Estimation of external disturbance torques on CubeSats to enhance full state attitude estimation accuracy and mission success

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dc.contributor.advisorSteyn, Hermanen_ZA
dc.contributor.authorHabila, Asia Saeed Kajoen_ZA
dc.contributor.otherStellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.en_ZA
dc.date.accessioned2023-03-03T12:27:29Zen_ZA
dc.date.accessioned2023-05-18T07:16:48Zen_ZA
dc.date.available2023-03-03T12:27:29Zen_ZA
dc.date.available2023-05-18T07:16:48Zen_ZA
dc.date.issued2023-03en_ZA
dc.descriptionThesis (PhD)--Stellenbosch University, 2023.en_ZA
dc.description.abstractENGLISH ABSTRACT: CubeSats are becoming increasingly popular, and the number of launches is growing rapidly. This is due to their low manufacturing costs and ease of launch. CubeSats were initially utilized for educational purposes; however, over time, they began to be used for more complex missions, such as astronomy and remote sensing applications. For these complex missions to be successful, precise control is required, which is the role of the attitude determination and control subsystem (ADCS). ADCS, on the other hand, has challenges achieving precise control due to the CubeSat's small moment of inertia, which makes it susceptible to disturbance torques. This thesis focuses on the accurate estimation and development of models for disturbance torques that considerably improve the full-state estimate accuracy and, as a result, the CubeSats' control and, eventually, preserve the mission. As measuring the disturbance torque that affects an object is as simple as measuring its angular acceleration, the gyroscope is chosen as the main attitude sensor in this thesis to estimate attitude disturbance torques. However, the gyroscope was found to have shortcomings due to noise and errors that affect its output and performance, resulting in an inaccuracy of measurement. As a consequence, two noise drift estimation algorithms are developed, tested, and evaluated in order to determine which is best to use to boost the accuracy of disturbance torque estimation. The general models for attitude disturbance torques, along with the estimators, are developed, tested, and evaluated. The outcomes from the models are used to assist in the eventual development of the estimators. For the estimators, deterministic and nonlinear recursive estimation methods are developed, tested, and evaluated through simulations in order to determine which are best to be used in the thesis to estimate the attitude disturbance torques. The deterministic algorithms that are utilized are QUEST and Linear Least Square, while the recursive ones are Extended Kalman Filter (EKF) and Unscented Kalman Filter (UKF). In addition, a suggested method (algorithm) for estimating attitude disturbance is proposed, followed by simulations for assessment. Furthermore, an identification technique is proposed for determining which attitude disturbance torques are acting on the satellite body, and their magnitude is also identified and evaluated through simulations. A design and practical implementation of a disturbance torque estimator on the ground is developed. An air bearing platform is used to represent the satellite in terms of potential space disturbances and to evaluate the effectiveness of the disturbance torque estimator. Firstly, the mass properties of the air bearing are obtained using two different methods to ensure the air bearing system dynamics is correct, and then the estimator is developed and evaluated. The EKF was found to be the most suitable choice that can be utilized in this research to estimate the disturbance torque. It gives a more accurate estimate compared to QUEST and Weighted Least Square (WLS), is more precise, and requires less execution time compared to UKF. Accordingly, a bank of EKFs is employed to independently estimate each of the disturbance torques and used in combination with the identification function to accurately estimate the total disturbance torque in orbit.en_ZA
dc.description.abstractAFRIKAANS OPSOMMING: CubeSats word al hoe meer gewild, en die belangstelling in die tipe ruimtevaartuie groei vinnig. Dit is as gevolg van hul lae vervaardigingskoste en toeganklike lanseergeleenthede. CubeSats is aanvanklik vir opvoedkundige doeleindes gebruik; mettertyd is hulle egter gebruik vir meer komplekse missies, soos sterrekunde en afstandswaarneming-toepassings. Vir hierdie komplekse missies om suksesvol te wees, is presiese beheer nodig, wat die rol is van orientasie-afskatting en beheerstelsel (OBBS). OBBS, aan die ander kant, het uitdagings om presiese beheer te bewerkstellig as gevolg van CubeSats se klein traagheidmomente, wat dit vatbaar maak vir steuring-wringkragte. Hierdie tesis fokus op die afskatting en ontwikkeling van modelle vir versteuringswringkragte wat die voltoestand afskattingsakkuraatheid aansienlik verbeter en, as gevolg daarvan, die Kubus-satelliete se beheer en, uiteindelik, die missiesukses verseker. Aangesien die meting van die versteuringswringkrag wat 'n voorwerp beinvloed so eenvoudig is soos om sy hoekversnelling te meet, word die giroskoop as die hoofsensor in hierdie tesis gekies om versteuringswringkragte af te skat. Daar is egter gevind dat die giroskoop tekortkominge het as gevolg van meetgeraas en foute wat sy uitset en werkverrigting beïnvloed, wat lei tot onakkurate metings. Gevolglik word twee geraasafsetdryfafskattings algoritmes ontwikkel, getoets en geëvalueer om te bepaal watter die beste is om van gebruik te maak om die akkuraatheid van die steuringwringkragafskatting te verbeter. Die algemene modelle vir versteurings-wringkragte, saam met die afskatters, word ontwikkel, getoets en geëvalueer. Die uitkomste van die modelle word gebruik om te help met die uiteindelike ontwikkeling van die afskatters. Vir die afskatters word deterministiese en nie-lineêre rekursiewe afskatmetodes ontwikkel, getoets en geëvalueer deur middel van simulasies. Dit om te bepaal watter metode die beste is om te gebruik vir die afskatting van versteuringswringkragte. Die deterministiese algoritmes wat gebruik word, is "QUEST" en Lineêre Kleinste Kwadraat, terwyl die rekursiewes "Extended Kalman Filter" (EKF) en "Unscented Kalman Filter" (UKF) is. Daarbenewens word 'n voorgestelde metode (algoritme) vir die afskatting van orientasieversteurings voorgestel, gevolg deur simulasies vir assessering. Verder word 'n identifikasietegniek voorgestel om te bepaal watter versteuringswringkragte op die satellietliggaam inwerk, en hul grootte word ook deur middel van simulasies geïdentifiseer en geëvalueer. 'n Ontwerp en praktiese implementering van 'n versteuringwringkrag-afskatter op die grond word ontwikkel. ’n Luglaer platform word gebruik om die satelliet in terme van potensiële ruimteversteurings voor te stel en om die doeltreffendheid van die steuringwringkrag afskatter te evalueer. Eerstens word die massa-eienskappe van die luglaer met twee verskillende metodes verkry om te verseker dat die luglaerstelseldinamika korrek is, en dan word die afskatter ontwikkel en geëvalueer. Daar is gevind dat die EKF die mees geskikte keuse is wat in hierdie navorsing gebruik kan word om die versteuringswringkrag af te skat. Dit gee 'n meer akkurate afskatting in vergelyking met "QUEST" en Geweegte Kleinste Kwadraat (WLS), is meer presies, en vereis minder uitvoertyd in vergelyking met UKF. Gevolglik word 'n bank van EKF's aangewend om elkeen van die versteuringswringkragte onafhanklik te beraam en word dit in kombinasie met die identifikasiefunksie gebruik om die totale versteuringswringkrag in 'n wentelbaan akkuraat af te skat.af_ZA
dc.description.versionDoctorateen_ZA
dc.format.extentxx, 147 pages : illustrationsen_ZA
dc.identifier.urihttp://hdl.handle.net/10019.1/127337en_ZA
dc.language.isoen_ZAen_ZA
dc.language.isoen_ZAen_ZA
dc.publisherStellenbosch : Stellenbosch Universityen_ZA
dc.rights.holderStellenbosch Universityen_ZA
dc.subject.lcshNanosatellites -- Control systemsen_ZA
dc.subject.lcshArtificial satellites -- Attitudeen_ZA
dc.subject.lcshTorqueen_ZA
dc.subject.lcshAerodynamic measurementsen_ZA
dc.titleEstimation of external disturbance torques on CubeSats to enhance full state attitude estimation accuracy and mission successen_ZA
dc.typeThesisen_ZA
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Doctoral Degrees (Electrical and Electronic Engineering)