Many satellites in LEO use a GNSS-based navigation system, taking advantage of the GNSS constellations in MEO to enhance navigation capabilities. The thesis work focused on developing the software enabling GNSS-based navigation for Hemeria's future small satellites operating in LEO. Real time algorithms were developed to perform on board accurate frame conversions based on the International Earth Rotation and Reference Systems Service 2010 convention. The implementation was tested and independently cross-validated using space mechanics libraries and data from Observatory of Weights and Measures of Paris. The method was based on the Earth Orientation Parameters, and the balance between autonomy and accuracy was assessed. In pursuit of an affordable navigation system, a commercial Off-The-Shelf GNSS receiver was used. The navigation solution, derived from single frequency measurements, suffered from a systematic bias caused by the ionosphere. Mitigation strategies with ionospheric corrections were included in the IONOS simulator. Several attitude control modes were simulated so the effect of spacecraft tumbling versus the availability of GNSS measurements in a degraded situation was quantified.  Through this thesis, algorithms for GNSS-based navigation of Hemeria's small satellites in LEO were developed. The results showed the successful implementation of real time frame conversions at the metre level at best. It was found that the implementation allowed an improved autonomy of the frame conversion at the decimetre level of accuracy over a period of two months. / Många satelliter i LEO använder GNSS-baserad navigering och drar nytta av GNSS-konstellationerna i MEO för att förbättra navigeringsförmågan. Avhandlingsarbetet fokuserade på att utveckla mjukvaran som möjliggör GNSS-baserad navigering för Hemerias framtida småsatelliter som opererar i LEO. Realtidsalgoritmer utvecklades för att utföra exakta ramkonverteringar ombord baserat . Implementeringen testades och korsvaliderades oberoende med hjälp av rymdmekanikbibliotek och data från Observatory of Weights and Measures of Paris. Metoden baserades på jordorienteringsparametrarna, och balansen mellan autonomi och noggrannhet utvärderades. I jakten på ett prisvärt navigationssystem användes en kommersiell off-the-shelf GNSS-mottagare. Denna navigeringslösning, som härrörde från mätningar med en enda frekvens, led av en systematisk bias orsakad av jonosfären. I IONOS-simulatorn ingick strategier för att mildra effekterna med jonosfäriska korrigeringar. Flera lägen för attitydkontroll simulerades så att effekten av rymdfarkostens tumlande kontra tillgängligheten av GNSS-mätningar i en försämrad situation kunde kvantifieras.  Genom denna avhandling utvecklades algoritmer för GNSS-baserad navigering av Hemerias små satelliter i LEO. Resultaten visade en framgångsrik implementering av ramkonverteringar i realtid på meternivå som bäst. Det visade sig att implementeringen möjliggjorde en förbättrad autonomi för ramkonverteringen på decimeternivå under en period av två månader.

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Orientador: João Francisco Galera Monico / Resumo: A tecnologia Global Navigation Satellite Systems (GNSS) tem sido amplamente utilizada em posicionamento, desde as aplicações cotidianas (acurácia métrica), até aplicações que requerem alta acurácia (poucos cm ou dm). Quando se pretende obter alta acurácia, diferentes técnicas devem ser aplicadas a fim de minimizar os efeitos que o sinal sofre desde sua transmissão, no satélite, até sua recepção. O sinal GNSS ao se propagar na atmosfera neutra (da superfície até 50 km), é afetado por gases hidrostáticos e vapor d’água. A variação desses constituintes atmosféricos causa uma refração no sinal que gera um atraso. Esse atraso pode ocasionar erros na medida de no mínimo 2,5 m (zenital) e superior a 25 m (inclinado). A determinação do atraso na direção inclinada (satélite-receptor) de acordo com o ângulo de elevação é realizada pelas funções de mapeamento. Uma das técnicas para o cálculo do atraso é o traçado de raio (ray tracing). Essa técnica permite mapear o caminho real que o sinal percorreu e modelar a interferência da atmosfera neutra sobre esse sinal. Diferentes abordagens podem ser usadas para obter informações que descrevem os constituintes da atmosfera neutra. Dentre as possibilidades pode-se citar o uso de medidas de radiossondas, modelos de previsão do tempo e clima (PNT), medidas GNSS, assim como modelos teóricos. Modelos de PNT regionais do Centro de Previsão de Tempo e Estudos Climáticos (CPTEC) do Instituto Nacional de Pesquisas Espaciais (INPE) apresentam-se como um... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Global Navigation Satellite Systems (GNSS) technology has been widely used in positioning, from day-to-day applications (metric accuracy) to applications that require high accuracy (few cm or dm). For high accuracy, different techniques may be applied to minimize the effects that the signal suffers from its transmission on the satellite to its reception. GNSS signal when propagating in the neutral atmosphere (from surface up to 50km) is influenced by hydrostatic gases and water vapor. The variation of these atmospheric constituents causes a refraction in the signal that generates a delay. This delay may cause errors of at least 2.5 m (zenith) and greater than 25 m (slant). The determination of the delay in the slanted direction (satellite-receiver) according to the elevation angle is performed by the mapping functions. One of the techniques for calculating the delay is raytracing. This technique allows us to map the actual path that the signal has traveled and to model the interference of the neutral atmosphere on it. Different approaches can be used to obtain information describing the neutral atmosphere constituents - temperature, pressure and humidity. The possibilities include the use of radiosonde measurements, weather and climate models (NWP), GNSS measurements, as well as theoretical models. Regional NWP models from the Center Weather Forecasting and Climate Studies (CPTEC) of the National Institute for Space Research (INPE) are a good alternative to provide atmospheri... (Complete abstract click electronic access below) / Doutor

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Made available in DSpace on 2014-12-17T15:51:26Z (GMT). No. of bitstreams: 1 PamelaMB.pdf: 1623623 bytes, checksum: 28d259510491b304e6a430ad385fc8e2 (MD5) Previous issue date: 2010-02-19 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / The dissertation examines the influence of relationships among actors from Brazilian Tourism Political Network who compose the National Council of Tourism in the drafting of the National Tourism Plans (PNT) - PNTs 2003/2007 and 2007/2010, focusing on two main types of interaction: cooperation and information exchange. Therefore, the study departed from the understanding that the concept of tourism as a human phenomenon is configured as an essential conceptual basis for the development, implementation and analysis of public policies. The application of Network Theory and Social Network Analysis serves as an analytical tool, in addition, the use of concepts of Policy Networks enabled to interpret, in distinct aspects, the social reality of tourism in a more precise and detailed way. The study had a cross-sectional with a longitudinal perspective and case study was adopted, thus enabling to apply the model of social network analysis and qualitative approach. Through the survey conducted, it was found that the drafting process of National Tourism Plans was the result of the interaction of a complex network of actors from public and private initiatives, who compose the National Council of Tourism, and that their power of influence came out simultaneously, but not symmetrically, for both their performance/intervention in the meetings, and the possession of economic and organizational resources. Hence, the establishment of partnerships and information exchanges among the actors were underlying to the PNT drafting process, both in problems perception and insertion in the government agenda, as in making proposals to solve them, thus guiding the construction of large programs and programs contained in both investigated plans. / A disserta??o analisa a influ?ncia das rela??es entre atores da Rede Pol?tica do Turismo Brasileiro que comp?em o Conselho Nacional de Turismo no processo de elabora??o dos Planos Nacionais de Turismo (PNT 2003/2007 e PNT 2007/2010), centrando-se em dois principais tipos de intera??o: coopera??o e interc?mbio de informa??es. Para tanto, o estudo parte do entendimento de que a concep??o do turismo como um fen?meno humano, conforma-se como uma base conceitual imprescind?vel para a elabora??o, implementa??o e an?lise de suas pol?ticas p?blicas. A aplica??o da Teoria de Redes e da An?lise de Redes Sociais, funciona como uma ferramenta anal?tica, al?m disso, o uso dos conceitos de Rede Pol?tica (Policy Networks), permitiram interpretar por meio de aspectos diferenciados, a realidade social presente no turismo de forma mais precisa e detalhada. O estudo teve um corte seccional com perspectiva longitudinal e adotou o estudo de caso, permitindo aplicar o modelo de an?lise de redes sociais e a abordagem qualitativa. Atrav?s da pesquisa realizada, constatou-se que o processo de elabora??o dos Planos Nacionais de Turismo foi resultado da intera??o de uma complexa rede de atores p?blicos e privados, os quais comp?em o Conselho Nacional de Turismo, e que o poder de influ?ncia deles se deu simultaneamente, mas n?o simetricamente, pela sua atua??o/ interven??o nas reuni?es, e pela posse de recursos econ?micos e organizacionais. Assim sendo, o estabelecimento de parcerias e as trocas de informa??es entre os atores foram subjacentes ao processo de elabora??o dos PNTs, tanto na percep??o e inser??o de problemas na agenda governamental, quanto na realiza??o de propostas que os solucionassem, norteando assim a constru??o dos macroprogramas e programas contidos em ambos os planos investigados.

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