Date of Award

Spring 2007

Project Type

Thesis

Program or Major

Mechanical Engineering

Degree Name

Master of Science

First Advisor

May-Win L Thein

Abstract

Current research with the NASA Goddard Space Flight Center (GSFC) involves the dynamic modeling and control of the NASA Magnetospheric Multiscale (MMS) Mission, a. Solar-Terrestrial Probe mission to study Earth's magnetosphere. Four observer-based attitude and nutrition controllers are designed and evaluated to determine the most effective feedback control system as it applies to MMS. Also, a dynamic analysis of each of the four identical satellites' two Axial Double Probe (ADP) booms is performed to provide an understanding of flexible boom dynamics.

The Finite Element method is used in evaluating boom modes of vibration for confirmation of NASA GSFC theoretical analysis and use in flexible model development. The dynamic transient and modal extraction technique are investigated for vibration analysis of constrained and unconstrained bodies. A fully flexible boom and rigid spacecraft model is also developed for vibrational analysis under steady-state rotation and thruster loads. Results indicate, however, the need for future research in numerical analysis of propagating systems through finite element methods and in the stability of the observer-based control system.

Linear and nonlinear observers are developed through simulations to estimate satellite attitude and angular body rates without the use of rate sensors. Control systems are then developed assuming perfect state measurements. Euler angles are used to describe satellite attitude in this research. Finally, linear and nonlinear (Sliding Mode Control) techniques are implemented in conjunction with the nonlinear observers to complete the observer-based control system.

The results of this research show that, of the methods analyzed, both the Extended Kalman Filter and Sliding Mode Observer implemented with Sliding Mode Control yield the most satisfactory performance. These observer-based control systems both meet NASA design requirements while reducing thruster control effort and reducing the effects of measurement noise and spacecraft uncertainties/disturbances. More simulations, however, are needed to verify performance of the proposed observer-based control system over all possible ranges of operation.

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