416 research outputs found

    The dynamics of tethers and space-webs

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    The thesis 'The dynamics of tethers and space-webs' investigates the motion of the Motorized Momentum Exchange Tether (MMET) on an inclined orbit, and while deploying and retracting symmetric payloads. The MMET system is used as a basis for examining the stability of space-webs using a triangular structure of tethers while rotating. The motion of small robots is introduced as they move on the space-web, and their motions are found to influence the behaviour of the structure. Several methods of limiting the destabilising influences of the robots are considered, and are found to stabilise the web in most circumstances. A structured method for describing the rotations of a tether system is outlined, and different rotational systems are compared. This lays the foundation for the further chapters examining MMET dynamics on an inclined orbit and while deploying and recovering the payloads. Lagrange's equations are generated for the three cases, and are solved using standard numerical integration techniques. To emphasise the practical uses of the MMET system, several missions are analysed by using the system as a re-usable launcher for micro-satellite payloads

    Analysis of perturbation effects in precise prediction of Low Earth Orbits

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    Tras analizar el problema de los dos cuerpos y revisar en profundidad las distintas perturbaciones a las que están sometidos los satélites, se explica la herramienta Orekit. Esta permite el cálculo de la órbita de los satélites afectados bajo diferentes tipos de perturbaciones. Mediante Orekit se realiza un extenso análisis abordando las fuerzas más importantes que pueden afectar a satélites en LEO y GEO, para posteriormente pasar a analizar datos reales de satélites proporcionados por la agencia espacial europea en formato OEM. Con estos datos se diseña un propagador que permita predecir con alta precisión la posición y velocidad de los satélites Sentinel-1A/B y Sentinel-2A/B y finalmente se extraen las conclusiones y se proponen futuras mejoras.The objective of this project is to develop an accurate, efficient propagator for Low Earth Orbit satellites designed and launched by the European Space Agency. Predicting where an object will be after several hours since the last time we measured its position is crucial in order to prevent accidents with other satellites during the time lapse we can not track the satellite’s position and direction of movement. This need resulted in this project, in which the analysis of different kind of perturbations is made in order to decide which ones we should take into account and which ones are disposables. Perturbations can be understood as the forces that disturb the classical Keplerian orbit of orbiting objects. The four main forces that must be taken into account are the non-spherical body’s gravity, the third-body perturbations, the solar-radiation pressure and the atmospheric drag, being the last one the most important in LEO. Other kind of perturbations, such as tides or the precession of Earth’s axis, are discussed throughout this project. To perform the computations to predict the position and velocity of the satellites under study, the tool Orekit is used. This low-level space dynamic library written in Java can be integrated into Matlab, and offers a wide scope when studying space dynamics. This tool is the base of this project, and it is used to analyse the effect that different kind of perturbations have in LEO and GEO satellites. Since it was released as an open source in 2008, its popularity grew exponentially due to the precision that this tool allows. In this project its library is presented, as well as the different uses that this tool can have. The data of the satellites is provided by ESA in the form of Orbit Ephemeris Messages, which are used to specify the position and velocity of a single object at one or multiple epochs. The OEMs format is presented in this project, along with several examples of different versions of the OEMs. In order to design a precise propagator, a comparison between several perturbation models offered by Orekit’s library is carried out. These models are compared with one another to decide which one behaves better when propagating the orbit of the satellites studied. The propagator designed to propagate the orbits with high precision is presented, along with the results obtained for the Sentinel-1 and Sentinel-2 classes.Universidad de Sevilla. Grado en Ingeniería Aeroespacial

    Study of the ground - to -Very Low Earth Orbit (VLEO) satellite communication link

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    The aim of this study is to analyse the problem of the reduced windows communication between Very Low Earth Orbit (VLEO) satellites and Ground Stations. The objective is to parametrize all elements involved in the data transmission between a satellite and its grounds stations, and to compare the results with the qbapp app. Furthermore, a practical case will be analysed. It will have to be decided between trying to problem or designing a space mission and analysing its data transmission

    Study on the system architecture of the ONION project

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    Continuar l'estudi iniciat pel projecte ONION, però a nivell més operatiu. Entre altres coses, s'haurà de dissenyar l'arquitectura del sistema, i més endavant, desenvolupar una simulació per acabar d'optimitzar els diferents paràmetres.Outgoin

    Study of large multistage rockets for HEO missions

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    This thesis presents a study on super heavy two-stage rockets targeting high Earth orbit, focusing on geostationary and lunar transfer orbits. The work has been done under the supervision of UPC professor Josep Oriol Lizandra since December 2021 to June 2022. The first part, presents the most important theoretical concepts necessary to develop the study. This includes nozzle ideal theory, rocket 2D flight equations, as well as the most common ascent flight strategies. In addition, some essential rocket design guidelines such as the optimum number of stages and propellant types are introduced. This part also explains the different existing engine cycles in terms of turbopump arranging and propellant combinations. In the second part, first of all, the mission is defined and characterised by considering two particular destinations (GEO and the Moon) and setting a general ascent strategy. This strategy consists of using the gravity turn to reach a low circular parking orbit and then perform a second burn to reach HEO. Thereafter, rocket configuration is studied, thus the oxidiser and fuel are selected, the number of engines is set and the general vehicle shape is defined. Then, the engines are preliminary designed using a perfect gas model and based on the SpaceX Raptor engine. A MatLab code has been developed to simulate engine performance and rocket flight, allowing to set the most advantageous nozzle area ratio. The code has allowed to simulate rocket ascent and study the optimal trajectory using the gravity turn. For this purpose, the indicated magnitude of the pitching manoeuvre is sought, which allows gravity to begin to curve the trajectory and the parking orbit reached to be as circular as possible. Afterwards the code has been modified to optimise rocket characteristics. Most of the study is based on SpaceX Starship rocket, which has been taken as reference, nevertheless the thrust to weight ratio and the propellant ratio between the two stages have been varied. The analysis of these two parameters has allowed to see their affect in rocket dimensions and payload performance. Furthermore, it has allowed to define an optimal configuration to HEO and LEO (regarding cargo capability). Moreover, an interview with MIT professor Manuel Martínez-Sánchez has been conducted, which provides information about ideal flow models in nozzles, the role of super-heavy rockets in the space sector and the future of the different Earth orbits

    The dynamics of tethers and space-webs

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    The thesis 'The dynamics of tethers and space-webs' investigates the motion of the Motorized Momentum Exchange Tether (MMET) on an inclined orbit, and while deploying and retracting symmetric payloads. The MMET system is used as a basis for examining the stability of space-webs using a triangular structure of tethers while rotating. The motion of small robots is introduced as they move on the space-web, and their motions are found to influence the behaviour of the structure. Several methods of limiting the destabilising influences of the robots are considered, and are found to stabilise the web in most circumstances. A structured method for describing the rotations of a tether system is outlined, and different rotational systems are compared. This lays the foundation for the further chapters examining MMET dynamics on an inclined orbit and while deploying and recovering the payloads. Lagrange's equations are generated for the three cases, and are solved using standard numerical integration techniques. To emphasise the practical uses of the MMET system, several missions are analysed by using the system as a re-usable launcher for micro-satellite payloads.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

    Trajectory Optimization in the Circular Restricted Three Body Problem

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    The main goal of this thesis is to prove the validity of an optimizer based on the MATLAB program GPOPS, for solving complex problems on orbital transfer dynamics. Nowadays, optimization is one of the most important fields in space exploration. The high cost of space missions makes that every project developed must be perfectly studied, calculated, optimized and well executed. Hence, optimization programs appear as a very suitable solution for trying not only to prove the validity of a solution already designed, but also to provide a more optimal solution for any problem proposed . In this study, a program has been developed based on an open source program called GPOPS, a MATLAB software for solving optimal control problems. This tool is able to return an optimal solution for problems approached as a dynamical system whenever it has a consistent initial guess. This initial guess generally is the mission wanted to be analysed and optimized. It is very important for the optimizer, since it will have a strong dependence on the performance of the tool, for example, computation time and accuracy. The problem studied has been a Jovian transfer previously proposed in a di erent study. This journey implies moving from the Jovian moon Callisto, to an other Jovian moon, Ganymede, using an interesting element from Space mechanics, invariant manifolds, a really useful element for Low Thrust manoeuvres. This mission in particular, has as main objective the exploration of these celestial bodies, being the transfer time not a key factor. This fact ends with a multi-revolution Low Thrust manoeuvre. During this thesis, di erent solutions were analysed such as: three and two body problem for the dynamics point of view, inertial and non-inertial reference systems and di erent mathematical methods. After the results obtained, it can be concluded that the tool was able to prove the validity of the solutions or initial guesses given. However, after all the time spent working on the program, it has been demonstrated that this tool has a considerable room of improvement and a considerable number of upgrades have been proposed.Ingeniería Aeroespacia

    Implementation and validation of the attitude and determination control system of a pico-satellite

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    This end-of-degree project focuses on the software development of a pico-satellite Attitude Determination and Control System, using MATLAB, as well as its subsequent integration in C. The software carried out will be implemented in a 5 cm sided pico-satellite, called PocketQube. The research project will form part of the IEEE Open PocketQube Kit mission developed in the NanoSat laboratory belonging to the UPC. The pico-satellite attitude system can be broken down into two distinct branches, attitude determination and attitude control. Attitude determination involves the process of determining the orientation of the satellite using the measurements acquired by its sensors (they include photodiodes, gyroscopes, and magnetometers). On the other hand, attitude control is the process by which the orientation of the pico-satellite is controlled using specific control algorithms (such as detumbling and nadir pointing) and actuators, (such as magnetorquers). To analyse and understand the attitude of the pico-satellite, a model is developed that allows simulating the environment in which the satellite is located. This model encompasses pico-satellite dynamics, a model that describes orbital dynamics, and another that represents the various perturbation forces that affect the pico-satellite. In this way, it is possible to describe the orbit followed by the pico-satellite, including its position, speed and the external forces that influence and affect its behaviour during the orbital flight. Once the modelling of the simulation environment is complete, the determination and control algorithms are implemented, as well as the mathematical models that describe the behaviour of the sensors and actuators. These algorithms and models are designed with the aim of meeting the requirements established for the Determination and Control System. Subsequently, an exhaustive analysis of the results obtained during the simulation is carried out. The purpose of this analysis is to verify if the previously established requirements for the Attitude Determination and Control System are met. The conclusion of this work allows to start the test campaigns of this system in the PocketQube hardware, as well as to check if the results obtained in the simulations correspond to reality

    Study on orbital propagators: constellation analysis with NASA 42 and MATLAB/SIMULINK

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    Desde el comienzo de la era espacial, la filosofía de diseño de satélites estuvo dominada por diseños conservadores construidos con componentes altamente duraderos para soportar condiciones ambientales extremas. Durante las últimas dos décadas, la aparición de los CubeSats ha cambiado esta filosofía permitiendo todo un mundo de nuevas posibilidades. El despliegue de grandes constelaciones de CubeSats en órbita terrestre baja (LEO, en inglés) revolucionará el sector espacial al permitir ciclos de innovación más rápidos y económicos. Sin embargo, la confiabilidad de los CubeSats todavía se considera un obstáculo debido a las considerables tasas de fallo entre universidades y empresas, generalmente atribuidas a casos de pérdida completa de misión tras la eyección del desplegador orbital y al fallo de los subsistemas. Esta tesis se desarrolla en el marco del proyecto de investigación PLATHON, que pretende desarrollar una plataforma de emulación Hardware-in-the-loop para constelaciones de nanosatélites con comunicación óptica entre satélites y enlaces tierra-satélite. Un aspecto crucial de este proyecto es tener un propagador orbital suficientemente preciso con control de maniobras y representación gráfica en tiempo real. Los programas de propagadores disponibles se han analizado para seleccionar el sistema OpenSatKit de la NASA, una plataforma multifacética con un propagador incorporado conocido como 42. El propósito de esta disertación es analizar la viabilidad de implementación del programa para la creación de un banco de pruebas de constelaciones en comparación con un propagador previo desarrollado en MATLAB/Simulink. La documentación inicial es un enfoque de exploración para examinar las capacidades del 42 en distintos escenarios con objeto de adaptar el sistema PLATHON al funcionamiento interno y las limitaciones del programa. Las modificaciones y simulaciones del programa allanan el camino para el futuro desarrollo de la red interconectada PLATHON; específicamente, las comunicaciones entre procesos se han probado para imitar las entradas de los sistemas de control de actitud de las naves espaciales a través de interfaces de comunicación bidireccionales.Since the beginning of the space age, satellite design philosophy was dominated by conservative designs built with highly reliable components to endure extreme environmental conditions. During the last two decades, the dawn of the CubeSats has changed this philosophy enabling a whole world of new possibilities. The deployment of monumental CubeSat constellations in low Earth orbit is set to revolutionise the space sector by enabling faster and economical innovation cycles. However, CubeSat reliability is still considered an obstacle due to the sizeable fail rates among universities and companies, generally attributed to the dead-on-arrival cases and subsystem malfunctions. This thesis is developed in the framework of the PLATHON research project that intends to develop a Hardware-in-the-loop emulation platform for nanosatellite constellations with optical inter-satellite communication and ground-to-satellite links. A crucial aspect of this project is to have a sufficiently precise orbital propagator with real-time manoeuvring control and graphical representation. The available propagator programmes are analysed to select NASA’s OpenSatKit, a multi-facet platform with an inbuilt propagator known as 42. The purpose of this dissertation is to analyse the implementation feasibility of the programme for the creation of a constellation testing bench compared to previously selfdeveloped propagators based on MATLAB/Simulink. The initial documentation is a scouting approach to examine 42’s capabilities under distinct scenarios to adapt the PLATHON system to the programme’s inner workings and constraints. The programme modifications and simulations pave the way for the future development of the interconnected PLATHON network; specifically, the inter-process communication capabilities have been tested to imitate the inputs of spacecraft attitude control systems through bidirectional socket interfaces
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