Dissertations / Theses on the topic 'Artificial satellites in navigation'

Effectiveness of solar radiation pressure in the three-axis attitude control of present day and next generation of large communications satellites is investigated. A simple two-flap configuration is used with optimization of the direction of the applied control moment rather than the magnitude of the weak solar radiation pressure. Simulations were carried out in the presence of varying orbital eccentricity and inclination, solar aspect angle and controller dynamics parameters. Time histories of librational response against orbital position are presented for controlled and uncontrolled conditions. The results suggest the semipassive controller to be quite effective over a wide range of system parameters and it can meet the exacting pointing accuracy demanded by large communications satellites.
Applied Science, Faculty of
Mechanical Engineering, Department of
Graduate

"Author biographies are available in the expanded on-line version of this article [http://www.insidegnss.com/auto/julyaug09-tetewsky-final.pdf]"
"July/August 2009." Web site title: Making Sense of GPS Inter-Signal Corrections : Satellite Calibration Parameters in Legacy and Modernized Ionosphere Correction Algorithms.

The existing air navigation services have many shortcomings and a reform was necessary. The new systems (CNS/ATM systems) will be largely dependent on Global Navigation Satellite Systems (GNSS) which can bring significant benefits to air navigation in terms of safety, efficiency, capacity, and economy. However, GNSS have weaknesses which can be reduced but will never be fully eliminated. Depending solely on a system that can be disrupted is not acceptable for safety of life applications, such as aviation. The implementation of GNSS also raises unique legal issues and ICAO has been working on the establishment of a legal framework for GNSS since 1992. Nevertheless, disagreement between states on the need for an international convention remains significant. Legal discussions should not slow down the implementation of GNSS which, when used in conjunction with terrestrial navigation aids, have the potential to revolutionize air navigation.

GPS has become very popular in recent years. It is used in wide range of applications including aircraft navigation, search and rescue, space borne attitude and position determination and cellular network synchronization. Each application places demands on GPS for various levels of accuracy, integrity, system availability and continuity of service. Radio frequency interference (RFI) which results from many sources such as TV/FM harmonics, radar or mobile satellite systems, presents a challenge to the use of GPS. It can affect all the service performance indices mentioned above. To improve the accuracy of GPS positioning, a continuously operating reference station (CORS) network can be used. A CORS network provides all the enabled GPS users in an area with corrections to the fundamental measurements, producing more precise positioning. A threat to these networks is a threat to all high-accuracy GPS users. It is therefore necessary to monitor the quality of the received signal with the objective of promptly detecting the presence of RFI and providing a timely warning of the degradation of system accuracy, thereby boosting the integrity of GPS. This research was focused on four main tasks: a) Detection. The focus here is on a power spectral density fluctuation detection technique, in which statistical inference is used to detect narrowband continuous-wave (CW) interference in the GPS signal band after being captured by the RF front-end. An optimal detector algorithm is proposed. At this optimal point, for a fixed Detection Threshold (DT), probability of false alarm becomes minimal and for a fixed probability of false alarm, we can achieve the minimum value for the detection threshold. Experiments show that at this point we have the minimum computational load. This theoretical result is supported by real experiments. Finally this algorithm is employed to detect a real GPS interference signal generated by a TV transmitter in Sydney. b) Characterization. In the characterization section, using the GNSS signal structure and the baseband signal processing inside the GNSS receiver, a closed formula is derived for the received signal quality in terms of effective carrier to noise ratio ( ). This formula is tested and proved by calculating the C/No using the I and Q data from a software GPS receiver. For pulsed CW, a similar analysis is done to characterize the effect of parameters such as pulse repetition period (PRP) and also duty cycle on the received signal quality. Considering this characterization and the commonality between the GPS C/A code and Galileo signal as a basis to build up a common term for satellite availability, the probability of satellite availability in the presence of CW interference is defined and for the two currently available satellite navigation systems (GPS L1 signal and Galileo signal (GIOVE-A BOC(1, 1) in the E1/L1 band)) it is shown that they can be considered as alternatives to each other in the presence of different RFI frequencies as their availability in the presence of CW RFI is different in terms of RFI frequency. c) Mitigation. The last section of the research presents a new concept of ?Satellite Exclusion Zone?. In this technique, using our previously developed characterization techniques, and considering the fact that RFI has different effects on different satellite signals at different times depending on satellite Doppler frequency, the idea of excluding the most vulnerable satellite signal from positioning calculations is proposed. Using real data and real interference, the effectiveness of this technique is proven and its performance analyzed. d) Hardware implementation. The above detection technique is implemented using the UNSW FPGA receiver board called NAMURU.

This Thesis covers the development of an alternative Global Navigation Satellite System (GNSS) augmentation technology that has become known as the Ground-based Regional Augmentation System (GRAS). GNSS augmentation technologies in support of aviation have largely been developed by countries with large economies such as the USA and members of the European Union. These technologies have focussed on solutions to the specific problems of the host nations, based on the demographics, political and economic factors relevant to them. Outside these countries, the role of GNSS augmentation has largely been ignored, specifically when considering wide area augmentation utilising Satellite Based Augmentation Systems (SBAS). SBAS technologies are expensive, and cannot be justified for nations like Australia with a relatively small number of aircraft, operated in a focussed geographic area. Utilising SBAS services provided by another country introduces cultural, legal and institutional issues that are not always easily addressed. GRAS was derived to provide a cost-effective wide area augmentation capability to nations that lacked the economic ability to field SBAS technologies. This work covers the evolution of the GRAS concept, the construction and testing of the GRAS test bed and its associated test avionics, as well as the development of standards needed to support GRAS as an internationally accepted aviation standard. The major outcome from this work was the confirmation that GRAS could meet the Required Navigation Performance (RNP) standards for Approaches with Vertical Guidance Level 2 (APV-II) as well as all less demanding modes of flight. Results from numerous ground and flight tests conducted under this research program have been reviewed by the International Civil Aviation Organisation (ICAO) GNSS Panel (GNSSP), and been instrumental in the development and validation of Standards and Recommended Practices (SARPs) which promulgate how ICAO standardised systems should perform. The final component of this work describes the project management and technology approval processes needed to get an internationally standardised system into operational use, and the particular problems that a small country like Australia has in progressing these tasks on the World stage.

The Global Navigation Satellite System (GNSS) is the main element of the CNS/ATM system elaborated by the International Civil Aviation Organization (ICAO).
The US GPS and Russian GLONASS are the two existing systems. Both of them were created by the military.
Europe is currently developing a civil navigation satellite system: Galileo.
This thesis will present some legal issues of the GNSS discussed in the framework of ICAO: sovereignty of States, universal accessibility, continuity and quality of the service, cost recovery and financing, certification and liability.
It will also present some legal issues due to the creation of the European Galileo program. The financing, organizational framework, certification and liability will be examined. Finally, ICAO's Charter on the Rights and Obligations of States Relating to GNSS Services will be considered.

In the next coming years global satellite navigation systems (GNSS) will make part of our daily life, as the world is becoming "GNSS-dependant in the same way that it has become Internet-dependant". Indeed, more than ten years folowing the opening up to civilians of satellite-based navigation systems initially designed for military purposes, civil satellite navigation applications are becoming more and more numerous. The potential benefits have proven enormous in terms of transport safety and efficiency as well as for non-transport-related industries.
Dans les toutes prochaines années, les systèmes globaux de navigation par satellite (GNSS) feront partie intégrante de notre vie quotidienne. En effet, un peu plus de dix ans après la libéralisation de l'accès des civils aux systèmes de navigation par satellite initialement conçus à des fins militaires, les applications civiles permises par la navigation par satellite sont de plus en plus nombreuses et les bénéfices potentiels sont énormes en matière de sécurité et d'efficacité des transports comme pour d'autres secteurs et industries. fr

The objective of this thesis is to design a model for a multi global navigation satellite system using Simulink. It explains a design procedure which includes the models for transmitter and receiver for two different navigation systems. To overcome the problem, where less number of satellites are visible to determine location degrades the performance of any positioning system significantly, this research has done to make use of multi GNSS satellite signals in one navigation receiver.

Deregulation, globalization, and commercialization are drastically changing the space industry. But commercial space activities entail considerable risks. This thesis is primarily an analysis of the risks that private entities in the space industry need to manage in order to be commercially successful. Due to the trend towards a buyer's market, satellite manufacturers increasingly have been forced to accept risks that do not fall within their traditional core business. Consequently, manufacturing companies become risk managers for a variety of legal space risks. Therefore, the legal framework for the commercial management of legal risks is analyzed and solutions to identified problems are offered. This thesis studies trends in contemporary risk management practices in the private sector, which is dominated by market forces. It is argued that risk management of legal issues should form an integral part of overall space project management, the rationale being that losses in any phase of space activities, while certain to occur, are uncertain in time and scale. This thesis, therefore, scrutinizes legal risk management throughout the life cycle of space projects. Few space applications have become commercially viable. Today, satellite navigation provided by the U.S. GPS is widely used, especially because it is free of direct charges. In Europe, a competing system, Galileo, is being developed. It will provide users with different service levels, ranging from free services to more reliable and accurate navigation services. As this system has both, public and commercial benefits, the industry is expected to participate in a Public Private Partnership for the Galileo satellite constellation. This thesis makes specific proposals to manage the legal risks of the Galileo project. At the same time, the allocation of legal space risks between the various parties is studied. The thesis of the author is that the management process, which is used to control technical space risks, can provide satellite manufacturers with a supportive analogy for dealing with legal space risks. Risks will be studied for all project phases of Galileo, i.e., the feasibility study, the establishment of specifications, development, manufacturing, the launch, operations, replenishment, and the final disposition of satellites.

L’orbite d’un satellite autour de la terre est perturbée en permanence par différents facteurs, tels que la variation du champ gravitationnel et la pression du vent solaire. La dérive de la position du satellite peut compromettre la mission, voire mener à une collision ou à une chute dans l’atmosphère. Les opérations de maintien à poste consistent donc à effectuer une mesure précise de la trajectoire du satellite puis à utiliser ses propulseurs pour corriger sa dérive. La solution classique de mesure de position est basée sur des radars au sol. Ce dispositif est couteux et ne permet pas d’avoir la position du satellite en permanence : les corrections de trajectoires se font donc de façon espacées dans le temps.Un système de positionnement et de navigation autonome utilisant les constellations de satellites de navigation, appelées Global Navigation Satellite System (GNSS), permettrait une réduction importante des coûts de conception et de maintenance opérationnelle. Plusieurs études ont été menées en ce sens et les premiers systèmes de navigation, basés sur des récepteurs GPS, voient le jour. Un récepteur en mesure de traiter plusieurs systèmes de navigation, tel que GPS et Galileo, permettrait d’obtenir une meilleure disponibilité de service. En effet, le système Galileo est conçu pour être compatible avec le système GPS,tant en terme de signaux émis que de données de navigation. La connaissance permanente de la position permettrait alors de réaliser un contrôle asservit du maintien à poste.Dans un premier temps, nous avons défini quelles seront les spécifications d’un récepteur spatial multi-mission.En effet, les contraintes pesant sur un tel récepteur sont différentes de celles d’un récepteur situé à la surface de la Terre. L’analyse de ces contraintes, ainsi que des performances demandées à un système de positionnement, est donc nécessaire afin de déterminer les spécifications du futur récepteur. Il existe peu d’études sur le sujet. Certaines d’entre elles sont classées secret industriel, d’autres présentent, à notre avis,un biais d’analyse qui fausse la détermination des spécifications.Nous avons donc modélisé le système : orbites des satellites GNSS et des satellites récepteurs, liaison radiofréquence. Certains paramètres de cette liaison ne sont pas donnés dans les documents de spécifications ou les documents constructeurs. De plus, les données théoriques disponibles ne sont pas toujours pertinentes pour une modélisation réaliste. Nous avons donc dû estimer ces paramètres en utilisant des données disponibles.Le modèle a été ensuite utilisé afin de simuler divers scenarii représentatifs de futures missions. Après avoir défini des critères d’analyse, les spécifications ont été déterminées à partir des résultats des simulations.Le calcul d’une position par un système de navigation par satellite se déroule en trois phases principales.Pour chacune de ces phases, il existe plusieurs algorithmes possibles, présentant des caractéristiques différentes de performance, de taille de circuit ou de charge de calcul. L’essor de nouvelles applications basées sur la navigation entraine également le développement de nouveaux algorithmes adaptés.Nous présentons le principe permettant la détermination d’une position, puis les signaux de navigation GPS et Galileo. A partir de la structure des signaux, nous expliquons les phases de la démodulation et de la localisation. Grâce à l’utilisation des constellations GPS et Galileo, les algorithmes standards permettent d’atteindre les performances nécessaires pour des applications spatiales. Ces algorithmes nécessitent néanmoins d’être adaptés ; ainsi certaines parties ont été conçues spécifiquement. Afin de valider les choix d’algorithmes, et les paramètres liés aux spécifications, nous avons simulés les différentes phases de fonctionnement du récepteur en utilisant des signaux GPS réels.Pour terminer, les retombées et perspectives sont exposées dans la conclusion
The orbit of a satellite around the earth is constantly disturbed by various factors, such as variations in the gravitational field and the solar wind pressure. The drift of the satellite position can compromise the mission, and even lead to a crash or a fall in the atmosphere. The station-keeping operations therefore consist in performing an accurate measurement of the satellite trajectory and then in using its thrusters to correct the drift. The conventional solution is to measure the position with the help of a ground based radar. This solution is expensive and does not allow to have the satellite position permanently: the trajectory corrections are therefore in frequent. A positioning and autonomous navigation system using constellations of navigation satellites, called Global Navigation Satellite System (GNSS), allows a significant reduction in design and operational maintenance costs. Several studies have been conducted in this direction and the first navigation systems based on GPS receivers, are emerging. A receiver capable of processing multiple navigation systems, such as GPS and Galileo, would provide a better service availability. Indeed, Galileo is designed to be compatible with GPS, both in terms of signals and navigation data. Continuous knowledge of the position would then allow a closed loop control of the station keeping. Initially, we defined what the specifications of a multi-mission space receiver are. Indeed, the constraints on such a receiver are different from those for a receiver located on the surface of the Earth. The analysis of these constraints, and the performance required of a positioning system, is necessary to determine the specifications of the future receiver. There are few studies on the subject. Some of them are classified; others have, in our view, an analytical bias that distorts the determination of specifications. So we modeled the system: GNSS and receivers satellite orbits, radio frequency link. Some parameters of this link are not given in the specification or manufacturers documents. Moreover, the available theoretical data are not always relevant for realistic modeling. So we had to assess those parameters using the available data. The model was then used to simulate various scenarios representing future missions. After defining analysis criteria, specifications were determined from the simulation results. Calculating a position of a satellite navigation system involves three main phases. For each phase, there are several possible algorithms, with different performance characteristics, the circuit size or the computation load. The development of new applications based on navigation also drives the development of new adapted algorithms. We present the principle for determining a position, as well as GPS and Galileo navigation signals. From the signal structure, we explain the phases of the demodulation and localization. Through the use of GPS and Galileo constellations, standard algorithms achieve the performance required for space applications. However, these algorithms need to be adapted, thus some parts were specifically designed. In order to validate the choice of algorithms and parameters, we have simulated the various operating phases of the receiver using real GPS signals. Finally, impact and prospects are discussed in the conclusion

Nowadays, Global Positioning System (GPS) which provide global coverage, continuous tracking capability and high accuracy has been preferred as the primary tracking system for onboard real-time precision orbit determination of Low Earth Orbiters (LEO). In this work, real-time orbit determination algorithms are established on the basis of extended Kalman, unscented Kalman, regularized particle, extended Kalman particle and extended H-infinity filters. Particularly, particle filters which have not been applied to the real time orbit determination until now are also performed in this study and H-infinity filter is presented using all kinds of real GPS observations. Additionally, performance of unscented Kalman filter using GRAPHIC (Group and Phase Ionospheric Correction) measurements is investigated. To evaluate performances of all algorithms, comparisons are carried out using different types of GPS observations concerning C/A (Coarse/Acquisition) code pseudorange, GRAPHIC and navigation solutions. A software package for real time orbit determination is developed using recursive filters mentioned above. The software is implemented and tested in MATLAB©
R2010 programming language environment on the basis of the object oriented programming schema.

Chacun de nous a connu des situations dans lesquelles il se trouve perdu dès qu'il quitte un endroit familier. Vue l'importance de la donnée "position", et face à l'incapacité des systèmes GNSS (Global Navigation Satellite Systems) à fournir une position valide en zones difficiles, les scientifiques et les industriels ont développé plusieurs techniques de localisations en intérieurs. La présente thèse porte sur le système de positionnement en intérieur à base de répéteurs GNSS. Cette technique se base sur l'emploi de répéteurs GNSS qui transmettent, à l'intérieur, d'une façon séquentielle, les signaux GNSS captés par une antenne extérieure. Le positionnement se base sur la détermination des sauts de la phase du code (ou sauts de phase) se produisant au moment du passage d'un répéteur au répéteur suivant. Les sauts de phase sont sujets à des erreurs dont les plus importantes sont le multi-trajet et le bruit thermique. Les travaux développés au cours de cette thèse portent sur la réduction de l'effet de ces sources de perturbation sur les sauts de phase. Pour cela, des techniques originales ont été proposées : la technique de la boucle ouverte pour la réduction de l'effet du bruit thermique, la SMICL, la MIDLL et la SxPRCT pour la réduction de l'erreur due au multi-trajet. La technique de la boucle ouverte consiste en l'usage d'une boucle de code ouverte aidée par la boucle de porteuse, profitant des propriétés statistiques du bruit. Cette technique a permis une amélioration significative de la mesure des sauts de phase. La technique SMICL consiste en un discriminateur de boucle de code insensible aux trajets multiples ayant des délais relatifs inférieurs à 0,5 chip, typiques d?un environnement intérieur de taille limitée. Les performances de la SMICL dépassent largement celles des techniques existantes pour les multi-trajets courts (1 à 2 m d'erreur résiduelle sur la mesure de code). La technique MIDLL réduit l'effet des trajets multiples sur la mesure de code sans limite de délai. L'idée de base repose sur le fait que le discriminateur standard possède un point invariant aux trajets multiples lorsqu'il est convenablement normalisé. Les résultats auxquels a abouti cette technique sont excellents (1 à 2 m d'erreur sur la mesure de code). La technique SxPRCT de réduction des trajets multiples moyens et longs consiste en l'usage de la fonction de corrélation entre la séquence reçue et le produit du PRN par une sous porteuse carrée. Cette approche agit comme un filtre pour les trajets multiples moyens et longs. Les résultats de simulations ont montré que cette technique était très efficace. La MIDLL ainsi que la SxPRCT peuvent servir pour le positionnement en extérieur utilisant les GPS, tout comme la SMICL dans une moindre mesure. Les trois techniques sont adaptées au cas du système à base de répéteurs. En outre, la technique MIDLL a été appliquée aux signaux Galileo du service ouvert de la bande E1. Ces techniques permettent au système de localisation à base de répéteurs d'atteindre ses performances théoriques de positionnement avec une précision inférieure à 2 mètres en 3D
The indoor localisation systems are increasingly needed in supporting future Location Based Services (LBS). This thesis deals with the indoor positioning system based on GNSS repeaters. This system is based on the use of four repeaters which transmit the GNSS signals collected by an outdoor antenna indoors, in a time multiplexing mode. The positioning is based on the code phase jumps produced at the instant of the signal transition between two repeaters. This phase jumps mainly suffer from two error sources: thermal noise and multipath. Therefore, this thesis develops theoretical aspects of the system of repeaters and proposes innovative techniques to reduce the effect of the error sources on the phase jumps. The open loop technique was proposed to reduce the effect of thermal noise on the phase jumps based on the statistical properties of the noise. It implements an open code loop aided by the phase loop. Practical results showed a significant improvement in the phase jump measurement quality. The SMICL (Short Multipath Insensitive Code Loop) technique implements a code loop discriminator insensitive to multipath having relative delays lower than 0. 5 chip, typical of indoor environments. It dramatically improves the code phase measurements in the presence of multipath (maximum error between 1 and 2 m). Another multipath mitigation technique, the MIDLL (Multipath insensitive delay lock loop), is presented. The MIDLL is based on the fact that the code discriminator has an invariant point when it is suitably normalized. This technique outperforms the existing multipath mitigation techniques both in terms of simplicity of implementation in current receivers and precision (maximum error between 1 and 2 m, too). The SxPRCT (Subcarrier x PRN Reference Code Technique) filters medium and long multipaths by using a reference replica which is the product between the PRN code and a square subcarrier. The SxPRCT yields excellent results. The MIDLL and the SxPRCT were developed for the outdoor positioning using the GPS, as is the case of the SMICL but to a lesser extent. These techniques were adapted to the case of the system of repeaters. Moreover, the MIDLL has successfully been applied to the Galileo open service codes on E1. These techniques allow the repeaters based system to reach its theoretical accuracy namely indoor positioning in the range 2 meters

Pour quelles raisons la question de la responsabilité du fait du signal spatial se pose-t-elle ? Si au regard des différentes initiatives nationales la question de l'allocation des risques et des responsabilités entre les acteurs du domaine spatial n'est pas nouvelle, lesdites initiatives ne traitent pourtant pas des conséquences des dommages engendrés par l'interruption ou la défaillance du signal spatial. D'une part, il existe des garanties juridiques classiques ou « traditionnelles » qui peuvent s'appliquer au signal spatial mais qui nécessitent que nous arrêtions une qualification juridique du signal spatial. Il doit être envisagé comme « contenant » ce qui implique de considérer les dommages et garanties du fait de ce « contenant ». Il doit également être envisagé en tant que « contenu » ce qui entraîne une réflexion sur la responsabilité du fait du transport et de la fourniture de ce « contenu ». Il s'agit alors de définir la responsabilité du transporteur de données du fait de la mise à disposition de celles-ci. Or ces garanties dites classiques sont nécessaires mais insuffisantes, car le « contenant » et le « contenu » peuvent être indissociables. La nécessité d'une nouvelle garantie juridique, que nous appellerons la garantie de service, apparaît, prémices de la définition d'un régime de responsabilité qui couvre les signaux spatiaux. C'est en partant de cette idée que nous développerons la notion de garantie de service, nouvelle solution juridique à un risque d'origine technique, nouvelle solution juridique à une obligation de résultat
For what reasons do we need to raise the question of liability regarding signals in outer space ? National laws already deal with the allocation of risk and liability of entities conducting activities in the domain of outer space. Nevertheless, national initiatives do not deal with the consequences of damage ocurring due to interruptions, interference with or failures of signal in outer space. Classical legal guarantees can aplly to signals in space, but necessitate the drafting of a legal definition of such signals. In this context we can envisage the signal as a "container" and need to study damages caused by, and guarantees covering, the container. We can equally envisage the signal to represent the "content", leading to an analysis of liability arising from transportation and the provision of contents. It is therefore necessary to define the liability of the data provider in supplying the data. While classical guarantees are nesessary, they are insufficient when the "container" and the "contents" are inseparable. This necessitates the need for a new legal guarantee, that we will call the "service guarantee". This is the starting point towards the definition of a liability regime, which covers signals in outer space. The following analysis will focus on the service guarantee concept as the new legal solution for technical risk and as a new legal solution for result guarantee

Le systeme de positionnement par satellite gps, peut etre utilise pour la localisation d'un satellite en orbite terrestre basse (moins de 500 kilometres) ou moyenne (de 500 a 1500 kilometres). Une experience de ce type a ete realisee en 1985 avec le satellite americain landsat 5 sur lequel un recepteur gps a ete embarque. Deux traitements ont ete developpes, l'un pour le calcul d'orbite des satellites gps (places a 20000 kilometres d'altitude), l'autre pour celui de l'orbite de landsat 5 (705 kilometres). Une precision de 10 centimetres dans la direction radiale a ete obtenue avec les satellites gps lors du traitement d'une campagne de mesures effectue en 1991 avec un reseau global de stations de reception reparti uniformement dans les deux hemispheres. Cette precision a ete atteinte en utilisant une combinaison des mesures de pseudo-distance et des mesures de phases non differentiees, en separant le traitement en une phase de pretraitement et une phase de restitution d'orbite, et en introduisant une acceleration empirique (subie par les satellites gps) deduite des equations de hill. Pour le satellite landsat 5, deux methodes ont ete developpees, l'une utilisant la solution geometrique de la position du satellite, calculee avec quatre mesures de distance, l'autre la difference de deux mesures de distance provenant de deux satellites gps a un instant donne. Ces deux methodes ont permis d'obtenir des orbites dont la precision est meilleure que cinq metres dans les trois directions de l'espace et sur des arcs de plusieurs jours. Ce resultat a ete rendu possible, d'une part grace a la grande precision des orbites gps utilisees, et d'autre part grace a une investigation approfondie des effets des modeles de force sur la qualite de l'orbite finale

Au cours de ces dernières années les applications des systèmes de navigation par satellites se sont beaucoup diversifiées, et le système Galileo doit tenir compte de ce grand nombre d'applications. Parmi toutes ces applications, la navigation en milieu urbain semble être l'une des plus importante. L'environnement urbain est caractérisé par d'importants angles de masquage et la présence d'un grand nombre d'obstacles qui produisent des trajets multiples. Un modèle de la propagation des ondes dans l'environnement considéré est donc nécessaire. Une méthode déterministe, basée sur l'optique géométrique, a été choisie. Afin de calibrer les simulations réalisées avec cet outil, des mesures sur la visibilité du système GPS dans différents environnements ont été réalisées et comparées avec les résultats obtenus avec notre outil de simulation. Les conditions contraignantes du milieu urbain ne rendent pas toujours possible le calcul de la position de l'usager avec le degré de précision désiré. Il est donc nécessaire de considérer des méthodes qui permettront d'améliorer les performances du système.

Title from PDF of title page (University of Missouri--Columbia, viewed on Feb 19, 2010). The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Thesis advisor: Dr. C. Mark Cowell. Includes bibliographical references.

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Among the technologies of spatial positioning, highlight the GNSS (Global Navigation Satellite System), which is widely used in various applications in the area of Geodesy, among others. The precise point positioning (PPP) has been shown to be a powerful tool for geodetic and geodynamics. applications Relative positioning is still the most widely used method for determination of coordinates in precision geodetic surveys. However, the PPP is increasingly in evidence and has provided satisfactory results. Given the above, remains to be seen, among the techniques mentioned, which provides more accurate results currently. The data used in this study were collected by the stations of RBMC (Brazilian Network for Continuous Monitoring of GNSS Systems) provided by IBGE (Brazilian Institute of Geography and Statistics), for the date January 01, 2014. For PPP analysis was used the free service online IBGE-PPP, and for analysis of static relative positioning was used the free online placement service AUSPOS, that processes network data, using the scientific software Bernese, and commercial software LGO (Leica Geo Office), which was used for processing single baselines and multiple baselines (vector adjustment).The GPS data were processed by varying the trace interval, covering the intervals of 1, 2, 4, 6, 8, 10 and 12 hours. In IBGE-PPP and AUSPOS the results provided was referenced to IGb08 (ITRF2008) at the time of data collection. To process the data in the LGO, the coordinates of the base stations, available in SIRGAS2000, epoch 2000.4, were transformed and updated to the reference system IGb08 (ITRF2008) at the time of data collection.Thus, the estimated coordinates at LGO were also estimated in IGb08 at the time of data collection. In sequence, the coordinates estimated in LGO, IBGE-PPP and AUSPOS were compared with the coordinates provided in descriptive of RBMC stations,which were also transformed and updated to the same reference system and time of coordinates estimated. With that, the movement of tectonic plates over time was minimized. In this way, from the calculation of discrepancies (trends) and with the clarifications provided in the adjustment, it was possible to perform the calculation of accuracies. According to the results, it was concluded that the method of relative positioning with the use of computational application and commercial use of receivers of dual frequency continues to be the most accurate method, regardless of the length of the baseline. The performance of relative positioning with a frequency receivers, involving short baselines also showed excellent results. In this case, at 64.3% of the results the accuracy was millimeter. It should be noted the potential of the IBGE-PPP and AUSPOS, which showed good results. In addition, these processing services are free and the users need only a receiver.
Dentre as tecnologias espaciais de posicionamento, destaca-se o GNSS (Global Navigation Satellite System), que é amplamente empregado em diversas aplicações na área de Geodésia, entre outras. O Posicionamento por Ponto Preciso (PPP) tem se mostrado uma poderosa ferramenta para aplicações geodésicas e geodinâmicas. O posicionamento relativo é ainda o método mais utilizado para determinação de coordenadas em levantamentos geodésicos de precisão. Contudo, o PPP está cada vez mais em evidência e tem proporcionado resultados satisfatórios. Diante do exposto, resta saber, dentre as técnicas mencionadas, qual apresenta resultados mais acurados atualmente. Os dados utilizados neste trabalho foram coletados pelas estações da RBMC (Rede Brasileira de Monitoramento Contínuo dos Sistemas GNSS) disponibilizados pelo IBGE (Instituto Brasileiro de Geografia e Estatística), referentes à data 01 de janeiro de 2014. Para análise do PPP foi utilizado o serviço gratuito online IBGE-PPP, e para análise do posicionamento relativo estático foram utilizados o serviço de posicionamento online gratuito AUSPOS, que processa os dados em rede, com uso do software científico Bernese, e o software comercial LGO (Leica Geo Office), que foi utilizado para processamento de linhas de base simples e de múltiplas linhas de base (ajustamento vetorial). Os dados GPS foram processados variando o intervalo de rastreio, abrangendo os intervalos de 1, 2, 4, 6, 8, 10 e 12 horas. No IBGE- PPP e no AUSPOS os resultados fornecidos são referenciados ao IGb08 (ITRF2008) na época de coleta dos dados. Para o processamento dos dados no LGO as coordenadas das estações base, disponibilizadas em SIRGAS2000, época 2000,4, foram transformadas e atualizadas para o sistema de referência IGb08 (ITRF2008) na época de coleta dos dados. Assim, as coordenadas estimadas no LGO também foram estimadas no IGb08 na época de coleta dos dados. Na sequência, as coordenadas estimadas no LGO, IBGE-PPP e AUSPOS foram comparadas com as coordenadas disponibilizadas nos descritivos das estações da RBMC, que também foram transformadas e atualizadas para o mesmo sistema de referência e época das coordenadas estimadas. Com isso, o deslocamento das placas tectônicas ao longo do tempo foi minimizado. Desta forma, a partir do cálculo das discrepâncias (tendências) e com as precisões disponibilizadas no ajustamento, foi possível realizar o cálculo das acurácias. De acordo com os resultados obtidos, conclui-se que o método de posicionamento relativo com o uso de aplicativo computacional comercial e uso de receptores de dupla frequência continua sendo o método mais acurado, independentemente do comprimento da linha de base. A performance do posicionamento relativo com receptores de uma frequência, envolvendo linhas de base curtas, também apresentou ótimos resultados. Neste caso, em 64,3% dos resultados a acurácia foi milimétrica. Deve-se salientar a potencialidade do IBGE-PPP e do AUSPOS, que apresentaram bons resultados. Além disso, esses serviços de processamento são gratuitos e o usuário deve dispor de apenas um receptor.

Dans la premiere partie de cette these, nous considerons le probleme de l'estimation de la trajectoire d'un engin sous-marin remorque, en se basant sur deux sources d'information differentes: des mesures precises d'acceleration de l'engin (ins) et des mesures de position du navire de surface (gps). Les mesures ins restituent fidelement les hautes frequences du mouvement de l'engin, mais derivent avec le temps. Nous utilisons l'information gps, fiable a long terme, pour recaler le mouvement moyen de l'engin. Nous introduisons un modele numerique du systeme cable-engin pour transferer l'information de positionnement depuis la surface jusqu'a l'engin, et nous proposons un estimateur hybride de sa trajectoire. Nous nous interessons ensuite au probleme de filtrage des processus de diffusion, dans le cas ou l'on dispose d'observations non-bruitees, en temps discret. Ce probleme est singulier car la loi conditionnelle est supportee a chaque instant par un ensemble de niveau de la fonction d'observation, qui est en general de mesure nulle (pour la mesure de lebesgue) dans l'espace d'etat. Dans le cas ou la valeur observee est reguliere, nous obtenons une expression explicite pour la densite de la loi conditionnelle, par rapport a la mesure canonique sur l'ensemble de niveau. Ce resultat est d'abord obtenue par une approche directe. Nous introduisons ensuite une approche asymptotique qui permet d'aborder le cas des valeurs singulieres. La methode ainsi developpee peut etre adaptee pour resoudre un probleme voisin en statistique des processus: il s'agit de l'asymptotique petit bruit de l'estimateur bayesien dans le cas non identifiable, lorsque l'observation est un signal deterministe perturbe. Nous donnons une expression explicite pour la densite de la loi limite, lorsque l'ensemble des points minimum de l'information de kullback-leibler est une sous-variete de l'espace des parametres

L'utilisation d'un sondeur multifaisceaux dans la cartographie des fonds marins souligne l'insuffisance d'une correction de la navigation à l'estime basée uniquement sur l'introduction d'un positionnement par satellite. La fiabilité des cartes bathymétriques nécessite la correction des décalages entre les différentes observations que l'on réalise d'une même zone géographique à chaque passage du navire. L'automatisation de la correction des points navigation s'impose pour réduire le temps passé par les cartographes pour effectuer cette opération, pour obtenir des cartes précises, et enfin pour enrichir les campagnes existantes des données nouvellement acquises. Le problème du recalage se ramène à la recherche d'une isométrie permettant de passer d'une famille de courbes planes à une autre famille dont les paramètres sont estimées à partir de données discrètes, incertaines et entachées d'erreurs. Une modélisation des incertitudes dans un système de voisinage a été introduite dans un test du rapport de vraisemblance pour dégager une classe de transformations admissibles de recalage. Une représentation topographique par un modèle numérique de terrain (facettes triangulaires) permet alors de préciser la correction. Les études de cas proposées montrent que la procédure ainsi élaborée est efficace.

Les systèmes globaux de navigation par satellite (GNSS) jouent un rôle fondamental dans l’élaboration du repère international de référence terrestre (ITRF). Cependant, les GNSS ne se sont jusqu’à présent pas révélés aptes à déterminer de manière fiable l’échelle terrestre ni la position du centre de masse de la Terre (géocentre) et n’ont donc pas contribué à définir l’échelle de l’ITRF ni son origine. L’incapacité des GNSS à déterminer l’échelle terrestre indépendamment de biais conventionnels de centres de phase satellites est un problème bien connu. En revanche, leur incapacité à correctement observer le mouvement du géocentre restait jusqu’alors inexpliquée. Nous avons étudié cette question sous l’angle de la colinéarité entre paramètres d’un ajustement par moindres carrés. Pour prendre en compte plusieurs particularités du problème de la détermination du géocentre par GNSS, un diagnostic de colinéarité généralisé a été développé. Il a ainsi été mis en évidence que la détermination du géocentre par GNSS est sujette à de sérieux problèmes de colinéarité à cause de l’estimation simultanée de décalages d’horloges et de paramètres troposphériques dans les analyses de données GNSS. Différentes pistes ont finalement été étudiées en vue d’une possible future contribution des GNSS à la définition de l’échelle et de l’origine de l’ITRF : l’étalonnage de l’antenne d’au moins un satellite GNSS, l’invariabilité temporelle des biais de centres de phase satellites, l’analyse simultanée de données GNSS acquises par des stations terrestres et des satellites bas, la modélisation d’horloges satellites ultra-stables et la réduction des erreurs de modélisation orbitale
Global Navigation Satellite Systems (GNSS) play a fundamental role in the elaboration of the International Terrestrial Reference Frame (ITRF). However, GNSS have so far not proven able to reliably determine the terrestrial scale nor the location of the Earth’s center of mass (geocenter) and have thus not contributed to defining the ITRF scale nor its origin. The weak ability of GNSS to determine the terrestrial scale apart from conventional satellite phase center offsets is well understood. On the other hand, their inability to reliably monitor geocenter motion was so far not clearly explained. We investigated this question from the perspective of collinearity among the parameters of a least-squares regression. A generalized collinearity diagnosis was therefore developed and allows handling several peculiarities of the GNSS geocenter determination problem. It revealed that the determination of all three components of geocenter motion with GNSS suffers from serious collinearity issues due to the simultaneous estimation of epoch-wise station and satellite clock offsets and of tropospheric parameters in global GNSS data analyses. Several prospects were finally investigated in view of a possible future contribution of GNSS to the definition of the ITRF scale and origin: the antenna calibration of at least one GNSS satellite, the time invariability of the satellite phase center offsets, the simultaneous analysis of GNSS data collected by ground stations and low Earth orbiting satellites, the modelling of ultra-stable satellite clocks and the mitigation of orbit modelling errors

Autonomous navigation is the determination of satellites position and velocity vectors onboard the satellite, using the measurements available onboard. The orbital information of a satellite needs to be obtained to support different house keeping operations such as routine tracking for health monitoring, payload data processing and annotation, orbit manoeuver planning, and prediction of intrusion in various sensors' field of view by celestial bodies like Sun, Moon etc. Determination of the satellites orbital parameters is done in a number of ways using a variety of measurements. These measurements may originate from ground based systems as range and range rate measurements, or from another satellite as in the case of GPS (Global Positioning System) and TDUSS (Tracking Data Relay Satellite Systems), or from the same satellite by using sensors like horizon sensor^ sun sensor, star tracker, landmark tracker etc. Depending upon the measurement errors, sampling rates, and adequacy of the estimation scheme, the navigation accuracy can be anywhere in the range of 10m - 10 kms in absolute location. A wide variety of tracking sensors have been proposed in the literature for autonomous navigation. They are broadly classified as (1) Satellite-satellite tracking, (2) Ground- satellite tracking, (3) fully autonomous tracking. Of the various navigation sensors, it may be cost effective to use existing onboard sensors which are well proven in space. Hence, in the current thesis, the Horizon scanner is employed as the primary navigation sensor-. It has been shown in the literature that by using horizon sensors and gyros, a high accuracy pointing of the order of .01 - .03 deg can be achieved in the case of low earth orbits. Motivated by such a fact, the current thesis deals with autonomous orbit determination using measurements from the horizon sensors with the assumption that the attitude is known to the above quoted accuracies. The horizon scanners are mounted on either side of the yaw axis in the pitch yaw plane at an angle of 70 deg with respect to the yaw axis. The Field Of View (FOV) moves about the scanner axis on a cone of 45 deg half cone angle. During each scan, the FOV generates two horizon points, one at the space-Earth entry and the other at the Earth-space exit. The horizon points, therefore, lie• on the edge of the Earth disc seen by the satellite. For a spherical earth, a minimum of three such horizon points are needed to estimate the angular radius and the center of the circular horizon disc. Since a total of four horizon points are available from a pair of scanners, they can be used to extract the satellite-earth distance and direction.These horizon points are corrupted by noise due to uncertainties in the Earth's radiation pattern, detector mechanism, the truncation and roundoff errors due to digitisation of the measurements. Owing to the finite spin rate of the scanning mechanism, the measurements are available at discrete time intervals. Thus a filtering algorithm with appropriate state dynamics becomes essential to handle the •noise in the measurements, to obtain the best estimate and to propagate the state between the measurements. The orbit of a low earth satellite can be represented by either a state vector (position and velocity vectors in inertial frame) or Keplerian elements. The choice depends upon the available processors, functions and the end use of the estimated orbit information. It is shown in the thesis that position and velocity vectors in inertial frame or the position vector in local reference frame, do result in a simplified, state representation. By using the f and g series method for inertial position and velocity, the state propagation is achieved in linear form. i.e. Xk+1 = AXK where X is the state (position, velocity) and A the state transition matrix derived from 'f' and 'g' series. The configuration of a 3 axis stabilised spacecraft with two horizon scanners is used to simulate the measurements. As a step towards establishing the feasibility of extracting the orbital parameters, the governing equations are formulated to compute the satellite-earth vector from the four horizon points generated by a pair of Horizon Scanners in the presence of measurement noise. Using these derived satellite-earth vectors as measurements, Kalman filter equations are developed, where both the state and measurements equations are linear. Based on simulations, it is shown that a position accuracy of about 2 kms can be achieved. Additionally, the effect of sudden disturbances like substantial slewing of the solar panels prior and after the payload operations are also analysed. It is shown that a relatively simple Low Pass Filter (LPF) in the measurements loop with a cut-off frequency of 10 Wo (Wo = orbital frequency) effectively suppresses the high frequency effects from sudden disturbances which otherwise camouflage the navigational information content of the signal. Then Kalman filter can continue to estimate the orbit with the same kind of accuracy as before without recourse to re-tuning of covariance matrices. Having established the feasibility of extracting the orbit information, the next step is to treat the measurements in its original form, namely, the non-linear form. The entry or exit timing pulses generated by the scanner when multiplied by the scan rate yield entry or exit azimuth angles in the scanner frame of reference, which in turn represents an effective measurement variable. These azimuth angles are obtained as inverse trigonometric functions of the satellite-earth vector. Thus the horizon scanner measurements are non-linear functions of the orbital state. The analytical equations for the horizon points as seen in the body frame are derived, first for a spherical earth case. To account for the oblate shape of the earth, a simple one step correction algorithm is developed to calculate the horizon points. The horizon points calculated from this simple algorithm matches well with the ones from accurate model within a bound of 5%. Since the horizon points (measurements) are non-linear functions of the state, an Extended Kalman Filter (EKF) is employed for state estimation. Through various simulation runs, it is observed that the along track state has got poor observability when the four horizon points are treated as measurements in their original form, as against the derived satellite-earth vector in the earlier strategy. This is also substantiated by means of condition number of the observability matrix. In order to examine this problem in detail, the observability of the three modes such as along-track, radial, and cross-track components (i.e. the local orbit frame of reference) are analysed. This difficulty in observability is obviated when an additional sensor is used in the roll-yaw plane. Subsequently the simulation studies are carried out with two scanners in pitch-yaw plane and one scanner in the roll-yaw plane (ie. a total of 6 horizon points at each time). Based on the simulations, it is shown that the achievable accuracy in absolute position is about 2 kms.- Since the scanner in the roll-yaw plane is susceptible to dazzling by Sun, the effect of data breaks due to sensor inhibition is also analysed. It is further established that such data breaks do not improve the accuracy of the estimates of the along-track component during the transient phase. However, filter does not diverge during this period. Following the analysis of the' filter performance, influence of Earth's oblateness on the measurement model studied. It is observed that the error in horizon points, due to spherical Earth approximation behave like a sinusoid of twice the orbital frequency alongwith a bias of about 0.21° in the case of a 900 kms sun synchronous orbit. The error in the 6 horizon points is shown to give rise to 6 sinusoids. Since the measurement model for a spherical earth is the simplest one, the feasibility of estimating these sinusoids along with the orbital state forms the next part of the thesis. Each sinusoid along with the bias is represented as a 3 state recursive equation in the following form where i refers to the ith sinusoid and T the sampling interval. The augmented or composite state variable X consists of bias, Sine and Cosine components of the sinusoids. The 6 sinusoids together with the three dimensional orbital position vector in local coordinate frame then lead to a 21 state augmented Kalman Filter. With the 21 state filter, observability problems are experienced. Hence the magnetic field strength, which is a function of radial distance as measured by an onboard magnetometer is proposed as additional measurement. Subsequently, on using 6 horizon point measurements and the radial distance measurements obtained from a magnetometer and taking advantage of relationships between sinusoids, it is shown that a ten state filter (ie. 3 local orbital states, one bias and 3 zero mean sinusoids) can effectively function as an onboard orbit filter. The filter performance is investigated for circular as well as low eccentricity orbits. The 10-state filter is shown to exhibit a lag while following the radial component in case of low eccentricity orbits. This deficiency is overcome by introducing two more states, namely the radial velocity and acceleration thus resulting in a 12-state filter. Simulation studies reveal that the 12-state filter performance is very good for low eccentricity orbits. The lag observed in 10-state filter is totally removed. Besides, the 12-state filter is able to follow the changes in orbit due to orbital manoeuvers which are part of orbit acquisition plans for any mission.

Autonomous navigation is the determination of satellites position and velocity vectors onboard the satellite, using the measurements available onboard. The orbital information of a satellite needs to be obtained to support different house keeping operations such as routine tracking for health monitoring, payload data processing and annotation, orbit manoeuver planning, and prediction of intrusion in various sensors' field of view by celestial bodies like Sun, Moon etc. Determination of the satellites orbital parameters is done in a number of ways using a variety of measurements. These measurements may originate from ground based systems as range and range rate measurements, or from another satellite as in the case of GPS (Global Positioning System) and TDUSS (Tracking Data Relay Satellite Systems), or from the same satellite by using sensors like horizon sensor^ sun sensor, star tracker, landmark tracker etc. Depending upon the measurement errors, sampling rates, and adequacy of the estimation scheme, the navigation accuracy can be anywhere in the range of 10m - 10 kms in absolute location. A wide variety of tracking sensors have been proposed in the literature for autonomous navigation. They are broadly classified as (1) Satellite-satellite tracking, (2) Ground- satellite tracking, (3) fully autonomous tracking. Of the various navigation sensors, it may be cost effective to use existing onboard sensors which are well proven in space. Hence, in the current thesis, the Horizon scanner is employed as the primary navigation sensor-. It has been shown in the literature that by using horizon sensors and gyros, a high accuracy pointing of the order of .01 - .03 deg can be achieved in the case of low earth orbits. Motivated by such a fact, the current thesis deals with autonomous orbit determination using measurements from the horizon sensors with the assumption that the attitude is known to the above quoted accuracies. The horizon scanners are mounted on either side of the yaw axis in the pitch yaw plane at an angle of 70 deg with respect to the yaw axis. The Field Of View (FOV) moves about the scanner axis on a cone of 45 deg half cone angle. During each scan, the FOV generates two horizon points, one at the space-Earth entry and the other at the Earth-space exit. The horizon points, therefore, lie• on the edge of the Earth disc seen by the satellite. For a spherical earth, a minimum of three such horizon points are needed to estimate the angular radius and the center of the circular horizon disc. Since a total of four horizon points are available from a pair of scanners, they can be used to extract the satellite-earth distance and direction.These horizon points are corrupted by noise due to uncertainties in the Earth's radiation pattern, detector mechanism, the truncation and roundoff errors due to digitisation of the measurements. Owing to the finite spin rate of the scanning mechanism, the measurements are available at discrete time intervals. Thus a filtering algorithm with appropriate state dynamics becomes essential to handle the •noise in the measurements, to obtain the best estimate and to propagate the state between the measurements. The orbit of a low earth satellite can be represented by either a state vector (position and velocity vectors in inertial frame) or Keplerian elements. The choice depends upon the available processors, functions and the end use of the estimated orbit information. It is shown in the thesis that position and velocity vectors in inertial frame or the position vector in local reference frame, do result in a simplified, state representation. By using the f and g series method for inertial position and velocity, the state propagation is achieved in linear form. i.e. Xk+1 = AXK where X is the state (position, velocity) and A the state transition matrix derived from 'f' and 'g' series. The configuration of a 3 axis stabilised spacecraft with two horizon scanners is used to simulate the measurements. As a step towards establishing the feasibility of extracting the orbital parameters, the governing equations are formulated to compute the satellite-earth vector from the four horizon points generated by a pair of Horizon Scanners in the presence of measurement noise. Using these derived satellite-earth vectors as measurements, Kalman filter equations are developed, where both the state and measurements equations are linear. Based on simulations, it is shown that a position accuracy of about 2 kms can be achieved. Additionally, the effect of sudden disturbances like substantial slewing of the solar panels prior and after the payload operations are also analysed. It is shown that a relatively simple Low Pass Filter (LPF) in the measurements loop with a cut-off frequency of 10 Wo (Wo = orbital frequency) effectively suppresses the high frequency effects from sudden disturbances which otherwise camouflage the navigational information content of the signal. Then Kalman filter can continue to estimate the orbit with the same kind of accuracy as before without recourse to re-tuning of covariance matrices. Having established the feasibility of extracting the orbit information, the next step is to treat the measurements in its original form, namely, the non-linear form. The entry or exit timing pulses generated by the scanner when multiplied by the scan rate yield entry or exit azimuth angles in the scanner frame of reference, which in turn represents an effective measurement variable. These azimuth angles are obtained as inverse trigonometric functions of the satellite-earth vector. Thus the horizon scanner measurements are non-linear functions of the orbital state. The analytical equations for the horizon points as seen in the body frame are derived, first for a spherical earth case. To account for the oblate shape of the earth, a simple one step correction algorithm is developed to calculate the horizon points. The horizon points calculated from this simple algorithm matches well with the ones from accurate model within a bound of 5%. Since the horizon points (measurements) are non-linear functions of the state, an Extended Kalman Filter (EKF) is employed for state estimation. Through various simulation runs, it is observed that the along track state has got poor observability when the four horizon points are treated as measurements in their original form, as against the derived satellite-earth vector in the earlier strategy. This is also substantiated by means of condition number of the observability matrix. In order to examine this problem in detail, the observability of the three modes such as along-track, radial, and cross-track components (i.e. the local orbit frame of reference) are analysed. This difficulty in observability is obviated when an additional sensor is used in the roll-yaw plane. Subsequently the simulation studies are carried out with two scanners in pitch-yaw plane and one scanner in the roll-yaw plane (ie. a total of 6 horizon points at each time). Based on the simulations, it is shown that the achievable accuracy in absolute position is about 2 kms.- Since the scanner in the roll-yaw plane is susceptible to dazzling by Sun, the effect of data breaks due to sensor inhibition is also analysed. It is further established that such data breaks do not improve the accuracy of the estimates of the along-track component during the transient phase. However, filter does not diverge during this period. Following the analysis of the' filter performance, influence of Earth's oblateness on the measurement model studied. It is observed that the error in horizon points, due to spherical Earth approximation behave like a sinusoid of twice the orbital frequency alongwith a bias of about 0.21° in the case of a 900 kms sun synchronous orbit. The error in the 6 horizon points is shown to give rise to 6 sinusoids. Since the measurement model for a spherical earth is the simplest one, the feasibility of estimating these sinusoids along with the orbital state forms the next part of the thesis. Each sinusoid along with the bias is represented as a 3 state recursive equation in the following form where i refers to the ith sinusoid and T the sampling interval. The augmented or composite state variable X consists of bias, Sine and Cosine components of the sinusoids. The 6 sinusoids together with the three dimensional orbital position vector in local coordinate frame then lead to a 21 state augmented Kalman Filter. With the 21 state filter, observability problems are experienced. Hence the magnetic field strength, which is a function of radial distance as measured by an onboard magnetometer is proposed as additional measurement. Subsequently, on using 6 horizon point measurements and the radial distance measurements obtained from a magnetometer and taking advantage of relationships between sinusoids, it is shown that a ten state filter (ie. 3 local orbital states, one bias and 3 zero mean sinusoids) can effectively function as an onboard orbit filter. The filter performance is investigated for circular as well as low eccentricity orbits. The 10-state filter is shown to exhibit a lag while following the radial component in case of low eccentricity orbits. This deficiency is overcome by introducing two more states, namely the radial velocity and acceleration thus resulting in a 12-state filter. Simulation studies reveal that the 12-state filter performance is very good for low eccentricity orbits. The lag observed in 10-state filter is totally removed. Besides, the 12-state filter is able to follow the changes in orbit due to orbital manoeuvers which are part of orbit acquisition plans for any mission.

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Over time has increased the need for low cost positioning of the populatio, and for this reason the demand for navigation devices has grown considerably in all levels of users of these devices, the population in general has greater access to smartphones because of its many features. Smartphones using micro GNSS receiver has a main component of positioning, where the pseudorange is its basic observable. The data sources for GPS corrections are increasingly available to the community through institutions as the IBGE with the Brazilian Network for Continuous Monitoring (RBMC). Thus, there is a greater possibility of improvement in accuracy of positioning these devices with the post- processed relative positioning and even in real time. With these possibilities and needs, this study aims the establishment of methodology that improves the accuracy in the positioning devices using micro GNSS receiver with a recursive least squares estimation with the Kalman gain matrix applied in relative positioning static by double difference of pseudorange in short baselines. To verify the effectiveness of this methodology is used SiRFstar IV micro receiver data which receives data only in L1 frequency GPS constellation. Was used reference RBMC stations to process these data. With tracking 15 minutes in known points had a mean deviation in the horizontal component of the plane coordinates 29 cm for post-processing and 98 cm for the real time processing, and, for the single point positioning average deviation was 6 meters. With this, it was concluded that the use of static methods for processing on recursive least squares estimation improves the accuracy of positioning significantly, where mobile devices that were previously given only to navigation may also be used for mapping.
Com o passar do tempo aumentou a necessidade da população em posicionamento a baixo custo, e por este motivo a procura por aparelhos de navegação tem crescido consideravelmente em todos os níveis de usuários. Destes dispositivos, a população no geral tem maior acesso aos smartphones devido a suas diversas funcionalidades. Os smartphones utilizam de microrreceptor GNSS como principal componente de posicionamento, sendo que sua observável básica é a pseudodistância derivada do código C/A. As fontes de dados para correções GPS estão cada vez mais disponíveis para a comunidade por meio de instituições como o IBGE com a Rede Brasileira de Monitoramento Continuo dos Sistemas GNSS (RBMC). Com isso, tem-se uma maior possibilidade de melhorias na acurácia do posicionamento destes dispositivos com o posicionamento relativo pós-processado e até mesmo em tempo real. Com estas possibilidades e necessidades, este trabalho tem como objetivo o estabelecimento de metodologia que melhore a acurácia no posicionamento de dispositivos móveis que utilizam microrreceptor GNSS, utilizando a estimativa de mínimos quadrados recursiva com a matriz de ganho de Kalman aplicada no posicionamento relativo estático por dupla diferença da pseudodistância em linhas de base curtas. Para verificar a eficácia desta metodologia utilizou-se dados do microrreceptor SiRFstar IV que recebe dados na frequência L1 da constelação GPS. Foram utilizadas as estações de referência da RBMC para o processamento destes dados. Com rastreios de 15 minutos em pontos de coordenadas conhecidas teve-se um desvio médio na componente horizontal das coordenadas planas de 29 centímetros para o pós- processamento e 98 centímetros para o processamento em tempo real, sendo que, para o posicionamento por ponto simples o desvio médio foi de 6 metros. Com isso, concluiu-se que a utilização da metodologia de processamento relativo estático por estimativa dos mínimos quadrados recursiva melhorou a acurácia do posicionamento de forma significativa, onde dispositivos móveis 14que até então eram indicados somente para navegação podem ser utilizados também para mapeamento.

De nombreuses solutions sont développées pour diminuer l'influence des multitrajets sur la précision et la disponibilité des systèmes GNSS. L'intégration de capteurs supplémentaires dans le système de localisation est l'une des solutions permettant de compenser notamment l'absence de données satellitaires. Un tel système est certes d'une bonne précision mais sa complexité et son coût limitent un usage très répandu.Cette thèse propose une approche algorithmique destinée à améliorer la précision des systèmes GNSS en milieu urbain. L'étude se base sur l'utilisation des signaux GNSS uniquement et une connaissance de l'environnement proche du récepteur à partir d'un modèle 3D du lieu de navigation.La méthode présentée intervient à l'étape de filtrage du signal reçu par le récepteur GNSS. Elle exploite les techniques de filtrage statistique de type Monte Carlo Séquentiels appelées filtre particulaire. L'erreur de position en milieu urbain est liée à l'état de réception des signaux satellitaires (bloqué, direct ou réfléchi). C'est pourquoi une information sur l'environnement du récepteur doit être prise en compte. La thèse propose également un nouveau modèle d'erreurs de pseudodistance qui permet de considérer les conditions de réception du signal dans le calcul de la position.Dans un premier temps, l'état de réception de chaque satellite reçu est supposé connu dans le filtre particulaire. Une chaîne de Markov, valable pour une trajectoire connue du mobile, est préalablement définie pour déduire les états successifs de réception des satellites. Par la suite, on utilise une distribution de Dirichlet pour estimer les états de réception des satellites

Thesis (M.S. in Hydrographic Science)--Naval Postgraduate School, September 1990.
Thesis Advisor(s): Wash, C. H. Second Reader: Schnebele, K. J. "September 1990." Description based on title screen as viewed on December 22, 2009. DTIC Descriptor(s): Radiometers, Navigation Reference, Interactions, Accuracy, Theses, Identification, Navigation, Images, Searching, Navigation Satellites, Artificial Satellites, Windows, Vector Analysis, Operators(Personnel), Earth(Planet), Birds, Matching, Automatic Pilots, Shores, Position(Location), Global. DTIC Identifier(s): Satellite Navigation, Program Listings. Author(s) subject terms: Image navigation, binary correlation, automatic landmarking. Includes bibliographical references (p. 78-81). Also available in print.

Master of Science
Department of Electrical and Computer Engineering
William B. Kuhn
With the increasing number of satellites and space debris in all orbits the need for individual satellites to be able to autonomously detect and determine methods to navigate around them is increasing. Even with continued input and control from a ground station, the ability for a satellite to act to save itself from obstacles not visible from ground stations, or if communications were temporarily lost could be key to saving millions of dollars in hardware as well as improving overall performance and operational lifetimes.

Orbit determination from artificial satellite observations is a key process in obtaining information about the Earth and its environment. A study of the perturbations experienced by these satellites enables knowledge to be gained of the upper atmosphere, the gravity field, ocean tides, solid-Earth tides and solar radiation. The gravity field is expressed as a double infinite scries of associated Legendre functions (tesseral harmonics). In contemporary global gravity field models the overall geoid is well determined. An independent check on these gravity field harmonics of a particular order may be made by analysis of satellites that pass through resonance of that order. For such satellites the perturbations of the orbital elements close to resonance are analysed to derive lumped harmonic coefficients. The orbital parameters of 1984-106A have been determined at 43 epochs, during which time the satellite was close to 14th order resonance. Analysis of the inclination and eccentricity yielded 6 lumped harmonic coefficients of order 14 whilst analysis of the mean motion yielded additional pairs of lumped harmonics of orders 14, 28 and 42, with the 14"1 order harmonics superseding those obtained from analysis of the inclination. This thesis concentrates in detail on the theoretical changes of a near-circular satellite orbit perturbed by the Earth's gravity field under the influence of minimal air-drag whilst in resonance with the Earth. The satellite 1984-106A experienced the interesting property of being temporarily trapped with respect to a secondary resonance parameter due to the low air-drag in 1987. This prompted the theoretical investigation of such a phenomenon. Expressions obtained for the resonance parameter led to the determination of 8 lumped harmonic coefficients, coincidental to those already obtained. All the derived lumped harmonic values arc used to test the accuracy of contemporary gravity field models and the underlying theory in this thesis.

Thesis (M.S.)--University of Missouri--Rolla, 2007.
Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed May 16, 2007) Includes bibliographical references (p. 96-97).

Space mission engineering has always been recognized as a very challenging and innovative branch of engineering: since the beginning of the space race, numerous milestones, key successes and failures, improvements, and connections with other engineering domains have been reached. Despite its relative young age, space engineering discipline has not gone through homogeneous times: alternation of leading nations, shifts in public and private interests, allocations of resources to different domains and goals are all examples of an intrinsic dynamism that characterized this discipline. The dynamism is even more striking in the last two decades, in which several factors contributed to the fervour of this period. Two of the most important ones were certainly the increased presence and push of the commercial and private sector and the overall intent of reducing the size of the spacecraft while maintaining comparable level of performances. A key example of the second driver is the introduction, in 1999, of a new category of space systems called CubeSats. Envisioned and designed to ease the access to space for universities, by standardizing the development of the spacecraft and by ensuring high probabilities of acceptance as piggyback customers in launches, the standard was quickly adopted not only by universities, but also by agencies and private companies. CubeSats turned out to be a disruptive innovation, and the space mission ecosystem was deeply changed by this. New mission concepts and architectures are being developed: CubeSats are now considered as secondary payloads of bigger missions, constellations are being deployed in Low Earth Orbit to perform observation missions to a performance level considered to be only achievable by traditional, fully-sized spacecraft. CubeSats, and more in general the small satellites technology, had to overcome important challenges in the last few years that were constraining and reducing the diffusion and adoption potential of smaller spacecraft for scientific and technology demonstration missions. Among these challenges were: the miniaturization of propulsion technologies, to enable concepts such as Rendezvous and Docking, or interplanetary missions; the improvement of telecommunication state of the art for small satellites, to enable the downlink to Earth of all the data acquired during the mission; and the miniaturization of scientific instruments, to be able to exploit CubeSats in more meaningful, scientific, ways. With the size reduction and with the consolidation of the technology, many aspects of a space mission are reduced in consequence: among these, costs, development and launch times can be cited. An important aspect that has not been demonstrated to scale accordingly is operations: even for small satellite missions, human operators and performant ground control centres are needed. In addition, with the possibility of having constellations or interplanetary distributed missions, a redesign of how operations are management is required, to cope with the innovation in space mission architectures. The present work has been carried out to address the issue of operations for small satellite missions. The thesis presents a research, carried out in several institutions (Politecnico di Torino, MIT, NASA JPL), aimed at improving the autonomy level of space missions, and in particular of small satellites. The key technology exploited in the research is Artificial Intelligence, a computer science branch that has gained extreme interest in research disciplines such as medicine, security, image recognition and language processing, and is currently making its way in space engineering as well. The thesis focuses on three topics, and three related applications have been developed and are here presented: autonomous operations by means of event detection algorithms, intelligent failure detection on small satellite actuator systems, and decision-making support thanks to intelligent tradespace exploration during the preliminary design of space missions. The Artificial Intelligent technologies explored are: Machine Learning, and in particular Neural Networks; Knowledge-based Systems, and in particular Fuzzy Logics; Evolutionary Algorithms, and in particular Genetic Algorithms. The thesis covers the domain (small satellites), the technology (Artificial Intelligence), the focus (mission autonomy) and presents three case studies, that demonstrate the feasibility of employing Artificial Intelligence to enhance how missions are currently operated and designed.

Thesis (M.S. in Electrical Engineering) Naval Postgraduate School, December 1996.
"December 1996." Thesis advisor(s): Tri T. Ha and Vicente Garcia. Includes bibliographical references (p. 95-97). Also available online.

Mobile robots that encounter people on a regular basis must react to them in some way. While traditional robot control algorithms treat all unexpected sensor readings as objects to be avoided, we argue that robots that operate around people should react socially to those people, following the same social conventions that people use around each other. This thesis presents our COMPANION framework: a Constraint-Optimizing Method for Person–Acceptable NavigatION. COMPANION is a generalized framework for representing social conventions as components of a constraint optimization problem, which is used for path planning and navigation. Social conventions, such as personal space and tending to the right, are described as mathematical cost functions that can be used by an optimal path planner. These social conventions are combined with more traditional constraints, such as minimizing distance, in a flexible way, so that additional constraints can be added easily. We present a set of constraints that specify the social task of traveling around people. We explore the implementation of this task first in simulation, where we demonstrate a robot’s behavior in a wide variety of scenarios. We also detail how a robot’s behavior can be changed by using different relative weights between the constraints or by using constraints representing different sociocultural conventions. We then explore the specific case of passing a person in a hallway, using the robot Grace. Through a user study, we show that people interpret the robot’s behavior according to human social norms, and also that people ascribe different personalities to the robot depending on its level of social behavior. In addition, we present an extension of the COMPANION framework that is able to represent joint tasks between the robot and a person. We identify the constraints necessary to represent the task of having a robot escort a person while traveling side-by-side. In simulation, we show the capability of this representation to produce behaviors such as speeding up or slowing down to travel together around corners, as well as complex maneuvers to travel through narrow chokepoints and return to a side-by-side formation. Finally, we present a newly designed robot, Companion, that is intended as a platform for general social human–robot research. Companion is a holonomic robot, able to move sideways without turning first, which we believe is an important social capability. We detail the design and capabilities of this new platform. As a whole, this thesis demonstrates both a need for, and an implementation and evaluation of, robots that navigate around people according to social norms.

Es defineix un satèl·lit d'òrbita baixa aquell que es troba a una alçada de fins a 2000 km per sobre de la superfície de la Terra. Degut al ràpid decaïment dels objectes propers a la superfície degut al fregament atmosfèric, s'accepta que l'alçada típica per un LEO esta entre 200 i 2000 km.
Aquesta rang d'alçades fa que els LEO siguin utilitzats per un ampli rang d'aplicacions, com a repetidors de comunicacions, sensors remots, determinació gravimètrica i magnetomètrica, altimetria oceànica, determinació atmosfèrica i en operacions de Search and Rescue (Cerca i rescat). El seu posicionament precís és de gran importància per a poder complir correctament amb els seus objectius. En aquest sentit, una gran quantitat de satèl·lits LEO tenen un receptor GPS, que permet fer mesures GPS durant tot el seu recorregut al voltant de la Terra. Aquestes mesures poden ser utilitzades per determinar la trajectòria del satèl·lit. Aquesta operació es fa normalment a terra, després que el satèl·lit hagi transmès totes les mesures que ha pres. La capacitat de fer aquest posicionament en temps real a bord del satèl·lit és una necessitat per algunes aplicacions. El posicionament autònom es molt diferent del que es pot fer a terra, ja que el processador del satèl·lit te grans limitacions en recursos computacionals, per tant els complexos models i càlculs fets en un ordinador normal a terra, son completament excessius per un ordinador espacial. A més, alguns dels models utilitzats en l'estimació de la trajectòria necessiten dades addicionals (com activitat solar, o paràmetres de rotació de la Terra) que no son disponibles en temps real, per tant s'han de fer algunes aproximacions per tal de no necessitar cap d'aquestes dades. Aquesta tesis estudiarà la navegació autònoma amb GPS de satèl·lits LEO, tendència que esta incrementant la seva importància per les aplicacions tan científiques com tecnològiques que se'n poden derivar. La tesi desenvoluparà nous algoritmes i mètodes per obtenir una posició acurada i continua per LEOs. S'han cobert diferent aspectes:
· Mitigació de multipath e interferències. Les reflexions de senyals GPS en l'estructura del satèl·lit crea una distorsió que afecta la distància mesurada. La repetibilitat d'aquests efectes en relació amb l'orientació del satèl·lit pot ser utilitzat per a mitigar el seu impacte en la solució de navegació. S'han desenvolupat tècniques de mitigació de multipath i interferències per receptors d'una i de dos freqüències.
· Models dinàmics de forces. L'alta predictibilitat de la trajectòria d'objectes orbitant la Terra pot ser utilitzat en sinergia amb el GPS per a aconseguir solucions més precises que fent servir únicament GPS. Això s'utilitza normalment en estratègies en postprocess, però te grans requeriments computacionals, i necessita paràmetres no disponibles en temps real. La simplificació d'aquests models, i la supressió de paràmetres no disponibles es necessari per poder aplicar aquesta tècnica de processat en condicions de temps real.
· Maniobres. Els cossos en òrbita al voltant de la Terra no segueixen una trajectòria perfectament predeible. Hi han petites pertorbacions que modifiquen la seva trajectòria a llarg termini, i a més, el fregament atmosfèric frena poc a poc al satèl·lit, disminuint la seva alçada. Això fa necessari una correcció periòdica de la seva trajectòria, realitzat amb petits impulsos del sistema de propulsió del satèl·lit en lo que s'anomena una maniobra. Quan un satèl·lit es troba en una maniobra, deixa de seguir els models de caiguda lliure, per tant la maniobra s'ha de tenir en conte en l'estimació del filtre.
Tots els algoritmes i mètodes dissenyats han sigut testejats amb dades reals de diferents missions: SAC-C, CHAMP, JASON-1 i GRACE. S'han fet servir diversos tests cobrint diferents opcions de parametrització per tal d'avaluar el seu comportament.
Se define un satélite de órbita baja aquel que se encuentra en una altura de hasta 2000 km sobre la superficie terrestre. Debido al rápido decaimiento de los objetos cercanos a la superficie debido al fregamiento atmosférico se acepta que la altura típica para un LEO se sitúa entre 200 y 2000 km.
Este rango de alturas hace que los LEO sean utilizados para un amplio rango de aplicaciones como repetidores de comunicaciones, sensores remotos, determinación gravimétrica y magnetométrica, altimetría oceánica, determinación atmosférica y en operaciones de Search and Rescue (Búsqueda y rescate). Su posicionamiento preciso es de gran importancia para poder cumplir correctamente con sus objetivos. En este sentido, una gran cantidad de satélites LEO disponen de un receptor GPS, que permite realizar medidas GPS durante todo su recorrido alrededor de la Tierra. Estas medidas puede ser utilizadas para determinar la trayectoria del satélite. Esta operación se suele realizar en tierra, después que el satélite haya retransmitido todas las medidas que ha tomado. La capacidad de hacer este posicionamiento en tiempo real a bordo del satélite es una necesidad para algunas aplicaciones. El posicionamiento autónomo es muy diferente al que se puede realizar en tierra, ya que los procesadores de satélites tienen limitaciones en recursos computacionales, y por tanto los complejos modelos y cálculos realizados en un ordenador normal en tierra son excesivos para un ordenador espacial. Además, algunos de los modelos utilizados en la estimación de la trayectoria necesitan datos adicionales (como actividad solar, o parámetros de rotación de la Tierra) que no están disponibles en tiempo real, por lo que hay que realizar algunas aproximaciones para no necesitar ninguno de estos datos. Esta tesis estudiará la navegación autónoma mediante GPS en satélites LEO, tendencia que esta aumentando su importancia por las aplicaciones tanto científicas como tecnológicas que se pueden derivar. La tesis desarrollara nuevos algoritmos y métodos para obtener una posición precisa y continua para LEOs. Se han cubierto diferentes aspectos:
· Mitigación de multipath e interferencias. Las reflexiones de las señales GPS en la estructura del satélite crea una distorsión que afecta la distancia medida. La repetibilidad de estos efectos en relación con la orientación del satélite puede ser utilizado para mitigar su impacto en la solución de navegación. Se han desarrollado técnicas de mitigación de multipath e interferencias para receptores de una o dos frecuencias.
· Modelos dinámicos de fuerzas. La trayectoria de objetos orbitando la Tierra es muy predecible, lo cual puede ser usado en sinergia con GPS para conseguir posiciones más precisas que usando solo GPS. Esto se utiliza normalmente en estrategias en postproceso, pero tiene grandes necesidades computacionales, y requiere de parámetros no disponibles en tiempo real. La simplificación de estos modelos, y la supresión e esos parámetros es necesario para poder aplicar esta técnica de procesado en condiciones de tiempo real.
· Maniobras. Los cuerpos en órbita alrededor de la Tierra no siguen una trayectoria perfectamente predecible. Hay pequeñas perturbaciones que modifican su trayectoria a largo plazo. Además el fregamiento atmosférico frena poco a poco el satélite, reduciendo su altura. Esto hace que sea necesaria una corrección periódica de su trayectoria, realizado en pequeños impulsos por el sistema de propulsión del satélite en lo que se llama una maniobra. Cuando un satélite realiza una maniobra deja de comportarse según los modelos de caida libre, por tanto su maniobra se ha de tener en cuenta en la estimación del filtro. Todos los algoritmos y métodos diseñados han sido testeados con datos reales de diferentes misiones: SAC-C, CHAMP, JASON-1 y GRACE. Se han realizado un amplio abanico de tests cubriendo diferentes opciones de parametrización para evaluar su comportamiento.
Satellites in low Earth orbits (LEO) are generally defined to be up to an altitude of 2000 km above Earth's surface and given the rapid decay of objects on the lower altitude range due to atmospheric drag, it is commonly accepted that a typical LEO height lies between 200 and 2000 km. This altitude range makes LEO satellites useful for a wide range of applications such as communication transponders, remote sensing, gravimetric and magnetometric sounding, ocean altimetry, atmospheric retrieval and Search and Rescue alarm operations. Its accurate positioning is of great importance in the successful accomplishment of their objectives. In this sense, most LEO satellites have a GPS receiver, which allows to collect GPS measurements in its full revolution around the Earth. These measures can be used to precisely estimate the trajectory of the spacecraft. This operation is normally done on ground, after the satellite was able to downlink all the data it collected. The capacity to do this positioning in real-time onboard the satellite is a necessity for some of the applications, and would also allow a faster science product delivery.
This autonomous positioning is very different that the one that can be done on ground, as the satellite processor has large limitations in computational resources, so the complex models and calculus done in a normal computer on ground are completely unaffordable for the onboard processor. Besides, some of the models used in the trajectory estimation need some additional data (such as solar activity, or Earth rotation parameters) that are not available in real-time, so some approximations must be done to cope with these lack of data. This thesis will deepen into the study of autonomous GPS navigation of LEO satellites, a trend that is increasing its importance for their applications in both science and technological fields. It will develop new algorithms and methods in order to provide accurate and continuous positions for the satellites. Different aspects have been covered:
· Multipath and interference mitigation. Reflections of GPS signals in the spacecraft structure cause a distress that affects the measured distance. On the other hand, some spacecraft have more than one GPS antenna on its payload. This creates a cross-talk interference that also affects the measures. The repeatability of these effects in relation to the attitude of the spacecraft can be used to mitigate its impact into the final navigation solution. Multipath mitigation techniques have been developed for both single- and dual-frequency receivers.
· Dynamic force models. The high predictability of the trajectory of Earth orbiters is used in conjunction to GPS measurements to provide a more accurate solution than GPS standalone positions. This is a widely used technique in postprocessing strategies, but has high computational requirements and needs parameters not available in real-time. The simplifications of these models, along with the suppression of the parameters not available in an onboard environment is necessary to use these kind of positioning by a satellite processing in real-time conditions.
· Maneuver handling. Earth orbiters do not follow a fully predictable orbit, some low-order perturbations modifies its trajectory on the long term, and atmospheric drag slowly brakes the satellite, decreasing its altitude. This makes necessary a periodic correction of its trajectory.
This is done by short impulses produced by the satellite propulsion systems in what is called a maneuver. When a spacecraft is in a maneuver, it no longer follows the free-flight dynamic models, so this should be taken into account in the estimation filter. All the algorithms and methods have been tested with real data from different missions: SAC-C, CHAMP, JASON-1 and GRACE. Several test cases covering a wide range of days and parametrization options have been done in order to assess its performance.

Dans le cadre des systèmes de positionnement par satellite GNSS (« Global Navigation Satellite Systems »), l’intégritéde la navigation d’un utilisateur est gérée en réception par la détection, l’identification voire l’exclusion de mesures depseudo-distance jugées erronées. Généralement basés sur le concept a posteriori RAIM (« Receiver Autonomous IntegrityMonitoring »), les algorithmes de contrôle autonome d’intégrité fournissent de hautes performances pour l’aviation civile,dont le contexte de navigation est caractérisé par une forte visibilité des satellites et peu de signaux parasites captéspar l’antenne réceptrice. L’algorithme WLSR RAIM est communément utilisé dans ce cadre. Néanmoins, les techniquesRAIM ne sont pas compatibles avec la navigation terrestre en milieu contraint. En effet, le contexte urbain est notammentcaractérisé par un masquage récurrent des signaux satellitaires directs ainsi que la réception de multi-trajets générés parl’environnement proche du récepteur. RAIM ne prend pas en compte l’ensemble des données disponibles en réception,dégradant ainsi fortement ses performances. Il est donc nécessaire de développer des méthodes de contrôle d’intégritécompatibles avec un tel contexte de navigation. Pour cela, la thèse propose d’étudier l’apport d’informations GNSS a priorinon utilisées par les techniques RAIM. Deux paramètres principaux ont été exploités : le signal GNSS brut reçu et lesestimations de directions d’arrivée des signaux satellitaires DOA (« Direction Of Arrival »). La première étape a consisté à implémenter une méthode a priori qui évalue la cohérence du positionnement estimé par rapport au signal brut directement reçu. Cette méthode a été nommée Direct-RAIM (D-RAIM) et a démontré une forte sensibilité de détection, permettant d’anticiper d’éventuels risques sur la navigation et de caractériser plus finement la qualité de l’environnement proche du récepteur. Toutefois, le caractère a priori de l’approche engendre de potentielles non détection d’erreurs en cas de modèle de signal défectueux. Afin de contourner cette limitation, un couplage WLSRRAIM – D-RAIM a été développé, nommé Hybrid-RAIM (H-RAIM). Une telle approche permet de combiner robustesse etsensibilité apportées par ces techniques respectives. Le second axe de recherche a mis en évidence la contribution de l’information des DOA dans un contrôle autonome d’intégrité. L’intégration d’un réseau d’antennes en réception permet d’obtenir l’estimation des DOA pour l’ensemble dela constellation visible. Théoriquement, l’évolution jointe des DOA est directement liée à l’attitude du réseau. Cet aspectpermet donc de détecter toute incohérence sur une ou plusieurs voies en cas d’estimation(s) de DOA biaisée(s), par rapportà l’ensemble de la constellation. L’algorithme RANSAC (« RANdom SAmple Consensus») a été utilisé afin de détecter toutcomportement aberrant dans l’estimation des DOA, et ainsi mesurer la confiance que l’utilisateur peut placer dans chaquevoie. L’algorithme WLSR RAIM RANSAC a ainsi été implémenté. L’intégration de la composante DOA permet d’ajouterun degré de liberté dans le contrôle autonome d’intégrité côté récepteur et ainsi d’affiner la détection voire l’exclusiond’erreurs. Au cours de cette thèse, un récepteur logiciel a été implémenté, permettant de traiter des signaux Galileo, de lagénération du signal jusqu’au positionnement puis au contrôle d’intégrité. Ce récepteur a pu être évalué à partir de donnéessimulées en environnement urbain
In Global Navigation Satellite Systems (GNSS) applications, integrity is managed at the reception side by detection,identification and exclusion of faulty pseudorange measurements. Usually based on the a posteriori Receiver AutonomousIntegrity Monitoring (RAIM) concept, integrity techniques provide high performances for civil aviation, with a navigationcontext defined by a clear-sky environment. WLSR RAIM is commonly used. Nevertheless, RAIM techniques are notcompatible with a terrestrial navigation in harsh environments. For instance, urban areas are characterized by a poorvisibility and the reception of many multipaths derived from the receiver closed-environment. RAIM does not consider allthe available data in the reception chain, which dramatically deteriorates the detection performances. Hence, it is necessaryto develop integrity process compatible with such a navigation context. This PhD work studies the contribution of GNSSa priori information, disused by conventional RAIM techniques. Two main parameters have been exploited : the receivedraw GNSS signal and the Directions Of Arrival (DOA) estimations.This first step was devoted to the development of an a priori method which evaluates the consistence of the estimatedPosition Velocity Time (PVT) vector of the receiver with respect to the raw GNSS signal. This method has been calledDirect-RAIM (D-RAIM) and has shown high detection sensitivity, allowing the user to anticipate navigation risks and todefine precisely the quality of the receiver closed-environment. However, the a priori aspect of this approach may lead tonavigation error missed detections if the signal model is getting flawed. In order to circumvent this limitation, a WLSRRAIM – D-RAIM coupling has been developed, called Hybrid-RAIM (H-RAIM). Such an approach merges the robustnessand the sensitivity brought by both techniques.The second research step has brought to light the contribution of the DOA information in an autonomous integritymonitoring. Using an antenna array, the user can get the DOA estimations for all satellites in view. Theoretically, the DOAjoint evolution is directly correlated with the array rotation angles. Hence, any mismatch on the DOA estimations withrespect to the global constellation can be detected. RANdom Sample Consensus (RANSAC) algorithm has been used inorder to detect any faulty DOA evolution, derived from inconsistencies in reception linked to potential navigation risks :RANSAC measures the trust that the user can place in each channel. Therefore, a WLSR RAIM RANSAC algorithmhas been developed. The integration of the DOA component adds a degree of freedom in receiver autonomous integritymonitoring, refining the error detection and exclusion.Last but not least, a software receiver has been implemented processing Galileo data, from the signal generation to positioningand integrity monitoring. This software has been evaluated by simulated data characterizing urban environments

This thesis looks at the development of Canadian satellite policy between 1960 and 1980 through a study of the policy decisions relating to Telesat Canada, its specific corporate structure, and mandates and ownership patterns. The analysis draws upon a modified "interplay" model, which examines public policy as an amalgam of interacting ideas, interests and institutions. On the basis of available documents, supplemented by interviews, and supporting secondary analyses, the sometimes contradictory decisions made by the DOC and the CRTC with regards to Telesat's Agreement with the Trans Canada Telephone system during this period are argued to reflect a policy process driven by the interplay of competing views of Telesat's primary purpose and, by extension, competing visions of what constitutes the public interest.

Thesis (Ph.D.)--School of Mechanical Engineering, Georgia Institute of Technology, 2005.
Singhose, William, Committee Chair ; Banerjee, Arun, Committee Member ; Chen, Ye-Hwa, Committee Member ; Ebert-Uphoff, Imme, Committee Member ; Olds, John, Committee Member. Includes bibliographical references.

The equations of motion for a satellite with a rigid central body and a pair of appendages deforming due to thermal effects of the solar radiation are derived. The dynamics of the system is studied in two stages: (i) librational dynamics of the central body with quasi-steady thermally flexed appendages; (ii) coupled librational/vibrational dynamics of the spacecraft. Response of the system is investigated numerically over a range of system parameters and effect of the thermal deformations assessed. The study indicates that for a circular orbit, the flexible system can become unstable under critical combinations of system parameters and initial conditions although the corresponding rigid system continues to be stable. However, in eccentric orbits, depending on the initial conditions, thermally flexed appendages can stabilize or destabliIize the system. Attempt is also made to obtain an approximate closed-form (analytical) solution of the problem to quickly assess trends and gain better physical appreciation of response characteristics during the preliminary design. Comparisons with numerical results show approximate analysis to be of an acceptable accuracy for the intended objective. The closed-form solution can be used with a measure of confidence thus promising a substantial saving in time, effort, and computational cost.
Applied Science, Faculty of
Mechanical Engineering, Department of
Graduate