| Summary: | 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.
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