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Improved Star Identification Algorithms and Techniques for Monochrome and Color Star Trackers

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Improved Star Identification Algorithms and Techniques for Monochrome and Color Star Trackers sid.inpe.br/mtc-m21b/2017/08.10.22.44-TDI IMPROVED STAR IDENTIFICATION ALGORITHMS AND TECHNIQUES FOR MONOCHROME AND COLOR STAR TRACKERS Márcio Afonso Arimura Fialho Doctorate Thesis in Engineering and Space Technologies Graduate Studies, major area Engineering and Management of Space Systems, guided by Drs. Leonel Fernando Perondi, and Daniele Mortari, approved in August 17, 2017. URL of the original document: <http://urlib.net/8JMKD3MGP3W34P/3PE49N5> INPE São José dos Campos 2017 PUBLISHED BY: Instituto Nacional de Pesquisas Espaciais - INPE Gabinete do Diretor (GB) Serviço de Informação e Documentação (SID) Caixa Postal 515 - CEP 12.245-970 São José dos Campos - SP - Brasil Tel.:(012) 3208-6923/6921 E-mail: [email protected] COMMISSION OF BOARD OF PUBLISHING AND PRESERVATION OF INPE INTELLECTUAL PRODUCTION (DE/DIR-544): Chairperson: Maria do Carmo de Andrade Nono - Conselho de Pós-Graduação (CPG) Members: Dr. Plínio Carlos Alvalá - Centro de Ciência do Sistema Terrestre (CST) Dr. André de Castro Milone - Coordenação de Ciências Espaciais e Atmosféricas (CEA) Dra. Carina de Barros Melo - Coordenação de Laboratórios Associados (CTE) Dr. Evandro Marconi Rocco - Coordenação de Engenharia e Tecnologia Espacial (ETE) Dr. Hermann Johann Heinrich Kux - Coordenação de Observação da Terra (OBT) Dr. Marley Cavalcante de Lima Moscati - Centro de Previsão de Tempo e Estudos Climáticos (CPT) Silvia Castro Marcelino - Serviço de Informação e Documentação (SID) DIGITAL LIBRARY: Dr. Gerald Jean Francis Banon Clayton Martins Pereira - Serviço de Informação e Documentação (SID) DOCUMENT REVIEW: Simone Angélica Del Ducca Barbedo - Serviço de Informação e Documentação (SID) Yolanda Ribeiro da Silva Souza - Serviço de Informação e Documentação (SID) ELECTRONIC EDITING: Marcelo de Castro Pazos - Serviço de Informação e Documentação (SID) André Luis Dias Fernandes - Serviço de Informação e Documentação (SID) sid.inpe.br/mtc-m21b/2017/08.10.22.44-TDI IMPROVED STAR IDENTIFICATION ALGORITHMS AND TECHNIQUES FOR MONOCHROME AND COLOR STAR TRACKERS Márcio Afonso Arimura Fialho Doctorate Thesis in Engineering and Space Technologies Graduate Studies, major area Engineering and Management of Space Systems, guided by Drs. Leonel Fernando Perondi, and Daniele Mortari, approved in August 17, 2017. URL of the original document: <http://urlib.net/8JMKD3MGP3W34P/3PE49N5> INPE São José dos Campos 2017 Cataloging in Publication Data Fialho, Márcio Afonso Arimura. F441i Improved star identification algorithms and techniques for monochrome and color star trackers / Márcio Afonso Arimura Fialho. – São José dos Campos : INPE, 2017. xxxii + 226 p. ; (sid.inpe.br/mtc-m21b/2017/08.10.22.44-TDI) Thesis (Doctorate in Engineering and Space Technologies Graduate Studies, major area Engineering and Management of Space Systems) – Instituto Nacional de Pesquisas Espaciais, São José dos Campos, 2017. Guiding : Drs. Leonel Fernando Perondi, and Daniele Mortari. 1. Star trackers. 2. Star identification algorithms. 3. Image processing. 4. Photometric systems. 5. Fundamental limits. I.Title. CDU 621.376.5:524.3 Esta obra foi licenciada sob uma Licença Creative Commons Atribuição-NãoComercial 3.0 Não Adaptada. This work is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported License. ii iv To my parents Jorge and Glória, for all their love and support, and for Tatiana, my sister, for her friendship. This thesis is dedicated to all those who guided me in my life, illuminating my paths. v ACKNOWLEDGMENTS I would like to thank my advisors: Dr. Daniele Mortari for hosting me during 2016 and for being a great professor and human being, and Dr. Leonel Perondi for also being a great professor, a very kind man and my advisor at INPE. I also say thanks for all friends and colleagues I had during this journey, for their encouragement and friendship, especially for my parents, Jorge and Glória, and my sister, Tatiana. Without their effort and patience, I would not be here. I also want to thank CNPq and AEB for the scholarship grant 207308/2015-2. Without their financial support, it would be much more difficult to complete this doctorate thesis. Finally, I want to say thanks for God, for giving me life and strength to complete this journey. vii ABSTRACT Modern fixed head star trackers are among the most accurate attitude sensors available for spacecraft use. Their principle of operation is basically to take pictures of the celestial sphere and identify stars present on these images, using the identified stars as references for attitude determination. This process encompasses tasks such as image pre-processing, image segmentation, centroiding, star identification and attitude determination from vector observa- tions. In the task of stellar identification, this work investigates how brightness information (magnitudes) and color information (when available) can be used to improve the reliability and speed in star identification. Incorporating magnitude and color information checks in an state-of-the-art star-ID algorithm resulted in a reduction in the misidentification rate by more than two orders of magnitude. Many other improvements were proposed and implemented in this state-of-the- art star identification algorithm. Other contributions of this work are in the use of color indexes (common in Astronomy, but new to the area) to represent color information in star trackers, with advantages over the previous representation used in the literature, and a methodology to evaluate the suitability of different color indexes in stellar identification. An investigation on existing technologies for color star tracking is performed, with image sensors based on stacked pixels showing good potential for future application. This work also presents a simple image pre-processing technique capable of removing column bias in CMOS image sensor, developed for star trackers with limited memory and low computational power. An estimate of the theoretical lower bounds of attitude knowledge achieved by star trackers is derived. This lower bound represents, in a certain way, a fundamental limit to the accuracy attainable by star trackers that depends only on the stellar distribution in our stellar neighborhood, star tracker dimensions and the length of the temporal window used for observations; thus, being completely independent on star tracker technology employed. The usefulness of this estimate is that it provides a benchmark for comparing different star tracker designs. This estimate is computed using data from the Hipparcos, Tycho and 2MASS star catalogs. To the best knowledge of the author, the computation of this lower bound is a novel contribution to this research field. keywords: star trackers. star identification algorithms. image processing. photometric systems. fundamental limits. computer simulations. ix TÉCNICAS E ALGORITMOS DE IDENTIFICAÇÃO DE ESTRELAS APRIMORADOS PARA SENSORES DE ESTRELAS COLORIDOS E MONOCROMÁTICOS RESUMO Sensores de estrelas de cabeça-fixa modernos estão entre os sensores de atitude mais precisos disponíveis para uso em veículos espaciais. Seu princípio básico de operação consiste em adquirir imagens do céu e identificar as estrelas presentes nestas imagens, usando as estrelas identificadas como referências de atitude. Este processo engloba tarefas como pré-processamento de imagens, segmentação de imagens, cálculo de centroides, identificação de estrelas e determinação de atitude a partir de versores observados. Na tarefa de identificação de estrelas, este trabalho investiga como as informações de brilho (magnitudes) e cor (quando disponível) podem ser aproveitadas para melhorar a confiabilidade e a velocidade do processo de identificação de estrelas. Ao se incorporar verificações de magnitude e cor em um algoritmo de identificação de estrelas estado da arte, obteve-se uma redução na taxa de identificações incorretas maior que duas ordens de grandeza. Várias outras melhorias foram propostas e implementadas neste algoritmo de identificação de estrelas. Outras contribuições deste trabalho estão no uso de índices de cor (comum em astronomia, mas novo neste campo) na representação de cor em sensores de estrelas, com vantagens em relação à representação anteriormente usada na literatura, e no desenvolvimento de uma metodologia para avaliar a adequação de diferentes índices de cor no processo de identificação de estrelas. Uma investigação sobre tecnologias para imageamento a cores voltada para sensores de estrelas é realizada, na qual se verificou que sensores de imagem baseados em pixels empilhados apresentam potencial para aplicações futuras. Este trabalho também apresenta um algoritmo de pré-processamento de imagens simples para remoção da não uniformidade de coluna em sensores CMOS, desenvolvido para sensores de estrelas com pouca memória e baixo poder computacional. Uma estimativa do limite teórico para a precisão de sensores de estrelas é apresentada. Este limite representa, de certa forma, um limite fundamental para a precisão de sensores de estrelas que depende apenas da distribuição de estrelas na nossa vizinhança estelar, das dimensões físicas do sensor de estrelas e da duração da janela de tempo usada para observação das estrelas, sendo, portanto, completamente independente da tecnologia empre- gada. A utilidade desta estimativa é que ela provê uma referência ao qual se podem comparar diferentes sensores de estrelas. Esta estimativa foi calculada usando dados dos catálogos de estrelas Hipparcos, Tycho e 2MASS. Até onde o autor tenha conhecimento, o cálculo desta estimativa
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