Development of autonomous in-fight navigation capability for a CubeSat mission is a challenging task, often ignored in favour of relying on a Global Navigation Satellite System (GNSS). However, the potential value in solving this problem becomes great for deep-space missions where such networks have limited coverage. This thesis presents a proof of concept for how autonomous navigation can be achieved using the star tracker already included in the design of the Hugin satellite, a 3U-CubeSat under development by Beyond Atlas AB in Stockholm. A navigation algorithm presented in existing literature was selected, processing optically derived angular measurements of distant celestial bodies in an Unscented Kalman Filter (UKF). The algorithm was then integrated with a custom-built orbit simulator to test the navigation in a fight environment. Results from these simulations demonstrate that this algorithm can be used to allow a satellite in geocentric orbit to consistently track its position using only optical measurements, and key parameters for tuning the navigation UKF have been identifed. Additionally, Hugin’s star tracker was tested in order to verify its capabilities and measure the accuracy and precision of angular measurements. Software for generating images containing stars and celestial bodies was custom-built and used for the tests. Results from these tests were inconclusive, as the star tracker was unable to identify stars displayed in the test images. The most probable cause for this inability was judged to be an insuffciently true-to-reality test environment, with several possible improvements identifed to increase the fidelity of future tests. Based on the results from the simulations this report concludes that autonomous navigation is possible on Hugin using the presented algorithm. Despite this, much work remains to be done with the major topics needing further investigation outlined in this report. / Utveckling av autonom satellitnavigation för CubeSats är en stor utmaning, och en som ofta väljs bort för att istället förlita sig på ett Global Navigation Satellite System (GNSS). Men tillgängligheten till sådana system är begränsad i yttre rymden, vilket gör förmågan att navigera autonomt mer värdefull. Detta examensarbete presenterar ett koncepttest för hur autonom navigering kan möjliggöras med hjälp av den stjärnkikare som är en del av satelliten Hugins design, en 3U CubeSat som utvecklas av Beyond Atlas AB i Stockholm. En navigationsalgoritm som presenterats i en kontemporär forskningsrapport har valts ut, vilken bearbetar optiska vinkelmätningar av avlägsna himlakroppar i ett Unscented Kalman Filter (UKF). Algoritmen har integrerats med en specialbyggd orbitalsimulator för att testa navigationens prestation i en rymdmiljö. Resultat från dessa simuleringar demonstrerar att med hjälp av denna algoritm kan en sattelit i geocentrisk omloppsbana konsekvent uppskatta sin position endast med hjälp av optiska mätningar. Nyckelparametrar för att ställa in navigationsfiltret har även identiferats. Utöver detta testades Hugins stjärnkikare för att verifera dess funktionalitet och mäta dess noggrannhet och precision. Mjukvara för att generera bilder innehållande stjärnor och himlakroppar specialbyggdes och användes för testerna. Testresultaten var ofullständiga, eftersom stjärnkikaren inte kunde identiferade stjärnor som visades i testbilderna. Det mest sannolika skälet till denna oförmåga bedömdes vara en ej tillräckligt verklighetstrogen testmiljö, med ett antal möjliga åtgärder identiferade. Utifrån simuleringsresultaten dras slutsaten att det är möjligt att utföra autonom navigation på Hugin med den framförda algoritmen. Trots detta återstår mycket arbete inom flera utvecklingsområden, varav de främsta beskrivs i denna rapport.

Hydrogen is seen as the green fuel of the future for the aeronautical sector allowing to reduce the carbon footprint of commercial aviation. It is well established that the release of carbon emissions triggers global warming. Aviation, like many other industries, must reduce them. This study aims to integrate cryogenic hydrogen storage onboard an existing aircraft and study two different propulsion systems, namely hydrogen combustion and fuel cells. A cryogenic tank was modelled and then designed to fit in the fuselage of an A321. Two configurations were studied, one consisting of one tank at the rear and the other with two tanks, one at the front and one at the aft. The result showed a significant variation of the centre of gravity for the rear tank configuration, whether the airplane is empty or with payload. Among the two propulsion systems investigated, hydrogen combustion requires less of a technological leap than hydrogen fuel cell aircraft. The limitation would be the range due to the lack of volume onboard the aircraft to store the hydrogen fuel. But this new type of propulsion could lay the groundwork for future fuel cell aircraft. The fuel cells technology still needs to improve its power density to compete with current engines but would o er more efficient aircraft and therefore greater range.

This thesis concerns the upgrade of APID One RPAS by The MainBase AB. Due to their wish to explore different options for tail drive of current RPAS and future heavier variant, several concepts have been generated and analyzed. Systemic elimination of proposed concepts has resulted with a belt drive transmission. Basic calculation has been performed to determine estimates of power requirements and positions of the new tail rotors relative to the fuselage. Furthermore, the design process encompassed components from the existing output power shaft within the fuselage to the final blades shaft, including the belt transmission, the truss-type structural support, and additional devices. The work includes material selection, FEA analyses of the structure, and bolts and welds calculations where loads were known. Final result is a tail boom that interchangeably fits both, new light and new heavy variant.

The study involves development of a methodology to simulate a fin-tube evaporator under icing conditions using CFD in Ansys® Academic Fluent 2021R1. It aims to build on previous studies performed on heat pumps. It was performed by Abhay M. Hervatte in collaboration with Bosch Thermoteknik AB, Tranås, SE during the spring term of the year 2021. The thesis is published by Linköping University. Initially, experiments were conducted to measure the ice growth on the fins of the evaporator as a function of time. A CAD model of the evaporator was then generated. The evaporator geometry was scaled down and simplified to reduce the simulation time. Due to restrictions in the software, the simulations were split into two parts - one for the flow of the refrigerant through the evaporator pipes and another for flow of air over the fins. The internal flow simulation was a steady state simulation consisting of the phase-change of the refrigerant after absorbing heat from the ambient. through the pipes and a transient simulation for the external flow over the fins. The internal flow consisted of multi-phase simulation of the evaporation of the refrigerant - propane - after absorbing heat through the pipe walls. The external flow involved the multi-phase simulation of ice being deposited from humid air on the surface of the fins. The inner surface of the evaporator pipes was used as a bridge, and surface profiles from the internal simulation would be used to transfer the boundary conditions to the other simulation. Results of the ice-film thickness over the fins were obtained and compared to the experimental value and found to be in reasonable agreement with each other, with scope for improvement in the future.

Overcrowding of the Low Earth Orbit (LEO) region is a growing problem. Decades of treating this part of space like a scrap yard has caused it to become a hazardous environment for operating satellites. At present, the largest pieces of debris are being continuously tracked and satellite operators avoid them by maneuvering their spacecrafts out of the way. This approach is not possible for pieces that are smaller than 10 cm, since they are hard to detect and track as well as numerous. The exact number is not known but it is believed to be around 190 000. A number of different mitigation methods have been suggested. In this project the Laser Orbital Debris Removal (LODR) has been investigated and a basic simulation model has been developed. Though many aspects have been studied, only a few have been implemented in this first version of the simulation program. The thesis has uncovered some limiting factors of the models and data that have been used to describe the physical phenomena that relate to this problem. These factors, and other suggestions, are mentioned in chapter 5. Though the model is far from perfected, it shows the technical feasibility of the suggested method, as well as some of the problems that need to be solved before it can be implemented. The fact that it would be possible to build a ground based LODR system, in no way assures that it is likely to occur. The political aspects of such a facility are too problematic at this day in age. How should it be operated? Could we trust that it would not be used as a weapon? The questions are many and the answers are uncertain. For now, it seems best to focus on improving the understanding of the phenomena, the precision of the model and hope that there will come a time when this research will lead to an implementable solution.

The study is motivated by the quest to lower the fuel consumption of trawlers and reduce green house gas emissions. Conventional trawl-doors contribute to about one third of the trawlers fuel consumption. Design and optimization of trawl-doors using computational models is vital in minimizing the fuel consumption.The main objective of this work is to develope an optimization algorithm for the shape design of trawl-doors using computational uid dynamic (CFD) models. High-fidelity CFD models are computationally expensive and therefore, conventional optimization methods, which often require large number of evaluations are not feasible. The proposed method is iterative and uses local second order response surface approximation models of the high-fidelity CFD model, constructed in each iteration. The RSA are constructed locally and are regenerated at each iteration in new domain. We use a trust region mechanism to move the center of the search domain and to increase or decrease the size ofthe search domain. This reduces the number of evaluations. We propose novel shaped trawl-door shapes and investigate their performance. These shapes are similar to multi-element airfoils on aircraft i.e., airfoil shapes with slats and flaps. We apply the proposed optimization algorithm to the novel-shaped design of two-dimensional multi-element trawl-door shapes with several design variables controlling the slat and flap positions and alignment. The objective is to increase the hydrodynamic efficiency for a given lift constraint. The results are then compared to the performance of a typical trawl-door shape. The results indicate that a satisfactory design can be obtained at the cost of few iterations of the algorithm. We also investigate controllable trawl-doors where the flap angle can be varied, depending on the operational condition.

No description available.

The multipactor phenomenon is a major concern in modern satellites that operate with highpower transmission in many frequency bands. It occurs when electrons inside RF componentsare accelerated by the RF fields. These electrons then hit walls inside the device, produc-ing secondary electrons. As the number of electrons increases, it may create noise inside thecomponent, thus deteriorating the original signal-to-noise ratio. When designing radio fre-quency equipment for space applications, it is therefore important to know at which powerlevels this occurs. Multicarrier simulations are time consuming and demand high amounts ofcomputer resources. In this thesis the hybrid L1/L2 method has been tested, which is a methodthat separates the geometric and multicarrier simulations into two parts resulting in a shortercomputation time. The conclusion is that the method is more reliable than single carrier sim-ulations, and that it can be used as a first step in the designing process of RF components.It is also a way of estimating a preliminary threshold before starting a full-scale multicarriersimulation.

The Advanced Telescope for High-Energy Astrophysics (ATHENA) has been selected as the second large (L-class) mission designed to address the Cosmic Vision science theme “The Hot and Energetic Universe”. The European Space Agency has produced a Mission Observation Plan which contains objectives and constraints of the mission. In addition, this plan includes a representative sequence of targets, the Mock Observation Sequence, which defines the order in which ATHENA has to observe the targets. The feasibility of the Mock Observation Plan has to be assessed and the Mission Timeline Simulator has been designed for this purpose. It is a tool developed by Airbus DS that includes all the spacecraft operations. The analysis of the Mock Observation Plan in the Mission Timeline Simulator showed that the ATHENA’s line of sight points into the sun during some observations. This would lead to a loss of the whole mission since sunlight damages the instruments. Consequently, a new Observation Sequence has been produced by Airbus DS, in which the spacecraft does not point to the sun. However, this new sequence does not meet one important requirement: the operational availability shall be above 90%. The operational availability is defined by the percentage of the total time which is used for science observation. The version at the start of the thesis of the artificial case study but representative to the ATHENA mission achieved a value of 87.3 %. One of the main objectives of this thesis is therefore to obtain a sequence that meets the operational availability requirement with the final goal of generating a functional timeline of several days. If any interrupt occurs to the timeline (Targets of Opportunity, safe mode events, etc.), the spacecraft shall be able to find the way back to the optimal timeline or replan a new one. The current status includes these events but the timeline does not get interrupted. In this aspect, the currently implemented Greedy algorithm, that chooses the observation sequence, must be extended in branch and horizon. In order to achieve these objectives, a Beam Search algorithm has been developed and implemented in the Mission Timeline Simulator. The operational availability has been increased by incrementing the width search (branching factor). The depth search (horizon factor) allows the user to restrict the longitude of the timeline in terms of number of targets. A first implementation not including interrupts was analysed and an operational availability higher than 90% was achieved. A second implementation with a functional timeline considering interrupts shows a decrease in the operational availability, which does not reach 90%; nevertheless improving the results of the previous version with a final operational availability of 89.24%. Note that this is a representative case study of the mission. The Beam Search algorithm has been demonstrated to be suitable for the defined problem and a future sensitivity analysis of different parameters, such as depth and width search, could increase further the performance of the algorithm and therefore the simulation results. / ATHENA mission

A central factor affecting spacecraft lifetime is the radiation environment, which isunpredictable due to an incomplete understanding of plasma dynamics. FORESAIL2 will build on the FORESAIL-1 results – measurements of radiation belt lossesand demonstrate deorbiting in LEO. FORESAIL-2 will demonstrate a feasibility toutilize and characterize a nanosatellite and its instruments for scientific purposes ina high-radiation environ The Foresail 2 mission shall carry a number of instrumentsto characterize the GTO environment. The ADCS shall ensure that: The particletelescope (REPE) works in a scanning mode with the spin axis perpendicular tothe magnetic field vector. The Foresail 2 maintains required spin rate for CoulombDrag experiment (CDE). The CDE measures 0the drag force by measuring thechanges in spin rate while a long charged tether interacts with the ambient plasma.In order to fulfill requirements. Thesis shall model a novel method to deploy aTether, which shall be a primary instrument for measuring and modelling the plasmaenvironment. The thesis shall further select a deployment scheme and analysethe tether dynamics in real-time for the selected orbit, modelling environmentalconditions and studying their effects on tether and on overall dynamic stability ofthe spacecraft bus.