Retrospective Cost-based Adaptive Spacecraft Attitude Control.

Fixed gain attitude control laws are sensitive to modeling errors and actuator nonlinearities. Adaptive control can solve many of these challenges. We present a retrospective cost-based adaptive spacecraft attitude controller designed using the system's impulse response as modeling information. The performance metric is based on rotation matrices and thus, the controller does not suffer from singularities or discontinuities present in vector attitude representations. We demonstrate robustness to inertia and actuator scaling as well as actuator misalignment and nonlinearities, unknown disturbances, sensor noise and bias for thrusters and reaction wheels through numerical simulations. We implement an averaged Markov parameter and decentralized control to address the problem of the singular input matrix of magnetic torquers. For control moment gyros, we develop a hybrid linearization and impulse response-based Markov parameter and present new guidelines to evaluate the feasibility of desired rest-to-rest maneuvers. Finally, we address the problem of angular velocity-free attitude control of a flexible spacecraft with noncollocated sensors and actuators. We present a new approach to controlling harmonic nonminimum-phase systems using the step and impulse response of the linearized system. We demonstrate robustness to model uncertainty through system analysis and numerical simulations.PhDAerospace EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/111607/1/gecruz_1.pd

Recovery of spinning satellites

The behavior of a space tug and a spinning satellite in a coupled configuration was simulated and analyzed. A docking concept was developed to investigate the requirements pertaining to the design of a docking interface. Sensing techniques and control requirements for the chase vehicle were studied to assess the feasibility of an automatic docking. The effects of nutation dampers and liquid propellant slosh motion upon the docking transient were investigated

Spacecraft flight control system design selection process for a geostationary communication satellite

The Earth's first artificial satellite, Sputnik 1, slowly tumbled in orbit. The first U.S. satellite, Explorer 1, also tumbled out of control. Now, as we launch the Mars observer and the Cassini spacecraft, stability and control have become higher priorities. The flight control system design selection process is reviewed using as an example a geostationary communication satellite which is to have a life expectancy of 10 to 14 years. Disturbance torques including aerodynamic, magnetic, gravity gradient, solar, micrometeorite, debris, collision, and internal torques are assessed to quantify the disturbance environment so that the required compensating torque can be determined. Then control torque options, including passive versus active, momentum control, bias momentum, spin stabilization, dual spin, gravity gradient, magnetic, reaction wheels, control moment gyros, nutation dampers, inertia augmentation techniques, three-axis control, reactions control system (RCS), and RCS sizing, are considered. A flight control system design is then selected and preliminary stability criteria are met by the control gains selection

Proportional-Derivative-Acceleration Feedback Controller Design for Single Axis Attitude Control of Rigid Spacecraft with Flexible Appendages

This study designs and analyzes a new type of controller that helps improve the performance of single axis attitude control of flexible appendages attached to a rigid spacecraft. Conventionally, PID with position feedback was used to control single axis attitude manoeuvre of flexible appendages on a spacecraft but designing a PID to control a higher order system is a limited strategy. Also, PID controllers are inherently unstable for third order systems and higher as will be demonstrated later. Thus, acceleration feedback is included in the design to demonstrate a more stable way of designing controllers for these systems and it is called PDA (Proportional Derivative Acceleration) controller. The controller is first designed using a root locus method and then applied to a simulated third order system om MATLAB. Then a higher order system model (rigid body with flexible appendage) is created on SIMULINK and the controller is applied to it. Finally, an experiment is performed and demonstrated to show the practical implementation of the control design

Propellant-Free Control of Tethered Formation Flight, Part 1: Linear Control and Experimentation

We introduce a decentralized attitude control strategy that can dramatically reduce the usage of propellant, by taking full advantage of the physical coupling of the tether. Motivated by a controllability analysis, indicating that both array resizing and spin-up are fully controllable by the reaction wheels and the tether motor, we report the first propellant-free underactuated control results for tethered formation flying spacecraft. This paper also describes the hardware development and experimental validation of the proposed method using the Synchronized Position Hold, Engage, and Reorient Experimental Satellites test bed. In particular, a new relative sensing mechanism that uses sixderee-of-freedom force-torque sensors and rate gyroscopes is introduced and validated in the closed-loop control experiments

Vertical Take-Off and Landing Control via Dual-Quaternions and Sliding Mode

The landing and reusability of space vehicles is one of the driving forces into renewed interest in space utilization. For missions to planetary surfaces, this soft landing has been most commonly accomplished with parachutes. However, in spite of their simplicity, they are susceptible to parachute drift. This parachute drift makes it very difficult to predict where the vehicle will land, especially in a dense and windy atmosphere such as Earth. Instead, recent focus has been put into developing a powered landing through gimbaled thrust. This gimbaled thrust output is dependent on robust path planning and controls algorithms. Being able to have a powered landing with on-board real-time control algorithms is absolutely essential to exploring the solar system as it is the only effective way to bring heavy equipment or people to a planetary surface. A robust, efficient, and easy-to-use controls algorithm will be formulated to solve this controls problem known as the \emph{soft landing problem}. Through representing rigid body motion with dual-quaternions, translation and rotation can be represented in a single compact form that is free of singularities and provides the shortest path interpolation compared to any other formulation. These rigid bodies will be shown to follow a desired time-dependent orientation and position through one of the most powerful methods of modern control known for its accuracy, robustness, and easy tuning and implementation -- sliding mode control

Modeling of an Autonomous Underwater Vehicle

Autonomous Underwater Vehicles (AUV) have multiple applications for military, commercial and research purposes. The main advantage of this technology is its independence. Since these vehicles operate autonomously, the need for a dedicated support vessel and human supervision is dismissed. However, the autonomous nature of AUVs also presents a complex challenge for the guidance, navigation and control system(s). The design of motion controllers for AUVs is model-based i.e. a dynamic model is used for the design of the control system. The dynamic model can also be used for simulation and performance analysis. In this context, the purpose of this thesis is to provide a dynamic model for a double-body research AUV being developed at CEiiA. This model is to be subsequently used for the design of the control system. Since the purpose is the design of the control system and, in the scope of providing multiple design approaches, the appropriate lateral and longitudinal subsystems are devised. These subsystems are subsequently validated by comparing simulation results for the subsystems with simulation results for the complete model. The AUV is modeled using Fossen’s dynamic model. The model is divided into kinematics and kinetics. Kinematics addresses the geometrical aspects of motion. For this purpose, both Euler angles and quaternions are used. Kinetics focuses on the relationship between motion and force. This model identifies four distinct forces that act on the underwater vehicle: rigid-body forces; hydrostatic forces; hydrosynamic damping (or drag) and added-mass. The estimation of model parameters is performed using analytical and computational methods. A detailed 3D CAD model, developed by CEiiA, proved helpful for estimating mass and inertia parameters as well as hydrostatic forces. Hydrodynamic damping estimation was performed by adapting CFD analysis, also developed by CEiiA, to satisfy model parameters. Added mass parameters were estimated using proven analytical methods. Due to limitations inherent to current modeling methods, simplifications were unavoidable. These, when analyzed considering the requirements of typical control systems, did not pose an impediment to the use of the dynamic model for this purpose. Regarding the dynamics of this AUV, the hydrodynamic analysis suggests that this AUV is unstable in the presence of angles of attack and side-slip. However the AUV’s motors should be capable of controlling such instabilities.Os veículos subaquáticos autónomos (Autonomous Underwater Vehicles – AUV’s) têm múltiplas aplicações militares, comerciais e para investigação científica. A grande vantagem destes veículos advém da sua independência, sendo que operam sem a necessidade de supervisão humana. No entanto esta capacidade implica que os sistemas de navegação, guia e controlo sejam completamente responsáveis pelo governo do veículo. O sistema de controlo destes veículos é tipicamente projetado tendo como base um modelo dinâmico do mesmo. Este modelo pode ser também usado para simulação e análise de desempenho. O propósito deste trabalho é desenvolver um modelo dinâmico para um AUV de investigação de duplo-corpo, a ser desenvolvido no CEiiA. Dado que o objetivo principal do modelo é projetar controladores e, de modo a fornecer várias abordagens para o efeito, os respetivos modelos (subsistemas) lateral e longitudinal são deduzidos. Estes modelos são posteriormente validados através da comparação de resultados de simulação para os subsistemas com os resultados de simulação para o modelo completo. A modelação deste veículo é efetuada usando o modelo dinâmico de Fossen. Este modelo pode ser dividido em cinemática e cinética. Cinemática aborda os aspetos geométricos do movimento. As equações de cinemática são fornecidas tanto para ângulos de Euler como para quaterniões. As equações de cinética centram-se na relação entre movimento e força. O modelo de Fossen identifica quatro forças distintas que influenciam a dinâmica dos veículos subaquáticos: forças de corpo rígido; forças hidrostáticas; amortecimento (atrito) hidrodinâmico e added mass. Estas forças são modeladas através de métodos analíticos e computacionais. O modelo CAD do veículo, desenvolvido pelo CEiiA, foi usado para estimar os parâmetros de massa e inércia, bem como forças hidrostáticas. O amortecimento hidrodinâmico foi estimado através da adaptação de análises CFD, também efetuadas pelo CEiiA, para satisfazer os parâmetros do modelo. Os parâmetros added mass foram estimados usando métodos analíticos comprovados. Devido a limitações inerentes aos métodos de modelação atuais, simplificações foram inevitáveis. As mesmas, quando analisadas tendo em conta os requisitos de sistemas de controlo típicos não provaram ser impeditivas da aplicação deste modelo para o desenvolvimento dos mesmos. No que diz respeito à dinâmica deste AUV, a análise hidrodinâmica sugere que este AUV é instável quando na presença de ângulos de ataque e derrapagem. No entanto os motores do AUV deverão ser capazes de corrigir tais instabilidades

Near Real-Time Closed-Loop Optimal Control Feedback for Spacecraft Attitude Maneuvers

Optimization of spacecraft attitude maneuvers can significantly reduce attitude control system size and mass, and extend satellite end-of-life. Optimal control theory has been applied to solve a variety of open-loop optimal control problems for terrestrial, air, and space applications. However, general application of real-time optimal controllers on spacecraft for large slew maneuvers has been limited because open-loop control systems are inherently vulnerable to error and the computation necessary to solve for an optimized control solution is resource intensive. This research effort is focused on developing a near real-time optimal control (RTOC) system for spacecraft attitude maneuvers on the Air Force Institute of Technology\u27s 2nd generation simulated satellite, SimSat II. To meet the end goal of developing a RTOC controller, necessary preliminary steps were completed to accurately characterize SimSAT II\u27s mass properties and attitude control system. Using DIDO, a pseudospectral-based optimal control solver package, to continuously solve and execute a sequence of optimized open-loop control solutions in near real-time, the RTOC controller can optimally control the state of the satellite over the course of a large angle slew maneuver. In this research, simulation and experimental results clearly demonstrate the benefit of RTOC versus other non-optimal control methods for the same maneuver

Simulation of actively controlled spacecraft with flexible appendages

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76688/1/AIAA-25388-716.pd

Control Of Flexible Structures-2 (COFS-2) flight control, structure and gimbal system interaction study

The second Control Of Flexible Structures Flight Experiment (COFS-2) includes a long mast as in the first flight experiment, but with the Langley 15-m hoop column antenna attached via a gimbal system to the top of the mast. The mast is to be mounted in the Space Shuttle cargo bay. The servo-driven gimbal system could be used to point the antenna relative to the mast. The dynamic interaction of the Shuttle Orbiter/COFS-2 system with the Orbiter on-orbit Flight Control System (FCS) and the gimbal pointing control system has been studied using analysis and simulation. The Orbiter pointing requirements have been assessed for their impact on allowable free drift time for COFS experiments. Three fixed antenna configurations were investigated. Also simulated was Orbiter attitude control behavior with active vernier jets during antenna slewing. The effect of experiment mast dampers was included. Control system stability and performance and loads on various portions of the COFS-2 structure were investigated. The study indicates possible undesirable interaction between the Orbiter FCS and the flexible, articulated COFS-2 mast/antenna system, even when restricted to vernier reaction jets