Award Date

May 2018

Degree Type

Thesis

Degree Name

Master of Science in Electrical Engineering (MSEE)

Department

Electrical and Computer Engineering

First Committee Member

Sahjendra Singh

Second Committee Member

Pushkin Kachroo

Third Committee Member

Brendan Morris

Fourth Committee Member

Woosoon Yim

Number of Pages

129

Abstract

This thesis presents the derivation of both a linear and nonlinear adaptive control law for the attitude states of a spacecraft in orbit around rotating asteroids. The asteroid is assumed to be irregularly shaped and in an elliptical orbit around the sun. The linearized, time-varying spacecraft model will assume to include unknown parameters and will have external disturbances present. The objective is to control the roll, pitch, and yaw angle trajectories of the spacecraft such that they track desired reference trajectories. To achieve this, the control law will be composed of (1) a feedback controller, sufficiently robust to disturbance such that the system is stable, and (2) an adaptation law to estimate unknown parameters. The design of the linear control law will assume that only the angle measurements of the attitude states will be available for feedback. A high-gain observer will then be designed to estimate the higher-order states necessary to synthesis the control law. It will be shown that the tracking error, as well as the observation error, approach zero in finite time within the closed-loop system. The controller is able to accomplish this while being bounded to a saturation limit to reflect genuine thruster constraints. When the nonlinear, time-varying model is considered, unknown parameters are again assumed to be present. To govern the nonlinearities, and uncertainties present in the model, an adaptive control law is designed using the backstepping method. The control law also incorporates an adaption law, derived from an appropriate Lyapunov function. Using state feedback, it can be seen that the tracking error approaches zero while managing the nonlinearities of the model. For the both the linear and nonlinear systems, simulation results present full attitude control of the spacecraft, despite unknown parameters within the model.

Keywords

adaptive; control; feedback; linear; nonlinear; spacecraft

Disciplines

Aerospace Engineering | Electrical and Computer Engineering

Language

English


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