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)--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. 1978. M.S.--Massachusetts Institute of Technology. Dept. of Aeronautics and Astronautics. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND AERONAUTICS. / Includes bibliographical references. / M.S.

Thesis. 1976. M.S. cn--Massachusetts Institute of Technology. Dept. of Aeronautics and Astronautics. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND AERO. / Includes bibliographical references. / M.S.cn

Thesis (MScEng)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: A new task scheduler for the Attitude Determination and Control System (ADCS) of the Stellenbosch University Satellite (SUNSAT) has been designed and tested on a personal computer. This new scheduler is capable of uploading new control tasks, or changing existing control tasks, on an individual basis. This is an improvement on the current ADCS task scheduler, where the control tasks are hard-coded in the scheduler, requiring the entire software image of the scheduler to be uploaded if a new task is to be added, or an existing task is to be changed. The new scheduler was developed using the Java programming language. The Java ClassLoader class is used to dynamically load tasks to a linked list. The scheduler thread runs through this linked list and schedules all the tasks that have become schedulable. New tasks can be added to the list without stopping the scheduler. The new scheduler has been successfully implemented on a personal computer, laying a good foundation for implementation in an embedded environment based on processors such as the T800 Transputer of the ADCS or the 80386 processor of the secondary onboard computer (OBC2). / AFRIKAANSE OPSOMMING: 'n Nuwe taak skeduleerder vir die orientasie beheerstelsel (Engels: Attitude Determination and Control System, of ADCS) van die Stellenbosch Universiteit Satelliet (SUNSAT) is ontwerp en getoets op 'n persoonlike rekenaar. Hierdie nuwe skeduleerder het die verrnoee om ekstra beheertake op te laai, of bestaande beheertake te wysig, onafhanklik van mekaar. Dit is 'n verbetering op die huidige ADCS taak skeduleerder waar take hard gekodeer is in die skeduleerder en waar vereis word dat die volledige sagteware beeld van die skeduleerder opgelaai moet word indien 'n nuwe taak bygevoeg wil word of 'n bestaande taak gewysig wil word. Die nuwe skeduleerder is ontwikkel met behulp van die Java programmeringstaal. Die Java C/assLoader klas is gebruik om take dinamies te laai en te voeg by 'n skakellys. Die skeduleerder proses stap dan deur hierdie skakellys en skeduleer aile take wat skeduleerbaar geword het. Nuwe take kan by die skakellys gevoeg word sonder om die skeduleerder te stop. Die nuwe skeduleerder is suksesvol ge'lmplementeer op 'n persoonlike rekenaar en Ie 'n goeie grondslag vir implementering in 'n toegewyde stelsel omgewing gebaseer op byvoorbeeld die T800 Transputer van die ADCS of die 80386 verwerker van die sekondere aanboord rekenaar (OBC2).

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.

Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: The use of electrodynamic tethers on-board satellites is an exciting scientific prospect. These conductive tethers provide the means for satellites to generate power and to do propulsion by electrodynamic interaction with the geomagnetic field. Although well researched in theory, the concept has not enjoyed much success in practice. This study aims to utilise low-cost CubeSats as experimental tool to verify many of the theoretical principles that govern the behaviour of conductive tethers in orbit. The study provides a theoretical background of the concept by evaluating past tether missions and analysing existing theory. A feasible application of an electrodynamic tether within the size and weight limitations of a Nano-satellite is formulated. Existing theoretical work is adapted to model the dynamics and electrodynamics of specifically Nano-satellites. Using these mathematical models, control and estimation algorithms are designed which would provide stable deployment of a tethered CubeSat pair and stable control of the orientation of the tethered system. To be able to implement these algorithms on a satellite mission, a prototype of a sensor capable of measuring the angle of the tether using a CMOS camera is designed and built. A hardware platform is built to test the deployment of the tether using an electric motor. Electronics are designed to control the operation of the camera, to do motor control, and to run control and estimation algorithms. Using the results obtained from the practical tests done on the hardware, and using the theoretical models and control algorithms designed, a full orbital simulation of the deployment was done. This simulation includes the performance of the deployment system, the electrodynamic performance of the tether in earth‟s plasmasphere, and the estimation and control algorithms to control the system. Different deployment strategies are analysed and their performance are compared. / AFRIKAANSE OPSOMMING: Die gebruik van elektrodinamiese toue aanboord satelliete is 'n opwindende wetenskaplike vooruitsig. Hierdie geleidende toue verleen aan die satelliete die vermoë om krag op te kan wek en propulsie deur elektriese interaksie met die geomagnetiese veld te kan doen. Alhoewel dit goed nagevors is in teorie, het die konsep nog nie veel sukses in die praktyk geniet nie. Hierdie studie het dit ten doel om lae-koste CubeSats aan te wend as 'n eksperimentele instrument om baie van die teoretiese beginsels wat geld vir die gedrag van geleidende toue in wentelbane te verifieer. Die studie bied 'n teoretiese agtergrond van die konsep deur die evaluering van vorige tou-missies sowel as die analise van bestaande teorie. 'n Uitvoerbare toepassing van 'n elektrodinamiese tou binne die grootte- en gewigsbeperkinge van 'n Nano-satelliet is geformuleer. Bestaande teoretiese werk is aangepas om die dinamika en elektrodinamika spesifiek van toepassing op Nano-satelliete, te modelleer. Deur hierdie wiskundige modelle te gebruik, is beheer- en afskattingsalgoritmes ontwerp wat stabiele ontplooiing van 'n verbinde CubeSat-paar en stabiele beheer van die oriëntasie van die verbinde stelsel sal verseker. Om hierdie algoritmes te implementeer op 'n satelliet-sending, is 'n prototipe van 'n sensor wat in staat is om die hoek van die tou met behulp van 'n CMOS kamera te meet, ontwerp en gebou. 'n Hardeware platform is gebou om die ontplooiing van die tou met behulp van 'n elektriese motor te toets. Elektronika is ontwerp om die kamera te beheer, motor beheer te doen asook om beheer- en afskattingsalgoritmes uit te voer. Deur gebruik te maak van die resultate wat verkry is tydens die praktiese toetse wat gedoen is op die hardeware, en deur gebruik te maak van die teoretiese modelle en beheeralgoritmes wat ontwerp is, is 'n volle wentelbaan-simulasie van die ontplooiing gedoen. Hierdie simulasie sluit die gedrag van die ontplooiingstelsel, die elektriese gedrag van die geleidende tou in die aarde se plasmasfeer, en die afskatting- en beheeralgoritmes om die stelsel te beheer in. Verskillende ontplooiingstrategieë word ontleed en hul gedrag word vergelyk.

Thesis (MEng)-- Stellenbosch University, 2013. / ENGLISH ABSTRACT: The next generation of CubeSats will require accurate attitude knowledge throughout orbit for advanced science payloads and high gain antennas. A star tracker can provide the required performance, but star trackers have traditionally been too large, expensive and power hungry to be included on a CubeSat. The aim of this project is to develop and demonstrate a CubeSat compatible star tracker. Subsystems from two other CubeSat components, CubeSense and CubeComputer, were combined with a sensitive, commercial image sensor and low-light lens to produce one of the smallest star trackers in existence. Algorithms for star detection, matching and attitude determination were investigated and implemented on the embedded system. The resultant star tracker, named CubeStar, can operate fully autonomously, outputting attitude estimates at a rate of 1 Hz. An engineering model was completed and demonstrated an accuracy of better than 0.01 degrees during night sky tests. / AFRIKAANSE OPSOMMING: Die volgende generasie van CubeSats sal akkurate orientasie kennis vereis gedurende 'n volle omwentelling van die aarde. 'n Sterkamera kan die vereiste prestasie verskaf, maar sterkameras is tradisioneel te groot, duur en krag intensief om ingesluit te word aanboord 'n CubeSat. Die doel van hierdie projek is om 'n CubeSat sterkamera te ontwikkel en te demonstreer. Substelsels van twee ander CubeSat komponente, CubeSense en CubeComputer, was gekombineer met 'n sensitiewe kommersiële beeldsensor en 'n lae-lig lens om een van die kleinste sterkameras op die mark te produseer. Algoritmes vir die ster opsporing, identi kasie en orientasie bepaling is ondersoek en geïmplementeer op die ingebedde stelsel. Die gevolglike sterkamera, genaamd CubeStar, kan ten volle outonoom orientasie afskattings lewer teen 'n tempo van 1 Hz. 'n Ingenieursmodel is voltooi en 'n akkuraatheid van beter as 0.01 grade is gedemonstreer.

Thesis (PhD)--Stellenbosch University, 1995. / ENGLISH ABSTRACT: New advanced control techniques for attitude determination and control of small (micro) satellites are presented. The attitude sensors and actuators on small satellites are limited in accuracy and performance due to physical limitations, e.g. volume, mass and power. To enhance the application of sophisticated payloads such as high resolution imagers within these confinements, a multi-mode control approach is proposed, whereby various optimized controller functions are utilized during the orbital life of the satellite. To keep the satellite's imager and antennas earth pointing with the minimum amount of control effort, a passive gravity gradient boom, active magnetic torquers and a magnetometer are used. A "cross-product" detumbling controller and a robust Kalman filter angular rate estimator are presented for the preboom deployment phase. A fuzzy controller and magnetometer full state extended Kalman filter are presented for libration damping and Z-spin rate control during inactive imager periods. During imaging, when high performance is required, additional fine resolution earth horizon, sun and star sensors plus 3-axis reaction wheels are employed. Full state attitude, rate and disturbance estimation is obtained from a horizon/sun extended Kalman filter. A quaternion feedback reaction wheel controller is presented to point or track a reference attitude during imaging. A near-minimum time, eigenaxis rotational reaction wheel controller for large angular maneuvers. Optimal linear quadratic and minimum energy algorithms to do momentum dumping using magnetic torquers, are presented. A new recursive magnetometer calibration method is designed to enhance the magnetic in-flight measurements. Finally, a software structure is proposed for the future onboard implementation of the multi-mode attitude control system. / AFRIKAANSE OPSOMMING: Nuwe gevorderde beheertegnieke vir die oriëntasiebepaling en -beheer van klein (mikro-) satelliete word behandel. Die oriëntasiesensors en -aktueerders op klein satelliete het 'n beperkte akkuraatheid en werkverrigting as gevolg van fisiese volume, massa en kragleweringbeperkings. Om gesofistikeerde loonvragte soos hoë resolusie kameras binne hierdie tekortkominge te kan hanteer, word 'n multimode beheerbenadering voorgestel. Hiermee kan 'n verskeidenheid van optimale beheerfunksies gedurende die wentelleeftyd van die satelliet gebruik word. Om die satellietkamera en -antennas aardwysend te rig met 'n minimale beheerpoging, word 'n passiewe graviteitsgradiëntstang, aktiewe magneetspoele en 'n magnetometer gebruik. 'n "Kruisproduk" onttuimellings beheerder en 'n robuuste hoektempo Kalmanfilter afskatter is ontwikkel vir die periode voordat die graviteitsgradiëntstang ontplooi word. 'n Wasige beheerder en 'n volledige toestand, uitgebreide Kalmanfilter afskatter is ontwikkel om librasiedemping en Z-rotasietempo beheer te doen gedurende tydperke wanneer die kamera onaktief is. Gedurende kamera-opnames word hoë werkverrigting verlang. Fyn resolusie aardhorison, son en stersensors met 3-as reaksiewiele kan dan gebruik word. 'n Volledige oriëntasie, hoektempo en steurdraaimoment Kalmanfilter afskatter wat inligting van bogenoemde sensors gebruik, is ontwikkel. 'n “Quaternion” reaksiewiel terugvoerbeheerder waarmee die satelliet na verwysings oriëntasiehoeke gerig kan word of waarmee oriëntasiehoektempos gevolg kan word, word behandel. 'n Naby minimumtyd, "eigen"-as reaksiewielbeheerder vir groothoek rotasies is ontwikkel. Optimale algoritmes om momentumontlading van reaksiewiele met lineêre kwadratiese en minimumenergie metodes te doen, word afgelei en aangebied. 'n Nuwe rekursiewe kalibrasietegniek waarmee 'n magnetometer outomaties gedurende vlug ingestel kan word, is ontwikkel. Ten slotte, word 'n programstruktuur voorgestel vir aanboord implementering van die nuwe multimode beheerstelsel.

Most present day spacecrafts have large interconnected solar panels. The dynamic behavior of the spacecraft in orbit can be modeled as a free rigid mass with flexible elements attached to it. The natural frequencies of such spacecrafts with deployed solar panels are very low. The low values of the natural frequencies pose difficulties for maneuvering the spacecraft. The control torque required to maneuver the spacecraft is influenced by the flexibility of the solar arrays. The control torque sets up transient oscillations in the flexible solar panels which in turn induces disturbances in the rigid satellite body and the payload within. Therefore the payload operations can be carried out only after the disturbances die out. For any reduction of the above disturbances it is necessary to understand the dynamic behavior of such systems to an applied torque. The present work first studies the nature of the disturbances. The influence of structural parameters on these disturbances is then investigated. Finally, the use of passive damping treatment using viscoelastic material is investigated for the reduction of the disturbances. In order to understand the nature of vibrations induced in the flexible appendages of a satellite during maneuvers, we model the maneuver loads in terms of applied angular acceleration as well as varying torque. The transient decay of the disturbance of the rigid element is characterized by the dynamic characteristics of the flexible panels or appendages. It is shown that by changing the stiffness of the panel the response of the rigid element can be modified. A simple model consisting of an Euler-Bernoulli beam attached to a free mass is next considered. The influence of various parameters of the EulerBernoulli beam in mitigating vibration and thereby the disturbance in the rigid mass is investigated. As the response of the rigid system mounted with the large flexible panels are influenced by the dynamics of the flexible panels, reduction of these disturbances can be achieved by reducing the vibration in the flexible panels. Therefore application of viscoelastic materials for passive damping treatment is investigated. The loss factor of a structure is significantly improved by using constrained viscoelastic layer damping treatment. However providing a constrained layer damping treatment on the entire structure is very inefficient in terms of the additional mass involved. Therefore damping material is applied at suitable optimal locations. In previous studies reported in literature, modal strain energy distribution in the viscoelastic material as well as the base structure is used as a tool to arrive at the optimum location for the damping treatment. It is shown in this study that such locations selected are not the optimum. A new approach is proposed in this study by which both the above shortcomings are overcome. It is shown that use of a parameter that is the ratio of the strain in the viscoelastic material to the angle of flexure is a more reliable measure in arriving at optimal locations for the application of constrained viscoelastic layers. The method considers the deformations in the viscoelastic material and it is shown that significant values of loss factors are achieved by providing material in a small region alone. We also show that loss factor can be improved by providing damping material near the interface region. The loss factor can be further improved by incorporating spacers by using spacer material having higher extensional modulus. Also shown is the fact that loss factor is unaffected by the shear modulus of the spacer material. Experiments have been conducted to validate these results. In a related study we consider honeycomb type flexible structures since in most of the spacecraft applications honeycomb sandwich constructions are employed. But loss factors of sandwich panels with constrained layer damping treatment are seldom discussed in the literature. Use of viscoelastic layers to improve the loss factors of the honeycomb sandwich beams is explored. The results show that the loss factors are enhanced by increasing the inplane stiffness of the constraining layer. These conclusions too are validated by experimental results. Finally a typical satellite with flexible solar panels is considered, and the use of the viscoelastic material for improving the damping is demonstrated.