Orientadora: Maria Cecília F. P. S. Zanardi / Banca: Ana Paula Marins Chiaradia / Banca: Sandro da Silva Fernandes / Resumo: Uma abordagem analítica para o movimento rotacional de satélites artificiais estabilizados por rotação é apresentada, considerando os satélites em órbita elíptica e a influência conjunta do torque aerodinâmico, o torque de gradiente de gravidade, o torque magnético residual e o torque magnético devido às correntes de Foucault. Modelos matemáticos são apresentados para todos os torques e os componentes médios de cada torque são determinados para um período orbital. O torque médio já inclui os principais efeitos de cada torque sobre o movimento rotacional e são necessários nas equações do movimento. As equações do movimento são descritas em termos do módulo da velocidade angular de rotação do satélite, da declinação e da ascensão reta do eixo de rotação do satélite. Uma solução analítica para as equações do movimento rotacional é determinada, considerando os valores do torques externos médios em um período orbital, sendo válida para um período orbital. Por esta solução observa-se que o torque gradiente de gravidade e torque magnético devido às correntes de Foucault afetam o módulo da velocidade angular de rotação, contribuindo também para as variações temporais da ascensão reta e declinação do eixo de rotação, associadas com a precessão e deriva do eixo de rotação do satélite. O torque magnético residual e o torque aerodinâmico afetam apenas a ascensão reta e declinação do eixo de rotação, pois seu componente no eixo z são nulo. Aplicações são realizadas para os Satélites de Coleta de Dados Brasileiros SCD1 e SCD2, através de uma primeira abordagem com atualização diária dos dados de atitude e órbita e uma segunda abordagem sem a atualização diária destes dados. Os resultados mostram uma boa concordância entre os resultados obtidos pela teoria e os dados fornecidos pelo Centro de Controle de... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: An analytical approach for the rotational motion of artificial satellites stabilized by rotation is presented, considering the satellites in elliptical orbit and the influence of the aerodynamic torque, gravity gradient torque, residual magnetic torque and magnetic torque due to the Foucault currents. Mathematical models for all the torques are shown and average components of each torque are determined for an orbital period. These components are needed in the equations of rotational motion. The average torque already included the main effects of each torque upon the rotational motion. The equations of rotational motion are described in terms of the satellite's spin velocity, the declination and right ascension of the spin axis of the satellite. An analytical solution for the equations of the rotational motion is determined, considering mean values in an orbital period for the external torques. This solution is valid for an orbital period. Through this solution, it is noticed that the gravity gradient torque and the magnetic torques affects the spin velocity and the spin axis. The temporal variations of right ascension and declination of the spin axis causes the precession and drift of the spin. The residual magnetic torque and the aerodynamic torque, doesn't affect the spin velocity because its component at z-axis is null. Applications are made for the Brazilian Data Collection Satellites SCD1 and SCD2, through a first approach with daily updates of the attitude and orbit data, and a second approach without the daily update of these data. The results show a good agreement between the results obtained by theory and data supplied by the Satellite Control Center of INPE in the first approach during 10 days. For the approach without updates, the results prove to be suitable only for 3 days of simulation. To validate the analytical solution, the pointing error (deviation from the rotational... (Complete abstract click electronic access below) / Mestre

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2007. / The focus of this project was to investigate the working of a liquefied gas micro satellite thruster. An introduction is given in which the significance of the project in relation to the literature is stated. The objectives of the project are also stated. In the literature survey the historical development and design specifications of some relevant thruster systems is discussed. An experimental model was designed and built to test the working of a thruster system. Attention is also given to the measurement and calibration techniques used to obtain experimental data. A computer program was written to simulate the thruster system. The experimental set-up was designed so that an accumulator could be charged with liquid butane from a storage tank. The accumulator was charged with 13 ml of liquid butane, which was heated and then exhausted through a nozzle. Copper mesh was placed in the accumulator to improve the heat transfer to the butane vapour before it was exhausted through the nozzle. A cantilever beam was used to measure the thrust of the system. The system was tested under atmospheric conditions of 100 000 Pa as well as under vacuum conditions of 20 Pa. Two nozzles were also tested: nozzle-1 with a throat diameter of 1 mm and an exit diameter of 5 mm and nozzle-2 with a throat diameter of 1 mm and an exit diameter of 1.6 mm. A computer program was written to simulate the flow of the butane vapour through the nozzle, as well as the complex two-phase behaviour of the butane in the accumulator. Traditional gas dynamic theory was used to model the flow through the nozzle. The transient behaviour of the system was modelled to predict the rate of liquid to vapour mass transfer in the accumulator. Additionally, the computer program was developed to simulate the system with copper mesh placed in the accumulator. From the experimental results it was shown that the addition of copper mesh in the accumulator improved the total thrust achieved with a 13 ml charge of liquid butane by more than 50 %. Under atmospheric conditions shockwaves were present in both of the two nozzles tested. Nozzle-2 showed an increase of 91 % in the total thrust achieved over a 5 second burst compared to the total thrust achieved using nozzle-1. With no copper mesh in the accumulator and using nozzle-1 a peak thrust of 39 mN was achieved under atmospheric conditions while under vacuum conditions a peak thrust of 495 mN was achieved. This resulted in a total thrust of 0.365 Ns under atmospheric conditions and 4.88 Ns under vacuum conditions with a 13 ml charge of liquid butane. Using the total thrust achieved the specific impulse of the system was calculated as 5 seconds under atmospheric conditions and 67.5 seconds under vacuum conditions with no mesh in the accumulator and using nozzle-1. The theoretical model compared well with the experimental results except when nozzle-1 was modelled under atmospheric conditions. Under vacuum conditions the results obtained from the theoretical model compared well with the experimental results using both of the nozzles. In the modelling of the mesh in the accumulator an overall heat transfer factor was incorporated into the model to take into account the uncertainty of the heat transfer area as well as the overall heat transfer coefficient. The theoretical model and experimental test results are discussed and thereafter conclusions are also drawn. There are also recommendations made for future work that could be done in the further development of a liquefied gas micro satellite thruster system. It is recommended that a “resistojet” type thruster should be tested at the University of Stellenbosch and that further testing be done with mesh in the accumulator to find the optimum amount of mesh that should be placed in the accumulator.

Thesis (MScEng)--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: The focus of this thesis is on South Africa's first micro space satellite SUNSAT, and the thermal modelling thereof. Background theory with relevance to thermal management and control of satellite systems and subsystems is presented. The mission profile and subsystem makeup of SUNSAT is also briefly discussed, with emphasis placed on the physical structure, possible orbit paths, internal heat generation, and the environmental heating. The environmental heating on the satellite surfaces from the direct and reflected earth solar radiation, as well as the earth emitted infrared radiation, is determined from the developed computer program ORBIT-FLUX. This program was used in tandem with numerical programs (developed in house), as well as an outsourced program TAS (Thermal Analysis Systems) to model SUNSAT for two possible orbit paths. The resistance-capacitance formulation method was used to develop the numerical programs, which served initially to establish the validity ofTAS. The first approximated thermal model of SUNSA T's batteries was the 7 lumped-mass model that focused on the batteries since their overheating is the suspected reason for SUNSA T'S failure to complete its mission. A numerical program as well as a similar TAS model was developed, and the results showed correlation to within 3°C. A lumped-mass model of SUNSAT was also developed, both numerically and using TAS. The models were tested and the results showed that the temperatures of the models were sensitive to changes in internal heating as well as varying emissivity and absorptivity. The numerical and TAS lumped-mass model results did not correlate well, possibly due to the higher number of control volumes used in the TAS lumped-mass model. The TAS SUNSAT 2 model was developed as advancement on the lumped-mass model. The higher number of control volumes and the effect of adding solar panels gave a more realistic model of SUNSA T. The results did not show good correlation with actual SUNSA T temperature data possibly due to the fact that the solar panels were not mounted on the model body as they were on SUNSA T; but the TAS SUNSA T 2 model did set the platform for the more advanced TAS SUNSAT 3 model. This thermal model included the effects of the solar panel mountings, and had a higher number of control volumes, which gave a better physical representation of the SUNSAT subsystems. The model was tested for possible orbit paths of SUNSA T. The results showed excellent correlation to actual SUNSA T data. For the comparison of the TAS SUNSA T 3 model results with data from SUNSAT for July 1999 showed that the SUNSA T battery temperature was modelled to within 8°C. And for June 2000, this same comparison was to within 1°C. A thermal management and control case study was done on a simple system (which included a cubic box and an internal solid block with heat generation) to illustrate the effects of using various passive and active thermal control hardware to regulate temperatures. The results showed that internal surfaces painted black provide for maximum heat sharing, and lowest block temperatures. The block temperatures were found to be very sensitive to changes in the cube external optical surface properties. A slight increase in emissivity lowered the block temperature, while a slight increase in absorptivity increased the block temperature. Heat pipes were also found to lower the temperatures of the block and immediate subsystems by providing a path of low thermal resistance to the flow of heat from the block directly to the radiator. The effect of thermal insulation was also investigated. For the two materials (rubber and plastic) that were tested, it was noticed that although insulation material does give more thermal control and predictability over a subsystem by thermally isolating it from its environment, it can cause a subsystem that has heat generation to become too hot. Recommendations were made relating to future micro satellite thermal management and control with regard to; thermal modelling techniques, acquisition of tried software, positioning of temperature sensors for optimisation of thermal data, and the verification of optical surface properties by physical measurement. / AFRIKAANSE OPSOMMING: Hierdie tesis fokus op Suid-Afrika se eerste mikro ruimte satelliet, SUNSAT, en die termiese ontwikkeling daarvan. Agtergrond teorie met betrekking tot die termiese bestuur en kontrole van die satelliet-sisteme en subsisteme word aangebied. Die missie-profiel en die samestelling van die subsisteme word ook kortliks bespreek met die klem op die fisiese strukture, moontlike wentelbane, interne hitte-opwekking, en die omgewingsverhitting. Die omgewingsverhitting op die oppervlaktes van die satelliet, veroorsaak deur direkte en weerkaatste aardlson bestraling, sowel as deur infrarooi bestraling afkomstig van die aarde, word bepaal deur die ontwikkelde rekenaarprogram ORBIT-FLUX. Hierdie program word gebruik in tandem met numeriese programme (intern ontwikkel), so weI as 'n uitgekontrakteerde program TAS (Termiese Analiese Sisteme) om SUNS AT vir twee moontlike wentelbane te modelleer. Die weerstandskapasitansie formuleringsmetode is gebruik om die numeriese programme te ontwikkel. Hierdie programme is oorspronklik gebruik om die validiteit van TAS vas te stel. Die eerste benaderde termiese model van SUNSAT se batterye was die 7 gekonsentreerdemassa model wat gefokus het op die batterye aangesien daar vermoed is dat oorverhitting van die batterye die rede is waarom SUNSAT nie sy missie voltooi het nie. 'n Numeriese program so weI as 'n gelyksoortige TAS model is ontwikkel en die resultate korreleer tot binne 3°C. 'n Gekonsentreerde-massa model van SUNSA T is ook ontwikkel, numeries en met gebruik van TAS. Die modelle is getoets en die resultate toon dat die temperature van die modelle gevoelig is vir veranderinge in interne hitte sowel as vir wissellende uitstralingsvermoe en absorpsievermoe, Die numeriese- en die TAS gekonsentreerde-massa model resultate het nie goed met mekaar korrelleer nie, moontlik weens die hoe aantal kontrole volumes wat in die TAS gekonsentreerde-massa model gebruik is. Die TAS SUNSA T 2 model is 'n verdere ontwikkeling van die gekonsentreerde-massa model. Die hoer aantal kontrole volumes en die byvoeging van solarpanele het tot gevolg gehad dat hierdie 'n meer realistiese model van SUNSA T is. Die resultate het nie goed gekorrelleer met die temperatuurdata van die werklike SUNSAT nie, moontlik weens die feit dat die solarpanele nie op die bakwerk monteer is, soos in die geval van SUNSA T nie. Nietemin het het die TAS SUNSAT 2 model gelei tot die meer gevorderde TAS SUNSAT 3 model. Hierdie termiese model het die solarpaneel montuur ingesluit en het 'n hoer aantal kontrole volumes gehad, wat 'n beter fisiese weergawe van die SUNSAT subsisteme tot gevolg gehad het. Die model is getoets vir moontlike wentelbane van SUNSAT. Die resultate het 'n hoe korrellasie getoon met die data van die werklike SUNSAT. 'n Vergelyking van die TAS SUNSAT 3 model resultate met data van SUNSAT vir Julie 1999 wys dat die SUNSAT battery temperatuur dieselfde is tot binne 8°C. Vergelyk met die resultate vir Junie 2000 was dit binne 1°C. 'n Termiese bestuurs- en kontrolestudie is gedoen op 'n eenvoudige sisteem (insluitende 'n kubieke boks en 'n interne soliede blok met hitte opwekking) om die uitwerking van die gebruik van passiewe en aktiewe termiese kontrole hardeware wat temperature reguleer, te illustreer. Die resultate toon dat interne oppervlaktes wat swart geverf is, lei tot die maksimum hitte-deling, en die laagste bloktemperature. Daar is gevind dat bloktemperature baie gevoelig is vir veranderinge in die eienskappe van die kubus se eksterne optiese oppervlaktes. 'n Effense vermedering van uitstralingsvermoe verlaag die bloktemperatuur, terwyl 'n effense vermedering van absorpsievermoe die bloktemperatuur verhoog. Daar is ook gevind dat hittepype die temperatuur van die blok en onmiddelike subsisteme verlaag deur om 'n pad van lae termiese weerstand teen die vloei van hitte vanaf die blok, direk na die verkoeler te verskaf. Die uitwerking van termiese isolasie is ook ondersoek. In die geval van die twee materiale (rubber en plastiek) wat getoets is, is daar opgemerk dat, alhoewel isolasie materiaal meer termiese beheer oor die subsisteem en voorspelbaarheid tot gevolg gehad het deurdat die subsisteem termies van die omgewing isoleer is, kan dit veroorsaak dat die subsisteem te warm word. Aanbevelings is gemaak met betrekking tot toekomstige mikro satelliet bestuur en kontrole en wel in verband met die volgende: termiese modelleringstegnieke, die aanskaffing van getoetste sagteware, die plasing van temperatuut sensors vir die beste termiese data, en die verifikasie van die eienskappe van optiese oppervlaktes deur fisiese meting.

Thesis (MScIng)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: The purpose of this study was to develop a Global Positioning System (GPS) receiver for use on a Low-Earth Orbit (LEO) satellite. The study includes an examination of some of the fundamental GPS theory and how the LEO environment affects the operation of a GPS receiver. The hardware and software that was selected for the implementation are discussed. The reasons for porting the software to a new hardware platform and methods employed in the port are given. Thereafter the process of adapting the receiver software for use in space is given. To verify the operation in space, the receiver was subjected to LEO simulations using a GPS signal simulator. These results are shown and discussed. The tests indicated that the adaptations were successful and that the receiver will function on a LEO satellite. / AFRIKAANSE OPSOMMING: Die doel van die tesis was om ’n Globale Posisionerings Stelsel (GPS) ontvanger to ontwikkel vir gebruik op ’n lae-wentelbaan satelliet. Die studie begin met fundamentele GPS teorie en hoe die funksionering van die ontvanger be¨ınvloed word deur die wentelbaan van ’n satelliet. Die hardeware en sagteware vir die implementasie word bespreek. Die rede en metodes om die sagteware aan te pas om te werk op nuwe hardeware word gegee. Daarna word die proses om die sagteware aan te pas vir ruimtegebruik gegee. Om the verifieer dat die ontvanger wel sal kan werk op ’n satelliet was dit getoets in ’n gesimuleerde ruimte-omgewing met ’n GPS seinsimulator. Hierdie resultate word gegee en bespreek. Die toetse het gewys dat die aanpassings suksesvol was en dat die ontvanger in die ruimte sal funksioneer.

Thesis (MScIng)--University of Stellenbosch, 2007. / ENGLISH ABSTRACT: Keywords: digital signal processing, OSI layer, network protocols, embedded systems, satellite technology This thesis describes the design and implementation of a rural e-mail system for the Sumbandila satellite. The rural e-mail system was developed during a project sponsored by the Department of Communications of the South African government. The complete Open Systems Interconnect (OSI) layer structure of the protocol architecture used on the satellite hardware and software is described. The equivalent implementation of the OSI layer on the ground station hardware is given. This includes the adaptation of the soundmodem Open Source Software modem to work for the e-mail system’s OSI layer. The design of the Application Layer e-mail system is described and the implementation of this design using the Python, Korn Shell and C programming environments is also given. The procedures used to test the system for reliability and the use of a database to create detailed logs of the e-mail system is shown to have generated a reliable system that is easily maintained. A critical evaluation of the system is provided in the last chapter. / AFRIKAANSE OPSOMMING: Sleutelwoorde: Syferseinverwerking, OSI-lae, netwerkprotokolle, toegewyde stelsels, satelliettegnologie Hierdie tesis beskryf die ontwerp en implementering van ’n plattelandse e-posstelsel vir die Sumbandila satelliet. Die plattelandse e-posstelsel is ontwikkel in opdrag van die Departement van Kommunikasie van die Suid-Afrikaanse regering. Die volledige Open Systems Interconnect (OSI) laagstruktuur van die protokol-argitektuur wat in die satelliet se apparatuur en programmatuur gebruik is, word beskryf. Die ekwivalente implementering van die OSI-laag op die grondstasie-apparatuur word gegee, insluitende die aanpassing van soundmodem, ’n oopbronkode sagteware-modem. Hierdie sagteware-modem word gebruik in die e-posstelsel se fisiese laag. Die ontwerp van die toepassingslaag van die e-posstelsel word beskryf, asook die implementering van hierdie ontwerp met behulp van Python, die Korninterpreteerder en C. Die prosedures waarvolgens stelselbetroubaarheid getoets is, en die gebruik van ’n databasis om noukeurige joernale van e-postransaksies te hou, demonstreer dat ’n betroubare, onderhoubare stelsel gemplementeer is. In die laaste hoofstuk word die stelsel krities geevalueer.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2006. / A low earth orbit satellite is to provide the telecommunications link to facilitate email services to rural areas, where the infrastructure necessary for e-mail is lacking (e.g. no telephone lines). Communication time with this satellite from any particular point on the ground is less than one hour per day. It is thus of utmost importance to maximise the data throughput rate for the system. The contribution of this thesis is to improve the performance of CSMA/CA by adapting and optimising it for the above application. This improved protocol is used to regulate data flow through the system. Specific attention is given to the comparison of various random variable distributions for use as the back-off random variable. Two pieces of software are further contributed. First, a set of MATLAB scripts which are used for comparing various back-off random variable distributions and optimising each of these distributions. Secondly, an extensive (more than 2500 lines of code) OMNeT++ simulation of the improved CSMA/CA protocol, complete with MATLAB scripts for setting up multiple simulation runs and plotting the results. Both pieces of software accept the system constraints as parameters, and are thus easily adaptable for a similar system which may use the same protocol, but has different parameters. It is concluded that the set of MATLAB scripts are a fairly accurate tool for optimising throughput, as is confirmed by the OMNeT++ simulations, and that OMNeT++ has merit for simulating the given type of system and protocol.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2007. / During an imaging pass of a remote sensing satellite, the satellite’s attitude has to be controlled so that the imager bore-sight sweeps out equal distances over time and so that images with a square aspect ratio are produced. The satellite attitude control system uses forward motion compensation (FMC) and time delay and integration (TDI) techniques to increase the quality of images. The motion of the scene relative to the satellite camera can be described by a two dimensional translation motion and a rotation about the camera bore-sight. This thesis describes an algorithm for measuring ground motion from viewfinder video data that can aid the satellite control system during imaging missions. The algorithm makes use of existing motion-from-video techniques – it operates in a hierarchical, feature-tracking framework. Features are identified on camera frames, and correspondences on consecutive frames are found by the Lucas and Kanade algorithm. A pyramidal image representation enables the estimation of large motions. The resultant sparse disparity map is used to estimate the three motion parameters, using a least squares fit to the projected motion equations. The algorithm was developed and implemented as part of the MSMI project. Results of tests carried out on simulated satellite viewfinder data (using the Matrix Sensor camera that was also developed for the MSMI project) confirms that the requirements are met.

Thesis (MEng (Electrical and Electronic Engineering))--University of Stellenbosch, 1995. / 189 leaves single sided printed, preliminary pages and numbered pages 1-126. Includes bibliography, list of appendixes, figures, notation and symbols. Digitized at 300 dpi (OCR), using a Bizhub 250 Scanner. / ENGLISH ABSTRACT: The Sunsat microsatellite is being developed at the University of Stellenbosch. It is equipped with a high resolution earth imager which requires a sophisticated attitude determination and control system. Precise control of the satellite is impossible without high precision attitude sensors. The most accurate attitude sensor presently used by satellites is the star sensor. The aim 'of this thesis is to develop a low cost, high precision star sensor for the Sunsat microsatellite. The development included the selection of electronic and optical hardware followed by the design, construction and testing of the sensor. Software algorithms were developed and programmed to control the imager, extract stars from images and match the observed constellations to a star catalogue. A set of matching observed and reference vectors are passed to the attitude determination and control system which calculates the three axis orientation of the satellite. / AFRIKAANSE OPSOMMING: Die Sunsat mikrosatelliet word tans by die Universiteit van Stellenbosch ontwikkel. Dit is toegerus met 'n hoeresolusie aardwaarnemingskamera en vereis 'n gevorderde orientasiebepaling-en beheerstelsel. Presiese beheer is onmoontlik sonder akkurate sensore. 'n Stersensor is die mees akkurate tipe sensor waarmee satelliete tans toegerus word. Die doelwit van hierdie tesis is die ontwikkeling van 'n hoe resolusie, laekoste stersensor vir die Sunsat mikrosatelliet. Die ontwikkeling behels die seleksie van elektroniese en optiese apparatuur wat gevolg is deur die ontwerp, opbou en toets van die sensor. Programmatuur algoritrnes is ontwerp om die kamera te beheer, sterre in fotos te herken en waargenome konstellasies in die sterkatalogus te vind. 'n Stel waargenome en verwysingsvektore stel die orientasiebepaling-en beheerstelsel in staat om die orientasie van die satelliet te bereken.

This research was conducted to determine the effectiveness of using commercial satellite data to detect covert nuclear weapons programs. Seven-band Landsat Thematic Mapper data covering the Pahute Mesa (an area within the United States Nevada Nuclear Testing Site), acquired on October 16, 1985, were analyzed to determine if underground nuclear test sites were spectrally distinguishable from the surrounding area. The analysis consisted of four steps: (1) analyzing the raw data, (2) manipulating the raw data through contrast stretching, filter application, matrix algebra, and principal components analyses, (3) identifying parameters that affect classification of underground nuclear tests and (4) selectively limiting parameters. The results of limiting parameters showed that a supervised classification of a signature created with a five-original-pixel seed of one representative, known test site provided an accurate classification of most known test sites. To further eliminate erroneous classification of roads and other areas of similar reflectance, these areas were seeded to create a second signature. This signature, whose spectral responses were different, was then used in a simultaneous classification. This classification further eliminated erroneous classification of non-test site areas, demonstrating that commercial satellite digital data can aid in the detection of covert nuclear weapons programs, in this case, underground nuclear testing. An application of the classification scheme used is proposed to confront a scenario in which a country seeks additional verification of another party's proposed violation of test ban treaties. / Department of Physics and Astronomy

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