Thesis (MScEng)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: The purpose of this study was to investigate the feasibility of a moon sensor as an alternative or supplemental sensor to supply attitude information to a satellite. The visibility of the moon was evaluated with regards to that of the sun from a satellite (i.e. the feasibility of the moon sensor is compared to that of a sun sensor). An algorithm was developed to calculate the center of the moon, regardless of phase or rotation, to offer increased accuracy of the center of the moon. The accuracy of this algorithm and the possible error margins were evaluated and discussed in both ideal and actual test cases. The sensor was implemented on embedded hardware. The conclusion of the feasibility analysis was that the sensor would function well as a supplemental sensor (e.g. in conjunction with a sun-sensor) rather than as an alternative sensor. The accuracy of the moon center algorithm was satisfactory for attitude deterrnina tion. This sensor could thus be seriously considered for use on a future satellite. / AFRIKAANSE OPSOMMING: Die doel van die studie is om die lewensvatbaarheid van 'n maan-sensor, as alternatiewe of aanvullende sensor, om oriëntasie data aan 'n sateliet te verskaf, te ondersoek. Die sigbaarheid van die maan en die sigbaarheid van die son is met mekaar vergelyk, vanaf 'n sateliet (m.a.w. die uitvoerbaarheid van 'n maan-sensor is vergelyk met dié van 'n son sensor). 'n Algorittne is ontwikkel om die middelpunt van die maan, ongeag van fase of rotasie, te bereken om verhoogde akuraatheid van die maan se middelpunt te bied. Die akuraatheid van die maan-middelpunt algoritme en moontlike foute is evalueer en bespreek in beide ideale sowel as werklike toets gevalle. Die sensor was op hardeware geimplenteer. Die gevolgtrekking van die lewensvatbaarheids analise is dat die sensor effektief sal funksioneer as 'n aanvullende sensor (d.w.s saam met 'n son sensor) eerder as 'n alternatiewe sensor. Die resultate verkry van die evaluasie van die maan-middelpunt algoritme is bevredegind en is voldoende vir oriëntasie bepaling. Die sensor kan dus ernstig oorweeg word vir gebruik op 'n sateliet in die toekoms.

Thesis (MEng)--University of Stellenbosch, 2000. / ENGLISH ABSTRACT: The Attitude Determination and Control System (ADCS) of the Stellenbosch University Satellite (SUNSAT I) is an integrated system providing some redundancy and the necessary data management to control the spacecraft. However, the redundancy is not easily accessible and there is a lack in flexibility when testing individual modules during integration or when the system needs to be extended. The objective of this thesis was thus to develop a high reliability, flexible, modular communication system that included some type of redundancy to manage real-time data and to prevent severe malfunctioning of the entire system. The first step in the project's development methodology was to summarise the requirements and specifications by studying the current ADCS architecture and data management. An investigation into the Controller Area Network (CAN) protocol showed that this technology would fit the requirements very well, leading to the design and implementation of several concept topologies based on CAN. Thereafter, a demonstration model consisting of three prototype nodes was composed. The performance of the so called dual CAN node was analysed and an extrapolation was 'made to determine whether the architecture could support the complete ADCS. It was demonstrated that the dual CAN node provides enough room to accommodate all the processors, actuators and sensors of the ADCS. At the same time, it was shown that reliability and robustness was increased by enhanced redundancy at a node-level as well as at the greater system-level. A dual CAN bus was provided for redundancy at a node-level. At the system-level, the command and data-gathering modules (ACP or OBC's) can now effectively be multiplexed on the network of actuators and sensors. Furthermore, it was shown that error detection capabilities and diagnostics can be enhanced and the complexity of the communication architecture and related wiring harnesses can be reduced. This allows easier access to modules and simplifies development. / AFRIKAANSE OPSOMMING: Die Attitude Determination and Control System (ADCS) van Stellenbosch University Satellite (SUNSAT I) is 'n geïntegreerde stelsel wat voorsiening maak vir 'n mate van oortolligheid en 'n vermoeë om stelseldata te bestuur vir goeie satellietbeheer. Nietemin, hierdie oortolligheid is nie baie toeganklik nie en daar is 'n gebrek aan aanpasbaarheid tydens die toets en integrasie van individuele modules of moontlike stelseluitbreidings. Die doelwit van hierdie tesis was dus die ontwikkeling van 'n betroubare, aanpasbare, modulêre kommunikasie stelsel wat 'n tipe oortolligheid insluit sodat intydse data bestuur kan word en algehele stelselondergang vermy kan word. Die eerste stap in die projek se ontwikkelings metodiek was om 'n opsomming te verkry van die vereistes en spesifikasies deur die huidige ADCS se argitektuur en databestuur te ondersoek. 'n Ondersoek na die Controller Area Network (CAN) protokol het getoon dat hierdie tegnologie aan baie van die vereistes voldoen. Dit het aanleiding gegee tot die ontwerp en implementering van 'n paar konsep ontwerpe gebaseer op CAN. Daarna is 'n demonstrasie model bestaande uit drie prototipe nodusse gebou. Die werksverrigting van die sogenoemde dual CAN node, is ondersoek en 'n ekstrapolasie was gemaak om vas te stelof die argitektuur die volkome ADCS kan huisves. Deur demonstrasie was daar getoon dat die dual CAN node wel genoeg ruimte verskaf om al die verwerkers, aktueerders en sensors van die ADCS te akkommodeer. Daar was terselfdertyd getoon dat betroubaarheid en robuustheid verhoog is deur die verbeterde oortolligheid op 'n node-vlak sowel as op die groter stelsel-vlak. 'n Dubbele CAN bus is gebruik vir oortolligheid op 'n node-vlak. Op 'n stelsel-vlak kan die bevel-en-dataversamelings modules (ACP en aBC's) effektief gemultipleks word op die netwerk van aktueerders en sensors. Daar was verder getoon dat die foutopspoorings vermoeë en diagnostiese vermoeë verbeter kan word en die kompleksiteit van die kommunikasie argitektuur en ooreenkomstige kabelharnasse vereenvoudig kan word. Die gevolg is vereenvoudigde toegang tot modules en vergemaklikde opgradering.

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.

Thesis (MScEng)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: A different approach of employing attitude sensors with incomplete measurements in an attitude determination system is investigated. The amount of available attitude sensors on small satellites are limited, and the failure of sensors can be fatal when accurate attitude determination is necessary. The problem with sensors with incomplete measurements is that they must be used in combination with other sensors to obtain three dimensional attitude information. The aim is to enhance the possible number of sensor combinations that can be employed, in an attempt to improve the ability of the attitude determination system to tolerate sensor failures. An alternative sensor structure consisting of a magnetometer and two horizon sensors is presented. A method to obtain vector observations of the attitude from a combination between magnetometer and horizon sensor measurements is derived and tested. A full state Extended Kalman Filter is used to determine the satellite's attitude, attitude rate and disturbance torque from these vector observations. A second Extended Kalman Filter structure, using only magnetometer measurements, is implemented. The magnetometer Extended Kalman Filter and the horizon/magnetometer Extended Kalman Filter are integrated to obtain a single Extended Kalman Filter structure to determine the satellite's full attitude state. Integration is done by switching between the different pairs of vector information. A systematic analysis of the integrated filter's dynamic behaviour during the switching stages is done by means of a series of case studies. / AFRIKAANSE OPSOMMING: Die gebruik van oriëntasiesensore met onvolledige metingsdata in oriëntasiebepalingsstelsels is ondersoek. Slegs 'n beperkte aantal oriëntasiesensore is beskikbaar op mikro satelliete. 'n Foutiewe sensor kan dus noodlottig wees wanneer akkurate oriëntasiebepaling nodig is. Die probleem met sensore met onvolledige metingsdata is dat dit in sensor kombinasies gebruik moet word om drie dimensionele oriëntasieinligting te verkry. Die doel is dus om die moontlike aantal sensor kombinasies sodanig te vermeerder dat die oriëntasiebepalingsstelsel beter bestand sal wees teen moontlike sensor falings. 'n Alternatiewe sensor struktuur, bestaande uit 'n magnetometer en twee horison sensore, is ondersoek. 'n Metode vir die verkryging van 3-as oriëntasie inligting vanaf 'n kombinasie van magnetometer en horison sensor metingsdata is afgelei en getoets. 'n Vol toestand uitgebreide Kalmanfilter is gebruik om the satelliet se oriëntasie, oriëntasie snelheid en versteurings draairnoment vanaf die vektor observasies af te lei. 'n Tweede uitgebreide Kalmanfilter struktuur, wat slegs magnetometer metingsdata gebruik, is geïmplementeer. Die magnetometer filter en die horison/magnetometer filter is geïntegreer sodat een uitgebreide Kalmanfilter struktuur volle oriëntasie inligting kan aflei vanaf verskillende pare vektors met oriëntasie inligting. Integrasie is gedoen deur te skakel tussen die verskillende vektorpare. 'n Sistematiese analise van die geïntegreerde filter se dinamiese gedrag gedurende die oorskakelingstye is gedoen deur middel van 'n reeks gevallestudies.

Les drones ou systèmes de drones aériens jouent un rôle de plus en plus important danstous les domaines, spécialement les drones à décollage et atterrissage verticaux. L’un desplus connus est le Quadrotor et, sans doute, il est la plateforme de recherche la plus utilisée.Cette thèse traite le problème de l’estimation et de la commande d’attitude appliqué àun corps rigide se déplaçant dans l’espace 3D tel que le Quadrotor. La première contributionde cette thèse est la conception et l’implémentation d’une solution d’estimation d’attitude.Celle-ci est basée sur un ensemble de filtres complémentaires combinés avec un algorithmealgébrique tel que TRIAD, QUEST, etc. avec la possibilité de choisir deux formes différentesdes filtres: la première dénommée forme Directe, et la seconde dénommée forme Passive.Les filtres proposés ont une flexibilité dans le choix de l’ordre qui peut être pris grand afinde bien réduire l’effet du bruit de mesure et permettent d’aboutir à un estimateur qui peutprendre en compte le biais éventuel des gyromètres. L’analyse par la théorie de Lyapunovprouve que les erreurs d’estimation tendent globalement et asymptotiquement vers zéro. Unesuite logique de cette première contribution est la proposition d’une solution pour la commanded’attitude qui constitue la deuxième contribution de cette thèse. Elle se traduit par ledéveloppement d’une nouvelle loi de commande d’attitude d’un corps rigide dans l’espace3D, dans laquelle seulement les vecteurs de mesures inertiels avec les mesures des gyromètressont utilisés. Elle utilise le principe de fusion des données à travers un filtre complémentairepermettant l’élimination des bruits des mesures tout en assurant une stabilité presque globalede l’équilibre désiré. La troisième contribution est une loi de commande pour la stabilisationd’attitude sans mesure de vitesse angulaire, ni mesure d’attitude. Pour cela, un systèmelinéaire auxiliaire basé sur les mesures des vecteurs inertiels a été introduit. Ce dernier sesubstitue au manque de l’information de la vitesse angulaire. L’analyse de stabilité du contrôleurproposé est basée sur la théorie de Lyapunov couplée avec le théorème de LaSalle. Ellepermet de conclure sur la stabilité presque globale de l’équilibre désiré. Les performances dessolutions proposées ont été validées par un ensemble de tests expérimentaux / Nowadays, we see a growing popularity of the use of Unmanned Aerial Vehicles (UAV) ofespecially Vertical Take-Off and Landing (VTOL) type. One of the most known VTOL is thequadrotor or Quadcopter which is probably the most used one as a research platform. Thisthesis deal with attitude control and estimation techniques applied to a rigid body movingin 3D space such as Quadcopter VTOL. The first contribution of this thesis is the design ofa new class of complementary linear-like filters allowing the fusion of inertial vector measurementswith angular velocity measurements and combined with algebraic algorithms asTRIAD, QUEST etc. to give an efficient attitude estimation solution. This class of filtersallows several possibilities of implementation such as the order of the filters which can bechosen high in order to reduce more the measurement noise and the form of the filters thatcan be direct or passive and the ability to take into account the possible gyro bias. Lyapunovanalysis shows the global asymptotic convergence of the estimation errors to zero. The sameprinciple of data fusion is used for the proposed new attitude control law in which the complementaryfilters were included to reduce the effect of measurement noise. The obtainedcontroller ensures almost global stability of the desired equilibrium point; it represents thesecond contribution of this thesis. The third contribution takes into consideration an interestingspecial case, where instantaneous measurements of attitude and angular velocity areunavailable. A first order linear auxiliary system based directly on vector measurements isused in an observer-like system to handle the luck of angular velocity. The proposed controllerensures almost global asymptotic stability of the trajectories to the desired equilibriumpoint. Detailed sets of experiments were done to validate the obtained results

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1980. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND AERO. / Includes bibliographical references. / by Edward Gregory Taylor. / Ph.D.

No description available.

UAVs have become an essential tool in many market segments, particularly the military where critical intelligence can be gathered by them. A tailsitter aircraft is a platform whose purpose is to efficiently merge the range and endurance of fixed-wing aircraft with the VTOL capabilities of rotorcraft and is of significant value in applications where launch and recovery area is limited or the use of launch and recovery equipment is not desirable. Developing autopilot software for a tailsitter UAV is unique in that the aircraft must be autonomously controlled over a much wider range of attitudes than conventional UAVs. Assumptions made in conventional estimation and control algorithms are not valid for tailsitter aircraft because of routine operation around gimbal lock. Quaternions are generally employed to overcome the limitations Euler angles; however, adapting the attitude representation to work at a full range of attitudes is only part of the solution. Kalman filter measurement updates and control algorithms must also work at any orientation. This research presents several methods of incorporating a magnetometer measurement into an extended Kalman filter. One method combines magnetometer and accelerometer sensor data using the solution to Wahba's problem to calculate an overall attitude measurement. Other methods correct only heading error and include using two sets of Euler angles to update the estimate, using quaternions to determine heading error and Euler angles to update the estimate, and using only quaternions to update the estimate. Quaternion feedback attitude control is widely used in tailsitter aircraft. This research also shows that in spite of its effective use in spacecraft, using the attitude error calculated via quaternions to drive flight control surfaces may not be optimal for tailsitters. It is shown that during hover when heading error is present, quaternion feedback can cause undesired behavior, particularly when the heading error is large. An alternative method for calculating attitude error called resolved tilt-twist is validated, improved, and shown to perform better than quaternion feedback. Algorithms are implemented on a commercially available autopilot and validation is performed using hardware in loop simulation. A custom interface is used to receive autopilot commands and send the autopilot simulated sensor information. The final topic covered deals with the tailsitter hovering in wind. As the tailsitter hovers, wind can cause the tailsitter to turn such that the wind is perpendicular to the wings. Wind tunnel data is taken and analyzed to explain this behavior.

This dissertation concerns the formation problems for multiple reduced attitudes, which are extensively utilized in many pointing applications and under-actuated scenarios for attitude maneuvers. In contrast to most existing methodologies on formation control, the proposed method does not need to contain any formation errors in the protocol. Instead, the constructed formation is attributed to geometric properties of the configuration space and the designed connection topology. We refer to this type of formation control as intrinsic formation control. Besides, the control protocols proposed in this work are designed directly in space S2, avoiding to use any attitude parameterisations. At last but not least, along the studies, some elementary tools for reduced attitudes control are developed.In paper A, a continuous control law is provided for a reduced attitude systems, by which a regular tetrahedron formation can achieve asymptotic stability under a quite large family of gain functions in the control. Then, with a further restriction on the control gain, almost global stability of the tetrahedron formation is also obtained. In this work, we introduce a novel coordinates transformation that represents the relative reduced attitudes be-tween the agents. The proposed method is an intrinsic formation control that does not need to involve any information of the desired formation before-hand. Another virtue of the method proposed is that only relative attitude measurement is required.Paper B further concerns the formation control of all regular polyhedral configurations (also called Platonic solids) for reduced attitudes. According to the symmetries possessed by regular polyhedra, a unified framework is proposed for their formations. Via using the coordinates transformation previously proposed, it is shown that the stability of the desired formations can be provided by stabilizing a constrained nonlinear system. Then, a methodology to investigate the stability of this type of constrained systems is also presented. Paper C considers the problem of tracking and encircling a moving target by agents in 3-dimensional space. By this work, we show that similar design techniques proposed for reduced attitudes formations can also be applied to the formation control for point mass systems. Therein, a group of agents are driven to some desired formation on a spherical surface and simultaneously keep the center of this spherical formation coinciding with the target to be tracked. By properly designing communication topology, the agents constitute a cyclic formation along the equator of an encircling sphere. / <p>QC 20170302</p>

As science instruments on CubeSats become more sensitive to the attitude of the spacecraft, better methods must be employed to provide the accuracy needed to complete the planned mission. While systems that provide the accuracy required are available commercially, these solutions are not cost-effective, do not allow the design to be tailored to a specific mission, and most importantly, do not give students hand-on experience with attitude control actuators. This thesis documents the design, modeling, and simulation of a low-cost, student-fabricated, reaction wheel system for use in 3U CubeSat satellites. The entire design process for the development of this reaction wheel is based on fundamental design principles and can be replicated for either larger or smaller spacecraft as needed. Additionally, plans for bringing this design up to a prototyping and testing phase are outlined for continued use of this design in the Cal Poly CubeSat Laboratory.