Path planning and position control and of an underactuated electromagnetic formation flight satellite system in the near field

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2013.This thesis was scanned as part of an electronic thesis pilot project.Cataloged from PDF version of thesisIncludes bibliographical references (p. 117-119).Electromagnetic formation flight is the process of using electromagnetic actuators (coils) on multiple spacecraft to produce relative (internal) forces in order to control the relative position and orientation of the spacecraft. This thesis demonstrates the ability to experimentally generate the relative internal electromagnetic forces in a short duration full 6DOF environment. Next the thesis limits itself to a two-satellite system and thus is able to perform a state reduction that constrains the motion to an arbitrary two-dimensional plane in 3-dimensional space showing that this is not actually a constraint on the real system for a two satellite formation. A feedback control law is proposed and simulated in this constrained space demonstrating position control of the underactuated system. Some theoretical guarantees are derived from contraction analysis. Finally time and energy optimal paths for a series of maneuvers are conceived by application of the GPOPS - II numerical optimization software. The results show further that the underactuated system is capable of arbitrary position control with the limitation being that it is unable to simultaneously control attitude and position to desired states because the attitude is used to "steer" the magnetic dipole therefore the desired angle is set by the position controller rather than an external reference. Overall this thesis shows the viability from the controllability perspective of underactuated electromagnetic formation flight for future space missions.by Alexander James Buck.S.M

Strategies for attitude control of reconfigurable modular spacecraft

The purpose of this thesis is to propose, investigate and develop an innovative approach to the attitude control of Cubesat-sized, modular and variable-shape spacecraft. These systems could ideally comply with the requirements of a larger variety of in-orbit functions and better adapt to the needs of specific subsystems in achieving and maintaining the desired attitude. The reference array is assumed to consist of a certain number of modules interconnected by means of revolute joints. One interesting aspect, which is the specific focus of the present thesis, is that such system can be capable of exploiting the dynamic effect of momentum conserving internal torques generated by the modules rotating with respect to each other for reorientation purposes. Initial inspiration for this proposed approach to spacecraft attitude control design has been drawn from the study of the well known 'falling cat' problem. In the long term, this innovative attitude control methodology, could justify the increase in cost and complexity modular reconfigurable systems require not only with advantages in the added versatility with respect to the mission tasks but also with better performance in attitude control system efficiency, accuracy, stability and even robustness. Specifically, this thesis discusses the available information present in literature about momentum preserving attitude control of multibody arrays and possible space applications, builds and validates a tool for the investigation of the peculiarities of these systems and finally investigates their non-linear behaviour for both the 2D and 3D cases. With respect to previous work in the field, optimal attitude control trajectories that take into account module impingement are discussed and the dynamics of momentum-preserving manoeuvres is analysed from the physical and mathematical points of view for both 2D and 3D manoeuvres. The results of the analysis demonstrate the validity of the concept and highlighted some the potentialities but also the critical points for a further development of the technology

Optimal Guidance and Control for Electromagnetic Formation Flying

学位の種別: 修士University of Tokyo(東京大学

OPTIMAL ATTITUDE MANEUVERS FOR THE KEPLER K2 MISSION

The Kepler satellite was designed to detect stars with planets capable of supporting life. After completing its primary mission, two of the satellite’s four reaction wheels failed, severely degrading the spacecraft attitude control system. In order to continue providing useful data to the scientific community, NASA has arranged a new mission for the Kepler satellite known as the K2 mission. The K2 mission currently uses a hybrid control approach for rotating the satellite that relies on thrusters for augmenting the authority of the remaining wheels. This thesis explores the application of optimal control for minimizing fuel consumption in support of the K2 mission. Such an approach is useful not only for momentum management during pointing but also for large angle slews needed to support non-science operation. Reducing fuel consumption will further extend the life of the K2 mission. Optimal control was shown in this thesis to reduce fuel consumption by as much as 28 percent during momentum management and 30 percent for large angle maneuvers. The results of this thesis are also applicable to other missions where it is desired to operate an underactuated spacecraft in the most fuel-efficient manner possible.Lieutenant Commander, United States NavyApproved for public release; distribution is unlimited

Dynamic humanoid locomotion: Hybrid zero dynamics based gait optimization via direct collocation methods

Hybrid zero dynamics (HZD) has emerged as a popular framework for dynamic and underactuated bipedal walking, but has significant implementation difficulties when applied to the high degrees of freedom present in humanoid robots. The primary impediment is the process of gait design–it is difficult for optimizers to converge on a viable set of virtual constraints defining a gait. This dissertation presents a methodology that allows for the fast and reliable generation of efficient multi-domain robotic walking gaits through the framework of HZD, even in the presence of underactuation. To achieve this goal, we unify methods from trajectory optimization with the control framework of multi-domain hybrid zero dynamics. We present a novel optimization formulation in the context of direct collocation methods and HZD where we rigorously generate analytic Jacobians for the constraints. Two collocation methods, local collocation and pseudospectral (global) collocation, are developed within an unified framework, and their performance in different circumstances is comparatively studied. As a result, solving the resulting nonlinear program becomes tractable for large-scale NLP solvers, even for systems as high-dimensional as humanoid robots. We experimentally validate our methodology on the spring-legged prototype humanoid, DURUS, showing that the optimization approach yields dynamic and stable walking gaits for different walking configurations, including unrestricted 3D dynamic walking.Ph.D

UNSCENTED GUIDANCE FOR POINT-TO-POINT REACTION WHEEL MANEUVERS

Attitude control system failures are often mission ending even when the mission payload remains operational. In this dissertation, the concept of unscented guidance is applied to reorient a reaction wheel satellite in the absence of feedback from star trackers or an inertial measurement unit (IMU). It is shown that an open-loop maneuver, properly designed using optimal control theory, can be used to achieve terminal attitude errors that are comparable with closed-loop control in the presence of uncertainty in the satellite inertia tensor. Typically, coarse closed-loop control is used to achieve < 1 degree pointing accuracy before more accurate pointing is done using fine guidance sensors to close the loop for science acquisition. It is shown that reaction wheel maneuvers designed using unscented guidance can also achieve sub-degree pointing accuracy of the spacecraft, making control hand-off to a functioning fine pointing control mode possible. The approach presented here enables large angle attitude control to be recovered so that mission operations may be continued despite IMU or star tracker failures.DoD Space, Chantilly, VA 20151Civilian, Department of the NavyApproved for public release. Distribution is unlimited

Control Implementation of Dynamic Locomotion on Compliant, Underactuated, Force-Controlled Legged Robots with Non-Anthropomorphic Design

The control of locomotion on legged robots traditionally involves a robot that takes a standard legged form, such as the anthropomorphic humanoid, the dog-like quadruped, or the bird-like biped. Additionally, these systems will often be actuated with position-controlled servos or series-elastic actuators that are connected through rigid links. This work investigates the control implementation of dynamic, force-controlled locomotion on a family of legged systems that significantly deviate from these classic paradigms by incorporating modern, state-of-the-art proprioceptive actuators on uniquely configured compliant legs that do not closely resemble those found in nature. The results of this work can be used to better inform how to implement controllers on legged systems without stiff, position-controlled actuators, and also provide insight on how intelligently designed mechanical features can potentially simplify the control of complex, nonlinear dynamical systems like legged robots. To this end, this work presents the approach to control for a family of non-anthropomorphic bipedal robotic systems which are developed both in simulation and with physical hardware. The first is the Non-Anthropomorphic Biped, Version 1 (NABi-1) that features position-controlled joints along with a compliant foot element on a minimally actuated leg, and is controlled using simple open-loop trajectories based on the Zero Moment Point. The second system is the second version of the non-anthropomorphic biped (NABi-2) which utilizes the proprioceptive Back-drivable Electromagnetic Actuator for Robotics (BEAR) modules for actuation and fully realizes feedback-based force controlled locomotion. These systems are used to highlight both the strengths and weaknesses of utilizing proprioceptive actuation in systems, and suggest the tradeoffs that are made when using force control for dynamic locomotion. These systems also present case studies for different approaches to system design when it comes to bipedal legged robots

Review of advanced guidance and control algorithms for space/aerospace vehicles

The design of advanced guidance and control (G&C) systems for space/aerospace vehicles has received a large amount of attention worldwide during the last few decades and will continue to be a main focus of the aerospace industry. Not surprisingly, due to the existence of various model uncertainties and environmental disturbances, robust and stochastic control-based methods have played a key role in G&C system design, and numerous effective algorithms have been successfully constructed to guide and steer the motion of space/aerospace vehicles. Apart from these stability theory-oriented techniques, in recent years, we have witnessed a growing trend of designing optimisation theory-based and artificial intelligence (AI)-based controllers for space/aerospace vehicles to meet the growing demand for better system performance. Related studies have shown that these newly developed strategies can bring many benefits from an application point of view, and they may be considered to drive the onboard decision-making system. In this paper, we provide a systematic survey of state-of-the-art algorithms that are capable of generating reliable guidance and control commands for space/aerospace vehicles. The paper first provides a brief overview of space/aerospace vehicle guidance and control problems. Following that, a broad collection of academic works concerning stability theory-based G&C methods is discussed. Some potential issues and challenges inherent in these methods are reviewed and discussed. Then, an overview is given of various recently developed optimisation theory-based methods that have the ability to produce optimal guidance and control commands, including dynamic programming-based methods, model predictive control-based methods, and other enhanced versions. The key aspects of applying these approaches, such as their main advantages and inherent challenges, are also discussed. Subsequently, a particular focus is given to recent attempts to explore the possible uses of AI techniques in connection with the optimal control of the vehicle systems. The highlights of the discussion illustrate how space/aerospace vehicle control problems may benefit from these AI models. Finally, some practical implementation considerations, together with a number of future research topics, are summarised

Simultaneous Capture and Detumble of a Resident Space Object by a Free-Flying Spacecraft-Manipulator System

The article of record as published may be found at https://doi.org/10.3389/frobt.2019.00014A maneuver to capture and detumble an orbiting space object using a chaser spacecraft equipped with a robotic manipulator is presented. In the proposed maneuver, the capture and detumble objectives are integrated into a unified set of terminal constraints. Terminal constraints on the end-effector’s position and velocity ensure a successful capture, and a terminal constraint on the chaser’s momenta ensures a post-capture chaser-target system with zero angular momentum. The manipulator motion required to achieve a smooth, impact-free grasp is gradually stopped after capture, equalizing the momenta across all bodies, rigidly connecting the two vehicles, and completing the detumble of the newly formed chaser-target system without further actuation. To guide this maneuver, an optimization-based approach that enforces the capture and detumble terminal constraints, avoids collisions, and satisfies actuation limits is used. The solution to the guidance problem is obtained by solving a collection of convex programming problems, making the proposed guidance approach suitable for onboard implementation and real-time use. This simultaneous capture and detumble maneuver is evaluated through numerical simulations and hardware-in-the-loop experiments. Videos of the numerically simulated and experimentally demonstrated maneuvers are included as Supplementary Material