This work comprises two main parts. The first part outlines our efforts to expand on the recent work of Gütlich et.al. by synthesizing Co(II) based spin crossover systems within a dendritic framework. We wanted to investigate the possibility of synthesizing different first generation, triazole containing dendrimers using “click” type reactions and their coordination ability with Co(II) ions. To this end we have had limited success mainly due to the numerous challenges in synthesizing a pure dendrimer product. The second part details our efforts in the synthesis of a mononuclear Co(II) based single molecule magnet. This comes as an extension to recent reports by Chang and Long where they have successfully obtained mononuclear Fe(II) single molecule magnets by inducing structural distortions within the complexes to amplify the spin-orbit coupling. We postulated that the use of Co(II) in conjunction with a bulky ligand framework would lead to desirable magnetic properties. We chose the known bis(imino)pyridine ligand scaffold due to its rich chemistry and its interesting and unexpected coordination behaviour, as we have seen in previous research efforts by our lab. To this end we were successful in isolating and characterizing 4 compounds, and we have carried out detailed magnetic measurements on the two most magnetically interesting species.

No description available.

Spacecraft (S/C) docking is the last and most challenging phase in the contact closure of two separately flying S/C. The design and testing of S/C docking missions using software-multibody simulations need to be complemented by Hardware-In-The-Loop (HIL) simulation using the real docking hardware. The docking software multibody simulation is challenged by the proper modeling of contact forces, whereas the HIL docking simulation is challenged by proper inclusion of the real contact forces. Existing docking HIL simulators ignore back-reaction force modeling due to the large S/C sizes, or use compliance devices to reduce impact, which alters the actual contact force. This dissertation aims to design a docking HIL testbed to verify docking contact dynamics for small and rigid satellites by simulating the real contact forces without artificial compliance. HIL simulations of docking contact dynamics are challenged mainly by: I. HIL simulation quality: quality of realistic contact dynamics simulation relies fundamentally on the quality of HIL testbed actuation and sensing instrumentation (non-instantaneous, time delays, see Fig. 1) II. HIL testbed design: HIL design optimization requires a justified HIL performance prediction, based on a representative HIL testbed simulation (Fig. 2), where appropriate simulation of contact dynamics is the most difficult and sophisticated task. The goal of this dissertation is to carry out a systematic investigation of the technically possible HIL docking contact dynamics simulation performances, in order to define an appropriate approach for testing of docking contact dynamics of small and rigid satellites without compliance and using HIL simulation. In addition, based on the investigations, the software simulation results shall be validated using an experimental HIL setup. To achieve that, multibody dynamics models of docking S/C were built, after carrying out an extensive contact dynamics research to select the most representative contact model. Furthermore, performance analysis models of the HIL testbed were built. In the dissertation, a detailed parametric analysis was carried out on the available models’ design-spaces (e.g., spacecraft, HIL testbed building-blocks and contact dynamics), to study their impacts on the HIL fidelity and errors (see Fig. 1). This was done using a generic HIL design-tool, which was developed within this work. The results were then used to identify the technical requirements of an experimental 1-Degree-of-Freedom (DOF) HIL testbed, which was conceived, designed, implemented and finally utilized to test and validate the selected docking contact dynamics model. The results of this work showed that the generic multibody-dynamics spacecraft docking model is a practical tool to model, study and analyze docking missions, to identify the properties of successful and failed docking scenarios before it takes place in space. Likewise, the 'Generic HIL Testbed Framework Analysis Tool' is an effective tool for carrying out performance analysis of HIL testbed design, which allows to estimate the testbed’s fidelity and predict HIL errors. Moreover, the results showed that in order to build a 6DOF HIL docking testbed without compliance, it is important to study and analyze the errors’s sources in an impact and compensate for them. Otherwise, the required figure-of-merits of the instruments of the HIL testbed would be extremely challenging to be realized. In addition, the results of the experimental HIL simulation (i.e., real impacts between various specimen) serve as a useful contribution to the advancement of contact dynamics modeling.

The main objective of this thesis is to introduce the reader to the problematics of air-launch and to a custom design solution applying this concept. The specifics of this method of bringing a payload into orbit are described and explained. Overview of projects which use aircraft to launch spacecraft is included. Determination of primary parameters of a launch vehicle designed to carry a payload of a specified mass is conducted. The required flight performance has been estimated, a computational model has been developed in software MATLAB, and a multidisciplinary optimization of the design parameters has been performed using a genetic algorithm optimization method. Parameters of the designed air-launched rocket are compared with those of a ground-launched rocket. According to the specific criteria, the Airbus A310-300 aircraft was selected as the most suitable transport aircraft to be used for launching the designed launch vehicle. The last part of the thesis is devoted to the proposal of necessary modifications and estimation of the flight performance.

Les ondes de spin sont une des voies technologiques proposées pour surmonter les obstacles que rencontre la miniaturisation des complementary metal-oxide-semiconductor (CMOS) dans la gamme du nanomètre, comme en témoignent les derniers développements en matière de dispositifs logiques à ondes de spin. Cependant, l'attrait industriel de ces preuves de concept est conditionné par leur intégration évolutive à la technologie CMOS. Ici, nous présentons des pistes ultrafines de Ta/CoFeB/MgO utilisées comme guides d'ondes de spin. Ce système a été choisi pour sa compatibilité avec les procédés CMOS, son anisotropie magnétique perpendiculaire et ses fortes interactions spin-orbite. Ces derniers sont intéressants pour manipuler les ondes de spin et ont été caractérisés par résonance ferromagnétique à couple de spin où il est démontré que l'effet Hall de spin inverse est responsable de la détection de la dynamique de magnétisation. Ensuite, nous utilisons des guides d'ondes coplanaires nanométriques intégrés pour exciter localement des ondes de spin dans une large gamme de vecteurs d'ondes. La comparaison du spectre d'ondes de spin mesuré avec les calculs analytiques montre que l'effet Hall de spin inverse permet la détection des ondes de spin indépendamment de leur vecteur d'onde avec des longueurs d'onde allant jusqu'à 150 nm. Des expériences complémentaires de diffusion de la lumière de Brillouin révèlent que les ondes de spin dans le guide d'ondes de spin ultra-mince à anisotropie magnétique perpendiculaire ont des longueurs de propagation étonnamment élevées compte tenu de l'amortissement relativement élevé des systèmes Ta/CoFeB/MgO. Ces résultats ouvrent la voie à des dispositifs à ondes de spin ultraminces compatibles CMOS avec des techniques d'excitation et de détection évolutives jusqu'à l'ordre du nanomètre, avec la perspective de contrôler les ondes de spin via des couples spin-orbite. / Spin-waves have been proposed as a possible technological path to overcome the hurdles encountered by the miniaturization of complementary metal-oxide-semiconductor (CMOS) into the nanometer range, demonstrated by recent developments in spin-wave-based logic devices. However the industrial appeal of these proofs-of-concept is conditional upon their scalable integration with CMOS technology. Here, we report on ultrathin Ta/CoFeB/MgO wires used as spin-wave waveguides. This system is chosen for its compability with CMOS processes, its perpendicular magnetic anisotropy and strong spin-orbit interactions. The latter are of interest for manipulating spin waves and are characterized via spin-torque ferromagnetic resonance where it is shown that the inverse spin Hall effect is responsible for the detection of magnetization dynamics. Following this, we use integrated nanometric coplanar waveguides to locally excite spin-waves in a broad range of wavevectors. Comparison of the measured spin-wave spectrum with analytical calculations show that the inverse spin Hall effect allows the wavevector-independent detection of spin-waves with wavelengths down to 150 nm. Complementary Brillouin light scattering experiments reveal that spin-waves in the ultrathin spin-wave waveguide with perpendicular magnetic anisotropy have unexpectedly high propagation lengths considering the relatively high damping in Ta/CoFeB/MgO systems. These findings pave the way for ultrathin CMOS-compatible spin-wave devices with excitation and detection techniques that are scalable into the nanometer range, with the prospect of controlling spin-waves via spin-orbit torques.

In this thesis we consider various questions and problems about graphs that appear in the framework of descriptive set theory. The main object of study are graphons, graphings and variations of the graph G0. We establish an approach to the compactness of the graphon space via the weak* topology and introduce the notion of a fractional isomorphism for graphons. We use a variant of the G0-dichotomy in the context of the classification problem. Finally, we show a measurable version of the Vizing's theorem for graphings. 1

<div>As the number of Resident Space Objects around Earth continues to increase, the need for an optimal sensor tasking strategy, specifically with Ground-Based Optical sensors, continues to be of great importance. This thesis focuses on the single and multi-sensor tasking problem with realistic optical sensor modeling for the observation of objects in the Geosynchronous Earth Orbit regime. In this work, sensor tasking refers to assigning the specific?c observation times and viewing directions of a single or multi sensor framework to either survey for or track new or existing objects. For this work specifically, the sensor tasking problem will seek to maximize the total number of Geosynchronous Earth Orbiting objects to be observed from a catalog of existing objects with a single and multi optical sensor tasking framework. This research focuses on the physical assumptions and limitations on an optical sensor, and how these assumptions affect the single and multi sensor tasking scenario. First, the concept of the probability of detection of a resident space object is calculated based on the viewing geometry of the resident space object. Then, this probability of detection is compared to the system that avoids the computational process by implementing a classical heuristic minimum elevation constraint to an electro-optical charged coupled optical sensor. It is shown that in the single and multi-sensor tasking scenario if the probability of detection is not considered in the sensor tasking framework, then a rigid elevation constraint of around 25^o-35^o is recommended for tasking Geosynchronous objects. Secondly, the topic of complete geo-coverage within a single night is explored. A sensor network proposed by Ackermann et al. (2018) is studied with and without the probability of detection considerations, and with and without uncertainties in the resident space objects' states. (then what you have). For the multi-sensor system, it is shown that with the assumed covariance model for this work, the framework developed by Ackermann et al. (2018) does not meet the design requirements for the cataloged Geosynchronous objects from March 19th, 2019. Finally, the concept of a variable repositioning time for the slewing of the ground-based sensors is introduced and compared to a constant repositioning time model. A model for the variable repositioning time is derived from data retrieved from the Purdue Optical Ground Station. This model is applied to a single sensor scenario. Optimizers are developed using the two repositioning time functions derived in this work. It is shown that the constant repositioning models that are greater than the maximum repositioning time produce results close to the variable repositioning solution. When the optimizers are tested, it is shown that there is a small increase in performance only when the maximum repositioning time is significant.</div>

Due to the unsustainable space debris environment in Low Earth Orbit, debris objects must be removed to ensure future safe satellite operations. One proposed concept for deorbiting larger space debris objects, such as decommissioned satellites or spent upper rocket stages, is to use a chaser spacecraft connected to the debris object by an elastic tether, but the required technology is immature and there is a lack of flight experience. The inoperable satellite, Envisat, has been chosen as a representative object for controlled re-entry by performing several high thrust burns. The aim of this paper is to develop a control system for the deorbit phase of such a mission. Models of the spacecraft dynamics, the tether, and sensors are developed to create a simulator. Two different tether models are considered: the massless model and the lumped mass model. A switched linear-quadratic-Gaussian (LQG) controller is designed to control the relative position of the debris object, and a switched proportional-integral-derivative (PID) controller is designed for attitude control. Feedforward compensation is used to counteract the couplings between relative position and attitude dynamics. An analysis of the system suggests that the tether should be designed in regard to the control system and it is found that the lumped mass model comes with higher cost than reward compared to the massless tether model in this case. Simulations show that the control system is able to control the system under the influence of modeling errors during a multi-burn deorbit strategy and even though more extensive models are suggested to enable assessment of the feasibility to perform this mission in reality, this study has resulted in extensive knowledge and valuable progress in the technical development. / En ökande mängd rymdskrot har lett till en ohållbar miljö i låga omloppsbanor och föremål måste nu tas bort för att säkerställa framtida satellitverksamhet. En föreslagen metod för att avlägsna större skrotföremål, såsom avvecklade satelliter och använda övre raketsteg, är att koppla en jagande rymdfarkost till föremålet med en elastisk lina. Dock är den teknik som behövs inte mogen och det finns en brist på praktisk erfarenhet. Den obrukbara satelliten Envisat har valts som representativt objekt för kontrollerat återinträde genom flera perigeumsänkande raketmanövrar. Syftet med detta arbete är att utveckla ett system för att kontrollera de två sammankopplade rymdfarkosterna under avlägsningsfasen under ett sådant uppdrag. Modeller för farkosternas dynamik, den sammankopplande linan och sensorer byggs för att utveckla en simulator. Två olika modeller för linan undersöks: den masslösa modellen och den klumpade nodmassmodellen. En omkopplande regulator designas genom minimering av kvadratiska kriterier för att kontrollera skrotföremålets relativa position till den jagande farkosten. Vidare designas en omkopplande proportionerlig-integrerande-deriverande (PID) regulator för att reglera pekningen hos den jagande farkosten. Kompensering genom framkoppling används för att motverka de korskopplingar som förekommer mellan translations- och rotationsdynamiken. En analys av systemet visar att linan bör designas med reglersystemet i åtanke och det framkommer att nackdelarna överväger fördelarna för den klumpade nodmassmodellen jämfört med den masslösa modellen. Simuleringar visar att reglersystemet klarar att kontrollera systemet under ett scenario med flera manövrar och under inverkan av modellfel. Även om mer omfattande modeller föreslås för att möjliggöra en fullständig bedömning av genomförbarheten för detta uppdrag så har denna studie resulterat i en omfattande kunskapsvinst och värdefulla framgångar i det tekniska utvecklingsarbetet.

In this report I present a feasibility study of using open astronomical data to make Initial Orbit Determination (IOD) for Resident Space Objects (RSO) appearing as streaks in telescope images. The purpose is to contribute to Space Surveillance and Tracking (SST) for maintaining Space Situation Awareness (SSA). Data from different wide-field survey telescopes were considered but due to availability constraints only mask images from Zwicky Transient Facility (ZTF) survey were chosen for the analysis. An algorithm was developed to detect streaks in the mask images and match them to RSO known to be within the Field of View (FoV) at the observation time. Further, the IOD was made with angles-only Laplace’s method and the state vectors calculated for the streaks from the IOD were compared to those from the TLE for the matching RSO. The algorithm was tested with 6 different image fields acquired between the 14th to the 16th December 2019, of which 4 are characterised as non-crowded and 2 as crowded. The streak finding algorithm has a better precision and sensitivity for the non-crowded field, with an F1-score of 0.65, but is worse for the crowded fields with an F1-score of 0.035. In the non-crowded fields 95% of all streak and object matches are true matches to unique RSO, while for the crowded field only 10% are true matches. It was found that the 1''/pixel resolution in the images is too low for doing an IOD with Laplace’s method, despite how well the streak finding algorithm performs. However, with some improvements, the method is suitable as a cost effective way to verify known RSO in catalogues. / I den här rapporten presenterar jag en studie om att använda öppen astronomiska data för att göra initial banbestämning för artificiella rymdobjekt avbildade som streck i teleskopbilder. Syftet är att tillhandahålla information för att upprätthålla en god rymdlägesbild. Data från olika kartläggnings teleskop övervägdes men på grund av begränsningar i tillgänglighet valdes endast mask-bilderna från Zwicky Transient Facility för analysen. En algoritm utvecklades för att upptäcka streck i mask-bilderna och matcha dem med kända objekt i bildens synfält vid observationstillfället. Vidare gjordes den initiala banbestämningen med Laplaces metod, som använder vinkelkoordinaterna för streckens position vid observationen. Tillståndsvektorerna för strecken och de matchade objekten jämfördes, de beräknades från den initiala banbestämningen respektive objektets TLE. Algoritmen testades med 6 olika bildfält från observationsdatum mellan den 14:e till den 16:e december 2019, av dessa karakteriseras 4 som glesa och 2 som fyllda. Algoritmen för streck detektering har bättre precision och känslighet för de glesa fälten, med ett F1-värde på 0.65, men sämre för de fulla fälten med ett F1-värde på 0.035. I de glesa fälten är 95% av alla streck- och objektmatchningar korrekta matchningar med unika objekt, medan för det fulla fälten är endast 10% korrekta matchningar. Det visar sig att upplösningen på 1''/pixel i bilderna är för låg för att göra en initial banbestämning med Laplaces metod, oavsett hur bra algoritmen för streck detektering presterar. Genom att göra vissa förbättringar i algoritmen är metoden lämplig för att, på ett kostnadseffektivt sätt, verifiera kända objekt i kataloger.

A newly proposed F-class mission by the European Space Agency (ESA) in 2019,Comet Interceptor, aims to dynamically intercept a New Solar System Objectsuch as a Dynamically New Comet (DNC). The Spacecraft will be placed in aperiodic (Halo) orbit around the Sun-Earth L2 Lagrangian point, waiting for furtherinstructions about the passage of a comet or an asteroid, which could well bereached within the stipulated mission constraints.A major part of the detection of these bodies will be owed to the Large SynopticSurvey Telescope (Currently under construction in Chile), which hopes to vastlyincrease the ability to discover a possible target using the catalogue of LongPeriod Comets and a set of its orbits. It is suggested that, in a mission length of&lt;5 years, discoveries and warnings are possible so that optimization of thetrajectory and characterisation of the object are done within the set windows.This thesis is aimed at facilitating a transfer to a Potentially Hazardous Asteroid(PHA), a subset of the Near-Earth Objects (NEO), as a secondary choice on theoff-chance that the discovered comet could not be reached from the L2 Librationpoint within the mission constraints.The first section of this thesis deals with the selection of a Potentially HazardousAsteroid for our mission from the larger database of the Near-Earth Objects,based on a measure of impact hazard called the Palermo Scale, while the secondsection of the thesis aims to obtain a suitable Halo orbit around L2 through ananalytical construction method. After a desired orbit is found, the invariantmanifolds around the Halo orbit are constructed and analysed in an attempt toreduce the ΔV, where from the spacecraft can intercept the Potentially Hazardous Asteroid through the trajectory demanding the least energy.