Thesis (MScEng)--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: The purpose of this thesis was to design and test the interfaces of sensors and actuators. In the complete Attitude Determination and Control System CADCS) the Interface Control Processor (ICP) must be interfaced to various sensors and torquers. The testing of interfaces involves the simulation of sensors and actuators and also two of the Attitude Control Processor's functions, i.e. sending actuator commands and receiving sensor data. The tested interfaces are for two actuators and three sensors. Both analog and digital sensors and actuators are interfaced i.e. reaction wheels, magnetorquers, magnetometer and horizon /fine sun sensor. The simulated sensors and actuators are to be employed on three axis controlled, low earth o~biting micro-satellites. To test the interfaces, a test circuit was developed and the design is presented. Finally the software to facilitate the testing was developed and is also presented with the analysis based on protocol implementation and data rates. / AFRIKAANSE OPSOMMING: Die doel van hierdie tesis was om sensor en aktueerder koppelvlakke te ontwerp en te toets. In die volledige Attitude Determination and Control System CADCS) moet die Interface Control Processor CICP) aan verskeie sensore en torquers gekoppel word. Die toets van koppelvlakke behels die simulasie van sensore en aktueerders en ook twee van die Attitude Control Processor (ACP) se funksies, naamlik die stuur van aktueerder bevele en die ontvang van sensor data. Die koppelvlakke vir twee aktueerders en drie sen sore is getoets. Beide analoog en digitale sensore en aktueerders is gekoppel, naamlik die reaksiewiele, magneetspoele, magnetometer en horison I fyn son sensor. Die gesimuleerde sensore en aktueerders sal gebruik word op drie-as beheerde, lae aardbaan mikrosatelliete. Om die koppelvlakke te toets is 'n stroombaan ontwikkel waarvan die ontwerp hier aangebied word. Sagteware om die toetse te fasiliteer is ontwikkel en word ook hier aangebied tesame met . analises gebaseer op protokol implementering en data tempo's.

Geosynchronous communications satellites provide a wide variety of services. They carry wideband signals, such as television, and narrowband signals, such as business data networks. This paper describes a signal recognition system for the narrowband signals found on Ku-band satellites. Using readily available equipment, it saves observed signals which are later processed into an observation report. Observed signals are labeled using a decision tree, which is a pattern recognition technique. Each observation report also includes center frequency, bandwidth, and carrier-to-noise ratio. This paper presents the design and implementation of the signal recognition system. Results from the system are included. / Master of Science

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2007. / The aim of this project was to design and test a partial attitude determination and control system for a nanosatellite. The reaction wheel system was designed and tested as an actuator for the nanosatellite. This reaction wheel system consists of four reaction wheels mounted in a tetrahedral formation. A rate sensor system was also designed and its viability for this space application was examined. The rate sensor system consists of 3 orthogonally mounted planes, each with three rate sensors mounted on it. Hardware-inthe- loop tests were used along with an air bearing experimentational setup, which created near frictionless circumstances, to prove the effectiveness of the designed reaction wheel setup. The results following from this project were the following: The reaction wheel system proved to be an adequate actuator for this nanosatellite application and the rate sensor systemwhich was analysed proved to be inadequate for a nanosatellite application.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2005. / In this thesis, the maneuvering and orientation of an inspection/service satellite is investigated. This thesis will demonstrate a simplified satellite maneuver around another satellite (for docking purposes). This is illustrated with a cart on an air bearing table (frictionless environment) which simplifies the problem to two dimensions. A mathematical model of the system was designed and simulated (Matlab) for this maneuver. With the simulation, different strategies were considered to maneuver the cart in a circle around another object. The conclusion was made that approximating the circle with segments would conserve propellant. This strategy was implemented on the air bearing table.

Thesis (MscEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: The Cape Peninsula University of Technology, in collaboration with Stellenbosch University, is developing a 3-unit CubeSat for a low earth polar orbit. The two main payloads are a camera and a radio frequency beacon. This beacon will be used to calibrate the radar antenna patterns of an antenna of the Hermanus Magnetic Observatory at their base in Antarctica. This thesis describes the development of an aerodynamic attitude determination and control system needed to achieve three-axis stabilisation of the satellite and to perform accurate pointing of the camera. The satellite structure is designed to utilise aerodynamic means of control. It includes four feather antennae for passive pitch-yaw stabilisation and two active aerodynamic roll control paddles. The sensors used are a three-axis magnetometer, ne sun sensor and nadir sensor. Three attitude determination methods are investigated, namely the Triad, Rate Kalman Filter and Extended Kalman Filter algorithm. Apart from the aerodynamic control elements of the satellite, three magnetic torque rods and three nano-reaction wheels are also included in the design. Three control modes for the satellite are identi ed and various control methods are investigated for these control modes. The various attitude determination and control methods are evaluated through simulations and the results are compared to determine the nal methods to be used by the satellite. The magnetic Rate Kalman Filter is chosen as attitude determination method to be used when the satellite is tumbling and a combination of the sun Rate Kalman Filter and the Triad algorithm is to be used when the satellite experiences low angular rates. The B-dot and Y-spin controller is chosen for the detumbling control mode, the aerodynamic and cross-product control method for the three-axis stabilisation control mode and the quaternion feedback control method for the pointing control mode of the satellite. The combination of magnetic and aerodynamic control proved to be su cient for the initial stabilisation of the satellite, but the three nano-reaction wheels are required for the pointing control of the imaging process. / AFRIKAANSE OPSOMMING: Die Kaapse Skiereiland Universiteit van Tegnologie, in samewerking met die Universiteit van Stellenbosch, is tans besig met die ontwikkeling van 'n 3-eenheid CubeSat vir 'n pol^ere, lae aard-wentelbaan. Die twee loonvragte van die satelliet bestaan uit 'n kamera en 'n radiofrekwensie-baken. Die radiofrekwensie-baken sal gebruik word om 'n antenna van die Hermanus Magnetiese Observatorium, by hul basis in Antarktika, se radar antenna patrone te kalibreer. Hierdie tesis beskryf die ontwikkeling van 'n aerodinamiese ori entasiebepaling en -beheerstelsel wat benodig word om die satelliet in drie asse te stabiliseer en om die kamera noukeurig te rig. Die satelliet se struktuur word ontwerp vir aerodinamiese beheer. Dit sluit vier veerantennas in vir passiewe duik-gier beheer, asook twee aerodynamiese rolbeheer appies vir aktiewe beheer. Die sensors wat gebruik word sluit 'n drie-as magnetometer, fyn sonsensor en nadirsensor in. Drie ori entasiebepalingsmetodes word ondersoek, naamlik die Drietal, Tempo Kalman lter en die Uitgebreide Kalman lter algoritmes. Buiten die aerodinamiese beheerelemente van die satelliet, word daar ook drie magneetstange en drie nano-reaksiewiele ingesluit in die ontwerp. Daar word onderskeid getref tussen drie beheermodusse en verskeie beheermetodes word ondersoek vir hierdie beheermodusse. Die verskeie ori entasiebepalings- en ori entasiebeheermetodes word ge evalueer deur middel van simulasies en die resultate word vergelyk om die beste metodes vir die satelliet se gebruik te bepaal. Die magnetiese Tempo Kalman lter word gekies as ori entasiebepalingsmetode vir 'n tuimelende satelliet en die kombinasie van die son Tempo Kalman lter en Drietal algoritme word gebruik vir 'n satelliet met lae hoektempos. Die B-dot en Y-spin beheerder word gekies vir die tuimelbeheermodus, die aerodinamiese en kruisproduk beheermetode vir die drie-as-stabilisasie-beheermodus en die kwaternioon terugvoer beheermetode vir die rigbeheermodus van die satelliet. Daar word bepaal dat die samespanning van magnetiese en aerodinamiese beheer voldoende is vir die aanvanklike stabilisering van die satelliet, maar dat die drie nano-reaksiewiele benodig word om die kamera te rig tydens die beeldvormingproses.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2005. / The aim of the thesis is to design a Control Moment Gyro (CMG) actuator which can be used in small satellite applications. The hardware and software of the CMG has to be designed according to specifications given. A satellite fitted with these CMGs has to be able to do a 30 degree rotation within 10 seconds.

Thesis (MScEng (Electrical and Electronic Engineering))--Stellenbosch University, 2008. / This thesis describes the design and implementation of a software platform for software defined radio (SDR). This platform was to form part of an experimental satellite payload. Several other experiments were also housed on this platfrom and subsequently had to be incorporated into the design. The hardware components of the payload were already de- termined at the start of the project but firmware had to be created as part of the project. The software platform was based on the Linux kernel. Device drivers had to be designed for the hardware and firmware components. These drivers were designed so that standard Unix utilities could be used to interact with them. This allowed for easy testing of the system and the programs running on it. The use of the platform for modulation and demodulation of analogue signals was demonstrated using a proof-of-concept SDR application.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2006. / This project investigates two problems related to satellites that contain cold gas thrusters and reaction wheels. The first problem concerns the estimation of the thruster force response to a pulse command. An optimal data integration method is developed and implemented to estimate the thruster force output from a number of noisy sensors. The second problem occurs when the output force vector of a thruster mounted on a satellite is misaligned with the centre of mass with the satellite. As a result a disturbance torque is generated on the satellite during thruster operation.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: The telecommunications link between a LEO satellite and a rural ground station with a non-tracking antenna, has a strongly varying link quality and a short communications window. The satellite acts as a store-and-forward node between ground stations. The TC-SDLP and an FTP protocol form a shallow protocol stack, which excludes unneeded protocol functionality and the resulting overhead. Coding gain, introduced by BCH FEC in the TCSDLP, allows for link quality improvement. The core of this thesis is an improvement of the TC-SDLP to maximise effective payload data throughput, or goodput. This improvement was achieved by creating an optimal segment length selection metric based on the BER. Since the BER is not determinable from within the TC-SDLP, the metric was twice determined; once based on the FER and finally based on time delays. The work includes an extensive background study, which consists of space standardisation, orbital physics, error detection and correction, space datalink protocols, data throughput and culminating in the protocol stack design. The project specific link budget calculation is presented. The optimal segment length policy was mathematically determined. Asimulation model of the TC-SDLP was used as a proof of concept for the effective throughput and give a performance benchmark. Finally a TC-SDLP implementation offers a real world performance demonstration. / AFRIKAANSE OPSOMMING: Die telekommunikasie skakel tussen ’n lae aardomwenteling (LEO) sateliet en ’n plattelandse grondstasie met ’n nie-volg antenna, het ’n skakelkwaliteit wat in ’n groot mate varieer en ’n kort kommunikasievenster. Die sateliet tree op as ’n stoor- en- aanstuur node tussen grondstasies. Die TC-SDLP en ’n leêr oordrag protokol (FTP) vorm ’n vlak protokol stapel, wat onnodige protokol funksionaliteit en die gevolglike opkoste uitsluit. Kode aanwins, wat deur die BCH FEC in die TC-SDLP, aangebring word, verbeter die skakelkwaliteit. Die kern van hierdie tesis is ’n verbetering van die TC-SDLP om sodoende die ware deurvoer van nuttige vragdata te maksimimeer. Hierdie verbetering is bereik deur die skep van ’n optimale segmentlengte-seleksie metode gebaseer of die bit fout tempo (BER). Aangesien die BER nie bepaal kan word vanuit die TC-SDLP nie, is die maatstaf twee keer bepaal; die eerste keer is die bepaling gebaseer op die raamwerk fout tempo (FER) en die finale bepaling op tyd vertragings. Die tesis sluit ’n omvattende agtergrondstudie in, wat bestaan uit ruimte standardisering, wentelbaan fisika, die opspoor en regstel van foute, ruimte inligtingskakel protokol en deurstuur van data wat uitloop op die protokol ontwerp. Daar word aangedui hoe die berekening van die begroting vir die skakel van toepassing op die spesifieke projek, gedoen is. ’n Wiskundige analise van die optimale segmentlengte s ook gedoen. ’n Simulasie model van die TC-SDLP is gebruik as ’n bewys van die konsep vir die ware deurset en gee ’n prestasie maatstaf. Laastens bied die TCSDLP implementering ’n ware wereld prestasie demonstrasie.

Thesis (MScEng)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: One of the main subsystems of SUNSAT is the Attitude Determination and Control System (ADCS), responsible for the orientation and positioning of the satellite. Due to the integrated architecture of the system, several shortcomings were identified. A possible solution to the problems is the implementation of a distributed system. The design of a communication protocol for a distributed system is the focus of this thesis. An investigation on different network topologies and communication protocols as well as error control techniques is carried out to establish a combination that meets the requirements of the ADCS. Based on defined protocol specifications a detailed protocol design is proposed. Then the protocol is implemented using a layered software structure that emanates from the OSI layering model, to provide well defined software structures and interfaces. A series of measurements have shown that the protocol meets the functional requirements of the ADCS and further provides reliable data transfer on the network. / AFRIKAANSE OPSOMMING: Een van die vernaamste dele van SUNSAT is die "Attitude Determination and Control System" (ADCS) wat verantwoordelik is vir die orientasie en posisionering van die satelliet. Verskeie tekortkomminge as gevolg van die geYntegreerde argitektuurvan die stelsel, is geYdentifiseer. 'n Moontlike oplossing vir die probleme is die implementering van 'n verspreide stelsel. Die ontwerp van 'n kommunikasie protokol vir 'n verspreide stelsel is die fokus van die tesis. 'n Ondersoek na verskeie netwerk topoloqie en kommukasie protokolle, asook foutbeheer tegnieke is uitgevoer om vas te stel watter kombinasie die ADCS se vereistes sal bevredig. 'n Gedetaileerde protokol ontwerp is voorgestel gebaseer op gedefineerde protokol spesifikasies. Hierdie protokol is toe geYmplementeer deur gebruik te maak van vlak gestruktureerde sagteware wat afkomstig is van die OSI model, met die oog op goed gedefineerde sagteware strukture en koppelvlakke. 'n Reeks meetings het aangedui dat die protokol die funksionele vereistes van die ADCS bevredig en dat dit verder betroubare data verplasing oor die netwerk verskaf.