Thesis (MScEng)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: One of the requirements for satellite telemetry systems is the provision of reliable telemetry data to allow accurate monitoring of the satellite status. This thesis focuses on the design of telemetry software that meets this data reliability requirement. An improved synchronization strategy to allow efficient ground reception of the telemetry data is implemented on SUNSAT's direct link. The data collection and transmission functions are also enhanced by the addition of the necessary redundant information to the data while meeting the real-time requirements of the system. To enhance the software quality a development methodology entailing structured programming practices and modular decomposition is proposed. It is shown that the resulting telemetry software fulfils the functional requirements. / AFRIKAANSE OPSOMMING: Een van die vereistes vir die satelliet telemetrie stelsel is die verskaffing van betroubare telemetrie date om akkurate monitering van die satelliet status te verseker. Hierdie tesis fokus op die ontwerp van die telemetrie sagteware wat hierdie data betroubaarheid bevredig. 'n Verbeterde sinkronisasie strategie is geïmplementeer om meer effektiewe grond ontvangs te verseker van die telemetrie data op SUNSAT se direkte skakel. Die data versameling en transmissie funksies is ook verder verbeter deur die aanvulling van nodige oortollige informasie in die data terwyl die intydse vereistes van die stelsel steeds bevredig word. Om die sagteware kwaliteit te verbeter is 'n ontwikkelings metodiek voorgestel wat gestruktureerde programeering strukture en modulêre oplossings tot gevolg het. Die voltooide telemetrie sagteware het getoon dat dit al die vereistes bevredig.

Thesis (MScEng)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: The co-existence of electronic devices and their attached transmission cables requires a careful planning regarding the energy leakage across cable shields. This leakage poses potential serious problems and impedes system functioning. This thesis pursues an investigation into the EMC cabling protocols for microsatellite systems. Network analysis techniques are applied in calibrating current probes and to recover the cable transfer impedance, Zr. The calibration approach provides accurate results for frequencies up to 600MHz. The methods used to determine Zr are based on injecting a disturbance current onto the outside of the cable-under-test (CUT) and measuring the corresponding voltage induced on the centre conductor. Useful results are obtained up to 80MHz with the use of a O.5m length of cable. It is thus proposed that Zr is a practical concept for shielding performance evaluation and for the testing of cable philosophy. The results are usable in classifying cables for verification and signal usage. Further research involves a prediction tool called an EMC ITS that simulates the hardware of a microsatellite system to allow studies on design trade-offs, transmission cable criteria and placement of devices. / AFRIKAANSE OPSOMMING: Die gelyktydige bestaan van elektroniese toestelle en hul aangehegte transmissielynkabels benodig deeglike beplanning met betrekking tot die lek van energie deur die kabels se afskerming. Hierdie lekkassie kan ernstige probleme tot gevolg hê en die stelsel se funksionering belemmer. Hierdie tesis loods 'n ondersoek na die EMV bekabelingprotokolle vir mikrosatellietstelsels. Netwerk analise tegnieke word gebruik in die kalibrasie van stroom-probes en die verkryging van die kabel se oordragsimpedansie, Zr. Die benadering wat gevolg is in die kalibrasie verskaf akkurate resultate tot en met frekwensies van 600MHz. Die metode wat gebruik word om Zr te bepaal is gebaseer op die injeksie van 'n versteuringstroom op die buitekant van die toetskabel en die meting van die ooreenstemmende spanning wat opgewek word op die binne-geleier. Bruikbare resultate is tot en met 80MHz verkry met die gebruik van 'n kabel met 'n lengte van O.Sm. Daar word dus voorgestel dat Zr 'n praktiese wyse is om afskermingsprestasie mee te evalueer, asook vir die toetsing van kabel-filosofie. Die resultate is bruikbaar in die klassifikasie van kabels vir verifikasie en seingebruik. Verdere navorsing sluit in 'n voorspellingswyse wat 'n EMV GTS genoem word, wat die hardewaarde van 'n mikrosatellietstelsel simuleer om studie aangaande ontwerpkompromieë, transmissielyn kriteria en die plasing van toestelle binne die gebruiksomgewing moontlik te maak.

Orientador: Rodolpho Vilhena de Moraes / Banca: Maria Cecília França de Paula Santos Zanardi / Banca: Valdemir Carrara / Resumo: Devido à sua dependência a um grande número de parâmetros de difícil determinação, o cálculo de coeficiente de arrasto para satélites artificiais torna-se extremamente complexo. Teorias, como as desenvolvidas por Schamberg e Sehnal levam em consideração o coeficiente de acomodação térmico e os ângulos de incidência e reflexão das moléculas na superfície do satélite. Outras teorias como a de Stalder e Zurick utilizam nas suas formulações os seguintes parâmetros: a razão entre as velocidades do satélite e das moléculas da atmosfera, o coeficiente de acomodação térmico, o ângulo de ataque e a razão entre as temperaturas da superfície do satélite e a temperatura das moléculas incidentes. Neste trabalho algumas teorias para o cálculo do coefienciente de arrasto são analisadas comparativamente. Exemplos são exibidos, utilizando como modelo os satélites SCD1, SCD2 e CBERS1. / Abstract: Drag coefficient computation for artificial satellite is extremely complex due to its dependence on several parameters that are difficult to determine. Some theories for drag coefficient computation, such as those developed by Schamberg and Sehnal, took into account the thermal accommodation coefficient and the incident and reflection angles of the molecules in the satellite surface. Others theories, such as the Stalder and Zurick theories, use in their formulations the following parameters: the ratio between the satellite velocity and the velocity of the molecules in the atmosphere, the thermal accommodation coefficient, the attack angle and the ratio between the temperatures of the satellite surface and of the incident molecules. In this work some theories for drag coefficients computation are comparatively analyzed. Examples are exhibited using the satellites SCD1, SCD2 and CBERS1 as models. / Mestre

Made available in DSpace on 2014-06-11T19:25:30Z (GMT). No. of bitstreams: 0 Previous issue date: 2007-04Bitstream added on 2014-06-13T19:12:15Z : No. of bitstreams: 1 carvalho_jps_me_guara.pdf: 1120789 bytes, checksum: 42d7f707a41ef83886b116f000a33c22 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Universidade Estadual Paulista (UNESP) / 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. / 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.

Made available in DSpace on 2014-06-11T19:25:30Z (GMT). No. of bitstreams: 0 Previous issue date: 2001Bitstream added on 2014-06-13T19:06:47Z : No. of bitstreams: 1 silva_tr_me_guara.pdf: 448943 bytes, checksum: 69cd9d252dfbcf9b51952987c7904c0b (MD5) / Devido à sua dependência a um grande número de parâmetros de difícil determinação, o cálculo de coeficiente de arrasto para satélites artificiais torna-se extremamente complexo. Teorias, como as desenvolvidas por Schamberg e Sehnal levam em consideração o coeficiente de acomodação térmico e os ângulos de incidência e reflexão das moléculas na superfície do satélite. Outras teorias como a de Stalder e Zurick utilizam nas suas formulações os seguintes parâmetros: a razão entre as velocidades do satélite e das moléculas da atmosfera, o coeficiente de acomodação térmico, o ângulo de ataque e a razão entre as temperaturas da superfície do satélite e a temperatura das moléculas incidentes. Neste trabalho algumas teorias para o cálculo do coefienciente de arrasto são analisadas comparativamente. Exemplos são exibidos, utilizando como modelo os satélites SCD1, SCD2 e CBERS1. / Drag coefficient computation for artificial satellite is extremely complex due to its dependence on several parameters that are difficult to determine. Some theories for drag coefficient computation, such as those developed by Schamberg and Sehnal, took into account the thermal accommodation coefficient and the incident and reflection angles of the molecules in the satellite surface. Others theories, such as the Stalder and Zurick theories, use in their formulations the following parameters: the ratio between the satellite velocity and the velocity of the molecules in the atmosphere, the thermal accommodation coefficient, the attack angle and the ratio between the temperatures of the satellite surface and of the incident molecules. In this work some theories for drag coefficients computation are comparatively analyzed. Examples are exhibited using the satellites SCD1, SCD2 and CBERS1 as models.

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

Thesis (MTech (Electrical Engineering))--Cape Peninsula University of Technology, 2015. / A precise orbit propagator was developed for implementing on a CubeSat's on-board computer for real-time orbital position and velocity determination and prediction. Knowledge of the accurate orbital position and velocity of a Low Earth Orbit (LEO) Cubesat is required for various applications such as antenna and imager pointing. Satellite motion is governed by a number of forces other than Earth's gravity alone. The inclusion of perturbation forces such as Earth's aspheric gravity, third body attraction (e.g. Moon and Sun), atmospheric drag and solar radiation pressure, is subsequently required to improve the accuracy of an orbit propagator. Precise orbit propagation is achieved by numerically integrating a set of coupled second order differential equations derived from satellite's perturbed equations of motion. For the purpose of this study two numerical integrators were selected: RK4 - Fourth order Runge Kutta method and RKF78 - results from embedding RK7 into RK8. The former is a single-step integrator while the latter is a multi-step integrator. These integrators were selected for their stability, high accuracy and computational efficiency. An orbit propagation software tool is presented in this study. Considering the processing power of Central Processing Unit (CPU) of CubeSat's on-board computer and a trade-off between precision and computational cost, the 10 x 10 and 20 x 20 gravity field models, the Exponential atmospheric model and Jacchia 70 static atmospheric model, were implemented. A 60 x 60 gravity field model is also investigated for reference. For validation purpose the developed software tool results were compared with results from Systems Tool Kit (STK) and Satellite Laser Ranging (SLR) using SUNSAT satellite reference orbit. / National Research Foundation

Thesis (MTech (Electrical Engineering))--Cape Peninsula University of Technology, 2010. / Stable and reliable source of electrical energy is a requirement for efficient operation of satellites. Several sources of electrical power for satellites exist such as fuel cells, nuclear or battery stored Direct Current energy but of late concentration has been on solar cells as the advantages compared to the other sources are many. Solar cells are p-n semiconductor devices which convert light energy into electrical energy by photovoltaic effect. The biggest drawback of solar cell energy system is the low light to electricity conversion efficiency. Apart from powering satellites, solar cells and panels have found other numerous applications such as in water pumping systems, rural electrification, street lightning. Photovoltaic principle of solar cells started way back in 1839 when Alexandre Edmund Becquerel observed that electrical currents arose from certain light induced chemical reactions. A comprehensive understanding of this phenomenon became clear when the science of quantum theory was unveiled in the early parts of the 20th century. Most solar cells and panels available today in the market are silicon based made of single junction technology. The disadvantage with single junction technology is that the p-n junction is made of a single type of solar cell material which absorbs a fraction of light wavelengths from the spectrum of light. The disability of the single p-n junction to convert all the light energy to electricity accounts for the low efficiency for the solar cells. One way to go around the problem of efficiency is to use multi-junction solar cells. Multijunction solar cells are designed to absorb a large fraction of the light spectrum and convert them to electrical energy. They are made of multiple p-n junctions made of different solar cell materials which absorb different parts of light spectrum and convert them to electrical energy. In this thesis, a design of a multi-junction solar cell for developing space solar panel is presented. The multi-junction cell has been designed from simulation results of different solar cell materials simulated with space conditions. Ideas and recommendations for future work are also presented.

Digital satellite remote sensing and Geographic Information Systems (GIS) have been used effectively to determine the Universal Soil Loss Equation (USLE) output for a number of North Texas watersheds. This method involves determining the values of each of the USLE factors and using these factors as information layers within the GIS.

Multiaccess protocols for integrated voice and data transmissions over satellite channels are studied, based on the SENET(slotted envelope network) structure. The satellite system is characterized as a wide band system with a large number of geographically distributed small voice and data users. Performance evaluations of commonly used protocols, i.e., ALOHA and reservation protocols, are first conducted, both analytically and by simulations. The effect of different voice backgrounds on data access protocols are shown explicitly. Based on these results, a control algorithm is proposed. Analyses and simulations show that ALOHA protocol incorporated with such a control mechanism is globally stable under the integrated environment; moreover, the performance deterioration due to voice backgrounds is dramatically reduced. The actual implementation aspects of the control algorithm are considered. An extension of the above results leads to a combined random/reservation protocol. Simulation and analysis results show that the combined protocol exhibits desired low delay and high throughput performance characteristics, with satisfactory voice blocking probability, under the worst user population assumption, i.e., all the voice sources and data sources are independent of each other — reflecting the nature of small earth station environment. The absence of the need for mini-slot structure lends ease and simplicity to the implementation of the combined protocol. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate