Contribution à la modélisation de la rentrée atmosphérique des débris spatiaux

In order to determine the conditions in which fragments reach the Earth as well as their impact point locations, a deep comprehension of the physical phenomena occurring during the atmospheric re-entry of space debris is necessary, as well as an important effort in the development of models. Especially, it is important to analyse and develop models for the physical phenomena neglected in the existing and known approaches. During this thesis, some effort was put into the development of a fragment interaction model in continuum hypersonic and supersonic regime, in perfect and real gas at equilibrium. It was critical to understand the significant influence of this phenomenon on the dynamics and survival of a sphere situated in the shock wave generated by a primary fragment. On the other hand, a model allowing the aerodynamic force and moment coefficients estimation and a model to evaluate the heat flux coefficient in hypersonic regime from free-molecular to continuum flow have been proposed. Subsequently, a first model to compute the aerodynamic coefficients in transonic regime has been developed. A thermal conduction model adapted to the study of atmospheric re-entry of space debris has been developed. The significant influence of the conduction model, the wall thickness and the thermal dependence of material properties such as thermal conductivity and specific heat capacity on the wall thermal distribution have been shown. A first wall ablation model by melting has been set up. On the other hand, an experimental study on the oxidation of the TA6V titanium alloy has been conducted at PROMES-CNRS laboratory, Odeillo, in plasma air environment. The results confirm the necessity to take into account the wall oxidation, especially in a high temperature environment where oxygen is dissociated, as encountered in Earth atmospheric re-entry of space debris. A model for the thermal degradation of the wall by melting (ablation) has been developed. These models have been implemented in the ONERA code named MUSIC/FAST. This one, initially designed for spacecraft re-entry pre-mission analysis, has been evaluated, consolidated and improved for space debris atmospheric re-entry applications. For validation purpose, the aerodynamics and aerothermodynamics coefficients computed by the code have been compared to the ones found in literature, for various geometries. Finally, the atmospheric re-entry of a spherical tank has been simulated allowing the evaluation of the influence of different parameters (angle of climb, material properties, internal wall properties and wall thickness) on the fragment trajectory and its state when it reaches the ground.Afin de déterminer l’état dans lequel les fragments arrivent au sol et leurs points d’impact, une compréhension fine des phénomènes physiques intervenant lors de la rentrée atmosphérique des débris spatiaux, ainsi qu’un effort important de modélisation sont nécessaires. Il s’agit en particulier d’analyser et de modéliser des phénomènes physiques peu pris en compte jusqu’à présent par les approches existantes et connues. Durant cette thèse une modélisation des interactions entre fragments en régime continu hypersonique et supersonique pour des écoulements de gaz parfait et de gaz réel a été proposée. Ceci a permis de montrer l’influence significative de ce phénomène sur la dynamique et la survie d’une sphère située dans la couche de choc générée par un premier fragment. D’autre part, un modèle pour l’estimation des coefficients aérodynamiques de force et de moment ainsi que le coefficient de flux de chaleur en régime hypersonique du moléculaire libre au continu est proposé. En complément des régimes hypersonique et supersonique, un modèle préliminaire pour le calcul des coefficients aérodynamiques en régime transsonique a été développé. Un modèle de conduction thermique adapté à la rentrée des débris spatiaux a été développé.Les influences du modèle de conduction, de l’épaisseur de paroi et de la prise en compte de la dépendance en température de la conductivité thermique et de la capacité calorifique sur la distribution de température dans la paroi ont été montrées. D’autre part, une étude expérimentale sur l’oxydation de l’alliage de titane TA6V a été menée au laboratoire PROMES-CNRS d’Odeillo sous plasma d’air. Les premiers résultats confirment la nécessité de tenir compte de l’oxydation de la paroi en particulier dans un environnement à haute température où l’oxygène est dissocié comme c’est le cas pour les rentrées atmosphériques terrestres de débris spatiaux. Par ailleurs, un modèle de dégradation thermique de la paroi par fusion (ablation) a été mis en place. Ces modèles ont été implantés dans le code MUSIC/FAST de l’ONERA. Celui-ci, initialement conçu pour l’analyse pré-mission de la rentrée de véhicules ou de capsules, a été évalué, consolidé et amélioré pour son application à la rentrée des débris spatiaux.Les coefficients aérodynamiques et aérothermodynamiques calculés par le code ont été confrontés aux données issues de la littérature pour différentes géométries. Enfin, la rentrée atmosphérique d’un réservoir sphérique a été simulée permettant d’évaluer l’influence de différents paramètres (pente, propriétés des matériaux, propriétés de la paroi interne du réservoir, épaisseur de la paroi) sur la trajectoire du fragment et son état lors de son impact au sol

Advanced European Re-Entry System Based on Inflatable Heat Shields EFESTO project overview: system and mission design and technology roadmap

European Union H2020 EFESTO project is coordinated by DEIMOS Space with the end goals of improving the European TRL of Inflatable Heat Shields for re-entry vehicles from 3 to 4/5 and pave the way to In-Orbit Demonstration that can further raise the TRL to 6. This paper presents the project objectives and provides a general overview of the latest advancements, promoting the relevance of the EFESTO know-how in the frame of a European re-entry technology roadmap. The system, aerodynamic and mission design of two Hypersonic Inflatable Aerodynamic Decelerator use case scenarios, the AVUM VEGA stage recovery and a high-mass Mars exploration EDL mission, have been selected for deriving requirements and constraints to be injected in the EFESTO ground testing phase. The focus of this phase was on the aerothermal verification of the Flexible-Thermal Protection System in the DLR Arcjet facility and the analysis of the mechanical properties of the Inflatable Structure exploiting a manufactured 1:2 demonstrator, both representing key aspects of this peculiar and innovative technology

Numerical and experimental study of the thermal degradation process during the atmospheric re-entry of a TiAl 6 V 4 tank

International audienc

Advanced European Re-Entry System Based on Inflatable Heat Shields EFESTO project overview: system and mission design and technology roadmap

European Union H2020 EFESTO project is coordinated by DEIMOS Space with the end goals of improving the European TRL of Inflatable Heat Shields for re-entry vehicles from 3 to 4/5 and pave the way to In-Orbit Demonstration that can further raise the TRL to 6. This paper presents the project objectives and provides a general overview of the latest advancements, promoting the relevance of the EFESTO know-how in the frame of a European re-entry technology roadmap. The system, aerodynamic and mission design of two Hypersonic Inflatable Aerodynamic Decelerator use case scenarios, the AVUM VEGA stage recovery and a high-mass Mars exploration EDL mission, have been selected for deriving requirements and constraints to be injected in the EFESTO ground testing phase. The focus of this phase was on the aerothermal verification of the Flexible-Thermal Protection System in the DLR Arcjet facility and the analysis of the mechanical properties of the Inflatable Structure exploiting a manufactured 1:2 demonstrator, both representing key aspects of this peculiar and innovative technology

Mission Analysis, GNC and ATD for Reusable Launch Vehicles within ASCenSIon: Multi-Orbit Multi-Payload Injection, Re-Entry and Safe Disposal

Reusable Launch Vehicles (RLVs) are not only key for an economically and ecologically sustainable space access but also represent a paramount innovation towards the increasing demand for smaller satellites and mega- constellations. In order to ensure Europe's independent space access capabilities, ASCenSIon (Advancing Space Access Capabilities - Reusability and Multiple Satellite Injection) is born as an innovative training network with fifteen Early Stage Researchers, ten beneficiaries, and fourteen partner organisations across Europe. This paper provides an overview of the mission, ranging from the ascent to the re-entry of the reusable stages and including the multi-orbit injection and the safe disposal. A special focus is put on the activities developed within ASCenSIon regarding Mission Analysis (MA), Guidance Navigation and Control (GNC) and Aerothermodynamics (ATD). The foreseen methods, approaches and goals of the project are presented. These topics require innovation within and a high level of collaboration due to their interconnection. The pre-flight design capability drives the necessity of a MA and GNC missionisation tool coupled with ATD software to test/explore re-entry solutions. Such a reliable and efficient tool will require the development of GNC algorithms for the re-entry of the launcher. Additionally, specific challenges of trajectory optimization for RLVs are addressed, such as integrated multi-disciplinary vehicle design and trajectory analysis, fast and reliable on-board methods. The results of this study are subsequently used to develop the controlled strategy. Moreover, to perform the novel multi-orbit multi-payload injection. This activity is followed by the development of, a GNC architecture capable of optimally steering the vehicle towards a targeted landing site under precision and soft-landing constraints. In addition, ATD affects the mission profile at multiple phases and needs to be considered at each design step. Due to complexity and limited computational resources during the preliminary design phase, surrogate models with low response times are required to predict wall heat fluxes along the considered trajectories based on the pressure topology. The complete profile is wrapped up with the Post Mission Disposal strategies to be used by the launchers in order to ensure the compliance with the space debris mitigation guidelines, as well as preliminary reliability aspects of these strategies. The paper provides a preliminary analysis of the discussed topics and their interconnections within the work-frame of ASCenSIon paving the way towards the development of novel cutting-edge technologies for RLVs

Advanced European Re-Entry System Based on Inflatable Heat Shields EFESTO project overview: system and mission design and technology roadmap

The European Union H2020 EFESTO project is coordinated by DEIMOS Space with the end goals of improving the European TRL of Inflatable Heat Shields for re-entry vehicles (from 3 to 4/5) and paving the way towards further improvements (TRL 6 with a future In-Orbit Demonstrator, IOD). This paper provides an overview of the project, the consolidated results of the detailed design of atmospheric entry missions for Mars exploration and Earth applications and an overview of the technology roadmap. The project includes design and ground tests activities, covering the key subsystems of inflatable structure and flexible TPS that compose a Hypersonic Inflatable Aerodynamic Decelerator (HIAD). Two key applications, have been identified to enable Mars Robotic Exploration and Reusable Small Launchers Upper Stages. For the Mars Application, the robotic exploration mission design results in a 9m diameter Hypersonic Inflatable Aerodynamic Decelerator (HIAD) class, combined with Supersonic Retro-Propulsion for safely landing the 2.5 ton payload at MOLA +3km target altitude. For the Earth Application, the VEGA upper stage (AVUM) has been selected as baseline case study. The current mission foresees a deorbiting from Polar Orbit followed by a controlled entry phase (Ballistic Coefficient of about 46 kg/m2). Deceleration is achieved using a 4.5m diameter class HIAD combined with parachutes during the descent phase, A parafoil enables Mid-Air-Capturing (MAR) of the entry vehicle with a helicopter. For the Mars applications, the mission analysis shows that, compared to state-of-the-art technology, implementation of the HIAD efficiently provides larger drag during the entry phase, thus allowing to increase both landed mass and MOLA altitude at which a soft landing is possible. For the Earth applications, the mission analysis confirms the HIAD as an appealing, performing and robust solution for the purpose of safely returning the VEGA upper stage to a targeted recovery area. These results demonstrate that HIAD systems represent an enabling technology for the next class of high-mass Mars exploration missions and this technology can be key in reducing the cost of access to space through upper stage reusability. The need for advancing the TRL of this technology, which is the primary objective of the EFESTO project, is thus confirmed and the relevance of an IOD mission that will enhance the European know-how in the field, of which the EFESTO consortium represents the core, is reinforced. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 821801

ASCenSIon: An innovative network to train the space access leaders of tomorrow

The trend towards smaller satellites and mega-constellations has enormously changed the space sector and its utilisation in the last decades, allowing new players to enter the market and to introduce stringent requirements to enable a variety of novel applications. Alongside, also the launcher market is undergoing a transformation epoch: the development, manufacturing and integration of launcher systems is being shifted from the hands of governmental institutions to commercial industry. Moreover, nations like Unites States, China, India and New Zealand are increasing the competition and pressure on Europe, urging the goal to ensure European autonomy in accessing and using space in a safe and secure environment. Europe does not only need innovations, but primarily a new generation of engineers, capable of understanding the full complexity of launcher development and trained to create and realise the necessary innovations. In this context, ASCenSIon is a multidisciplinary training programme involving 15 Early Stage Researchers (ESRs) from anywhere in the world, focused on several specific areas of cutting-edge space access research, particularly on launcher systems that are (partially) reusable and capable of injecting multiple payloads into multiple orbits. The network aims to identify and advance critical technologies in the space access field, and prove their feasibility. ASCenSIon, whose acronym stands for “Advancing Space Access Capabilities -Reusability and Multiple Satellite Injection”, is a consortium of 11 beneficiaries and 17 partners across Europe, eager to contribute to the establishment of an ecologically and economically sustainable space access for Europe, oriented towards user needs. Unlike other single-aspect research projects, the core objective of ASCenSIon is not only to train 15 PhD students to become excellent specialists in their respective field, but also to provide them a thorough understanding of the complexity, multidisciplinary and internationality of launcher development, in order to become leaders in the European effort of utilising space. This will be achieved through secondments, events and lessons from experts, but mostly through strong interconnections among the ESRs, who will work on Individual Research Projects with a multi-disciplinal and multi-sectoral approach. This paper aims to provide an overview of ASCenSIon programme. Its values and core objectives will be introduced, together with the innovative aspects and content structure. An overview of the research methodology and recruitment strategy will be given, with a particular focus on the contributions and synergies of all participating organisations, core of such a novel training approach

ASCenSIon: An Innovative Network to Train the Space Access Leaders of Tomorrow

reserved15simixedGloder, A.; Apel, U.; Bianchi, D.; Bonetti, D.; Deeken, J.; Hendrick, P.; Hijlkema, J.; Lavagna, M.; Pasini, A.; Prevereaud, Y.; Sippel, M.; Stoll, E.; Waxenegger-Wilfing, G.; Tajmar, M.; Bach, C.Gloder, A.; Apel, U.; Bianchi, D.; Bonetti, D.; Deeken, J.; Hendrick, P.; Hijlkema, J.; Lavagna, M.; Pasini, A.; Prevereaud, Y.; Sippel, M.; Stoll, E.; Waxenegger-Wilfing, G.; Tajmar, M.; Bach, C

ASCenSIon: An Innovative Network to Train the Space Access Leaders of Tomorrow

The trend towards smaller satellites and mega-constellations has enormously changed the space sector and its uti-lisation in the last decades, allowing new players to enter the market and to introduce stringent requirements to enable a variety of novel applications. Alongside, also the launcher market is undergoing a transformation epoch: the devel-opment, manufacturing and integration of launcher systems is being shifted from the hands of governmental institutions to commercial industry. Moreover, nations like Unites States, China, India and New Zealand are increasing the com-petition and pressure on Europe, urging the goal to ensure European autonomy in accessing and using space in a safe and secure environment. Europe does not only need innovations, but primarily a new generation of engineers, capable of understanding the full complexity of launcher development and trained to create and realise the necessary innova-tions. In this context, ASCenSIon is a multidisciplinary training programme involving 15 Early Stage Researchers (ESRs) from anywhere in the world, focused on several specific areas of cutting-edge space access research, particu-larly on launcher systems that are (partially) reusable and capable of injecting multiple payloads into multiple orbits. The network aims to identify and advance critical technologies in the space access field, and prove their feasibility. ASCenSIon, whose acronym stands for “Advancing Space Access Capabilities –Reusability and Multiple Satellite Injection”, is a consortium of 11 beneficiaries and 17 partners across Europe, eager to contribute to the establishment of an ecologically and economically sustainable space access for Europe, oriented towards user needs. Unlike other single-aspect research projects, the core objective of ASCenSIon is not only to train 15 PhD students to become excel-lent specialists in their respective field, but also to provide them a thorough understanding of the complexity, multidis-ciplinary and internationality of launcher development, in order to become leaders in the European effort of utilising space. This will be achieved through secondments, events and lessons from experts, but mostly through strong inter-connections among the ESRs, who will work on Individual Research Projects with a multi-disciplinal and multi-sec-toral approach. This paper aims to provide an overview of ASCenSIon programme. Its values and core objectives will be introduced, together with the innovative aspects and content structure. An overview of the research methodology and recruitment strategy will be given, with a particular focus on the contributions and synergies of all participating organisations, core of such a novel training approach