Thesis (MScEng)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: The Linux operating system and shared Ethernet are alternative technologies with the potential to reduce both the development time and costs of satellites as well as the supporting infrastructure. Modular satellites, ground stations and rapid proto typing testbeds also have a common requirement for distributed real-time computation. The identified technologies were investigated to determine whether this requirement could also be met. Various real-time extensions and modifications are currently available for the Linux operating system. A suitable open source real-time extension called Real-Time Application Interface (RTAI) was selected for the implementation of an experimental distributed real-time system. Experimental results showed that the RTAI operating system could deliver deterministic realtime performance, but only in the absence of non-real-time load. Shared Ethernet is currently the most popular and widely used commercial networking technology. However, Ethernet wasn't developed to provide real-time performance. Several methods have been proposed in literature to modify Ethernet for real-time communications. A token passing protocol was found to be an effective and least intrusive solution. The Real-Time Token (RTToken) protocol was designed to guarantee predictable network access to communicating real-time tasks. The protocol passes a token between nodes in a predetermined order and nodes are assigned fixed token holding times. Experimental results proved that the protocol offered predictable network access with bounded jitter. An experimental distributed real-time system was implemented, which included the extension of the RTAI operating system with the RTToken protocol, as a loadable kernel module. Real-time tasks communicated using connectionless Internet protocols. The Real-Time networking (RTnet) subsystem of RTAI supported these protocols. Under collision-free conditions consistent transmission delays with bounded jitter was measured. The integrated RTToken protocol provided guaranteed and bounded network access to communicating real-time tasks, with limit overheads. Tests exhibited errors in some of the RTAI functionality. Overall the investigated technologies showed promise in being able to meet the distributed real-time requirements of various applications, including those found in the satellite environment. / AFRIKAANSE OPSOMMING: Die Linux bedryfstelsel en gedeelde Ethernet is geïdentifiseer as potensiële tegnologieë vir satelliet bedryf wat besparings in koste en vinniger ontwikkeling te weeg kan bring. Modulêr ontwerpte satelliete, grondstasies en ontwikkeling platforms het 'n gemeenskaplike behoefte vir verspreide intydse verwerking. Verskillende tegnologieë is ondersoek om te bepaal of aan die vereiste ook voldoen kan word. Verskeie intydse uitbreidings en modifikasies is huidiglik beskikbaar vir die Linux bedryfstelsel. Die "Real-Time Application Interface" (RTAI) bedryfstelsel is geïdentifiseer as 'n geskikte intydse uitbreiding vir die implementering van 'n eksperimentele verspreide intydse stelsel. Eksperimentele resultate het getoon dat die RTAI bedryfstelsel deterministies en intyds kan opereer, maar dan moet dit geskied in die afwesigheid van 'n nie-intydse verwerkingslas. Gedeelde Ethernet is 'n kommersiële network tegnologie wat tans algemeen beskikbaar is. Die tegnologie is egter nie ontwerp vir intydse uitvoering nie. Verskeie metodes is in die literatuur voorgestelom Ethernet te modifiseer vir intydse kommunikasie. Hierdie ondersoek het getoon dat 'n teken-aangee protokol die mees effektiewe oplossing is en waarvan die implementering min inbreuk maak. Die "Real-Time Token" (RTToken) protokol is ontwerp om voorspelbare netwerk toegang tot kommunikerende intydse take te verseker. Die protokol stuur 'n teken tussen nodusse in 'n voorafbepaalde volgorde. Nodusse word ook vaste teken hou-tye geallokeer. Eksperimentele resultate het aangedui dat die protokol deterministiese netwerk toegang kan verseker met begrensde variasies. 'n Eksperimentele verspreide intydse stelsel is geïmplementeer. Dit het ingesluit die uitbreiding van die RTAI bedryfstelsel met die RTToken protokol; verpak as 'n laaibare bedryfstelsel module. Intydse take kan kommunikeer met verbindinglose protokolle wat deur die "Real-Time networking" (RTnet) substelsel van RTAI ondersteun word. Onder ideale toestande is konstante transmissie vertragings met begrensde variasies gemeet. Die integrasie van die RTToken protokol het botsinglose netwerk toegang aan kommunikerende take verseker, met beperkte oorhoofse koste as teenprestasie. Eksperimente het enkele foute in die funksionaliteit van RTAI uitgewys. In die algemeen het die voorgestelde tegnologieë getoon dat dit potensiaal het vir verskeie verspreide intydse toepassings in toekomstige satelliet en ook ander omgewings.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: Keywords: digital signal processing, embedded systems, telecommunications, satellite technology. The rapid growth of the telecommunications industry is a worldwide phenomenon with people and computers generating and transmitting more and more information daily. Despite this growth, there are still areas in South Africa which lack terrestrial communications coverage. People inhabit these rural areas and their essential communication needs are not met. Satellite based communication coverage can provide a valuable service in these circumstances. In this thesis, the design of a satellite-based communications payload which makes use of software de ned radio techniques is presented in terms of the Open Systems Interconnect layer structure. A robust hardware platform using a space-quali ed on-board computer, a Xilinx Virtex-5 Field Programmable Gate Array (FPGA) and a Freescale digital signal processor (DSP) is designed, implemented and thoroughly tested. A device driver is designed for hardware and rmware components. A prototype ground station is also designed and constructed using a low-power PC, a Xilinx Spartan-3E FPGA, a Freescale DSP and radio frequency hardware. A wide range of testing methodologies were successfully utilised to deploy a functional system which is critically evaluated in the last chapter. / AFRIKAANSE OPSOMMING: Sleutelwoorde: syferseinverwerking, toegewyde stelsels, telekommunikasie, satelliettegnologie. Die vinnig groeiende telekommunikasieindustrie is 'n wêreldwye verskynsel waarin mense en rekenaars daagliks meer en meer data genereer. Ten spyte van die groei, is daar nog steeds gebiede in Suid-Afrika wat aan 'n gebrek van aardse kommunikasiedekking lei. Mense bewoon dié areas maar daar word nie aan hul noodsaaklike kommunikasiebehoeftes voldoen nie. Satelliet-gebaseerde kommunikasiedekking kan 'n waardevolle diens in hierdie omstandighede wees. Hierdie tesis beskryf die ontwerp van 'n ruimtegebaseerde kommunikasieloonvrag wat gebruik maak van sagteware-gede nieerde radiotegnieke aangebied in terme van die Open Systems Interconnect laagstruktuur. 'n Robuuste apparatuurplatform wat gebruik maak van 'n ruimte-gekwali seerde rekenaar, 'n Xilinx Virtex-5 Veldprogrameerbare Hek-Skikking (VPHS) en 'n Freescale syferseinverwerker is ontwerp, geïmplementeer en deeglik getoets. 'n Toestelbestuurder moes ontwerp word vir die apparatuur- en fermatuur-komponente. 'n Prototipe grondstasie is ook ontwerp en gebou met behulp van' n lae-krag PC, 'n Xilinx Spartan-3E VPHS, 'n Freescale seinverwerker en radiofrekwensie apparatuur. 'n Wye verskeidenheid van toetsmetodes is suksesvol benut om 'n funksionele stelsel te ontwikkel wat krities geëvalueer word in die laaste hoofstuk.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: This thesis forms part of the Control Surfaces in Confined Spaces (CoSICS) project conducted at Stellenbosch University. The aim of this project is reduction of control surface actuator footprints on the existing wing structures of commercial airliners such as the Airbus A320 and A330. This is achieved by reducing control surface hinge moments through the application of trailing edge tabs. This results in smaller actuator requirements. The first tier of the project focussed on the geometric optimisation of the tab applied to an aileron. This thesis focusses on the development of dynamic control of the aileron through either tab-only or concurrent tab and aileron actuation. In the effort to develop dynamic control, a fully coupled generalised dynamic model of the tab and aileron is derived and presented. Through linearisation of this model, linear controllers are developed. Two distinctly different controllers are presented; the first controller makes use of classical methods for control of the tab-only actuated aileron and the second controller makes use of modern control techniques such as full state feedback to facilitate controlled concurrent tab and aileron actuation. Each proposed controller is evaluated in terms of dynamic performance, robustness, disturbance rejection and noise immunity. Based on the controller development, a summary of dynamic actuator requirements is given. Practical verification of the model and the controller performance is then undertaken. The development of the necessary hardware and software is also presented. The concept of aileron control through tab-only actuation and concurrent tab and aileron actuation is then validated. Conclusion are then drawn about the accuracy of the theoretical model and the practical performance of the controllers. The thesis is concluded with recommendations for future work to increase the fidelity of the model. Important aspects about the practical implementation of the concept on commercial jetliners are also summarised. / AFRIKAANSE OPSOMMING: Hierdie tesis is deel van die Control Surfaces in Confined Spaces1 projek by Stellenbosch Universiteit. Die doel van hierdie projek behels die verkleining van die aktueerder spasie en ondersteunings struktuur vereistes, op die bestaande vlerk struktuur van kommersiële vliegtuie soos die Airbus A320 en Airbus A330. Dit is bereik deur die vermindering van die beheeroppervlak skarnier se draaimoment met behulp van aerodinamiese hulpvlakke. Kleiner aktueerders word dus benodig. Die eerste stadium van die projek fokus op die geometriese optimisering van die hulpvlak op ’n aileron. Hierdie tesis fokus op die ontwikkeling van dinamiese beheer van die aileron deur middel van hulpvlak aktueering alleenlik of met die gelyktydige aktueering van die hulpvlak en aileron. In die proses van onwikkeling is ’n volgekoppelde veralgemeende dinamiese model van die hulpvlak en aileron afgelei en voorgelê. Deur middel van linearisasie van die model is linieêre beheerders ontwikkel. Tans is twee verskillende beheerders ontwikkel. Die eerste beheerder is gebaseer op die klassieke metodes en maak staat op die aktueering van die hulpvlak alleenlik. Die tweede beheerder maak gebruik van moderne beheer tegnieke soos vol toestand terugvoer om gelyktydige hulpvlak en aileron aktueering te realiseer. Die beheerders is elk geëvalueer in terme van dinamiese gedrag, robuustheid, versteurings verwerping en ruis verwerping. Die beheerstelsel ontwikkeling lei tot ’n opsomming van die dinamiese aktueerder vereistes. Dit word gevolg deur praktiese verifikasie van die model en die beheerstelsel gedrag. ’n Opsomming van die ontwikkeling van nodige hardeware en sagteware word voorgelê. In hierdie proses is die konsep van beide hulpvlak alleenlike aktueering en gelyktydige hulpvlak en aileron aktueering bewys. Gevolgtrekkings word gemaak oor die akkuraatheid van die model en die praktiese gedrag van die beheerders. Die tesis word afgerond met voorstelle vir toekomstige werk wat die model se betroubaarheid kan verbeter. Verder word belangrike punte oor die praktiese aspekte van konsep implementering op kommersiële vliegtuie ook uitgelig.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: Accurate water usage information is very important for municipalities in order to provide accurate billing information for high volume water users. Meter reading are currently obtained by sending a person out to every meter to obtain a manual reading. This is very costly with regards to time and money, and it is also very error prone. In order to improve on this system, an image based telemetry system was developed that can be retrofitted on currently installed bulk water meters. Images of the meter dials are captured and transmitted to a central server where they are further processed and enhanced. Character recognition is performed on the enhanced images in order to extract meter readings. Through tests it was found that characters can be recognised to 100% accuracy for cases which the character recognition software has been trained, and 70% accuracy for cases which is was not trained. Thus, an overall recognition accuracy of 85% was achieved. These results can be improved upon in future work by statistically analysing results and utilizing the inherent heuristic information from the meter dials. Overall the feasibility of the approach was demonstrated and a way forward was indicated. / AFRIKAANSE OPSOMMING: Dit is belangrik vir munisipaliteite om akkurate water verbruikingssyfers te hê sodat hulle akkurate rekeninge aan hoë volume water gebruikers kan stuur. Tans besoek ’n persoon fisies elke meter om meterlesings te verkry. Dit is egter baie oneffektief ten opsigte van tyd en geld. Die metode is ook baie geneig tot foute. Ten einde te verbeter op hierdie stelsel was ’n beeld gebaseerde telemetrie stelsel ontwerp wat geïnstalleer word op huidig geïnstalleerde hoë volume water meters. Beelde van die meters word na ’n sentrale bediener gestuur waar dit verwerk word en die beeld kwaliteit verbeter word. Karakter herkenning sagteware word gebruik om die meter lesings te verkry vanuit die verbeterde beelde. Deur middel van toetse is gevind dat karakters herken kan word tot op 100% graad van akkuraatheid in gevalle waar die karakter herkenning sagteware opgelei is, en 70% akkuraatheid vir gevalle waarvoor dit nie opgelei was nie. Dus was ’n algehele herkennings akkuraatheid van 85% behaal. Hierdie resultate kan verbeter word in die toekoms deur die resultate statisties te analiseer en die inherente heuristieke inligting van die meter syfers te benutting. Ten slotte, in die tesis was die haalbaarheid van die benadering gedemonstreer en ’n weg vorentoe vir toekomstige werk aangedui.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: Search and Rescue is an essential service provided by States and Militaries to search for, locate and rescue survivors of accidents and incidents. Civil Search and Rescue utilizes a system of well-trained professionals or volunteers, an effective Search and Rescue organization, supported by industry and other providers of infrastructure and assets. The service is rendered to save the lives of civilian individuals in imminent danger of losing their lives. Military (Combat) Search and Rescue is provided by militaries to save the lives of military practitioners in a similar predicament. In addition, Search and Rescue is performed over land and over the sea. All forms of Search and Rescue rely on capable, specialized assets for efficiency en affectivity. Assets are specified and chosen on the grounds of various factors, amongst others operating environment, operational profile, performance and special abilities. This thesis has determined the need for a Search and Rescue asset, capable of performing effective and efficient Search and Rescue over the entire national maritime Search and Rescue Region, up to the Region extremities. An analysis was performed to prove this deficit, and quantify the key performance and special equipment requirements for such an asset. An analysis was also performed which proves that an Unmanned Aircraft System should be an ideal choice to meet this need. Finally, an Unmanned Aircraft System concept was specified that could potentially meet this need. / AFRIKAANSE OPSOMMING: Soek en Redding is ‘n essentiële diens wat deur State en militêre organisasies gebied word om oorlewendes van ongelukke en insidente te soek, op te spoor en na veiligheid te bring. Siviele Soek en Redding maak gebruik van ‘n stelsel van goedopgeleide professionele persone, sowel as vrywilligers, asook ‘n effektiewe Soek en Reddingsorganisasie, ondersteun deur die industrie en ander voorsieners van infrastruktuur en toerusting. Derglike dienste word daargestel om die lewens van siviele persone, wie se lewens in gevaar is, te red. Militêre Soek en Redding word deur militêre organisasies daargetel om die lewens van militêre persone, wie in gevaar is, te red. Soek en Redding word oor land sowel as oor die see uitgevoer. Alle vorms van Soek en Redding maak staat op die beskikbaarheid van gespesialiseerde toerusting met gespesialiseerde gebruiksaanwending, vir maksimale effektiwiteit en doeltreffendheid. Toerusting word gekies op grond van verskeie faktore, onder meer die gebruiksomgewing, operasionele profiele, verlangde prestasie en spesiale vermoëns. Hierdie tesis het die behoefte aan ‘n gespesialiseerde Soek en Redding platform, wat die vermoë het om effektiewe en doeltreffende Soek en Redding uit te voer oor die hele nationale Soek en Redding Gebied, tot en met die ekstreme daarvan, vasgestel. ‘n Analise is uitgevoer om hierdie tekortkoming uit te wys, asook om die sleutel prestasie- en gespesialiseerde toerustingbehoeftes vir so ‘n platform te kwantifiseer. ‘n Verdere analise is uitgevoer om te bewys dat ‘n Onbemande Vliegtuig die beste opsie sou wees vir ‘n platform om aan hierdie behoeftes te voldoen. Ten slotte is ‘n konsep vir ‘n Onbemande Vliegtuig Stelsel voorgetsel wat potensieël hierdie behoefte sou kon vervul.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: The development of a control allocation system for use as part of a fault-tolerant control (FTC) system in unmanned aerial vehicles (UAVs) is presented. This system plays a vital role in minimising the possibility that a fault will necessitate the reconfiguration of the control, guidance or navigation systems of the aircraft by minimising the difference between the desired and achievable aircraft performance parameters. This is achieved by optimising the allocation of control effort commanded by the virtual actuators to the physical actuators present on the aircraft. A simple general six degree of freedom aircraft model is presented that contains all of the relevant terms needed to find the trim biases of the aircraft actuators and evaluate the performance of the virtual actuators. This model was used to develop a control allocation formulation that optimises the performance of the virtual actuators of the aircraft while minimising adverse effects and avoiding actuator saturation. The resulting problem formulation was formulated as a multi-objective optimisation problem which was solved using the sequential quadratic programming method. The control allocation system was practically implemented and tested. A number of failure categories of varying severity were defined and two aircraft with different levels of actuator redundancy were used to test the system. The control allocation algorithm was evaluated for each failure category, aircraft test case and for a number of differing control allocation system configurations. A number of enhancements were then made to the control allocation system which included adding frequency-based allocation and adapting the algorithm for an unconventional ducted-fan UAV. The control allocation system is shown to be applicable to a number of different conventional aircraft configurations with no alterations as well as being applicable to unconventional aircraft with minor alterations. The control allocation system is shown to be capable of handling both single and multiple actuator failures and the importance of actuator redundancy is highlighted as a factor that influences the effectiveness of control allocation. The control allocation system can be effectively used as part of a FTC system or as a tool that can be used to investigate control allocation and aircraft redundancy. / AFRIKAANSE OPSOMMING: Die ontwikkeling van ’n beheertoekenning sisteem vir gebruik as deel van ’n fout verdraagsame beheersisteem in onbemande lugvaartuie word voorgelê. Hierdie sisteem speel ’n essensiële rol in die vermindering van die moontlikheid dat ’n fout die herkonfigurasie van die beheer, bestuur of navigasiesisteme van die vaartuig tot gevolg sal hê, deur die verskil te verminder tussen die verlangde en bereikbare werkverrigtingsraamwerk van die vaartuig. Dit word bereik deur die optimisering van die toekenning van beheerpoging aangevoer deur die virtuele aktueerders na die fisiese aktueerders teenwoordig op die vaartuig. ’n Eenvoudige algemene ses grade van vryheid lugvaartuig model word voorgestel wat al die relevante terme bevat wat benodig word om die onewewigtigheid verstelling van die vaartuig se aktueerders te vind en die werksverrigting van die virtuele aktueerders te evalueer. Hierdie model is gebruik om ’n beheer toekenning formulering te ontwikkel wat die werkverrigting van die virtuele aktueerders van die vaartuig optimiseer terwyl nadelige gevolge verminder word asook aktueerder versadiging vermy word. Die gevolglike probleem formulering is omskryf as ’n multi-doel optimiserings probleem wat opgelos is deur gebruik van die sekwensiële kwadratiese programmerings metode. Die beheertoekenning sisteem is prakties geïmplementeer en getoets. ’n Aantal fout kategorieë van verskillende grade van erns is gedefinieer en twee vaartuie met verskillende vlakke van aktueerder oortolligheid is gebruik om die sisteem te toets. Die beheer toekenning algoritme is geëvalueer vir elke fout kategorie, vaartuig toetsgeval, asook vir ’n aantal verskillende beheertoekenning sisteem konfigurasies. ’n Aantal verbeterings is aangebring aan die beheertoekenning sisteem, naamlik die toevoeging van frekwensie gebaseerde toekenning en wysiging van die algoritme vir ’n onkonvensionele onbemande geleide waaier lugvaartuig. Die beheertoekenning sisteem is van toepassing op ’n aantal verskillende konvensionele vaartuig konfigurasies met geen verstellings asook van toepassing op onkonvensionele vaartuie met geringe verstellings. Die beheertoekenning sisteem kan beide enkel- en veelvoudige aktueerder tekortkominge hanteer en die belangrikheid van aktueerder oortolligheid is beklemtoon as ’n faktor wat die effektiwiteit van beheertoekenning beïnvloed. Die beheertoekenning sisteem kan effektief geïmplementeer word as deel van ’n fout verdraagsame beheersisteem of as ’n werktuig om beheertoekenning en vaartuig oortolligheid te ondersoek.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: The computational power of mobile smart-phone devices are ever increasing and high-end phones become more popular amongst consumers every day. The technical speci cations of a high-end smart-phone today rivals those of a home computer system of only a few years ago. Powerful processors, combined with cameras and ease of development encourage an increasing number of Augmented Reality (AR) researchers to adopt mobile smart-phones as AR platform. Implementation of marker-based Augmented Reality systems on mobile phones is mostly a solved problem. Markerless systems still o er challenges due to increased processing requirements. Some researchers adopt purely computer vision based markerless tracking methods to estimate camera pose on mobile devices. In this thesis we propose the use of a hybrid system that employs both computer vision and integrated sensors present in most new smartphones to facilitate pose estimation. We estimate three of the six degrees of freedom of pose using integrated sensors and estimate the remaining three using feature tracking. A proof of concept hybrid system is implemented as part of this thesis. / AFRIKAANSE OPSOMMING: Die berekeningskrag van nuwe-generasie selfone neem elke dag toe en kragtige "slim-fone" word al hoe meer populêr onder verbruikers. Die tegniese spesifikasies van 'n nuwe slim-foon vandag is vergelykbaar met die van 'n persoonlike rekenaar van slegs 'n paar jaar gelede. Die kombinasie van kragtige verwerkers, kameras en die gemaklikheid waarmee programmatuur op hierdie toestelle ontwikkel word, maak dit 'n aantreklike ontwikkelingsplatform vir navorsers in Toegevoegde Realiteit. Die implimentering van 'n merker-gebaseerde Toegevoegde Realiteitstelsel op selfone is 'n probleem wat reeds grotendeels opgelos is. Merker-vrye stelsels, aan die ander kant, bied steeds interessante uitdagings omdat hulle meer prosesseringskrag vereis. 'n Paar navorsers het reeds rekenaarvisie-gebaseerde merker-vrye stelsels aangepas om op selfone te funksioneer. In hierdie tesis stel ons die ontwikkeling voor van 'n hibriede stelsel wat gebruik maak van rekenaarvisie sowel as geintegreerde sensore in die foon om die berekening van kamera-orientasie te vergemaklik. Ons gebruik geintegreerde sensore om drie uit ses vryheidsgrade van orientasie te bereken, terwyl die oorblywende drie met behulp van rekenaarvisie-tegnieke bepaal word. 'n Prototipe stelsel is ontwikkel as deel van hierdie tesis.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: The Square Kilometre Array (SKA) is an international project to build the world’s largest and most sensitive radio telescope interferometer. It will consist of thousands of antennas distributed over many kilometers, with the hosting country being either South Africa or Australia. Various pathfinders have been initiated to demonstrate the technologies needed to implement the SKA. The astronomy community has defined five Key Science Projects (KSP), which are the drivers for the SKA. The science goals determine the technical requirements needed to design SKA systems. Many years of planning and development are still needed in order to meet to the requirements of such a large and complex project. This thesis aims to present the various SKA pathfinder systems in terms of their application to the SKA key science projects, with main focus that of pulsar observations. In order to achieve this, a thorough overview of basic radio astronomy principles and techniques is presented, followed by a detailed look at the various pathfinders. Throughout the work, aspects of pulsar observations are given particular attention with the goal of designing optimal systems for the SKA. / AFRIKAANSE OPSOMMING: Die Square Kilometre Array (SKA) is ’n internasionale projek om die wêreld se grootste en mees sensitiewe radio teleskoop interferometer te bou. Dit sal bestaan uit duisende antennas versprei oor etlike kilometers, met die gasheer land óf Suid-Afrika óf Australië. Verskeie koersbepalers is geïnisieer om die tegnologie te demonstreer wat benodig is om die SKA te implementeer. Die astronomie gemeenskap het vyf sleutel wetenskap projekte (KSP) gedefinieër wat dien as die drywers vir die SKA. Die wetenskap doelwitte bepaal die tegniese vereistes wat nodig is om SKA stelsels to ontwerp. Talle jare van beplanning en ontwikkeling word steeds benodig om te voldoen aan die vereistes van so ’n groot en komplekse projek. Hierdie tesis het ten doel die aanbieding van verskeie SKA koersbepaler stelsels in terme van hulle aanwending tot die SKA sleutel wetenskap projekte, met hoof fokus op die van pulsar waarnemings. Om dit te behaal, word ’n deeglike oorsig van basiese radio astronomie beginsels en tegnieke aangebied, gevolg deur ’n gedetailleerde kyk na die verskeie koersbepalers. Regdeur die werk word spesifieke aandag gegee aan aspekte van pulsar waarnemings met die doel om optimale stelsels vir die SKA te ontwerp.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: CubeSats are small, lightweight satellites which are often used by academic institutions due to their application potential and low cost. Because of their size and weight, less powerful attitude controllers, such as solar sails, can be used. In 2010, the Japanese satellite, Ikaros, was launched to illustrate the usage of solar sails as a propulsion system. Similarly, by exploiting the solar radiation pressure, it is possible to use a solar sail, together with three magnetorquers, to achieve 3-axis attitude control of a 3-unit CubeSat. Simulations are required to demonstrate the attitude control of a sun-synchronous, low Earth orbit CubeSat using a solar sail. To allow the adjustment of the solar sail, and its resulting torque, a mechanical structure is required which can be used to position the sail within two orthogonal axes. Although the magnetorquers and solar sail are sufficient to achieve 3-axis attitude control, the addition of a reaction wheel can be implemented in an attempt to improve this control. / AFRIKAANSE OPSOMMING: CubeSats is klein, ligte satelliete wat dikwels deur universiteite gebruik word weens hul lae koste en groot toepassings potensiaal. As gevolg van hulle gewig en grootte, kan minder kragtige posisie beheerders, soos byvoorbeeld sonseile, gebruik word. Die Japannese satelliet, Ikaros, was in 2010 gelanseer om die gebruik van ’n sonseil as aandrywingstelsel te illustreer. Net so is dit moontlik om die bestraling van die son te gebruik, met behulp van ’n sonseil, en drie magneetstange om 3-as posisiebeheer op ’n 3-eenheid CubeSat te bekom. Simulasies word benodig om die posisie beheer van ’n sonsinkrone, lae-aard wentelbaan CubeSat met ’n sonseil te demonstreer. ’n Meganiese struktuur word benodig vir die posisionering van die sonseil in twee ortogonale asse sodat die sonseil, en dus die geassosieerde draaimoment, verskuif kan word. Alhoewel die magneetstange en sonseil voldoende is om 3-as posisiebeheer te bekom, kan ’n reaksiewiel bygevoeg word om hierdie beheer te probeer verbeter.

Thesis (MScEng)-- Stellenbosch University, 2012. / ENGLISH ABSTRACT: This thesis presents the analysis, design, simulation and practical implementation of a control system to achieve an accurate autonomous landing of a fixed-wing unmanned aerial vehicle in the presence of wind gust atmospheric disturbances. Controllers which incorporate the concept of direct-lift control were designed based on a study of the longitudinal dynamics of the UAV constructed as a testbed. Direct-lift control offers the prospect of an improvement in the precision with which aircraft height and vertical velocity can be controlled by utilising actuators which generate lift directly, instead of the conventional method whereby the moment produced by an actuator results in lift being indirectly generated. Two normal specific acceleration controllers were designed. The first being a conventional moment-based controller, and the second a direct-lift-augmented controller. The moment-based controller makes use of the aircraft’s elevator while the direct-lift augmented controller in addition makes use of the flaps of the aircraft which serve as the direct-lift actuator. Controllers were also designed to regulate the airspeed, altitude, climb rate, and roll angle of the aircraft as well as damp the Dutch roll mode. A guidance controller was implemented to allow for the following of waypoints. A landing procedure and methodology was developed which includes the circuit and landing approach paths and the concept of a glide path offset to calibrate the touchdown point of a landing. All controllers and the landing procedure were tested in a hardware-in-the-loop simulation environment as well as practically in a series of flight tests. Five fully autonomous landings were performed, three of these using the conventional NSA controller, and the final two the direct-lift-augmented NSA controller. The results obtained during the landing flight tests show that the project goal of a landing within five meters along the runway and three meters across the runway was achieved in both normal wind conditions as well as in conditions where wind gusts prevailed. The flight tests also showed that the direct-lift-augmented NSA controller appears to achieve a more accurate landing than the conventional NSA controller, especially in the presence of greater wind disturbances. The direct-lift augmented NSA controller also exhibited less pitch angle rotation during landing. / AFRIKAANSE OPSOMMING: Hierdie tesis verteenwoordig die analise, ontwerp, simulasie en praktiese implementering van ’n beheerstelsel wat ten doel het om ’n akkurate en outonome landing van ’n onbemande vastevlerk vliegtuig in rukwind atmosferiese toestande te bewerkstellig. Gegrond op ’n studie van die longitudinale dinamika van die vliegtuig wat as proeftuig gebruik is, is beheerders ontwerp wat die beginsel van direkte-lig insluit. Direkte-lig beheer hou die potensiaal in om die vliegtuig se hoogte en vertikale snelheid akkuraat te beheer deur gebruik te maak van aktueerders wat lig direk genereer in teenstelling met die konvensionele metode waar die moment van die aktueerder indirek lig genereer. Twee normaal-versnellings beheerders is ontwerp. Die eerste is ’n konvensionele moment-gebaseerde beheerder wat gebruik maak van die hys-aktueerder van die vliegtuig, en die tweede is ’n direkte-lig-bygestaande beheerder wat addisioneel gebruik maak van die flappe van die vliegtuig wat as die direkte-lig aktueerder dien. Vedere beheerders is ontwerp wat die lugspoed, hoogte, klimkoers, en rolhoek van die vliegtuig reguleer asook die “Dutch roll” gedrag afklam. ’n Leiding-beheerder wat die volg van vliegbakens hanteer, is ingestel. Die landingsprosedure en -metodologie is ontwikkel wat die landingspad sowel as die sweef-pad bepaal en wat terselfdertyd ’n metode daarstel om die posisie van die landingspunt te kalibreer. Die beheerders en landingsprosedure is in ’n hardeware-in-die-lus omgewing gesimuleer en deur middel van ’n reeks proefvlugte getoets. Vyf ten volle outonome landings is uitgevoer waarvan drie van die konvensionele normaal-versnellings beheerder gebruik gemaak het, en die laaste twee die direkte-lig-bygestaande normaal-versnellings beheerder. Die vlugtoetsuitslae bevestig dat die navorsingsdoel om ’n landing binne vyf meter in lyn met en drie meter dwarsoor die landingstrook te bewerkstellig, behaal is. Hierdie akkuraatheid is verkry in beide goeie atmosferiese toestande sowel as toestande met rukwinde. Volgens die vlugtoetse blyk dit dat die direkte-lig-bygestaande normaalversnellings beheerder ’n meer akkurate landing kan bewerkstellig as die konvensionele normaal-versnellings beheerder, veral dan in toestande met rukwinde. Die direkte-ligbygestaande normaal-versnellings beheerder het ook ’n laer hei-hoek rotasie tydens die landing vertoon.