This dissertation proposes analytic tools for dynamics and control problems in the perspective of large-scale relative motion without perturbations. Specifically, we develop an exact and efficient analytic solution of satellite relative motion using a direct geometrical approach in spherical coordinates. The resulting solution is then transformed into general parametric equations of cycloids and trochoids. With this transformation, the dissertation presents new findings for design rules and classifications of closed and periodic parametric relative orbits. A new observation from the findings states that the orbit shape resulting from the relative motion dynamics of circular orbit cases in polar views are exactly the same as the parametric curves of cycloids and trochoids. The dynamics problem of satellite relative motion is expanded to include the design of satellite constellations for multiple satellite systems. A Parametric Constellation (PC) is developed to create an identical constellation pattern, or repeating space track, of target satellites with respect to a base satellite. In this PC theory, the number of target satellites is distributed using a real number system for node spacing. While using a base satellite orbit as the rotating reference frame, the PC theory consists of satellite phasing rules and closed form formulae for designing repeating space tracks. The evaluation of the PC theory is illustrated through it’s comparison to the existing Flower Constellation theory in terms of node spacing distribution and constellation design process. For the control problems, the efficient analytic solution is applied to the reference trajectory of satellite relative tracking control systems for inter-satellite links. Two types of relative tracking control systems are developed and each is evaluated to determine which is more appropriate for practical applications of inter-satellite links. All of the proposed analytic solutions and tools in this dissertation will be useful for the mission analysis and design of relative motions involving a two or more satellite system. / Ph. D.

Wildlife habitat mapping strongly supports applications in natural resource management, environmental conservation, impacts of anthropogenic activity, perturbed ecosystem restoration, species-at-risk recovery and species inventory. Remote sensing has long been identified as a feasible and effective technology for large-area wildlife habitat mapping. However, existing and future uncertainties in remote sensing will definitely have a significant effect on relevant scientific research, such as the limitation of Landsat-series data; the negative impact of cloud and cloud shadows (CCS) in optical imagery; and landscape pattern analysis using remote sensing classification products. This thesis adopted a manuscript-style format; it addresses these challenges (or uncertainties) and opportunities through exploring the state-of-the-art optical and radar remotely sensed data for large-area wildlife habitat mapping, and investigating their feasibility and applicability primarily by comparison either on the level of direct remote sensing products (e.g. classification accuracy) or indirect ecological model (e.g. presence/absence and frequency of use model based on landscape pattern analysis). A framework designed to identify and investigate the potential remotely sensed data, including Disaster Monitoring Constellation (DMC), Landsat Thematic Mapper (TM), Indian Remote Sensing (IRS), and RADARSAT-2, has been developed. The chosen DMC and RADARSAT-2 imagery have acceptable capability of addressing the existing and potential challenges (or uncertainties) in remote sensing of large-area habitat mapping, in order to produce cloud-free thematic maps for the study of wildlife habitat. A quantitative comparison between Landsat-based and IRS-based analyses showed that the characteristics of remote sensing products play an important role in landscape pattern analysis to build grizzly bear presence/absence and frequency of use models.

Wildlife habitat mapping strongly supports applications in natural resource management, environmental conservation, impacts of anthropogenic activity, perturbed ecosystem restoration, species-at-risk recovery and species inventory. Remote sensing has long been identified as a feasible and effective technology for large-area wildlife habitat mapping. However, existing and future uncertainties in remote sensing will definitely have a significant effect on relevant scientific research, such as the limitation of Landsat-series data; the negative impact of cloud and cloud shadows (CCS) in optical imagery; and landscape pattern analysis using remote sensing classification products. This thesis adopted a manuscript-style format; it addresses these challenges (or uncertainties) and opportunities through exploring the state-of-the-art optical and radar remotely sensed data for large-area wildlife habitat mapping, and investigating their feasibility and applicability primarily by comparison either on the level of direct remote sensing products (e.g. classification accuracy) or indirect ecological model (e.g. presence/absence and frequency of use model based on landscape pattern analysis). A framework designed to identify and investigate the potential remotely sensed data, including Disaster Monitoring Constellation (DMC), Landsat Thematic Mapper (TM), Indian Remote Sensing (IRS), and RADARSAT-2, has been developed. The chosen DMC and RADARSAT-2 imagery have acceptable capability of addressing the existing and potential challenges (or uncertainties) in remote sensing of large-area habitat mapping, in order to produce cloud-free thematic maps for the study of wildlife habitat. A quantitative comparison between Landsat-based and IRS-based analyses showed that the characteristics of remote sensing products play an important role in landscape pattern analysis to build grizzly bear presence/absence and frequency of use models.

Constellation reconfi guration consists of transforming an initial constellation of satellites into some final constellation of satellites to maintain system optimality. Constellations with phased deployment, changing mission requirements, or satellite failures would all benefi t from reconfi guration capability. The constellation reconfiguration problem can be broken into two broad sub-problems: constellation design and constellation transfer. Both are complicated and combinatorial in nature and require new, more efficient methods. Having reviewed existing constellation design frameworks, a new framework, the Elliptical Flower Constellations (EFCs), has been developed that offers improved performance over traditional methods. To assist in rapidly analyzing constellation designs, a new method for orbit propagation based on a sequential solution of Kepler's equation is presented. The constellation transfer problem requires an optimal assignment of satellites in the initial orbit to slots in the final orbit based on optimal orbit transfers between them. A new method for approximately solving the optimal two-impulse orbit transfer with fixed end-points, the so-called minimum Delta v Lambert's problem, is developed that requires the solution of a 4th order polynomial, as opposed to the 6th or higher order polynomials or iterative techniques of existing methods. The recently developed Learning Approach to sampling optimization is applied to the particular problem of general orbit transfer between two generic orbits, with several enhancements specifi c to this problem that improve its performance. The constellation transfer problem is then posed as a Linear Assignment Problem and solved using the auction algorithm once the orbit transfers have been computed. Constellations designed for global navigation satellite systems and for global communications demonstrate signifi cant improvements through the use of the EFC framework over existing methods. An end-to-end example of constellation recon figuration for a constellation with changing regional coverage requirements shows the effectiveness of the constellation transfer methods.

No description available.

<p>Large space-based communication networks have been growing in numbers of satellites, with plans to launch more than 10,000 satellites into Low Earth Orbit (LEO). While these constellations offer many advantages over ground-based communication systems, they pose a significant threat when they fail and generate space debris. Given the reliability of current satellites, engineers can use failure modeling to design satellite constellations that are more resilient to satellite failures. Several authors have analyzed the reliability of geostationary satellites, but few have expanded the work to multiple-satellite systems. </p> <p>To address this gap, we constructed a simulation model to show the performance of satellite constellations with different satellite reliability functions over time. The simulation model is broken down into four key parts: a satellite constellation model, a network model, a failure model, and a performance metric. We use a Walker star constellation, which is the most common constellation for LEO broadband satellite constellations. The network consists of satellite-to-satellite connections and satellite-to-groundstation connections, which routes data using a shortest-path algorithm. The failure model views satellites as either operational or failed (no partial failures) and considers the groundstation operator’s knowledge or lack thereof of the satellites’ operational status and uses satellite reliability to estimate the expected data throughput of the system. We also created a performance metric that measures how well the entire network is operating and helps us compare candidate constellations.</p> <p>We used the model to estimate performance for a range of satellite reliabilities, and for groundstations with different numbers of communication dishes (effectively, satellite-ground links). Satellite reliability is a significant contributing factor to the long-term constellation performance. Using the reliability of small-LEO satellites, we found that a constellation of 1,200 small-LEO satellites completely fails after less than 30 days, given that we do not consider partial failures. Satellite constellations with higher satellite reliability, such as large geostationary satellites, last less than 50 days. We expect the constellations in our model to perform worse than real satellite systems, since we are only modeling complete failures, however these findings provide a useful worst-case baseline for designing sustainable satellite constellations. We also found that the number of groundstation-to-satellite communication links at each groundstation is not a significant factor for more than five communication links, meaning that adding more communication antennas to existing satellite groundstations would not improve constellation performance significantly.</p>

Earth's atmosphere is a dynamic region with a complex interplay of energetic inputs, outputs, and transport mechanisms. A complete understanding of the atmosphere and how various fields within it interact is essential for predicting atmospheric shifts relevant for spaceflight, the evolution of Earth's climate, radio communications, and other practical applications. In-situ observations of a critical altitude region within Earth's atmosphere from 100-200 km in altitude, a subset of a larger 90 – 400 km altitude region deemed the "Thermospheric Gap", are required for constraining atmospheric models of wind, temperature, and density perturbations caused by atmospheric tides. Observations within this region that are sufficient to fully reconstruct and understand the evolution of tides therein are nonexistent. Certain missions have sought to fill portions of this observation gap, including Daedalus which was selected as a candidate for the Earth Explorer program by the European Space Agency in 2018. This study focuses on the design and optimization of a two-satellite, highly elliptical satellite constellation to perform in-situ observations and reconstruction of tidal features in the 100-200 km region. The model atmosphere for retrieving sample data is composed of DE3 and DE2 tidal features from the Climatological Model of the Thermosphere (CTMT) and background winds from the Thermosphere-Ionosphere-Electrodynamic General Circulation Model (TIEGCM). BoTorch, a Bayesian Optimization package for Python, is integrated with the Ansys Systems Tool Kit (STK) to model the constellation's propagation and simulated atmospheric sampling. A least squares fitting algorithm is utilized to fit the sampled data to a known tidal function form. Key results include 14 Pareto optimal solutions for the satellite constellation based on a set of 7 objective functions, 3 constellation input parameters, and a sample set of n = 86. Four of these solutions are discussed in more detail. The first two are the best and second-best options on the Pareto front for sampling and reconstruction of the input tidal fields. The third is the best solution for latitudinal tidal fitting coverage. The fourth is a compromise solution that nearly minimizes delta-v expenditure, while sacrificing some quality in tidal fitting and fitting coverage. / Master of Science / Earth's atmosphere, the envelope of gaseous material surrounding the planet from an altitude of 0 km to approximately 10,000 km, is a dynamic system with a diverse set of energy inputs, outputs, and transfer mechanisms. A complete understanding of the atmosphere and how various fields within it interact is essential for predicting atmospheric shifts relevant for spaceflight, the evolution of Earth's climate, radio communications, and other practical applications. The atmosphere life breathes on Earth's surface evolves in physical and chemical properties, such as temperature, pressure, and composition, as distance from Earth increases. In addition, the atmosphere varies temporally, with shifts in its properties occurring on several timescales, some as short as a few minutes and some on the order of the age of the planet itself. This thesis project seeks to study the optimization of a satellite system to further understand an important source of atmospheric variability – atmospheric tides. Just as the forces of gravity from the moon and sun cause tides in the oceans, the Earth's rotation and the periodic absorption of heat into the atmosphere from the sun cause atmospheric tides. A model atmosphere with a few tides and a background wind is generated to perform simulated tidal sampling. The latitude, longitude, and altitude coordinates of the satellites as they propagate through the atmosphere are used to model samples of the northward and southward atmospheric winds and determine how well the constellation does at regenerating the input tidal data. The integration of several software tools and a Bayesian Optimization algorithm automate the process of finding a range of options for the constellation to best perform the tidal fitting, minimize satellite fuel consumption, and cover as many latitude bands of the atmosphere as possible.

With increasing world tensions and improvements of satellites and their sensors, the interest and possibility of using space and satellites for defensive purposes has increased greatly. However, not much research has been conducted into the needs and possibilities of satellite constellations over Sweden, especially using SAR and optical sensors combined with AI object detection. This thesis provides insight in to the needs and requirements to achieve certain coverage and gap times and explores different constellation design methods to do so. This is done by combining large scale tests performed with genetic algorithm and a dual-axis propagator with theoretical and analytical methods. Results show that for micro-satellites under 100 kg based on current commercial technology, it is found that between 24 to 63 satellites are needed for 1 hour gap times depending on what combination of SAR and optical satellites are used. The genetic algorithm was found to not generate optimal constellations as the number of satellites increased beyond 12. It was however useful in mapping out possibilities and finding certain optimal parameters such as the inclination. The dual-axis propagator tested for its low processing load was found to be good for coverage analysis and estimating the shapes of the orbits. It was noted to have large positional errors however, limiting its use to analysis and not full constellation design. / Med ökande världsspänningar och förbättringar av satelliter och deras sensorer har intresset och möjligheterna att använda rymden och satelliter för försvarssyften ökat avsevärt. Dock har inte mycket forskning gjorts om behoven och möjligheterna med satellitkonstellationer över Sverige, särskilt när det gäller användningen av SAR och optiska sensorer i kombination med AI-objektdetektering. Denna avhandling ger insikt i behoven och kraven för att uppnå viss täckning och tidsgap samt utforskar olika metoder för konstellationsdesign för att uppnå detta. Detta görs genom att kombinera storskaliga tester med genetiska algoritmer och en dual-axis propagator med teoretiska och analytiska metoder. Resultaten visar att för mikrosatelliter under 100 kg, baserat på nuvarande kommersiell teknik, krävs mellan 24 och 63 satelliter för att uppnå gapptider på 1 timme, beroende på vilken kombination av SAR- och optiska satelliter som används. Det konstaterades att genetiska algoritmen inte tillförlitligt kunde hitta optimala konstellationer när antalet satelliter ökade bortom 12 st. Dualaxelpropagatorn, som testades för sin låga processbelastning, ansågs vara bra för täckningsanalys och uppskattning av omloppsbanornas former. Den hade dock stora positionsfel, vilket begränsade dess användning till analys och inte fullständig konstellationsdesign.

As satellites become smaller, cheaper, and quicker to manufacture, constellation systems will be an increasingly attractive means of meeting mission objectives. Optimizing satellite constellation geometries is therefore a topic of considerable interest. As constellation systems become more achievable, providing coverage to specific regions of the Earth will become more common place. Small countries or companies that are currently unable to afford large and expensive constellation systems will now, or in the near future, be able to afford their own constellation systems to meet their individual requirements for small coverage regions. The focus of this thesis was to optimize constellation geometries for small coverage regions with the constellation design limited between 1-6 satellites in a Walker-delta configuration, at an altitude of 200-1500km, and to provide remote sensing coverage with a minimum ground elevation angle of 60 degrees. Few Pareto-frontiers have been developed and analyzed to show the tradeoffs among various performance metrics, especially for this type of constellation system. The performance metrics focus on geometric coverage and include revisit time, daily visibility time, constellation altitude, ground elevation angle, and the number of satellites. The objective space containing these performance metrics were characterized for 5 different regions at latitudes of 0, 22.5, 45, 67.5, and 90 degrees. In addition, the effect of minimum ground elevation angle was studied on the achievable performance of this type of constellation system. Finally, the traditional Walker-delta pattern constraint was relaxed to allow for asymmetrical designs. These designs were compared to see how the Walker-delta pattern performs compared to a more relaxed design space. The goal of this thesis was to provide both a framework as well as obtain and analyze Pareto-frontiers for constellation performance relating to small regional coverage LEO constellation systems. This work provided an in-depth analysis of the trends in both the design and objective space of the obtained Pareto-frontiers. A variation on the εNSGA-II algorithm was utilized along with a MATLAB/STK interface to produce these Pareto-frontiers. The εNSGA-II algorithm is an evolutionary algorithm that was developed by Kalyanmoy Deb to solve complex multi-objective optimization problems. The algorithm used in this study proved to be very efficient at obtaining various Pareto-frontiers. This study was also successful in characterizing the design and solution space surrounding small LEO remote sensing constellation systems providing small regional coverage.

Transportation across the globe's oceans increases every year and is expected to keep increasing in the following decades. Consequently, there is a need to establish communication over the horizon through the Automatic Identification System (AIS) and the Very High Frequency (VHF) Data Exchange System (VDES), still in development, to track and communicate with vessels all over the globe regardless of the distance from shore. In this Master thesis a feasibility study for the development of a system that fulfils that need is proposed consisting of a Low Earth Orbit (LEO) constellation providing VDES communication continuously all over the globe. A system engineering approach has been followed, identifying stakeholders and producing system requirements setting up a framework for the system. The key stakeholders were found to be the customers/users, the satellite provider, the satellite operator, the service provider and the payload provider. Furthermore, possible use-cases were presented and a system architecture was defined to outline the system, dividing the system into three segments: the space segment, the ground segment and the launch segment. In addition, design proposals for a satellite constellation and a typical satellite in such a constellation were implemented. The satellite constellation was proposed to consist of 91 satellites at an orbit altitude of around 550 km in polar orbits of common inclination, this was regarding a minimum elevation angle of 10 degrees. The satellite is recommended to consist of a 6 U CubeSat using as payload the existing airborne transponder R5A from Saab TransponderTech, it builds on the Software Defined Radio (SDR) technology and is to be further developed for VDES applications. Moreover, a link- and a data budget were implemented. Different launch options were addressed concluding that launching as secondary payload on a ride-share mission or as primary payload on a small satellite launch vehicle are the preferable options. A market analysis has been made providing details on how many AIS/VDES satellites that have been launched into LEO and by which service provider, as well as further details on small/nano satellites of extra interest to this work. A short risk evaluation was also done, identifying the most evident risks with developing, operating and disposing the system. In addition, Saab's potential role in the development of satellite VDES is discussed.  In conclusion to this work it has been shown that it is possible to build a global continuous satellite constellation in LEO utilising as payload an SDR-platform to provide VDES services to vessels at open seas. / Transport globalt till havs ökar varje år och förväntas fortsätta att öka de följande årtiondena. Följaktligen finns ett behov av att etablera över horisonten kommunikation genom det automatiska identifieringssystemet (AIS) och det väldigt högfrekventa datautbytessystemet (VDES), under utveckling, för att spåra och kommunicera med fartyg över hela världen oberoende av avståndet från land. I detta examensarbete har en förstudie utförts för utvecklingen av ett system som uppfyller detta behov. Systemet föreslås bestå av en låg jordbana satellitkonstellation som kontinuerligt tillhandahåller VDES-kommunikation över hela världen. Ett systemtekniskt tillvägagångssätt har följts, intressenter har identifierats och utifrån dessa har systemkrav tagits fram. De viktigaste intressenterna befanns vara användare/kunder, satellitleverantören, satellitoperatören, tjänsteleverantören och nyttolastleverantören. Vidare lyftes olika möjliga användningsområden för systemet fram och en systemarkitektur framställdes vari systemet delades in i tre segment: rymdsegmentet, marksegmentet och uppskjutningssegmentet. Dessutom genomfördes designförslag för en satellitkonstellation samt en typisk satellit i en sådan konstellation. Satellitkonstellationen föreslogs bestå av 91 satelliter på en altitud på omkring 550 km i polära banor med gemensam inklination, detta var gällande för en minimum elevationsvinkel på 10 grader. Satelliten rekommenderades bestå av en 6 U CubeSat med den befintliga luftburna transpondern R5A från Saab TransponderTech som nyttolast, vilken bygger på mjukvaruradioteknik och är tänkt att vidareutvecklas för VDES-applikationer.  Vidare, implementerades en länk- och data budget. Olika uppskjutningsmöjligheter undersöktes, varav slutsatsen att uppskjutning som sekundär nyttolast på ett delningsuppdrag eller som primär nyttolast medhjälp av ett mindre uppskjutningsfordon anpassat för små satelliter var de föredragna alternativen. Även en marknadsanalys har genomförts, där det redogjorts för hur många AIS / VDES - satelliter som har uppskjutits i LEO och av vilken tjänsteleverantör, samt ytterligare detaljer om små / nano satelliter av extra intresse för arbetet. En kort riskbedömning har också gjorts, där de mest uppenbara riskerna med utveckling, drift och undanröjande av systemet identifierats. Dessutom diskuteras Saabs möjliga roll i utvecklingen av satellit VDES. Slutsatsen av detta arbete har visat att det är möjligt att bygga en global kontinuerlig satellitkonstellation i låg jordbana med en mjukvaruradio som nyttolast som tillhandahåller VDES-tjänster till fartyg på öppna hav.