Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1980. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND AERO. / Vita. / Includes bibliographical references. / by Andrew Joseph Green. / Ph.D.

published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy

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Orientador : Rodolpho Vilhena de Moraes / Banca: Antonio Fernando Bertachini de Almeida Prado / Banca: Hans-Ulrich Pilchowski / Resumo: Aplicações recentes de satélites artificiais, principalmente aquelas com finalidades geodinâmicas e altimétricas, requerem órbitas determinadas com bastante precisão. Em particular as marés terrestres alteram o geopotencial, causando perturbações adicionais no movimento do satélite. Tais perturbações, apesar de pequenas, têm sido detectadas. O presente trabalho trata de perturbações de órbitas de satélites artificiais devidas às marés terrestres. Ênfase é dada aos termos seculares e de longo período. O potencial foi desenvolvido em termos dos elementos orbitais e substituídos nas equações planetárias de Lagrange. Soluções analíticas estão apresentadas para casos particulares considerando os números de Love constantes. Um programa foi elaborado, e colocado a disposição do usuário, permitindo calcular, para um dado satélite, a amplitude e o período dos termos perturbadores mais significativos. / Abstract: Recent applications of artificial satellites, mainly those of geodynamics and altimetric purposes, requires high precise orbit determination. Particularly, Earth tides change the geopotencial causing additional perturbation in the satellite orbital motion. Inspite of being very small such perturbations, has been detected. The present work concerns about orbit perturbations of artificial satellites due do terrestrial tides. Treatment of secular and long period terms is emphasized. The potencial was developed in terms of the orbital elements and substituted in the Lagrange equations. Analytical solutions are presented for particular cases considering the Love's number as constant. A computer enabling to compute, for a given satellite, the amplitude and period of the more significant disturbing terms, was constructed and it is, at the disposal for users. / Mestre

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

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The solution to the problem of a satellite with a small constant thrust and under the influence of a central force field presents difficulties due to equations non-linearity. An investigation was made to determine what range of values of the thrust parameter could be utilized to obtain a valid approximate solution for the case of tangential thrusting. The investigation was accomplished by developing programs for the 1620 High Speed Digital Computer, since the solution to the exact and approximate equations would otherwise be exceedingly laborious. Under the assumption of no atmosphere, and neglecting the earth's oblateness, the study showed that the validity of the Kryloff and Bogoliuboff method was dependent on both the specific thrust aud the vehicle speed. For a Speed corresponding to an orbit of smaller eccentricity it was determined that the method of Kryloff and Bogoliuboff remained valid for larger values of W than when V was a velocity corresponding to an orbit with a greater eccentricity. The method of Kryloff and Bogoliuboff represents a practical approach to the solution of satellite motion both from the aspect of ease of application and reasonable calculation times. / Master of Science

There is an ever increasing need for low-cost communication systems in the world. One such system, low-earth-orbit satellites, can provide store-and-forward, as opposed to real time, communication for many earth stations. The advantages and disadvantages of such a system is presented. Material covering protocols and communications architectures is elaborated upon for the use of amateur radio communications. Doppler shift and its effect on satellites in low-earth-orbit is examined. Efficiency and throughput of the Amateur X.25 Protocol will be explored. The last chapter entails the analysis of the PACSAT experiment. / Master of Science

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