Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2005. / The next generation of small satellites will require significant onboard data processing and information extraction capabilities to keep up with industry demands. The need for value added information products is growing as accessibility and user education is improving. Image geo-referencing is one of the image processing steps needed to transform raw images into usable information. Automating this process would result in a vast improvement in processing time and cost. As part of the background study, the imaging process is described and a model of the process is created. The sources of distortion that are present in the imaging process are described and techniques to compensate for them are discussed. One method that stands out is using wavelet analysis for the precision geo- referencing of images. Wavelets are used in this thesis for automatic ground control point identification. Finally, the automatic ground control point algorithm is used for band-alignment of a set of aerial images at sub pixel accuracy as a demonstration of the quality of ground control points that can be found.

Approved for public release, distribution is unlimited / Converging voice and data networks has the potential to save money and is the main reason Voice over Internet Protocol (VoIP) is quickly becoming mainstream in corporate America. The potential VoIP offers to more efficiently utilize the limited connectivity available to ships at sea makes it an attractive option for the Navy. This thesis investigates the usefulness of VoIP for the communications needs of a unit level ship. This investigation begins with a review of what VoIP is and then examines the ship to shore connectivity for a typical unit level ship. An OMNeT++ model was developed and used to examine the issues that affect implementing VoIP over this type of link and the results are presented. / Lieutenant Commander, United States Navy

Approved for public release; distribution is unlimited / Systems engineering is a vital element of systems acquisition, and yet, as a result of previous Department of Defense (DoD) and United States Air Force (USAF) policies and practices, many government systems engineers today lack the systems engineering/management skills required to successfully execute national security space programs. The purpose of this thesis is to study and understand common issues that have impacted the ability of the USAF to cost-effectively acquire satellite systems. The research performed here involves an analysis of the differences between the traditional DoD systems acquisition and the national security space systems acquisition processes and an investigation of previous national efforts to improve these processes. The analysis results, together with the findings from a review of successful and struggling space programs, are then used to discover trends that aid in the formulation of the recommendations in this thesis. Specifically, to improve USAF systems engineering management skills and thereby improve the national security space systems acquisition process, the role of the government systems engineer should be defined as one of risk management, and the government systems engineers should be trained, equipped, and tracked in order to efficiently perform systems engineering in support of the space systems acquisition process. Finally, the research findings will provide a foundation for future researchers to expand upon the recommendations and make steady progress toward improving DoD and USAF space systems engineering expertise. / Outstanding Thesis

Approved for public release; distribution in unlimited. / This thesis develops and implements a Control Moment Gyroscope (CMG) steering law, controller and active balancing system for a three-axis satellite simulator (TASS). The CMGs are configured in a typical pyramid configuration (the fourth CMG position being null). The development was done primarily with simulation and experiments utilizing Real Time Workshop and XPC Target of MATLAB and SIMULINK. The TASS is a double circular platform mounted on a spherical air bearing with the center of rotation (CR) about the approximate physical geometric center of the simulator. The TASS utilizes three moveable masses in the three body axes for balancing which actively eliminate any center of gravity (CG) offset and return the CG to the CR. The TASS supports an optics payload designed to acquire, track and point a received laser beam onto an off-satellite target. The target may be stationary or moving. Actively balancing the TASS reduces the torque output requirement for the CMGs while maintaining either a stabilized level platform or a particular commanded attitude. Reduction or elimination of torque output from the CMGs results in a more stabilized platform, less structural induced vibration, less jitter in payload optics and less power required in spacecraft applications. / Lieutenant Commander, United States Navy

Orientador: Tadashi Yokoyama / Banca: Rodolpho Vilhena de Moraes / Banca: Nelson Callegari Junior / Resumo: A estabilidade dos membros das constelações Galileo e GPS é investigada. Devido à ressonância 2:1 entre w e W, ocorre um aumento significativo da excentricidade. Este aumento causa riscos de colisão entre os satélites descartáveis e os ativos. Como a ressonância não depende do semi-eixo do satélite, estratégias usuais de aumentar a altitude não resolvem o problema. Então, condições iniciais especiais são achadas tais que os satélites descartáveis permanecem estáveis, com baixa excentricidade por pelo menos 250 anos. Outra estratégia de atacar o problema é mover o objeto descartável para uma órbita particular, acelerando o crescimento da excentricidade. Este estudo é brevemente apresentado. A dinâmica de satélites heliossíncronos é também estudada. Devido o arrasto atmosférico, a altitude do satélite sempre decai e portanto ele cruza o valor ressonante do semi-eixo. Sempre que isso ocorre, um salto na inclinação é observado e em alguns casos, há alguns cruzamentos tais que a inclinação permanece aprisionada (durante algum tempo) no centro de libração. Este evento é importante, pois isso pode ser explorado para realizar manobras de baixo custo para controlar o satélite numa determinada inclinação. Através do sistema exato, investigamos estas quasecapturas e seu aproveitamento em manobras de manutenção de inclinação. / Abstract: The stability of the disposed members of the Galileo and GPS constellations is investigated. Due to the 2:1 resonance between w and W, a significant increase of the eccentricity occurs. These increase cause risk of collisions between the operational and disposed satellites. As the resonance does not depend on the semi-major axis of the satellite, usual strategies of raising the altitude do not solve the problem. Therefore, special initial conditions are found such that the disposed satellites remain stable with small eccentricity, for at least 250 years. Another strategy to attack the problem is to move the disposed object to a particular orbit, accelerating the growth of the eccentricity. This study is briefly presented. The dynamics of the sun-synchronous satellite is also studied. Due to the atmospheric drag, the altitude of the satellite always decays and therefore it crosses the resonant value of the semi-major axis. Whenever this happens, a jump in the inclination is observed and in some cases, there are some crossing such that the inclination remains locked (during some time) in the center of the libration. This event is interesting since it can be exploited to perform inexpensive maneuvers to control the satellite at desired inclination. / Mestre

The Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) mission provides unique measurements of vertical profiles of aerosols and clouds and their properties during day and night-time over all types of surfaces. This information has the potential to significantly improve our understanding of the properties and effects of aerosol and clouds. This dissertation presents the results of a comprehensive analysis of CALIPSO lidar (version 2 and version 3.01) data in conjunction with A-Train satellite and ground-based observations aimed at characterizing mineral aerosol in East Asia and other major dust sources. The specific objectives were to characterize the spatial distribution and properties of atmospheric dust in the dust source regions using new CALIOP (version 3.01) data in conjunction with satellite MODIS, OMI, and CloudSat data and ground-based meteorological and lidar data; investigate changes in the vertical distribution and properties of dust during mid- and long-range transport; perform a modeling of the optical properties of nonspherical dust particles, and assess the radiative forcing and heating/cooling rates of atmospheric dust by performing radiative transfer modeling constrained by satellite data in major dust source regions.

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references. Available also from UMI/Dissertation Abstracts International.

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 218-228). Available also in a digital version from Dissertation Abstracts.

Understanding variations in remote sensing data with illumination and sensor angle changes is important in agricultural crop monitoring. This research investigated field bidirectional reflectance factor (BRF) in crop differentiation and PROSAIL leaf area index (LAI) estimation. BRF and LAI data were collected for planophile and erectophile crops at three growth stages. In the solar principal plane, BRF differed optimally at 860 nm 60 days after planting (DAP) for canola and pea, at 860 nm 45 and 60 DAP for wheat and barley, and at 860 nm and 670 nm 45 and 60 DAP for planophiles versus erectophiles. The field BRF data helped better understand PROSAIL LAI estimation. NDVI was preferred for estimating LAI, however the MTVI2 vegetation index showed high sensitivity to view angles, particularly for erectophiles. The hotspot was important for crop differentiation and LAI. Availability of more along-track, off-nadir looking spaceborne sensors was recommended for agricultural crop monitoring. / xiii, 161 leaves : ill., map ; 29 cm

Thesis (MEng)--University of Stellenbosch, 2000. / ENGLISH ABSTRACT: Satellites are not all made equal. The large number of possible orbits, desired functionality and budget constraints are but a few of the factors that influence the design of a satellite. Given a particular set of design requirements, a number of designs may meet these requirements. Each of these designs will typically entail a trade-off between a number of (conflicting) parameters, whilst still satisfying the system requirements. The On-Board Computer (OBC) of a satellite, the satellite subsystem primarily responsible for the operational control of a satellite, can consequently be designed in any of a number of different ways. As the factors that influence the flight performance of an OBC differs to those of a terrestrial computer, the OBC design will therefore be significantly different. A high-level overview of the factors that impact OBC design and operation is presented. Improvements to the existing designs are proposed. In conclusion, a number of guidelines for a future OBC design also are given. / AFRIKAANSE OPSOMMING: Elke satelliet het unieke eienskappe wat bepaal word deur onderandere, die teiken wentelbaan, verwagte funksionaliteit en koste oorweegings. Vir 'n spesefieke stelselontwerp bestaan daar 'n aantal moontlike ontwerpe wat aan die stelsel vereistes voldoen. Elk van hierdie ontwerpe sal tipies behels dat verskillende parameters teen mekaar afgespeel word, terwyl die stelsel vereistes steeds aan voldoen word. Die Aanboord Rekenaar (AR) van 'n satelliet, die satelliet substelsel hoofsaaklik verantwoordelik vir die beheer van die satelliet, kan vervolgens uit een van veele moontlike ontwerpe bestaan. Aangesien die faktore wat die werkverrigting van 'n AR beinvloed verskil van die van 'n rekenaar wat op die aard oppervlak gebruik word, sal die AR ontwerp dienooreenkomstig verskil. 'n Hoevlak oorsig van die faktore wat AR ontwerp beinvloed sal gegee word. Verbeteringe wat aan die huidige AR ontwerpe gedoen kan word sal bespreek word. Ter afsluiting sal 'n aantal riglyne vir toekomstige AR ontwerpe gegee word.