# Browsing by Subject "Attitude control"

Now showing 1 - 5 of 5

- Results Per Page
1 5 10 20 40 60 80 100

- Sort Options
Ascending Descending

Item Adaptation, gyro-ree stabilization, and smooth angular velocity observers for attitude tracking control applications(2014-08) Thakur, Divya, active 21st century; Akella, Maruthi Ram, 1972-Show more This dissertation addresses the problem of rigid-body attitude tracking control under three scenarios of high relevance to many aerospace guidance and control applications: adaptive attitude-tracking control law development for a spacecraft with time-varying inertia parameters, velocity-free attitude stabilization using only vector measurements for feedback, and smooth angular velocity observer design for attitude tracking in the absence of angular velocity measurements. Inertia matrix changes in spacecraft applications often occur due to fuel depletion or mass displacement in a flexible or deployable spacecraft. As such, an adaptive attitude control algorithm that delivers consistent performance when faced with uncertain time-varying inertia parameters is of significant interest. This dissertation presents a novel adaptive control algorithm that directly compensates for inertia variations that occur as either pure functions of the control input, or as functions of time and/or the state. Another important problem considered in this dissertation pertains to rigid-body attitude stabilization of a spacecraft when only a set of inertial sensor measurements are available for feedback. A novel gyro-free attitude stabilization solution is presented that directly utilizes unit vector measurements obtained from inertial sensors without relying on observers to reconstruct the spacecraft's attitude or angular velocity. As the third major contribution of this dissertation, the problem of attitude tracking control in the absence of angular velocity measurements is investigated through angular velocity observer (estimator) design. A new angular velocity observer is presented which is smoothed and ensures asymptotic convergence of the estimation errors irrespective of the initial true states of the spacecraft. The combined implementation of a separately designed proportional-derivative type controller using estimates generated by the observer results in global asymptotic stability of the overall closed-loop tracking error dynamics. Accordingly, a separation-type property is established for the rigid-body attitude dynamics, the first such result to the author's best knowledge, using a smooth (switching-free) observer formulation.Show more Item Center of gravity estimation for powered flight attitude control(2023-04-20) Busic, Christopher John; Akella, Maruthi Ram, 1972-Show more The problem of attitude control for an autonomous powered flight vehicle with an imprecise center of gravity (CG) characterization is addressed in this work. The proposed control structure consists of a proportional-derivative controller with feed-forward terms (PD+ structure), as well as a CG offset estimate equation. Stability is shown to hold when the two aforementioned components are implemented in a novel Lyapunov function, for which signal chasing arguments and results of Barbalat’s lemma are then applied. This Lyapunov-like analysis is done with no simplifying assumptions to the mass properties of the vehicle or small angular-rate restrictions, and proof of concept is shown first via low fidelity simulation experiments. The design is then integrated into an industry grade, high fidelity simulation environment, which leads to concluding remarks and areas for future work.Show more Item Quaternion regression and finite-time controllers for attitude dynamics(2019-12) Mendes De Almeida Neto, Marcelino; Akella, Maruthi Ram, 1972-; Humphreys, Todd E.; Zanetti, Renato; D'Souza, Christopher; Coltin, BrianShow more This dissertation presents two major research contributions to the field of attitude dynamics and control. The first topic comprises of estimating the angular velocity of a rigid body purely with orientation measurements expressed in terms of the quaternion parameterization. At first, the object of interest is assumed to be in pure-spin, and a simple two-step algorithm is derived and analyzed as part of this dissertation. These results are further extended for the general case of angular velocity estimation by way of relaxing the pure-spin restriction. The proposed angular velocity estimator is particularly useful in the context of vision-based navigation, as demonstrated through simulations. The second major research contribution from this dissertation is represented through a pair of new Lyapunov-based controllers that steer a fully actuated rigid body attitude system from an arbitrary initial configuration to any desired one within prescribed finite-time. The stability and convergence properties owing to these two controllers are analyzed through Lyapunov analysis and extensive numerical simulation studies. Finite-time attitude controllers, as opposed to asymptotic controllers, can be particularly useful in satellites that need to repeatedly reorient themselves with hard-deadline constraintsShow more Item Robustness properties of quaternion-based attitude control systems(2016-05) Yang, Sungpil; Akella, Maruthi Ram, 1972-; Bakolas, Efstathios; Arapostathis, Aristotle; Acikmese, Behcet; Mazenc, FredericShow more Both stabilizing and tracking solutions of the rigid-body attitude control problem, using various attitude representations, are now well understood. Based on the sensor availability, numerous full-state feedback or gyro-free output feedback controllers have been proposed and studied. In the dissertation, we revisit classical proportional-derivative (PD) type attitude controllers when the system is subject to uncertainties like time-delay in the feedback loop, measurement errors, external disturbance torques and modeling uncertainties. We not only analyze existing PD-type controllers while considering various types of uncertainties, but also design tracking controllers robust to the system parameter uncertainties. We adopt the quaternion representation for the attitude kinematics so that we can avoid the geometric singularities coming with minimal 3-dimensional parameter representations. For stability and robustness analysis of the PD-type controllers, we do not rely on the linear system framework in which the original dynamics are considered as the sum of the nominal linear part and the nonlinear perturbation part. Instead, another approach is suggested as suitable for the quaternion kinematic representation so that results are not restricted to a neighborhood of the origin. We first deal with one of the common Lyapunov functions used for quaternion-based attitude control problem. Then, through the strictification process, a new Lyapunov function is constructed which can be analyzed based on the standard Lyapunov stability analysis method. As a result, we establish sufficient conditions for locally stability or boundedness of the system subject to aforementioned uncertainties for both PD full-state feedback and PD-like gyro-free output feedback controllers. When our scope is narrowed to the system parameter uncertainties, we propose adaptive controllers that track predefined reference trajectories and estimate the unknown inertial parameters. Specifically, we apply a dynamic scaling-based Immersion and Invariance method for the first time to the attitude tracking problem. We also provide a way to control and estimate the upper bound of a dynamic scaling factor which has not yet been seen in the literature.Show more Item Uncertainty management in solar sail attitude control(2016-12) Eldad, Ofer; Fowler, Wallace T.; Lightsey, Glenn; Claudel, Christian; Bakolas, Efstathios; Jones, BrandonShow more Solar sails are emerging as a viable alternative to conventional forms of propulsion. Still at their infancy and relatively untested, many sources of uncertainty remain that are unique to solar sails and which will continue to affect their design as solar sails increase in performance and size. Controlling their attitude in the context of these uncertainties therefore becomes critical to spaceflight missions that will explore our solar system and beyond from new, previously-unattainable perspectives. Two distinct frameworks are developed to manage these uncertainties to control the attitude of solar sails. The first utilizes a provided system model and utilizes an observation of the control history to operate the sail about an equilibrium position that is passively stable. The approach utilizes past information about controller input for the purposes of rejecting disturbances that arise from several sources of uncertainty. The second approach is forward-looking and is inspired by trajectory-based reachability analysis. This approach was developed in the context of six degree-of-freedom supervised control of an unmanned aerial vehicle whose faster dynamics in a disturbance-rich environment provide a computational challenge and thus require machine-learned approximations to a reachable set of safe inputs. These methodologies are then applied to the original solar sail attitude control problem. Predictions are made about the future state of the sail after performing a minimum-time large angle maneuver. Uncertainty distributions are assumed a priori and are then used to create a buffer angle for the maneuver such that no overshoot occurs within a tunable statistical measure of safety. Uncertainties handled in this way include the sail effective reflectivity, flexural rigidity, and moment of inertia. However, the framework is designed to be very adaptable and so is able to accommodate arbitrary sources of uncertainties and flexible modeling techniques. Utilization of machine learning allows for arbitrary complexity in the simulation and modeling framework without impacting the on-board computational requirements of the solar sail hardware.Show more