Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: The Electronic Systems Laboratory at Stellenbosch University is currently developing a fully 3-axis controlled Attitude Determination and Control Subsystem (ADCS) for CubeSats. This thesis describes the design and development of an Onboard Computer (OBC) suitable for ADCS application. A separate dedicated OBC for ADCS purposes allows the main CubeSat OBC to focus only on command and data handling, communication and payload management. This thesis describes, in detail the development process of the OBC. Multiple Microcontroller Unit (MCU) architectures were considered before selecting an ARM Cortex-M3 processor due to its performance, power efficiency and functionality. The hardware was designed to be as robust as possible, because radiation tolerant and redundant components could not be included, due to their high cost and the technical constraints of a CubeSat. The software was developed to improve recovery from lockouts or component failures and to enable the operational modes to be configured in real-time or uploaded from the ground station. Ground tests indicated that the OBC can handle radiation-related problems such as latchups and bit-flips. The peak power consumption is around 500 mW and the orbital average is substantially lower. The proposed OBC is therefore not only sufficient in its intended application as an ADCS OBC, but could also stand in as a backup for the main OBC in case of an emergency. / AFRIKAANSE OPSOMMING: Die Elektroniese Stelsels Laboratorium by die Universiteit van Stellenbosch is tans besig om ’n volkome 3-as gestabiliseerde oriëntasiebepaling en -beheerstelsel (Engels: ADCS) vir ’n CubeSat te ontwikkel. Hierdie tesis beskryf die ontwerp en ontwikkeling van ’n aanboordrekenaar (Engels: OBC) wat gebruik kan word in ’n ADCS. ’n Afsonderlike OBC wat aan die ADCS toegewy is, stel die hoof-OBC in staat om te fokus op beheer- en datahantering, kommunikasie en loonvragbestuur. Hierdie tesis beskryf breedvoerig die werkswyse waarvolgens die OBC ontwikkel is. Verskeie mikroverwerkers is as moontlike kandidate ondersoek voor daar op ’n ARM Cortex-M3-gebaseerde mikroverwerker besluit is. Hierdie mikroverwerker is gekies vanweë sy spoed, effektiewe kragverbruik en funksionaliteit. Die hardeware is ontwikkel om so robuust moontlik te wees, omdat stralingbestande en oortollige komponente weens kostebeperkings, asook tegniese beperkings van ’n CubeSat, nie ingesluit kon word nie. Die programmatuur is ontwikkel om van ’n uitsluiting en ’n komponentfout te kan herstel. Verder kan programme wat tydens vlug in werking is, verstel word en vanaf ’n grondstasie gelaai word. Grondtoetse het aangedui dat die OBC stralingverwante probleme, soos ’n vergrendeling (latchup) of bis-omkering (bit-flip), kan hanteer. Die maksimum kragverbruik is ongeveer 500 mW en die gemiddelde wentelbaankragverbruik is beduidend kleiner. Die voorgestelde OBC is dus voldoende as ADCS OBC asook hoof-OBC in geval van nood.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: Low earth orbit (LEO) satellite communication presents a unique environment which inherently di ers from most other communication channels. Due to the varying orbital patterns of LEO satellites the link exhibits varying link margins. Limited communication time windows need to be optimised to maximise the volumetric data throughput. Large coding gains can be obtained by the implementation of forward error correction codes. This thesis presents a means for optimising the data throughput of LEO satellite communication through the implementation of a mission speci c error control strategy. Low density parity check (LDPC) codes are versatile and present good error performances at many di erent code rates and block lengths. With power limitations on the space segment and remote ground stations, hardware utilisation e ciency must be optimised to reduce power consumption. In response to this requirement, this thesis evaluates various algorithms for LDPC decoders. An iterative LDPC decoder, implementing an approximation algorithm, is presented as a low complexity solution with good error performance. The proposed solution provides a very good balance between required hardware complexity and coding performance. It was found that many parameters of the decoders and codes can be altered to allow the implementation of these codes in systems with varying memory and processing capabilities. / AFRIKAANSE OPSOMMING: Kommunikasiekanale van satelliete met lae wentelbane, bied 'n unieke omgewing wat inherent verskil van meeste ander kommunikasiekanale. As gevolg van veranderende wentelbaanpatrone, vertoon die kanaal 'n wisselende foutgedrag. Kommunikasievensters is beperk en moet geoptimeer word om die totale deurset van die stelsel te maksimeer. Groot koderingswinste kan verkry word deur die implementering van foutkorreksie kodes. Hierdie tesis voorsien 'n metode om die datadeurset van satelliete met lae wentelbaan te optimeer, deur middel van implementering van 'n missie-spesi eke foutbeheer strategie. Lae digtheid pariteit toetskodes (LDPC) is veelsydige kodes, bied goeie foutbeheer en is doeltre end vir verskillende kodekoerse en bloklengtes. Met drywingsbeperkinge op die ruimtesegment en afgesonderde grondstasies, moet hardeware komponente doeltreffend gebruik word om drywingsverbruik te verminder. Ten einde aan hierdie ontwerpsvereiste te voldoen, evalueer hierdie tesis verskeie LDPC dekodeerderalgoritmes. Deur 'n iteratiewe LDPC dekodeerder met 'n benaderingsalgoritme te implementeer, word 'n oplossing van lae kompleksiteit aangebied, maar wat steeds goeie foutkorreksie eienskappe toon. Die voorgestelde oplossing bied 'n baie goeie balans tussen benodigde hardeware kompleksiteit en koderingsprestasie. Daar is gevind dat heelwat parameters van die dekodeerders en kodes aangepas kan word, ten einde implementering in stelsels met 'n wye verskeidenheid van geheuespasie en verwerkingsvermoëns moontlik te maak.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2008. / A communications protocol is designed for real time control and data handling for a Nanosatellite application. The communication protocol is based on the Controller Area Network (CAN) technology. The protocol handles different message types such as time synchronization, telecommand messages, telemetry acquisition, unsolicited telemetry messages, large file transfers and debug messages. The design of the protocol entails finding a suitable target microcontroller in which the protocol implementation is demonstrated. This requires consideration of a number of development factors such as cost, complexity, availability, reliability and operational environment (space). The AVR AT90CAN128 microcontroller was chosen as a target microcontroller as it gave most of the required factors mentioned above. The protocol implementation involves developing low level software drivers, the middleware and the application programs to demonstrate handling of each supported message. In the implementation the media access scheme and low layer communication is provided by the CAN low level kernel (physical and data link layers). The protocol performance was evaluated by measuring the software response latencies, the bus throughputs and the software efficiencies. Power consumption due to CAN communication was also measured. System reliability was tested by loading the CAN bus with extreme communication traffic and letting the system run for a long time. The observation was that messages were handled consistently.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: A joint project between the KU Leuven and Stellenbosch Universities was at the time of this thesis underway to develop a space borne electronically beam steerable antenna and the associated ground-space segments. This thesis covers the development of an aircraft based satellite emulator to facilitate convenient aircraft based testing of an antenna array, intended for low earth orbit satellite deployment and subsystems to control the antenna array. A flight strategy is developed to emulate such a satellite pass as best possible, with the strategy implemented in software on in-flight PC hardware. A full interface between the aircraft avionics and satellite bus system has been developed to enable generation of the required antenna steering commands and to create a satellite bus image to the payload. Successful test results are presented, as obtained from the actual aircraft ight simulator. The thesis describes the successful development and testing of a low altitude flight test strategy for certain satellite borne systems, as a cost-effective and realistic interim step to actual and very expensive space flight testing. / AFRIKAANSE OPSOMMING: 'n Gesamentlike projek deur KU Leuven en Stellenbosch Universiteit was tydens die verloop van hierdie tesis besig met die ontwikkeling om 'n ruimte gebaseerde elektroniese straal beheerde antenna en geassosieerde substelsels daar te stel. Hierdie tesis handel oor die ontwikkeling van 'n vliegtuig gebaseerde satelliet emulator om die toetsing van 'n elektroniese stuurbare antenna, wat bedoel is vir 'n lae aardse wentelbaan, te fasiliteer en die ontwikkeling van substelsels wat die stuurbare antenna beheer. 'n Vlug strategie is ontwikkel om so 'n satelliet wentelbaan so na as moontlik te emuleer. Die strategie word dan geïmplementeer in die sagteware van die aanboord vlug rekenaar. 'n Intervlak tussen die vliegtuig instrumente en satellietbus is ontwikkel om die generering van die nodinge instruksies te fasiliteer en om 'n virtuele satellietbus vir die res van die satelliet stelsel te skep. Suksesvolle toets resultate word getoon wat met behulp van 'n vliegtuig simulator verkry is. Die tesis beskryf die suksesvolle ontwikkeling en toetsing van 'n lae vlugtoets strategie vir satelliet stelsels, as 'n koste effektiewe en realistiese tussenstap, tot baie duur ruimte vlugtoetsing.

Thesis (MScIng)--Stellenbosch University, 2004. / ENGLISH ABSTRACT: This dissertation's research aims at studying the viability of using both low cost consumer Commodity Off The Self (COTS) PCs and libn~software in implementing a distributed real-time system modeled on a real-world engineering problem. Debugging and developing a modular satellite system is both time consuming and complex, to this end the SUNSATteam has envisioned the Interactive Test System that would be a dual mode simulator/monitoring system. It is this system that requires a real-time back-end and is used as a real world problem model to implement. The implementation was accomplished by researching the available parallel processing software and real-time extensions to GNU/Linux and choosing the appropriate solutions based on the needs of the model. A monitoring system was also implemented, for system verification, using freely available system monitoring utilities. The model was successfully implemented and verified with a global synchronization of < 10ms. It was shown that GNU/Linux and libn~ software is both mature enough and appropriate in solving a real world distributed real-time problem. / AFRIKAANSE OPSOMMING: Die tesis se navorsing is daarop gemik om die toepaslikheid van beide lae koste verbruikers Komoduteits Van Die Rak (KVDR)persoonlike rekenaars en vemiet sagteware in die implementasie van verspreide intydse stelsels te ondersoek aan die hand van die oplossing van 'n gemodelleerde ingenieurs probleem. Die ontfouting en ontwikkeling van 'n modulere satelliet is beide tyd rowend en kompleks, om hierdie te vergemaklik het die SUNSAT span die Interaktiewe Toets Stelsel gekonseptualiseer, wat in wese'n dubbel modus simulator/moniteerings stelsel sou wees. Dit is hierdie stelsel wat 'n verspreide intydse onderstel benodig en dien as die regte wereld probleem model om op te los. Die implementasie is bereik deur die beskikbare verspreide verwerkings sagteware en intydse uitbreidings vir GNU/Linux te ondersoek en die toepaslike opsies te kies gegrond op die behoeftes van die model. 'n Moniteerings stelsel is ook geimplimenteer, met behulp van libn~sagteware, vir stelsel verifikasie. Die model was suksesvol geimplimenteer en geverifieer met 'n globale sinkronisasie van < 10ms. Daar is getoon dat GNU/Linux en libn~sagteware beide volwaardig en geskik is vir die oplossing van regte wereld verspreide intydse probleme.

Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Within a complex electronic system, sub-system communication forms the backbone of the functionality of any satellite. It allows multiple processors to run simultaneously and data to be shared amongst them. Without it, a single processor would have to control the entire satellite. Not only would such a design then be overly complicated, but the processor would also not have sufficient capacity to service all the components efficiently. Furthermore the detrimental effects that radiation have on integrated circuits are well documented and can be anything from a single bit flip to a complete integrated circuit failure. If not repaired, a failure on a sub-system communication bus could lead to the loss of the entire satellite. Die goal is to create more radiation resistant Controller-Area-Network (CAN) node. Since a full triple modular redundant design will have a large footprint and high power consumption, a combination of techniques will be applied and tested. The goal is to achieve improved footprint utilisation over triple modular redundancy, while still maintaining good resistance to Single Event Upsets (SEU). By applying simulation, it was sufficiently proven that the implementation of the individual techniques used functioned according to expectations. These techniques included error detection and correction using Hamming Codes, single event transient filter and triple modular redundancy. Having applied these mitigation techniques, the footprint of the CAN controller increased by only 116%. Simulation showed that the Error Detection and Correction and Triple Modular Redundancy worked effectively with the CAN controller, and that the CAN controller could function as originally intended. Using radiation testing, the design proved to be more resistant to SEUs than the unmitigated CAN controller. It was thus shown that through using a combination of mitigation techniques, it is possible to develop an optimal design with a high level of resistance against Single Event Upsets, utilizing a smaller footprint than implementing Triple Modular Redundancy. / AFRIKAANSE OPSOMMING: Sub-stelsel kommunikasie vorm die basis van die funksionaliteit in ’n komplekse elektroniese stelsel soos ’n satelliet. Dit skep die vermoë om veelvoudige verwerkers gelyktydig te laat funksioneer en inligting tussen hulle te deel. Sonder sub-stelsel kommunikasie, sal ’n enkele verwerker die hele sateliet moet beheer. Dit sal nie net die hele ontwerp oorkompliseer nie, maar die verwerker sal ook nie genoeg kapisteit hê om al die komponente effektief te diens nie. Die newe-effekte van bestraling op geïntegreerde stroombane is goed gedokumenteer en kan wissel van ’n enkele omgekeerde bis, tot die vernietiging van die geïntegreerde stroombaan. Indien die fout in die kommunikasiestelsel nie herstel word nie, kan dit lei tot die verlies van die hele sateliet. Die doel is om ’n meer bestraling bestande Controller-Area-Network (CAN) nodus te skep. Aangesien ’n volle drie-dubbele-modulêre-oortollige ontwerp ’n baie groot area beslaan en hoë krag verbruik het, gaan ’n kombinasie van versagting tegnieke toegepas en ge-evalueer word. Die doel is om beter area benutting as die drie-dubble-modulêre-oortollige ontwerp te kry, terwyl ’n goeie weerstand teen foute behoue bly. Deur middel van simulasies is voldoende bewyse gelewer dat die implimentasie van die individuele versagting tegnieke soos verwag funktioneer. Hierdie tegnieke sluit in, fout opsporing en regstelling deur middel van Hamming kodes, enkele geval oorgangs verskynsel filter asook drie-dubbele-modulêre-oortollige ontwerp. Nadat versagting meganismes toegepas is, het die area verbruik van die CAN beheerder toegeneem met slegs 116%. Simulasies het bewys dat Fout Opsporing en Regstelling en Drie-Dubbele-Modulêre-Oortollige ontwerp tegnieke binne die CAN beheerder korrek funktioneer, terwyl die CAN beheerder self funktioneer soos dit oorspronklik gefunksioneer het. Deur middel van bestralingstoetse, is dit bewys dat die ontwerp meer bestand is teen foute geïnduseer deur bestraling as die onbeskermde CAN beheerder. Dit is dus bewys dat deur gebruik te maak van verskeie versagting tegnieke dit moontlik is om ’n optimale ontwerp te implimenteer, met ’n hoë weerstand teen foute, maar met ’n laer area verbruik as die van ’n Drie-dubbele-Modulêre-Oortollige ontwerp.