Thesis. 1978. M.S.--Massachusetts Institute of Technology. Dept. of Aeronautics and Astronautics. / Includes bibliographical references. / M.S.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1981. / Microfiche copy available in Archives and Barker / Bibliography: leaves 108-109. / by William Neil McCasland. / M.S.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1981. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / by Joseph Y. N. Hui. / M.S.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1981. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND AERONAUTICS. / Includes bibliographical references. / by Sean Kevin Collins. / Ph.D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1977. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / by Robert Philip Gilmore. / M.S.

Orientador: Ernesto Vieira Neto / Coorientador: Antônio Delson Conceição de Jesus / Banca: Othon Cabo Winter / Banca: Cristiano Fiorilo de Melo / Resumo: Neste trabalho, estudamos o problema da viabilidade de missões espaciais em ambiente de detritos espaciais. Geralmente, um veículo espacial em curso de colisão com um detrito espacial é destruído ou danificado e tem sua missão prejudicada. A preservação destas missões depende da capacidade do satélite de evitar a colisão, como por exemplo, através de uma manobra orbital conhecida como manobra evasiva. Neste estudo, estabelecemos estratégias de manobras evasivas realizadas por um satélite através de um sistema de propulsão, cuja eficiência é medida por parâmetros tecnológicos. Os parâmetros tecnológicos são configurados no planejamento da missão, e descrevem a quantidade de combustível a bordo e a capacidade de expelir propelente do sistema de propulsor. As manobras evasivas foram estudadas para serem aplicadas de tal forma que o satélite escape do detrito espacial sem a evasão da sua órbita nominal de missão, e para este objetivo, incluímos uma propulsão de controle e tratamos o sistema de propulsão como uma perturbação na órbita do satélite. Também foi estabelecido, para realizar manobras evasivas econômicas, uma propulsão que é ligada em uma fração do tempo total disponível para a manobra. Esta fração de tempo é definida como um tempo de pulso de propulsão. As manobras evasivas são estudadas por simulações numéricas da dinâmica de um detrito e um veículo espacial sob a ação da força gravitacional da Terra e de perturbações orbitais oriundas de um sistema de propulsão e da atmosfera da Terra. Nestas simulações calculamos as condições de colisão do detrito e do satélite, que ocorrem ao redor da Terra, e utilizamos para criar catálogos de parâmetros tecnológicos acessíveis ao satélite para escapar destas colisões / Abstract: We studied the problem of the viability of space missions in debris environment space. Generally, a space vehicle in collision course with a space debris is destroyed or damaged and has impaired their mission. The preservation of these missions depends on the satellite capacity to avoid the collision, for example by an orbital maneuver known as evasive maneuver. In this study, we established strategies evasive maneuvers performed by a satellite via a propulsion system, whose efficiency is measured by technological parameters. Technological parameters are set in the planning of the mission, and describe the amount of fuel on board and the ability to expel propellant propulsion system. The evasive maneuvers were studied to be applied in such a way that the satellite escape the space debris without evasion of its nominal orbit mission, and for this purpose, include a propulsion control and treat the propulsion system as a disturbance in the orbit of satellite. It has also been established, to perform evasive maneuvers driven, propulsion which is connected at a fraction of the total time available for the maneuver. This fraction of time is defined as a propulsion pulse time. The evasive maneuvers are studied by numerical simulations of the dynamics of a debris and a vehicle space under the action of the Earth's gravitational and orbital perturbations arising from a propulsion system and the Earth's atmosphere. In these simulations calculate the debris of the collision conditions and the satellite, which occur around the Earth, and used to create technological parameters catalogs accessible to the satellite to escape these collisions / Mestre

Satellite communication and navigation applications suffer due to space weather phenomena. The effects are particularly pronounced in the equatorial regions, which are highly ionised and more easily susceptible to space weather effects than the mid latitude regions. Nevertheless, the bulk of the research on TEC profile and behaviour has been carried out with respect to mid-latitude regions. The contribution of the Upper Plasmasphere (the altitudes above semisynchronous orbit height up to the Plasmapause height) to the Total Electron Content at any given location has been and continues to be an un-quantified component. The PEACE instrument in the Chinese – European Space Agency Double Star TC1 satellite and its highly eccentric equatorial orbit provides an excellent opportunity to build Upper Plasmaspheric Electron Content (UPEC) components in the Equatorial region from empirical in-situ measurements of electron density along the orbit in the 20000km to 40000km altitude range. This work develops and presents a methodology for deriving Plasmaspheric Electron Content from In-Situ, empirical electron density measurements in highly eccentric, elongated equatorial orbits, using the data from the Double Star TC1 satellite. As such this thesis also generates a database of Upper Plasmaspheric Electron Content (UPEC) along the orbital path of the TC1. This work also proposes a dedicated mission to be launched with highly eccentric orbits to generate a comprehensive equatorial TEC database based on this methodology. This works envisions that future mission to be preferably launched in the equatorial belt, thus providing the opportunity to develop an archive of data as well as a real time source for better understanding of the Appleton anomaly Effects on Plasmaspheric Electron Content.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1981. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND AERO. / Includes bibliographical references. / by Alison Kay Brown. / M.S.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / by Stephen Paul Taylor. / M.S.

Cette thèse s’intéresse à la conception d’antennes ultra large bande reconfigurables. Cette étude a été motivée par le souhait de regrouper l’ensemble des antennes d’observation présentes sur les satellites en un panneau rayonnant unique afin de pouvoir réduire la taille de ces derniers. Les travaux présentés dans ce mémoire sont donc principalement axés sur la conception d’antennes spirales et sur les améliorations qui peuvent leur être apportées. Ainsi, une nouvelle topologie d’antenne spirale carrée reconfigurable en un réseau de quatre antennes spirales carrées plus petites sur la même ouverture rayonnante est exposée. Cette reconfiguration permet d’augmenter l’efficacité de surface de la structure tout en offrant de nouvelles possibilités d’utilisation à l’antenne et en améliorant ses performances. Les caractéristiques et les performances des deux configurations en états figés sont détaillées. Les maquettes réalisées et les résultats de mesure sont également présentés afin de valider le fonctionnement de l’antenne. Ensuite, différentes améliorations de cette structure sont présentées ainsi qu’une application possible. Enfin, une solution permettant d’améliorer le fonctionnement des antennes spirales imprimées au-dessus d’un plan de masse est décrite. En effet, cette solution permet de supprimer un nul de rayonnement lorsque l’antenne se situe à une demi-longueur d’onde du plan de masse. Sa bande passante d’utilisation peut ainsi être potentiellement doublée sans perdre la moitié de l’énergie comme avec l’utilisation d’absorbants. Cette technique consiste à ajouter un élément rayonnant parasite au-dessus de l’antenne. Cet élément est excité par couplage à l’antenne spirale et rayonne à la fréquence du nul de rayonnement. Cet élément étant faible bande, il ne dégrade pas le fonctionnement de l’antenne aux autres fréquences de la bande passante. Une structure utilisant ce concept a été réalisée afin de valider son fonctionnement. / This thesis focuses on the design of ultrawideband reconfigurable antennas. The objective of this study is to integrate all the antennas of observation on satellites into a single radiating panel and make it reconfigurable. Works presented in this document are focused on the design of spiral antennas and on their possible improvements. Thereby, a new topology of square spiral antenna reconfigurable into an array of four smaller square spiral antennas is shown. This reconfiguration allows increasing the surface efficiency of the structure while offering new possibilities of utilization to the antenna and improving its performance. Characteristics and performance of both configurations in frozen states are presented. Breadboards and measurements are also presented in order to validate the functioning of the antenna. Then, several improvements of this structure are studied and a possible application. Finally, a solution for improving the functioning of spiral antennas printed over a metallic ground plane is presented. This solution permits to remove a null of radiation when the distance between the antenna and the ground plane is a multiple of the half wavelength. In this way, its bandwidth can be doubled without losing the half of the energy like with absorbers. This technique consists in adding a parasitic radiating element over the antenna. This element is fed by coupling to the spiral antenna and radiates at the frequency of the null of radiation. This element is narrowband, so antenna performance remains unchanged at the other frequencies of the bandwidth. A structure using this concept has been made in order to validate its functioning.