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.

A three-rotational degree of freedom attitude control system has been developed for the NASA Jet Propulsion Laboratory’s INSPIRE Project by the Texas Spacecraft Laboratory at The University of Texas at Austin. Using 3D plastic printing manufacturing techniques, a cold gas thruster system was created in order to detumble and maintain the attitude of two 3U CubeSats traveling through interplanetary space. A total of four thruster units were produced, including two engineering designs and two flight units. The units feature embedded sensors and millisecond level thrust control while using an inert, commercially-available refrigerant as a propellant. The thrust, minimum impulse bit, and specific impulse performance of the cold gas units was characterized using a ballistic pendulum test stand within a microtorr vacuum chamber. A heating element was used to change the temperature conditions of the propellant and determine the relationship between temperature and performance. The flight units were delivered in January of 2014 and the INSPIRE satellites are expected to launch in the upcoming year. / text

O sistema de controle por alocação dos pólos com filtro foi utilizado para controlar a atitude de um modelo de veículo lançador de satélites. Com este intuito, foram confeccionados um modelo e uma base de fixação que permite a movimentação nos três graus de liberdade. Utilizando a resposta à entrada degrau em conjunto com um sistema de controle PID obtido de forma empírica para estabilizar o sistema, as características da planta foram identificadas e então o sistema de controle por alocação de pólos foi projetado. Este sistema apresentou uma oscilação em torno da referência com amplitude menor do que 0,5° e tempo de pico para a entrada degrau na ordem de 2,17 segundos. Um segundo controlador PID foi projetado de forma analítica para se obter uma referência, porém apresentou resposta com características inferiores ao controlador por alocação de pólos. Os dois sistemas de controle projetados conseguem manter o modelo estável mesmo quando um dos motores é desligado. / Pole placement control system with filter was implemented to control the attitude of a satellite launch vehicle model. With this purpose, a model and a fixing base with three degrees of freedom was made. Utilizing the system response to step input with PID controller empirically designed to stabilize the system, the model characteristics were identified and the pole placement control system was designed. This system oscillated around the reference with amplitude smaller than 0.5° and peak time around 2.17 seconds. Another PID controller was designed analytically for reference, however the pole placement controller had better response characteristics than the PID controller. Both controllers can stabilize the system even when one engine is shut off.

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

Neural networks play an important role in the execution of goal-oriented paradigms. They offer flexibility, adaptability and versatility, so that a variety of approaches may be used to meet a specific goal, depending upon the circumstances and the requirements of the design specifications. Development of higher-order neural units with higher-order synaptic operations will open a new window for some complex problems such as control of aerospace vehicles, pattern recognition, and image processing. The neural models described in this thesis consider the behavior of a single neuron as the basic computing unit in neural information processing operations. Each computing unit in the network is based on the concept of an idealized neuron in the central nervous system (CNS). Most recent mathematical models and their architectures for neuro-control systems have generated many theoretical and industrial interests. Recent advances in static and dynamic neural networks have created a profound impact in the field of neuro-control. Neural networks consisting of several layers of neurons, with linear synaptic operation, have been extensively used in different applications such as pattern recognition, system identification and control of complex systems such as flexible structures, and intelligent robotic systems. The conventional linear neural models are highly simplified models of the biological neuron. Using this model, many neural morphologies, usually referred to as multilayer feedforward neural networks (MFNNs), have been reported in the literature. The performance of the neurons is greatly affected when a layer of neurons are implemented for system identification, pattern recognition and control problems. Through simulation studies of the XOR logic it was concluded that the neurons with linear synaptic operation are limited to only linearly separable forms of pattern distribution. However, they perform a variety of complex mathematical operations when they are implemented in the form of a network structure. These networks suffer from various limitations such as computational efficiency and learning capabilities and moreover, these models ignore many salient features of the biological neurons such as time delays, cross and self correlations, and feedback paths which are otherwise very important in the neural activity. In this thesis an effort is made to develop new mathematical models of neurons that belong to the class of higher-order neural units (HONUs) with higher-order synaptic operations such as quadratic and cubic synaptic operations. The advantage of using this type of neural unit is associated with performance of the neurons but the performance comes at the cost of exponential increase in parameters that hinders the speed of the training process. In this context, a novel method of representation of weight parameters without sacrificing the neural performance has been introduced. A generalised representation of the higher-order synaptic operation for these neural structures was proposed. It was shown that many existing neural structures can be derived from this generalized representation of the higher-order synaptic operation. In the late 1960s, McCulloch and Pitts modeled the stimulation-response of the primitive neuron using the threshold logic. Since then, it has become a practice to implement the logic circuits using neural structures. In this research, realization of the logic circuits such as OR, AND, and XOR were implemented using the proposed neural structures. These neural structures were also implemented as neuro-controllers for the control problems such as satellite attitude control and model reference adaptive control. A comparative study of the performance of these neural structures compared to that of the conventional linear controllers has been presented. The simulation results obtained in this research were applicable only for the simplified model presented in the simulation studies.

Neural networks play an important role in the execution of goal-oriented paradigms. They offer flexibility, adaptability and versatility, so that a variety of approaches may be used to meet a specific goal, depending upon the circumstances and the requirements of the design specifications. Development of higher-order neural units with higher-order synaptic operations will open a new window for some complex problems such as control of aerospace vehicles, pattern recognition, and image processing. The neural models described in this thesis consider the behavior of a single neuron as the basic computing unit in neural information processing operations. Each computing unit in the network is based on the concept of an idealized neuron in the central nervous system (CNS). Most recent mathematical models and their architectures for neuro-control systems have generated many theoretical and industrial interests. Recent advances in static and dynamic neural networks have created a profound impact in the field of neuro-control. Neural networks consisting of several layers of neurons, with linear synaptic operation, have been extensively used in different applications such as pattern recognition, system identification and control of complex systems such as flexible structures, and intelligent robotic systems. The conventional linear neural models are highly simplified models of the biological neuron. Using this model, many neural morphologies, usually referred to as multilayer feedforward neural networks (MFNNs), have been reported in the literature. The performance of the neurons is greatly affected when a layer of neurons are implemented for system identification, pattern recognition and control problems. Through simulation studies of the XOR logic it was concluded that the neurons with linear synaptic operation are limited to only linearly separable forms of pattern distribution. However, they perform a variety of complex mathematical operations when they are implemented in the form of a network structure. These networks suffer from various limitations such as computational efficiency and learning capabilities and moreover, these models ignore many salient features of the biological neurons such as time delays, cross and self correlations, and feedback paths which are otherwise very important in the neural activity. In this thesis an effort is made to develop new mathematical models of neurons that belong to the class of higher-order neural units (HONUs) with higher-order synaptic operations such as quadratic and cubic synaptic operations. The advantage of using this type of neural unit is associated with performance of the neurons but the performance comes at the cost of exponential increase in parameters that hinders the speed of the training process. In this context, a novel method of representation of weight parameters without sacrificing the neural performance has been introduced. A generalised representation of the higher-order synaptic operation for these neural structures was proposed. It was shown that many existing neural structures can be derived from this generalized representation of the higher-order synaptic operation. In the late 1960s, McCulloch and Pitts modeled the stimulation-response of the primitive neuron using the threshold logic. Since then, it has become a practice to implement the logic circuits using neural structures. In this research, realization of the logic circuits such as OR, AND, and XOR were implemented using the proposed neural structures. These neural structures were also implemented as neuro-controllers for the control problems such as satellite attitude control and model reference adaptive control. A comparative study of the performance of these neural structures compared to that of the conventional linear controllers has been presented. The simulation results obtained in this research were applicable only for the simplified model presented in the simulation studies.

This thesis addresses the attitude control of satellites with similar and dissimilar actuators and control allocation methods on maneuvering. In addition, the control moment gyro (CMG) steering with gyroscopes having limited gimbal angle travel is also addressed. Full Momentum envelopes for a cluster of four CMG&#039 / s are obtained in a pyramid type mounting arrangement. The envelopes when gimbal travel is limited to plus-minus 90 degree are also obtained. The steering simulations using Moore Penrose (MP) pseudo inverse as well as blended inverse are presented and success of the pre planned blended inverse steering in avoiding gimbal angle limits is demonstrated through satellite slew maneuver simulations, showing the completion of the maneuver without violating gimbal angle travel restrictions. Dissimilar actuators, CMG and magnetic torquers are used as an approach of overactuated system. Steering simulations are carried out using different steering laws for constant torque and desired satellite slew maneuver scenarios. Success of the blended inverse steering algorithm over MP pseudo inverse is also demonstrated

The analysis, verification and emulation of attitude control hardware for nanosatellite spacecraft is described. The overall focus is on hardware that pertains to a multitude of missions currently under development at the University of Toronto Institute for Aerospace Studies - Space Flight Laboratory. The requirements for these missions push the boundaries of what is currently the accepted performance level of attitude control hardware. These new performance envelopes demand new acceptance test methods which must verify the performance of the attitude control hardware. In particular, reaction wheel and hysteresis rod actuators are the focus. Results of acceptance testing are further employed in post spacecraft integration for hardware emulation. This provides for a reduced mission cost as a function of reduced spare hardware. The overall approach provides a method of acceptance testing to new performance envelopes with the benefit of cost reduction with hardware emulation for simulations during post integration.

The analysis, verification and emulation of attitude control hardware for nanosatellite spacecraft is described. The overall focus is on hardware that pertains to a multitude of missions currently under development at the University of Toronto Institute for Aerospace Studies - Space Flight Laboratory. The requirements for these missions push the boundaries of what is currently the accepted performance level of attitude control hardware. These new performance envelopes demand new acceptance test methods which must verify the performance of the attitude control hardware. In particular, reaction wheel and hysteresis rod actuators are the focus. Results of acceptance testing are further employed in post spacecraft integration for hardware emulation. This provides for a reduced mission cost as a function of reduced spare hardware. The overall approach provides a method of acceptance testing to new performance envelopes with the benefit of cost reduction with hardware emulation for simulations during post integration.