Effectiveness of solar radiation pressure in the three-axis attitude control of present day and next generation of large communications satellites is investigated. A simple two-flap configuration is used with optimization of the direction of the applied control moment rather than the magnitude of the weak solar radiation pressure. Simulations were carried out in the presence of varying orbital eccentricity and inclination, solar aspect angle and controller dynamics parameters. Time histories of librational response against orbital position are presented for controlled and uncontrolled conditions. The results suggest the semipassive controller to be quite effective over a wide range of system parameters and it can meet the exacting pointing accuracy demanded by large communications satellites. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

CubeSats have become popular among universities, research organizations, and government agencies due to their low cost, small size, and light weight. Their standardized configurations further reduce the development time and ensure more frequent launch opportunities. Early cubesat missions focused on hardware validation and simple communication missions, with little requirement for pointing accuracy. Most of these used magnetic torque rods or coils for attitude stabilization. However, the intrinsic problems associated with magnetic torque systems, such as the lack of three-axis control and low pointing accuracy, make them unsuitable for more advanced missions such as detailed imaging and on-orbit inspection. Threeaxis control in a cubesat can be achieved by combining magnetic torque coils with other devices such as thrusters, but the lifetime is limited by the fuel source onboard. To maximize the mission lifetime, a fast attitude control management algorithm that could optimally manage the usage of the magnetic and thruster torques is desirable. Therefore, a recently developed method, the BSpline-augmented virtual motion camouflage, is presented in this defense to solve the problem. This approach provides results which are very close to those obtained through other popular nonlinear constrained optimal control methods with a significantly reduced computational time. Simulation results are presented to validate the capabilities of the method in this application

No description available.

Pontryagin's principle is applied to several significant problems associated with optimal large angle spacecraft rotational maneuvers. Both rigid and flexible body dynamical models for these vehicles are considered. Three relaxation/analytic continuation methods are developed for iteratively solving the two-point-boundary value problem which results in the treatment of these problems. The solutions obtained are required to rigorously satisfy the necessary conditions derived from Pontryagin's principle. These methods include: (1) boundary condition relaxation processes; (2) differential equation relaxation processes; and (3) hybrid relaxation processes, combining (1) and (2) above. In the literature these relaxation processes are closely related to a number of methods for solving nonlinear equations, known as Davidenko's method, imbedding, and homotopy chain methods. For rigid vehicles a general nonsingular optimal maneuver formulation is obtained, treating all kinematic and dynamical nonlinearities, for general orientation and angular velocity boundary conditions. For flexible vehicles restricted to single axis maneuvers and anti-symmetric elastic deflection modes, a general optimal maneuver formulation is obtained; treating all kinematic, dynamical, and first order structural nonlinearities. In the case of general motion for a flexible vehicle a general formulation is provided, though a solution is not obtained; due to a previously unidentified and as yet unresolved computational difficulty associated symmetry in the dynamical model for the spacecraft. / Ph. D.

Polynomial feedback controls are developed for large angle, nonlinear spacecraft attitude maneuvers. Scalar and two-state systems are presented as simple examples to demonstrate the method, and several systems of state variables to parameterize spacecraft motion are considered. Both external and internal control torques are treated; in the latter, attention is restricted to momentum transfer maneuvers that permit several order reductions. Several stability theorems with their application to polynomial feedback systems are discussed. / Ph. D.

Thesis (MScEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: With CubeSats becoming popular as a cheap alternative to larger satellites, the need for advanced miniature attitude determination and control systems (ADCS) arises to meet the pointing requirements of satellite operations such as earth imaging and orbit maintenance. This thesis describes the design of a complete ADCS for use on CubeSats. A previously designed CubeSat on-board-computer, CubeComputer, and ne sun and nadir sensor, CubeSense, is incorporated in the design. The remaining requirements with regard to sensors and actuators were met by CubeControl, an additional module, the design, manufacturing and testing of which are described. CubeControl can implement magnetic control with the use of a magnetometer and three magnetorquers. It is also capable of driving three reaction wheels for accurate active 3-axis stabilization. / AFRIKAANSE OPSOMMING: Met CubeSats wat gewild raak as 'n goedkoop alternatief tot groter satelliete ontstaan die behoefte vir gevorderde miniatuur ori entasiebepaling en -beheerstelsels wat satelliet operasies soos aardwaarneming en wentelbaan korreksies moontlik maak. Hierdie tesis beskryf die ontwerp van 'n volledige ori entasiebepaling en -beheerstelsel vir CubeSats. 'n Voorheen ontwikkelde CubeSat aanboordrekenaar, CubeComputer, en 'n fyn sonsensor en nadirsensor, CubeSense, is ingesluit in die ontwerp. Die orige benodighede met verband tot sensors en aktueerders word vervul deur CubeControl, 'n addisionele module waarvan die ontwerp, vervaardiging en toetsing beskyf word. CubeControl kan magnetiese beheer implementeer deur gebruik te maak van 'n magnetometer en drie magneetstange. Dit kan ook drie reaksiewiele aandryf vir akkurate aktiewe 3-as stabilisering.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2007. / During an imaging pass of a remote sensing satellite, the satellite’s attitude has to be controlled so that the imager bore-sight sweeps out equal distances over time and so that images with a square aspect ratio are produced. The satellite attitude control system uses forward motion compensation (FMC) and time delay and integration (TDI) techniques to increase the quality of images. The motion of the scene relative to the satellite camera can be described by a two dimensional translation motion and a rotation about the camera bore-sight. This thesis describes an algorithm for measuring ground motion from viewfinder video data that can aid the satellite control system during imaging missions. The algorithm makes use of existing motion-from-video techniques – it operates in a hierarchical, feature-tracking framework. Features are identified on camera frames, and correspondences on consecutive frames are found by the Lucas and Kanade algorithm. A pyramidal image representation enables the estimation of large motions. The resultant sparse disparity map is used to estimate the three motion parameters, using a least squares fit to the projected motion equations. The algorithm was developed and implemented as part of the MSMI project. Results of tests carried out on simulated satellite viewfinder data (using the Matrix Sensor camera that was also developed for the MSMI project) confirms that the requirements are met.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1981. / Microfiche copy available in Archives and Barker / Bibliography: leaves 108-109. / by William Neil McCasland. / M.S.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1979. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND AERONAUTICS. / Bibliography: leaf 72. / by Yuji Hanawa. / M.S.

Jia Peng. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references (leaves 85-87). / Abstracts in English and Chinese. / Abstract --- p.iv / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Overview of Output Regulation Problem --- p.2 / Chapter 1.2 --- Attitude Tracking Control of Rigid Spacecraft --- p.3 / Chapter 1.3 --- Overview of Continuous-time Nonlinear H∞ Control --- p.4 / Chapter 1.4 --- Overview of Discrete-time Nonlinear Hq∞ Control --- p.6 / Chapter 1.5 --- Flight Control in Windshears --- p.8 / Chapter 1.6 --- Nonlinear Benchmark System --- p.9 / Chapter 1.7 --- Outline of the Work --- p.11 / Chapter 2 --- Attitude Control and Asymptotic Disturbance Rejection of Rigid Spacecraft --- p.12 / Chapter 2.1 --- Model Description --- p.12 / Chapter 2.2 --- Problem Formulation --- p.16 / Chapter 2.3 --- Preliminaries of General Framework for Global Robust Output Regulation --- p.17 / Chapter 2.4 --- Application of Global Robust Output Regulation --- p.21 / Chapter 2.4.1 --- Case I: without unknown parameters --- p.21 / Chapter 2.4.2 --- Case II: with unknown parameters --- p.26 / Chapter 2.5 --- Simulation --- p.34 / Chapter 2.5.1 --- Case I: without unknown parameters --- p.34 / Chapter 2.5.2 --- Case II: with unknown parameters --- p.36 / Chapter 2.6 --- Conclusions --- p.38 / Chapter 3 --- Application of Approximation Continuous-time Nonlinear H∞ Control Law --- p.45 / Chapter 3.1 --- Preliminaries of Approximation Continuous-time Nonlinear Hq∞ Control Law --- p.45 / Chapter 3.2 --- Disturbance Attenuation of Flight Control System in Windshears --- p.50 / Chapter 3.2.1 --- Design of Control Law --- p.51 / Chapter 3.2.2 --- Computer Simulation --- p.56 / Chapter 3.3 --- Conclusions --- p.57 / Chapter 4 --- Application of Approximation Discrete-time Nonlinear H∞ Control Law --- p.65 / Chapter 4.1 --- Preliminaries of Approximation Discrete-time Nonlinear H∞ Control Law --- p.66 / Chapter 4.2 --- Explicit Expression of u --- p.69 / Chapter 4.3 --- Disturbance Attenuation of RTAC System --- p.73 / Chapter 4.4 --- Computer Simulation --- p.78 / Chapter 4.5 --- Conclusions --- p.80 / Chapter 5 --- Conclusions --- p.83 / Bibliography --- p.85 / A Programs --- p.88 / Vita --- p.112