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Range and,interferometric observations have been examined for their potential, application in a geometric approach to determination of satellite ephemeri. The approach differs from the normal (dynamic) approach in that each satellite position is treated as an independent state variable or benchmark. Programs have been developed that simulate and format the input, data for the least squares estimation routines, and perform statistical analyses of those results. Random error, tropospheric refraction errors, and atomic clock errors have been considered, and the range observation adjustment program directed to solve for clock errors. / Master of Science

Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.

“Comemorar efemérides” não é apenas uma expressão legítima utilizada para fazer referência à celebração de uma festa nacional. Desde o final do século XIX, ao menos em língua portuguesa, os dois termos têm sido associados como sinônimos. A presente tese representa um esforço em compreender o desenvolvimento de dois conceitos – comemorações e efemérides – na longa duração. Os encontros e desvios entre as práticas associadas a um e a outro serão pontuados através da seleção de episódios intelectuais, seguidos pelo exame de debates que os tocavam na periferia de suas articulações. Na primeira parte, dedicada às comemorações, montei uma revisão desse bem conhecido tópico de estudos endereçada a uma única hipótese, a saber: o “ofício” comemorativo pode ser entendido como uma forma de comunicação e transmissão geracional de valores. Inspirado pelas fontes, argumento que os eventuais pontos de encontro entre o par de objetos propostos nesta tese são análogos às interrelações entre a “ordem do tempo” e a “ordem da natureza”, entre o tempo dos homens e o movimento das estrelas. Neste drama conceitual, se pudermos assim chamá-lo, faríamos perceber como a superação dos antigos modelos cosmológicos não se esquivou em guardar, para assumir termo caro a Pomian, uma lógica cronosófica. Se eu for bem sucedido, esse argumento deverá se expressar na segunda parte. As efemérides, como tábuas do movimento dos corpos celestes, vieram sofrer uma lenta transição rumo ao registro dos feitos humanos. Bebendo em fontes antigas e nas práticas de emulação, personagens bem conhecidos da primeira modernidade associaram o termo primeiro aos diários pessoais, depois ao jornalismo e, nos séculos seguintes, à história literária, religiosa e política. Na França, as éphémérides emergem da revolução já como um subgênero historiográfico. No Brasil da segunda metade do século XIX, listas de efemérides encontram lugar comum junto às comemorações dentro dos debates do IHGB. É no horizonte do projeto de nação que busco observar a união dos paralelos. Esse horizonte – como um ponto de chegada – vai aparecer ao final de cada secção da tese, observado a partir da celebração do quadricentenário da descoberta de Cabral. / “Comemorar efemérides” is a Portuguese phrase that despite its academic ring, is often used in the mainstream press. It translates roughly as 'the commemoration of an auspicious occasion’ and is used in reference to the public marking of nationally significant events. By the end of the nineteenth century, the two terms of this phrase came to be synonymous in Portuguese. This thesis represents an effort to understand the development of these two terms – efemérides and comemorações – over the longue durée. The long-term similarities in the practical and public uses of these terms are explored by tracing their discursive deployments and examining the debates that surrounded such public uses. The first section, dedicated to commemorations, frames the analysis of this much discussed topic with the following hypothesis: the act of commemoration is a form of moral utterance between generations; it is the rehearsal and transmission of collective values. Drawing on historical sources, I argue that the eventual points of contact between these terms can be seen as analogs to the discursive exchange and conflict between the classical and peripatetic notions of the “order of time” and the “order of nature”. In this conceptual drama, one sees how the sublation of old cosmological perspectives nevertheless still contains what I shall call – following Pomian – a chronosophy. This analysis leads to the second part of the thesis. Efemérides, originally tables of the movements of the celestial bodies – also known as almanacs – underwent a slow transition from the celestial to the earthly, from the charting of the stars to the recording of human deeds. Drawing on classical texts, well-informed readers of early modernity would have associated those writings in the first instance with diaries, then with journalism and, in the following centuries, with political history. Emerging from the French Revolution as a historiographical subgenre, lists of Efemérides shared a common function with commemorations as nation-building practices that described the horizon of a project to create national identity. This horizon, as a meeting point of moral utterance and political project is explored at the end of both sections of the thesis, as it is observed in the quadricentenial celebration of Cabral’s Discovery of Brazil. It is at this horizon that the parallel developments of comemorações and efemérides promise to meet.

“Comemorar efemérides” não é apenas uma expressão legítima utilizada para fazer referência à celebração de uma festa nacional. Desde o final do século XIX, ao menos em língua portuguesa, os dois termos têm sido associados como sinônimos. A presente tese representa um esforço em compreender o desenvolvimento de dois conceitos – comemorações e efemérides – na longa duração. Os encontros e desvios entre as práticas associadas a um e a outro serão pontuados através da seleção de episódios intelectuais, seguidos pelo exame de debates que os tocavam na periferia de suas articulações. Na primeira parte, dedicada às comemorações, montei uma revisão desse bem conhecido tópico de estudos endereçada a uma única hipótese, a saber: o “ofício” comemorativo pode ser entendido como uma forma de comunicação e transmissão geracional de valores. Inspirado pelas fontes, argumento que os eventuais pontos de encontro entre o par de objetos propostos nesta tese são análogos às interrelações entre a “ordem do tempo” e a “ordem da natureza”, entre o tempo dos homens e o movimento das estrelas. Neste drama conceitual, se pudermos assim chamá-lo, faríamos perceber como a superação dos antigos modelos cosmológicos não se esquivou em guardar, para assumir termo caro a Pomian, uma lógica cronosófica. Se eu for bem sucedido, esse argumento deverá se expressar na segunda parte. As efemérides, como tábuas do movimento dos corpos celestes, vieram sofrer uma lenta transição rumo ao registro dos feitos humanos. Bebendo em fontes antigas e nas práticas de emulação, personagens bem conhecidos da primeira modernidade associaram o termo primeiro aos diários pessoais, depois ao jornalismo e, nos séculos seguintes, à história literária, religiosa e política. Na França, as éphémérides emergem da revolução já como um subgênero historiográfico. No Brasil da segunda metade do século XIX, listas de efemérides encontram lugar comum junto às comemorações dentro dos debates do IHGB. É no horizonte do projeto de nação que busco observar a união dos paralelos. Esse horizonte – como um ponto de chegada – vai aparecer ao final de cada secção da tese, observado a partir da celebração do quadricentenário da descoberta de Cabral. / “Comemorar efemérides” is a Portuguese phrase that despite its academic ring, is often used in the mainstream press. It translates roughly as 'the commemoration of an auspicious occasion’ and is used in reference to the public marking of nationally significant events. By the end of the nineteenth century, the two terms of this phrase came to be synonymous in Portuguese. This thesis represents an effort to understand the development of these two terms – efemérides and comemorações – over the longue durée. The long-term similarities in the practical and public uses of these terms are explored by tracing their discursive deployments and examining the debates that surrounded such public uses. The first section, dedicated to commemorations, frames the analysis of this much discussed topic with the following hypothesis: the act of commemoration is a form of moral utterance between generations; it is the rehearsal and transmission of collective values. Drawing on historical sources, I argue that the eventual points of contact between these terms can be seen as analogs to the discursive exchange and conflict between the classical and peripatetic notions of the “order of time” and the “order of nature”. In this conceptual drama, one sees how the sublation of old cosmological perspectives nevertheless still contains what I shall call – following Pomian – a chronosophy. This analysis leads to the second part of the thesis. Efemérides, originally tables of the movements of the celestial bodies – also known as almanacs – underwent a slow transition from the celestial to the earthly, from the charting of the stars to the recording of human deeds. Drawing on classical texts, well-informed readers of early modernity would have associated those writings in the first instance with diaries, then with journalism and, in the following centuries, with political history. Emerging from the French Revolution as a historiographical subgenre, lists of Efemérides shared a common function with commemorations as nation-building practices that described the horizon of a project to create national identity. This horizon, as a meeting point of moral utterance and political project is explored at the end of both sections of the thesis, as it is observed in the quadricentenial celebration of Cabral’s Discovery of Brazil. It is at this horizon that the parallel developments of comemorações and efemérides promise to meet.

“Comemorar efemérides” não é apenas uma expressão legítima utilizada para fazer referência à celebração de uma festa nacional. Desde o final do século XIX, ao menos em língua portuguesa, os dois termos têm sido associados como sinônimos. A presente tese representa um esforço em compreender o desenvolvimento de dois conceitos – comemorações e efemérides – na longa duração. Os encontros e desvios entre as práticas associadas a um e a outro serão pontuados através da seleção de episódios intelectuais, seguidos pelo exame de debates que os tocavam na periferia de suas articulações. Na primeira parte, dedicada às comemorações, montei uma revisão desse bem conhecido tópico de estudos endereçada a uma única hipótese, a saber: o “ofício” comemorativo pode ser entendido como uma forma de comunicação e transmissão geracional de valores. Inspirado pelas fontes, argumento que os eventuais pontos de encontro entre o par de objetos propostos nesta tese são análogos às interrelações entre a “ordem do tempo” e a “ordem da natureza”, entre o tempo dos homens e o movimento das estrelas. Neste drama conceitual, se pudermos assim chamá-lo, faríamos perceber como a superação dos antigos modelos cosmológicos não se esquivou em guardar, para assumir termo caro a Pomian, uma lógica cronosófica. Se eu for bem sucedido, esse argumento deverá se expressar na segunda parte. As efemérides, como tábuas do movimento dos corpos celestes, vieram sofrer uma lenta transição rumo ao registro dos feitos humanos. Bebendo em fontes antigas e nas práticas de emulação, personagens bem conhecidos da primeira modernidade associaram o termo primeiro aos diários pessoais, depois ao jornalismo e, nos séculos seguintes, à história literária, religiosa e política. Na França, as éphémérides emergem da revolução já como um subgênero historiográfico. No Brasil da segunda metade do século XIX, listas de efemérides encontram lugar comum junto às comemorações dentro dos debates do IHGB. É no horizonte do projeto de nação que busco observar a união dos paralelos. Esse horizonte – como um ponto de chegada – vai aparecer ao final de cada secção da tese, observado a partir da celebração do quadricentenário da descoberta de Cabral. / “Comemorar efemérides” is a Portuguese phrase that despite its academic ring, is often used in the mainstream press. It translates roughly as 'the commemoration of an auspicious occasion’ and is used in reference to the public marking of nationally significant events. By the end of the nineteenth century, the two terms of this phrase came to be synonymous in Portuguese. This thesis represents an effort to understand the development of these two terms – efemérides and comemorações – over the longue durée. The long-term similarities in the practical and public uses of these terms are explored by tracing their discursive deployments and examining the debates that surrounded such public uses. The first section, dedicated to commemorations, frames the analysis of this much discussed topic with the following hypothesis: the act of commemoration is a form of moral utterance between generations; it is the rehearsal and transmission of collective values. Drawing on historical sources, I argue that the eventual points of contact between these terms can be seen as analogs to the discursive exchange and conflict between the classical and peripatetic notions of the “order of time” and the “order of nature”. In this conceptual drama, one sees how the sublation of old cosmological perspectives nevertheless still contains what I shall call – following Pomian – a chronosophy. This analysis leads to the second part of the thesis. Efemérides, originally tables of the movements of the celestial bodies – also known as almanacs – underwent a slow transition from the celestial to the earthly, from the charting of the stars to the recording of human deeds. Drawing on classical texts, well-informed readers of early modernity would have associated those writings in the first instance with diaries, then with journalism and, in the following centuries, with political history. Emerging from the French Revolution as a historiographical subgenre, lists of Efemérides shared a common function with commemorations as nation-building practices that described the horizon of a project to create national identity. This horizon, as a meeting point of moral utterance and political project is explored at the end of both sections of the thesis, as it is observed in the quadricentenial celebration of Cabral’s Discovery of Brazil. It is at this horizon that the parallel developments of comemorações and efemérides promise to meet.

This study focuses on the Sun's influence on the motion near the triangular libration points of the Earth-Moon system. It is known that there exists a very strong resonant perturbation near those points that produces large deviations from the libration points, with an amplitude of about 250,000 km and a period of 1,500 days. However, it has been shown that it is possible to find initial conditions that negate the effects of that perturbation, even resulting in stable, although very large, periodic orbits. Using two different models, the goal of this research is to determine the initial configurations of the Earth-Moon-Sun system that produce minimal deviations from the libration points, and to provide a better understanding of the dynamics of this highly nonlinear problem. First, the Bicircular Problem (BCP) is considered, which is an idealized model of the Earth-Moon-Sun System. The impact of the initial configuration of the Earth-Moon-Sun system is studied for various propagation times and it is found that there exist two initial configurations that produce minimal deviations from L₄ or L₅. The resulting trajectories are very sensitive to the initial configuration, as the mean deviation from the libration points can decrease by 30,000 km with less than a degree change in the initial configuration. Two critical initial configurations of the system were identified that could allow a particle to remain within 30,000 km of the libration points for as long as desired. A more realistic model, based on JPL ephemerides, is also used, and the influence of the initial epoch on the motion near the triangular points is studied. Through the year 2007, 51 epochs are found that produce apparently stable librational motion near L₄, and 60 near L₅. But the motion observed depends greatly on the initial epoch. Some epochs are even found to significantly reduce the deviation from L₄ and L₅, with the spacecraft remaining within at most 90,000 km from the triangular points for upwards of 3,000 days. Similarly to what was observed in the BCP, these trajectories are found to be extremely sensitive to the initial epoch. / text

An increasing number of GPS applications require a high level of accuracy. To reduce the error contributed by the GPS ephemerides, an accurate modeling of the forces acting on GPS satellites is necessary. These forces can be categorized into gravitational and non-gravitational forces. The non-gravitational forces are a significant contribution to the total force on a GPS satellite but they are still not fully understood whereas the gravitational forces are well modeled. This study focuses on two non-gravitational forces: Solar Radiation Pressure (SRP) and the y-bias force. Different SRP models are available in the University of Texas Multi-Satellite Orbit Determination Program (MSODP). The recently developed University College London model was implemented for the purpose of this study. Several techniques to compute parameters associated with SRP models and the y-bias force during an orbit prediction were examined. Using the International GNSS Service (IGS) precise ephemerides as a reference, five different models were compared in the study. Satellite Laser Ranging (SLR) residuals were also studied to validate the approach. Results showed that the analytical UCL model performed as well as a purely empirical model such as the Extended CODE model. This is important since analytical models attempt to represent the physical phenomena and thus might be better suited to separate SRP from other forces. The y-bias force was then shown to have a once per revolution effect. The time evolution of the y-bias was found to be dependent on the SRP model used, the satellite Block type, the orbital plane, and the attitude of the satellite which suggests that estimates of y-bias contain errors from other sources, particularly the SRP models. The dependency of the y-bias evolution on the orbital plane suggests that the orientation of the plane towards the Sun is important. / text

Thesis (Ph. D.)--Harvard University, 1977. / Includes bibliographical references (p. 285-319).