Thesis (MScEng)--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: The primary payload of the University of Stellenbosch's micro-satellite, SUNSAT I, was a high quality imager, capable of taking stereoscopic images of the surface of the earth. Although the orbit of SUNSAT I will have the satellite pass over the whole earth, contact via the SUNSAT I ground station at the University will only be made for 3% of each day. To be able to photograph any part of the earth onboard memory was provided on the satellite to store the image until it can be downloaded to the ground station. A high speed downlink was also added to the satellite to be able to download a complete image from the onboard memory in one pass and also to take realtime pictures as the satellite passes over the ground station. At that stage there was no way to capture the data at the ground station. A high speed digital data capture mechanism was needed. The thesis discusses the development of a high speed capture card. Due to the high speeds needed it provided an excellent opportunity to develop the card using the PCI bus, the first design to do so at the University, as an interface with a computer. A prototype card was developed first to do proof of concept. It is shown that the prototype card fulfilled the functional requirements and it was also used to capture the first image from the complete satellite during the final tests before launch. Finally a production card for use in the ground station was designed and assembled. / AFRIKAANSE OPSOMMING: Die hoof loonvrag van die Universtieit van Stellenbosch se eerste mikrosatelliet, SUNSAT I, is "n hoë kwaliteit kamera wat stereoskopiese fotos van die oppervlak van die aarde kan neem. Alhoewel die satelliet oor die hele oppervlakte van die aarde gaan beweeg, is dit vir slegs 3% van die dag sigbaar vanaf die grondstasie by die Universiteit van Stellenbosch. Om 'n foto van enige plek op aarde te kan neem is daar aanboord geheue op die satelliet geplaas om die foto te stoor totdat dit by die grondsatsie afgelaai kan word. "n Hoë spoed skakel is ook daargestelom die data in die geheue van die satelliet in een verbyvlug te kan aflaai. Dit stel die satelliet ook in staat om intydse fotos gedurende In verbyvlug van die satelliet te kan neem. Op daardie stadium het daar nog nie "n manier bestaan om die hoë spoed data vas te lê nie. In Meganisme om die hoë spoed digitale data te vang was nodig. Hierdie tesis bespreek die ontwikkeling van so In data vang kaart. Weens die hoë snelhede wat benodig word, het die PCI bus die ideale oplossing gebied om die data teen "n hoë spoed op In persoonlike rekenaar te stoor. Dit was ook die eerste ontwerp aan die Universiteit wat van die PCI bus gebruik gemaak het. In die eerste instansie is In prototipe ontwikkel om te bewys dat dit wel moontlik is om die data teen die benodigde tempo te kan stoor. Daar word gewys dat die prototipe aan die behoefte voldoen en dit is ook gebruik om die eerste beeld vanaf die volledige satelliet te vang voordat dit gelanseer is. In die tweede instansie word In produksiekaart ontwikkel en aanmekaar gesit.

Thesis (MScEng)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: There is a large variety of telemetry recervmg software currently available for the reception of telemetry information from different satellites. Most of the software used in receiving telemetry data is satellite specific. Hence, a user-friendly way is needed to make telemetry data easily accessible. A satellite-based web server is aimed at providing telemetry information to any standard web browser as a way of bringing space technology awareness to the people. Two different satellite-based web server methods are examined in this thesis. Based on the evaluation, the on-board File server with proxy server was proposed for satellite-based web server development. This requires that the File server be ported to the on-board computer of the satellite. The web proxy server is placed on the ground segment with the necessary communication requirements to communicate with the on-board File server. In the absence of satellite, the satellite-based web server was successfully implemented on two computers, laying a good foundation for implementation on the on-board computer of the satellite (OBe). / AFRIKAANSE OPSOMMING: Daar is 'n groot verskeidenheid telemetrie ontvangs sagteware huidiglik beskikbaar vir die ontvangs van telemetrie informasie vanaf verskillende satelliete. Die meeste van die sagteware wat gebruik word om telemetrie data te ontvang is satelliet spesifiek. Gevolglik, 'n gebruikers vriendelike metode is nodig om telemetrie data maklik beskikbaar te maak. 'n Satelliet-gebaseerde web-bediener word beoog om telemetrie informasie te verskaf aan enige standaard web-blaaier as 'n metode om mense bewus te maak van ruimte tegnologie. Twee verskillende satelliet gebaseerde web-bediener metodes salondersoek word in hierdie tesis. Gebaseer op 'n evaluering, word die aanboord leêr-bediener met instaanbediener voorgestel vir satelliet-gebaseerde webbediener ontwikkeling. Hiervoor is dit nodig dat die leêr-bediener na die aanboord rekenaar van die satelliet gepoort word. Die web instaanbediener word op die grond segment geplaas met die nodige kommunikasie benodighede, om te kommunikeer met die aanboord leêr-bediener. In die afwesigheid van die satelliet was die satellietgebaseerde web-bediener met sukses geïmplementeer op twee rekenaars, met die gevolg dat 'n goeie fondasie gelê is vir die implementering op die aanboord rekenaar van die satelliet (OBC).

Thesis (MScEng)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: A different approach of employing attitude sensors with incomplete measurements in an attitude determination system is investigated. The amount of available attitude sensors on small satellites are limited, and the failure of sensors can be fatal when accurate attitude determination is necessary. The problem with sensors with incomplete measurements is that they must be used in combination with other sensors to obtain three dimensional attitude information. The aim is to enhance the possible number of sensor combinations that can be employed, in an attempt to improve the ability of the attitude determination system to tolerate sensor failures. An alternative sensor structure consisting of a magnetometer and two horizon sensors is presented. A method to obtain vector observations of the attitude from a combination between magnetometer and horizon sensor measurements is derived and tested. A full state Extended Kalman Filter is used to determine the satellite's attitude, attitude rate and disturbance torque from these vector observations. A second Extended Kalman Filter structure, using only magnetometer measurements, is implemented. The magnetometer Extended Kalman Filter and the horizon/magnetometer Extended Kalman Filter are integrated to obtain a single Extended Kalman Filter structure to determine the satellite's full attitude state. Integration is done by switching between the different pairs of vector information. A systematic analysis of the integrated filter's dynamic behaviour during the switching stages is done by means of a series of case studies. / AFRIKAANSE OPSOMMING: Die gebruik van oriëntasiesensore met onvolledige metingsdata in oriëntasiebepalingsstelsels is ondersoek. Slegs 'n beperkte aantal oriëntasiesensore is beskikbaar op mikro satelliete. 'n Foutiewe sensor kan dus noodlottig wees wanneer akkurate oriëntasiebepaling nodig is. Die probleem met sensore met onvolledige metingsdata is dat dit in sensor kombinasies gebruik moet word om drie dimensionele oriëntasieinligting te verkry. Die doel is dus om die moontlike aantal sensor kombinasies sodanig te vermeerder dat die oriëntasiebepalingsstelsel beter bestand sal wees teen moontlike sensor falings. 'n Alternatiewe sensor struktuur, bestaande uit 'n magnetometer en twee horison sensore, is ondersoek. 'n Metode vir die verkryging van 3-as oriëntasie inligting vanaf 'n kombinasie van magnetometer en horison sensor metingsdata is afgelei en getoets. 'n Vol toestand uitgebreide Kalmanfilter is gebruik om the satelliet se oriëntasie, oriëntasie snelheid en versteurings draairnoment vanaf die vektor observasies af te lei. 'n Tweede uitgebreide Kalmanfilter struktuur, wat slegs magnetometer metingsdata gebruik, is geïmplementeer. Die magnetometer filter en die horison/magnetometer filter is geïntegreer sodat een uitgebreide Kalmanfilter struktuur volle oriëntasie inligting kan aflei vanaf verskillende pare vektors met oriëntasie inligting. Integrasie is gedoen deur te skakel tussen die verskillende vektorpare. 'n Sistematiese analise van die geïntegreerde filter se dinamiese gedrag gedurende die oorskakelingstye is gedoen deur middel van 'n reeks gevallestudies.

No description available.

Made available in DSpace on 2015-12-10T14:22:59Z (GMT). No. of bitstreams: 0 Previous issue date: 2015-07-28. Added 1 bitstream(s) on 2015-12-10T14:29:14Z : No. of bitstreams: 1 000852063.pdf: 2040130 bytes, checksum: 458621c7faa04b8c2ac8a4f58adf2130 (MD5) / 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 / 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

Made available in DSpace on 2014-06-11T19:24:13Z (GMT). No. of bitstreams: 0 Previous issue date: 2005-07Bitstream added on 2014-06-13T18:51:55Z : No. of bitstreams: 1 pinto_jv_me_guara.pdf: 1385196 bytes, checksum: 8f4e005504bfa301a50295aa1563c0d7 (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Universidade Estadual Paulista (UNESP) / Aplicações recentes de satélites artificiais da Terra com finalidades geodinâmicas requerem órbitas determinadas com bastante precisão. Em particular, marés terrestres influenciam o potencial terrestre causando perturbações adicionais no movimento de satélites artificiais, as quais têm sido medidas por diversos processos. A atração exercida pela Lua e pelo Sol sobre a Terra produz deslocamentos elásticos em seu interior e uma protuberância em sua superfície. O resultado é uma pequena variação na distribuição da massa na Terra, conseqüentemente alterando o geopotencial. As perturbações nos elementos orbitais de satélites artificiais terrestres devidas à maré terrestre podem ser estudadas a partir das equações planetárias de Lagrange, considerando-se um potencial conveniente. Alguns modelos têm sido propostos para o cálculo de perturbações orbitais devidas à maré, tais como os modelos de Kaula, de Kozai, de Balmino e o utilizado pelo IERS. Os resultados encontrados na literatura são, em geral difíceis de serem comparados, pois os cálculos são feitos com diferentes modelos. Neste trabalho são apresentadas, para os potenciais mencionados, as expressões analíticas em forma expandida. Alguns cenários são propostos mostrando, para tais modelos, as diferenças nas perturbações de longo período e seculares, nos elementos orbitais de satélites artificiais, devidas á maré terrestre. / Recent applications of artificial Earth's satellites, as for instance with geodynamics purposes, require very high precision orbit determination. In particular, terrestrial tides affects the geopotential causing additional orbital perturbations that can be measured by several methods. The Sun and Moon attraction on the Earth produces both an elastics displacements in the Earth's interior and a bulge in its surface. The resulting effect is a small variation in the Earth's mass distribution. The perturbations in the orbital elements due to the terrestrial tides can be analysed using the Lagrange planetary equations considering a convenient potential. Some models have been proposed to compute orbital perturbations due to the terrestrial tides, such as the models proposed by Kozai, Kaula, Balmino and the model used by the IERS. The results found in the literature about orbit perturbations due to terrestrial tides were obtained using different models being difficult to be compared. In this work the above-referred models are presented. Expanded analytical expressions are presented. Some scenarios are proposed showing, for such models, the differences in the secular and long period perturbations of the orbital elements, due to the terrestrial tides.

Orientador: Rodolpho Vilhena de Moraes / Banca: Maria Cecília França de Paula Santos Zanardi / Banca: Hélio Koiti Kuga / Resumo: Aplicações recentes de satélites artificiais da Terra com finalidades geodinâmicas requerem órbitas determinadas com bastante precisão. Em particular, marés terrestres influenciam o potencial terrestre causando perturbações adicionais no movimento de satélites artificiais, as quais têm sido medidas por diversos processos. A atração exercida pela Lua e pelo Sol sobre a Terra produz deslocamentos elásticos em seu interior e uma protuberância em sua superfície. O resultado é uma pequena variação na distribuição da massa na Terra, conseqüentemente alterando o geopotencial. As perturbações nos elementos orbitais de satélites artificiais terrestres devidas à maré terrestre podem ser estudadas a partir das equações planetárias de Lagrange, considerando-se um potencial conveniente. Alguns modelos têm sido propostos para o cálculo de perturbações orbitais devidas à maré, tais como os modelos de Kaula, de Kozai, de Balmino e o utilizado pelo IERS. Os resultados encontrados na literatura são, em geral difíceis de serem comparados, pois os cálculos são feitos com diferentes modelos. Neste trabalho são apresentadas, para os potenciais mencionados, as expressões analíticas em forma expandida. Alguns cenários são propostos mostrando, para tais modelos, as diferenças nas perturbações de longo período e seculares, nos elementos orbitais de satélites artificiais, devidas á maré terrestre. / Abstract: Recent applications of artificial Earth's satellites, as for instance with geodynamics purposes, require very high precision orbit determination. In particular, terrestrial tides affects the geopotential causing additional orbital perturbations that can be measured by several methods. The Sun and Moon attraction on the Earth produces both an elastics displacements in the Earth's interior and a bulge in its surface. The resulting effect is a small variation in the Earth's mass distribution. The perturbations in the orbital elements due to the terrestrial tides can be analysed using the Lagrange planetary equations considering a convenient potential. Some models have been proposed to compute orbital perturbations due to the terrestrial tides, such as the models proposed by Kozai, Kaula, Balmino and the model used by the IERS. The results found in the literature about orbit perturbations due to terrestrial tides were obtained using different models being difficult to be compared. In this work the above-referred models are presented. Expanded analytical expressions are presented. Some scenarios are proposed showing, for such models, the differences in the secular and long period perturbations of the orbital elements, due to the terrestrial tides. / Mestre

Orientador: Rodolpho Vilhena de Moraes / Banca: Maria Cecilia França de Paula S. Zanardi / Banca: Sandro da Silva Fernandes / Resumo: Uma teoria para estudar o movimento orbital de satélites artificiais sobre efeitos do arrasto atmosférico e da pressão de radiação solar direta - considerando a sombra da Terrae alguns termos do geopotencial - é desenvolvida analiticamente. A sombra daTerra é modelada utilizando a função sombra, como introduzida por ferraz Mello: igual zero quando o satélite está na região de sombra e igual um quando é iluminado pelo sol. As componentes do arrasto são dadas por Vilhena de Moraes baseado no modelo atmosférico TD-88. O método de Hori para sistemas não canônicos é aplicado para resolver as equações de movimento. Um software para manipulação algébrica é fundamental apra fazer os cálculos necessários. Efeitos seculares e periódicos que influenciam no movimento orbital dos satélites artificiais são analisados. Expressões analíticas são apresentada explicitamente para os principais termos seculares nas variações dos elementos orbitais. É dada ênfase aos termos de acoplamento que surgem na solução do sistema de equações diferenciais. Utilizando dados orbitais do satélite CBERS-1 um estudo é feito para analisar ordens da variação do semi-eixo maior devidas as pertubações consideradas. / Abstract: A theory to study the orbital motion of artificial satellites under the effects of the atmospheric drag and of the direct solar radiatin pressure - considering the Earh's shadow and some terms of the geopotential - is developed analytically. The Earth shadow is modeled using the shadow function introduced by Ferrz Mello: equal zero when the satellite is in the shadow region and equal one when it is illuminated by the Sun. The drag components are given by Vilhena of Moraes based in the TD-88 temospheric model. The Hori's method for non-canonical systems is applied to solve the motion equation. A algebric manipulator software is fundamental to do the necessary calculations. Secular and periodic effects on the orbital motion of artificial satellites are analyzed. Analytic expressions are presented explicity for the main secular terms of the variations of the orbital elements. Emphasis is given to the coupling terms that appear in the solution of the differential euqatin systems. Using orbital data of the satellite CBERS-1 a study is done to analyze the order of magnitude of the variation of the semi-major axis due to the considered pertubation. / Mestre

O objetivo deste trabalho é investigar o processo das variações do campo gravitacional, obtidas através da missão espacial GRACE e seu relacionamento com a dinâmica das águas na região Amazônica. A partir disto, procurou-se desenvolver uma metodologia para as estimativas das cotas dágua em áreas inundáveis não monitoradas ou de difícil acesso. Para isso, os coeficientes de Stokes, disponibilizados pelo GRGS de Toulouse, foram convertidos, por um processo denominado inversão, no equivalente à altura dágua (EqW) para o período de aproximadamente 4 anos (julho de 2002 a maio de 2006) e os valores comparados às cotas do nível dágua in-situ obtidas pela Agência Nacional de Águas (ANA). A escolha da bacia Amazônica está relacionada ao fato da mesma apresentar, próximo ao centro, amplitudes de aproximadamente 1250 mm no nível do EqW, sendo as maiores do mundo. A regionalização dos modelos globais das variações deste campo pôde ser aplicada para uma boa estimativa nas cotas dágua in-situ. Assim, foram estimados os erros desta metodologia, que são da ordem de ~160 mm para o EqW, oriundos dos erros nos coeficientes de Stokes, truncamento do espectro e erros de vazamento de informações hidrológicas das bacias vizinhas. Esta metodologia trata, portanto, de estimar as cotas onde não existam estações de monitoramento, avaliando a ordem de grandeza dos erros. Por fim, são apresentadas cartas que relacionam hidrogeologicamente as defasagens apresentadas nos ciclos semi-anuais e as áreas onde a metodologia poderá ser melhor aplicada com estimativas mais precisas do EqW e com maior coerência entre os dados satelitais e terrestres. / A comparison between vertically-integrated equivalent water height (EWH) derived from GRACE gravity anomalies with in situ water level time series measured at ground-based hydrometric stations (HS) in the Amazon basin is figure out in the thesis. A methodology for EWH estimation at ungauged sites is presented. The Stokes coefficients disponibilized by GRGS - Toulouse at a 10-day interval were converted into EWH for a ~4-year period (July-2002 to May-2006) using the methodology so-called inversion, and then compared to HS level. In the basin, the amplitudes of EWH signal are the largest on the Earth and can reach on the order of 1250 mm at the center of the basin (e.g. Manaus station). The uncertainties represent ~160 mm of EWH, including Stokes coefficient uncertainties, leakage errors and spectrum truncation. A methodology for acquire water level historical series at ungauged places is proposed with the estimated incertitude. A hydrological map is compared with a correlation chart and figure out areas where this methodology works better, in addition, compared also with shift phased semi-annual cycles.

This paper presents a Lagrangian formulation for studying the dynamics and control of the proposed Space Station based Mobile Servicing System (MSS) for a particular case of in plane libration and maneuvers. The simplified case is purposely considered to help focus on the effects of structural and joint flexibility parameters of the MSS on the complex interactions between the station and manipulator dynamics during slewing and translational maneuvers. The response results suggest that under critical combinations of parameters, the system can become unstable. During maneuvers, the deflection of the MSS can become excessive, leading to positioning error of the payload. At the same time the libration error can also be significant. A linear quadratic regulator is designed to control the deflection of the manipulator and maintain the station at its operating configuration. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate