APRÈN. Portal de la producció docent del professorat de la UPC

The emergence of satellite constellations for telecommunications has notably increased in the recent years, enhancing the accessibility to space, and making satellite networks indispensable. The integration of Non-Terrestrial Networks (NTN) with Terrestrial Networks (TN) and the optimization of their management has become essential. This study focuses on addressing the uncertainties posed by this challenge, with particular emphasis on the unpredictability of traffic generation. In satellite operations, the focus on managing uncertainties has been mostly within Earth Observation (EO) applications, while in telecommunications scenarios, uncertainties (and specifically, those related to the unpredictable nature of traffic generation) have not been addressed as extensively. In this work, an analysis of the main uncertainty sources in satellite networks has been performed, and they have been aggregated into three main aggregated sources based on modeling similarities: satellite failure, link quality, and traffic model. These aggregated sources are described with a Weibull probabilistic distribution for satellite failure, bounded limits on the window duration for the link quality, and a generalized methodology for the integration of stochastic traffic models. In addition, an uncertainty management model has been designed. The proposed methodology for traffic generation is validated within an extensive framework that includes network-related metrics and constraints to optimize task scheduling. The steps for incorporating stochastic variables into the optimization process are described in detail, and a new optimization parameter is introduced: the schedule certainty. The impact of the schedule certainty is evaluated in an Internet of Things (IoT) scenario. Furthermore, the uncertainty model implementation and validation is performed in a constellation management tool for 5G/6G technologies, the Constellation Management System (CMS). The results compare the former CMS to the probability aware (P-aware) CMS. The findings show how the P-aware scheduling maintains a precise level of certainty consistent with operator-defined thresholds, providing greater certainty for the same performance metrics compared to the baseline CMS. This framework supports satellite operators in dynamically adjusting service coverage and system efficiency by means of stochastic information provided by the traffic model. To the best of our knowledge, this is the first time that such an analysis has been performed in the context of task scheduling for a satellite communication application. The insights gained from this study offer valuable contributions to optimizing operations in complex satellite networks.

There is an ongoing effort to improve the service life of cutting tools for machining aerospace materials, such as titanium and aluminum alloys. Although the design and coated materials for cutting tools have been widely studied and optimized along the last years, new requirements need to be accomplished since the additive manufacturing (commonly referred to as 3D printing) and subsequent post-printing processes has been introduced into the aerospace sector. In this regard, the surface finishing operation of complex shape and thin-walled 3D components could significantly reduce the life of cutting tools, due to the presence of complex loading conditions produced by unexpected vibrations. A coating composed by an interlayer of ¿¿(¿, ¿) followed by a top layer of ¿¿2¿3 is one the most used CVD bi-layer system specifically designed for cutting operations of titanium alloys. Nowadays, manufacturers of cutting tools explore the alternative of applying mechanical post-treatment processes after coating deposition, in an effort to reduce the premature failure of these tools. Take into account this scenario, the aim of this study is to document the micromechanisms of damage resulting from contact loading applied on coated system subjected to blasting and/or shot peening post-treatment processes. Coated system consisted in a bi-layer ¿¿ (¿, ¿)/ ¿¿2¿3 deposited on a cemented carbide with 7 wt% of Co binder. Two different bi-layer thickness were evaluated. Spherical indentation under monotonic loading condition was used to evaluate the contact resistance to crack appearance on coated samples surface. Advanced microscopy techniques were used to analyze the micro-cracking patterns achieved at the edge of residual imprints. Results shown that post-treatments could induced changes in surface roughness, and even more in the crack appearance under contact loading conditions. Thicker coatings provide higher resistance to crack nucleation, but post-processes such as SP and WB are necessary to optimize tool performance. Moreover, the combination of both micro-mechanical treatments presented the best overall resistance to crack initiation and propagation, despite some surface defects.

The cavity flow problem is of high interest for two main reasons: it is a benchmark in computational fluid mechanics for validating different numerical solvers of the Navier-Stokes equation, and it acts as a test benchmark for studying a variety of fluid flow phenomena. In this study, we will focus on the square cavity four-lid-driven by the tangential motion of its four sides at the same speed, with opposite walls moving in opposite directions. The fluid motion is determined by solving the Navier-Stokes equation. This study focuses on the periodic solutions that arise for this configuration. The problem is regularized by setting the wall speed to follow a double-exponential distribution to avoid corner singularities caused by the discontinuities of the velocity at the boundary. This allows for exponential convergence in spectral discretization schemes. The time integration of the discretized Navier-Stokes equation is carried out by the Implicit Euler Method. Limit cycles are found by the Newton-Krylov numerical solver, in which the method intends to search for the roots of the equation that compares a given initial state of the flow with a state after time integration has been applied. In particular, we study the upper and lower limits of the Long Periodic Orbit (LPO), mentioned in some recent studies, as well as, the behavior past these critical values. The lower bound the orbit disappears in a Heteroclinic bifurcation caused by the collision with an unstable steady state. On the other hand, at the upper bound the flow becomes chaotic. Finally, a Hopf bifurcation has been identified recently but no periodic orbit arising from it has been reported. This Hopf bifurcation is found to be subcritical.

Thanks to the wide variety of applications offered by drones, their density has been increasing. This growth in their number could cause consequences, such as possible collisions between these devices. The way to avoid collisions in a densely populated environment is to know the trajectory of moving objects. Although it is true that there are already models that can predict the trajectory of a drone, these represent a very large computational cost, which is why this document has as its main objective to predict the trajectory of drones in a U-space environment in a simple way. The document presents a study of the advances in the field of trajectory prediction (both for airplanes and drones), the concept of U-space, the kinematics of objects and the mathematical modeling of the object in question. The literature review raises the possible tools used to know the trajectories such as state estimation, kinematic or machine learning models. It is also necessary to know the concept of the U-space environment, where the definition of the concept, regulations within the environment and the flight phases that a drone must perform (pre-flight, in-flight and post-flight) are shown. Because the model is composed of particle kinematics equations, a chapter was added where the concepts of each of the equations are explained in both accelerated and non-accelerated models. The document also contains the main idea, which is the mathematical model. This mathematical model is developed in several sections of the path. The length of the path will depend on the characteristics of altitudes, lengths, inclinations and turns. In these small paths, the mixture of kinematics concepts is used together with the graphical behavior of turns and inclinations. To develop this model, a mixed sampling approach was used, where the behavior was numerically analyzed to ensure compatibility with the kinematics and the numerical history of the simulation in Mission Planner.Finally, each of the small trajectories is tested, which yields relative errors of less than five percentage points.

This thesis presents a solution for managing potential conflicts between general aviation air- craft and drones within U-space. As the use of drones in various sectors increases, the chal- lenge of safely integrating them into existing air traffic systems becomes crucial, especially in scenarios where both manned and unmanned aircraft operate in close proximity. The project aims to design and test a device capable of receiving Automatic Dependent Surveillance - Broadcast (ADS-B) messages from general aviation aircraft and forwarding this data to the U- space cloud for conflict detection. The device, which includes hardware and basic software, was tested under real-world conditions, proving its functionality in processing ADS-B mes- sages and managing power independently through an Uninterruptible Power Supply (UPS). However, certain technical limitations were identified, such as the UPS's dependency on grid power to initiate the switch to battery mode, and the need for additional cooling under high- temperature conditions.

In this master thesis an experiment is designed to analyse the effects of hypergravity on pre-implementation murine embryos. The thesis outlines previous findings in the field, experimental protocols, a model of the forces acting on the embryo, potential results, and a discussion of the results and potential sources of errors.

En aquest projecte s'ha realitzat un estudi de viabilitat per implementar un sistema de ”passive ranging” especialitzat per a satèl·lits en el règim orbital LEO, partint de la base d'un sistema prèviament desenvolupat per a GEO, anomenat Focusear. Amb aquest objectiu, s'ha utilitzat i modificat un simulador, Parasim, que a partir d'una població de satèl·lits i d'estacions de terra, simula tot el procés de ”passive ranging”, des de la creació de plans d'observació passant per l'obtenció de les mesures i la determinació orbital a partir d'aquestes mesures. Finalment, s'ha avaluat cadascun dels escenaris estudiats determinant quins són els viables i els més prometedors.

One of the biggest challenges of the establishment of a lunar base is ensuring the survival of the crew and the facilities. A critical factor for the survival of the crew and the installations is the provision of energy, which turns into a critical challenge due to the environmental conditions on the Moon and the lunar day-night cycle which ensures long periods of darkness. Several approaches have been considered to store and provide energy to a lunar base by means of In-Situ Resources Utilization. One of them is the possibility to use the lunar regolith as a thermal mass. The main objective of this work is to design an experiment for measuring regolith thermal properties in Lanzarote. It aims at establishing the temperature-dependance of regolith thermal properties. The measurement of the thermal properties will allow the evaluation of the relevance of using the lunar regolith as a thermal mass for energy storage purposes, more precisely for keeping the rovers warm during the lunar nights. As it will be explained, the thermal conductivity of regolith is very limited. Therefore, the sintering of regolith has been studied in order to improve its thermal properties. First, the environmental conditions and the characteristics of the materials used for the experiment are studied. The thermal properties of the different materials used in this experiment have been assessed with the aim of establishing reference values. In addition, temperature-dependant models are proposed for the thermal properties of the materials. Then, the resources needed for the experiment are determined and the configuration of the experiment is decided. The implementation of the experiment has been designed focusing on the solar concentrating system, used to increase the temperature of the materials, and the data acquisition systems. Finally, some simulations are carried out through COMSOL. The simulations help to determine the validity of the proposed models, determine the similarities between the thermal behaviour of Lanzarote's soil and lunar regolith, as well as outline the interest of sintering regolith to improve its thermal properties for energy storage purposes. In conclusion, this work proposes an experiment to measure some of the thermal properties of a regolith simulant in Earth conditions. Since a similar experiment is to take place on the Moon, the simplicity of the implementation has been prioritized during the development of this project.

A Dyson sphere is a hypothetical structure built by a supposed advanced civilization capable of capturing part or all the irradiated energy from a star. In the subsequent process of converting this energy into electrical, chemical, or any other form of energy, the laws of thermodynamics imply that part of this energy is dissipated in the form of heat emitted as infrared radiation. Hence, it is expected that the spectrum of the star will show an infrared excess as well as an energy deficit at optical wavelengths. Current space missions such as ESA's Gaia and NASA's WISE, among others, have provided a wealth of information about a peculiar type of stars known as white dwarfs. With half the mass of the Sun and a radius similar to that of Earth, these stars are considered natural candidates to host such structures. In fact, there are around a few hundred identified white dwarfs that display an infrared excess in their spectra. The prevailing hypotheses are the presence of cooler sub-stellar mass companions or dust disks surrounding the white dwarf. However, there are some objects that are not fully explained by either of these models. In this project we aim to analyze the effects of Dyson rings or spheres around a white dwarf with the same temperature as the Sun. To that end, we start by using current state-of-the-art in solar cell technology. That is, the performance for photovoltaic solar cells, material strength, etc., will be that of available current space missions. We aim to obtain an energy balance and determine how the spectrum of the white dwarf might be affected based on the size of the constructed structure.

The aim of the project is to design a fuselage from zero and the assembly of the aircraft (fuselage, wing, tail and propellers) for ONAerospace.

The objective of this investigation was to provide PIKSEL with EO data sources. Several steps were followed to achieve this goal. The initial phase of the research involved the identification and compilation of EO data sources available. The selection process aimed to encompass a wide range of geospatial, environmental, and climatic data to cater to the diverse needs of the PIKSEL use cases and its users. Subsequently, the EO data available was subjected to an evaluation to determine its relevance to the specific application and objectives of the PIKSEL platform. This assessment considered factors such as data accuracy, spatial and temporal resolution and data format. Once the relevant EO data sources were identified, the next step involved a detailed analysis of the data downloading procedures associated with each source. Each provider often presents unique requirements, access protocols, and data delivery formats, necessitating a thorough understanding of the technical intricacies and obtaining the necessary credentials for data acquisition. To streamline and automate the data retrieval process, a custom Python script was developed for the specific case of the evolution of the coastline. Recognizing the importance of user experience, a user-friendly interface was designed to facilitate straightforward data management. The interface aims to simplify the process of accessing and querying, ensuring that users, irrespective of their technical expertise, can efficiently interact with the platform's resources. However, various hurdles were encountered during the project, including diverse data access procedures, lack of standardization among data channels, and challenges in obtaining and understanding Copernicus data. Despite these challenges, this work presents a valuable resource for non-programming experts seeking to manage EO data with ease. The work also explores future opportunities to expand the platform, integrate other Copernicus services, include diverse relevant sources, and implement the user interface on the PIKSEL website.

Context: Understanding the origin of the oldest stars in the universe is crucial to shed light on its early chemical evolution and on the formation history of the Milky Way. The oldest stars were either the direct heirs of the Big-Bang nucleosynthesis (and thus mainly composed of H and He at their birth), or were born in clouds of primordial (zero metallicity) material polluted with the ejecta from one or a few stars. Thus their observational counterparts must be characterised by very low amounts of iron in their composition. Currently, there is a debate on whether the first stellar generations (and thus the first polluters of the interstellar medium) were composed only of massive stars, or were a combination of intermediate and massive objects. Goal: We aim to identify the nature of the progenitors of the most metal-poor stars observed ([Fe/H] ¿ ¿2 or Z ¿ 10¿4). Specifically, we intend to know whether these stars show the nucleosynthetic signatures of early supernova explosions of different types, or of a combination of the ejecta from massive and intermediate-mass stars. Methods: We compile theoretical nucleosynthetic yields existing in the literature for intermediate and massive stars. We propose a scenario in which the theoretical yields of either an intermediate mass star or a massive star, are mixed within a gas cloud of primordial matter. Our main assumption is that some of the currently observed most metal-poor stars were born in this polluted clouds and thus, their abundances should show the nucleosynthetic signatures of their parent stars. We intend to develop a code able to automatically derive abundances from theoretical nucleosynthetic yields at different degrees of dilution with primordial material, and subsequently identify statistically sound matches between the former theoretical abundances and the surface abundances of metal poor stars of [Fe/H] ¿ ¿2. Automatising this process is crucial, given the increasing number of new theoretical models and observations of very metal-poor stars presented in the recent literature. Results: The expected coincidences between the abundances of theoretical models and observations will give us information related to their progenitors¿ initial masses and metallicities. We will be able to determine, given state-of-the-art of theoretical nucleosynthetic yields, whether any of the observed stars could be the offspring of a genuine primordial (Z=0) star.

This master thesis presents the development of a genetic algorithm for optimizing interplanetary trajectories using multi-planetary gravity assists while considering time as an additional objective in the fitness evaluation. The objective of the research is to address the challenges of designing efficient trajectories that minimize both delta-v and travel duration. The aim of this thesis is to develop an all-encompassing deep space mission trajectory design tool where a trade-off between the total delta-v used and the arrival time can be made, in the interest of the overall mission profile. The results obtained highlight the effectiveness of genetic algorithms in finding optimal multi-planetary gravity assist trajectories and contribute to the advancement of trajectory optimization techniques for future space missions.

This master thesis presents the development of a genetic algorithm for optimizing multiplanetary gravity assist trajectories. The algorithm was designed to address the challenges of finding the most efficient trajectory for a spacecraft traveling into deep space using multiple planets while performing gravity-assist maneuvers. Given a model for the interplanetary trajectory, the algorithm is able to find a feasible optimal solution. The proposed approach was tested on a set of real missions and was shown to produce solutions more optimal than the real ones given our trajectory model. The results demonstrate the effectiveness of evolutionary algorithms, in concrete genetic algorithms, in finding optimal multi-planetary gravity assist trajectories, making it a valuable tool for mission planning in space exploration.

Magnetic attitude control systems are suitable for very small satellites, and yet provide a simple and robust method to detumbling and attitude control. In this work we analyse the use of hard ferromagnetic materials and magnetorquers to control the attitude of a spherical femtosatellite. The model will propagate the orbit of the satellite (disregarding the effects of the atmosphere) by means of SGP4 or SGP8. Once the orbit is propagated, we will use a suitable model of the geomagnetic field (IGRF13 or WMM) to determine the magnetic field in the location of the satellite. Passive ADCS will be obtained by means of the use of hysteresis rods. In order to add some control, a set of magnetorquers will be designed.

In this thesis project, a functional PMD device was designed for the implementation of a control system and thus achieve a more efficient and controlled way of the propellant extraction process. For this design process, an analysis was carried out on the different types of PMD devices and which ones could be used in a control system, as well as the selection of certain conditions of the meteosat second generation (MSG) satellite, to focus the design to something more attached to in practice.

This master thesis is part of an experimental project carried out at the Space Exploration Laboratory of the Universitat Politècnica de Catalunya, by a five master¿s students team, under the guidance of Ricard Gonzalez Cinca, to study the use of acoustic waves, for heat transfer enhancement, in a gas medium and with the innovation of been done under microgravity conditions, which have never been done before. The objective of the experiment is to obtain new knowledge in this field, which might help Scientifics develop a new version of a thermal control system. The students had the opportunity to experiment under microgravity conditions, by being selected for the Drop Your Thesis Programme, provided by ESA academy, allowing the students to develop the experiment at the Space Exploration Laboratory and test it in the ZARM drop tower. The experiment was divided into different subsystems: mechanical, software, electronics, mathematical simulations and testing. Each subsystem was developed by one of the masters students. This master thesis is focused on the software part of the experiment, designed using LabVIEW from National Instruments. This document is divided into three main parts, starting with the introduction to the experiment, which explains the experiment background information, as well as the Your Thesis Programme, then it continues with the introduction of the experiment software platform, LabVIEW. The thesis finalises with an explanation of the experiment control software developed.

On Earth, heat dissipation of electronics is produced through convective currents due to gravity, that allow the flow of energy to the environment. However, in microgravity, hot particles remain around the heat source due to the absence of buoyancy. In this project, an existing line of research from the Space Exploration Lab in the UPC is followed in the field of acoustic induced heat transfer in fluids. Our project aims to use acoustic actuation to enhance heat transfer in real microgravity conditions in the ZARM Drop Tower, thanks to the DropYourThesis! 2022 program, from the European Space Agency. The objective of this master thesis is to develop simulations that explain the phenomena and to help design an optimal setup for the study. A simple experiment is proposed with two main systems. The first generates an acoustic wave with a piezoelectric transducer and the second heats up a resistance, which actuates as a heat source. COMSOL Multiphysics is used to develop a validated model that will help us understand the Physics behind this phenomenon and achieve optimal setups to explain the governing factors of this interaction for different gravity levels. It is observed that acoustic heat transfer enhancement is highly dependent on time and gravity acceleration. For normal gravity conditions, the effect is noticeable at short timescales and then buoyancy turns into the dominant heat transfer factor over time. For microgravity conditions, data suggests that the effect is mild at short timescales, but it increases steadily over time without showing signs of regression. Heat transfer in microgravity conditions is increased by 10.9% after 16.2s of acoustic actuation using a resonance frequency of 45kHz. It is concluded that there is high potential for the development of a new cooling technology based on ultrasound in microgravity and this thesis establishes a theoretical framework in which future techniques could be based on.

This thesis presents a design of the system for the first stage of a mission in the NanoSat Lab, the 3Cat-8. There is an special focus on the control algorithm and the sizing of the actuators.

The focus of this thesis is to design and develop a complete electronic system consisting of a heating subsystem, an acoustic wave subsystem, and an instrumentation subsystem for an experiment in microgravity. The aim of this work is to ensure the correct performance of all these subsystems in order to demonstrate that convection can be achieved using acoustic waves in microgravity conditions.