use of more representative aluminum droplet combustion models, and leads to more advanced studies of the distributed combustion zone. Moreover, for unsteady two-phase flow simulations, we have developed a robust and accurate coupling strategy between phases that are modeled by a fully Eulerian approach based on operator splitting in order to treat such spatial and temporal very multi-scale problems with reasonable computational time. All the proposed developments have been carried out following two criteria : 1- an attractive cost/accuracy ratio for industrial simulations in the context of high fidelity simulations 2- a preservation of industrial code legacy. Verification of the models and methods have been conducted first using an in-house reseach code and then in the context of a two-phase acoustic study thus emphasizing the relevance of the splitting technique to capture accurately spray-acoustic interactions.

Les travaux de thèse traitent du problème de la planification de manoeuvres pour le maintien à poste de satellites géostationnaires équipés de tuyères électriques (à poussée faible). Nous évaluons l'opportunité de substituer une telle planification à celle traditionnellement utilisée pour les satellites géostationnaires équipés de tuyères chimiques (à poussée forte). Dès son apparition, la technologie des systèmes de propulsion à poussée faible a rencontré un vif intérêt auprès des agences et des sociétés spatiales. Grâce à sa haute impulsion spécifique (qui implique une basse consommation de carburant), cette technologie est devenue très compétitive par rapport à la technologie traditionnelle des propulseurs chimiques à poussée forte, surtout dans les phases de transfert et rendez-vous des missions spatiales. Pendant la définition des missions à poussée faible, les analyses de faisabilité des phases de transfert et rendez-vous (via la solution de problèmes d'optimisation de trajectoire) ont été réalisées avec des solutions d'optimisation alternatives. En effet, pendant ces phases, il est nécessaire d'activer les systèmes de propulsion à faible poussée sur des longues portions du temps de transfert. Par conséquent, les problèmes d'optimisation de trajectoire à poussée forte (typiquement formulés en temps discret) ont été remplacés par des problèmes d'optimisation de trajectoire à poussée faible formulés en temps continu et résolus par des techniques de contrôle en temps continu. Le premier objectif de cette thèse est de comprendre quel est l'impact de la technologie à faible poussée lors de l'analyse de faisabilité de la phase de maintien à poste de satellites géostationnaires. Nous étudions en particulier l'impact de l'utilisation des systèmes de propulsion à faible poussée sur la planification de manoeuvres et sur la boucle entière de maintien à poste géostationnaire. L'étude consiste à déduire si la planification de manoeuvres à poussée faible est compétitive au regard des stratégies classiques de planification couramment employées pour des manoeuvres à poussée forte. Généralement, les stratégies classiques à long terme pour le maintien à poste sont déduites de modèles de propagation d'orbite simplifiés (en fonctions des paramètres orbitaux moyennés) par la conjonction des trois facteurs suivants : la forte poussée des propulseurs, la dimension de la fenêtre de maintien à poste pas très contraignante ainsi que la possibilité d'exécuter des manoeuvres à basse fréquence. Dans le cadre de cette thèse, compte tenu du faible niveau des poussées et des contraintes strictes en position (fenêtres de maintien à poste petites), nous considérons comme plus appropriés l'hypothèse d'une plus haute fréquence de manoeuvres et l'utilisation d'un modèle de propagation d'orbite en fonction de paramètres osculateurs. Pour la planification de manoeuvres, nous proposons une solution par approche directe : le problème de maintien à poste en tant que problème de contrôle optimal est discrétisé et traduit en un problème d'optimisation paramétrique. Deux techniques différentes d'optimisation sont proposées : l'optimisation sous contraintes à horizon fixe et celle à horizon glissant. Cette deuxième technique est appliquée aux équations linéarisées du mouvement préalablement transformées via un changement de variable à la Lyapunov sur l'état des déviations des paramètres équinoxiaux osculateurs. Cette transformation de Lyapunov définit des nouveaux paramètres orbitaux. Elle rend le processus de planification plus compréhensible du point de vue du contrôle et plus facile à implémenter d'un point de vue numérique, grâce aux concepts de platitude et inclusion différentielles. Les résultats de la planification de manoeuvres à poussée faible sont obtenus dans un premier temps en fonction des changements de vitesse, dans un deuxième temps en fonction des forces engendrées par les tuyères des systèmes de propulsion classiques. Le but est de déterminer la solution la plus efficace en conditions nominales et en cas de panne d'un des propulseurs. Le problème du positionnement simultané de plusieurs satellites dans une même grande fenêtre de maintien à poste n'est pas adressé explicitement. Il est implicitement résolu en proposant une technique fine de contrôle pour maintenir chaque satellite à poste dans une fenêtre de dimension très petite.

Les propulseurs électriques sont de plus en plus utilisés pour des missions de correction de trajectoire des satellites et pourront dans un avenir proche être utilisés pour le transfert d’orbite. Ces propulseurs constituent une excellente alternative aux propulseurs chimiques grâce à leur rendement élevé et une substantielle économie de carburant réalisée par rapport aux propulseurs chimiques. Les propulseurs à effet Hall créent la poussée par l’accélération d’ions positifs de xénon ou de krypton dans un plasma confiné par un champ magnétique. L’objet de ce manuscrit concerne principalement les caractéristiques de l’accélération des ions et des atomes dans un propulseur à effet Hall. Les influences de la largeur du canal de décharge, de la topologie magnétique et de la cathode sur l’efficacité d’accélération des ions sont étudiées. Des pistes d’optimisation de l’architecture du propulseur sont alors proposées qui pourraient être particulièrement avantageuses sur les propulseurs de petite taille, comme l’élargissement du canal et l’augmentation du champ magnétique près des parois du canal. L’influence de la position et du potentiel de la cathode sur la déviation du faisceau ionique est révélée. L’évolution temporelle basse fréquence du champ électrique est mesurée par comptage synchrone de photons et suggère que la température atomique joue un rôle important dans les oscillations basse fréquence de la décharge. Par ailleurs, l’influence du champ magnétique sur les performances d’un propulseur proche des modèles de vol a été mesurée grâce à l’utilisation d’un moteur doté d’une topologie magnétique flexible. Ceci a montré la difficulté de définir un paramètre numérique capable de synthétiser l’information complexe de la répartition spatiale du champ magnétique dans le canal de décharge. Les très faibles modifications des performances par le champ magnétique soulignent l’importance de la précision dans la mesure. / Electric propulsion systems are more and more often used for trajectory correction of satellites and may soon be used for orbit transfer. These devices represent a great alternative to classic chemical propulsion devices thanks to their high efficiency and propellant mass savings. Hall effect thruster provide thrust by the acceleration of xenon or krypton ions in a magnetized confined plasma. The study presented in this manuscript mainly addresses characteristics of ion and atom acceleration in a Hall effect thruster. Influence of channel width, magnetic topology and cathode parameters on ion acceleration efficiency is investigated. Ways to optimize thruster architecture are suggested that may be particularly relevant for low power thrusters, such as widening thruster channel and increasing magnetic field amplitude near channel walls. Influence of cathode position with respect to the thruster channel exit plane and its potential with respect to ground on ion beam deviation has been revealed with two thrusters. Low frequency time evolution of the accelerating electric field was measured using lock-in photon counting system. Results strongly suggest that the atom temperature plays a crucial role in low frequency time evolution of the whole plasma discharge. Measurement of performances as a function of the magnetic field demonstrated that numeric parameters are compulsory to carry on a relevant parametric study. These parameters would summarize the 2D information of magnetic topology. Weak influence of magnetic topology revealed that thrust measurement precision needs to be increased by at least one order of magnitude if one wants to reach a better understanding of plasma confinement in a Hall effect thruster.

Le propulseur de PEGASES est un moteur ionique qui diffère des autres technologies. La particularité de ce propulseur est l’utilisation d’un gaz électronégatif, à savoir le SF₆. Un champ magnétique est utilisé pour piéger les électrons et augmenter la production des ions négatifs. Le plasma résiduel à faible densité d’électrons, dit plasma ion-ion, permet l’extraction et l’accélération des ions positifs et négatifs. Les ions recombinent par paire dans le faisceau et garantissent la neutralité dans le faisceau. L’extraction d’une quantité équivalente d’ions positifs et négatifs permet ainsi d’éviter l’emploi d’un neutraliseur. Afin d’étudier les propriétés du faisceau ionique, une sonde EXB est utilisée pour diagnostiquer les vitesses et les proportions des molécules formées puis accélérées. La sonde n’étant pas parfaite, une calibration permet de déterminer avec précision les différentes espèces présentes dans le plasma. La présence d’ions positifs et négatifs ont pu être démontré via des mesures par sonde EXB. La technique de photo-détachement par laser est employée afin d’étudier les ions de charge négative. Cette méthode permet d’obtenir la proportion d’ions négatifs par rapport aux électrons. L’électronégativité dans ce type de décharge est très importante. La technique a montré l’importance du filtre magnétique. Cependant, la configuration de celui-ci n’est pas optimale puisqu’une structure est créée par la dérive électronique. Un nouveau propulseur à géométrie circulaire a été conçu, construit et testé. Cette nouvelle architecture utilise une dérive électronique fermée circulaire grâce à des aimants permanents. Les expériences ont validé le concept et montre l’importance d’une géométrie en anneau. / The PEGASES ion thruster differs from standard electric propulsion technologies through its use of electronegative gases, such as SF₆, as a propellant. Its operation relies on the trapping of electrons using a magnetic field and the creation of a plasma dominated by positive and negative ions. These ions are alternately accelerated to produce thrust, and later undergo a recombination to ensure beam neutrality. This thruster eliminates the need for an electron-producing neutralizer, which is a standard feature in other sources such as the Hall thruster. This thesis is divided into three parts. The first describes the development and implementation of a new EXB probe for the study of the ion beam properties, the identification of the beam chemical composition and the verification of the presence of negative and positive ion species. The second part concerns the design and application of a new laser photodetachment diagnostic for the measurement of the negative ion fraction. Lastly, a new ion-ion thruster with a circular geometry, known as AIPE, has been designed, constructed and successfully tested. This prototype eliminates the plasma asymmetry present in PEGASES and reveals the importance of the magnetic filter to source operation.