Juran Hwang

Graduation Semester and Year




Document Type


Degree Name

Master of Science in Aerospace Engineering


Mechanical and Aerospace Engineering

First Advisor

Atilla Dogan


This research investigates the ability of stabilizing spacecraft rotational motion by internal mass actuation. The mass actuation mechanism consists of three internal masses placed along the three axes at some offset distance that can move to induce inertial forces and moments and change the inertia matrix and center of mass. A set of nonlinear equations of motion are developed to model the motion, both orbital and rotational dynamics and kinematics, of a spacecraft with mass and inertial variation due to internal mass actuation, under the gravitational field of Earth. The equations inherently include the inertia effect of the mass motion on the orbital and rotational dynamics. Translational kinematics is written in terms of altitude, longitude and latitude, and the rotational kinematics is expressed relative to the local horizontal and local vertical frame. The equations of motion are first used to analyze two nominal flight conditions: (1) spacecraft facing towards Earth on a circular orbit, and (2) spacecraft spinning around the axis towards Earth on a circular orbit. A NDI (Nonlinear Dynamic Inversion) based controller is designed to stabilize the spacecraft by mass actuation in the first nominal condition from a tumbling condition. This controller is evaluated at three levels in terms of the fidelity of the spacecraft model: (1) only rotational dynamics equations, (2) rotational dynamics coupled with the nominal orbital motion, and (3) the full nonlinear 6-DOF model. The simulation results demonstrate that mass actuation can achieve detumbling of the spacecraft in all three cases with some steady state error when acceleration, speed, and position constrains are imposed on the mass actuators.


Mass actuation, Spacecraft, Moving mass


Aerospace Engineering | Engineering | Mechanical Engineering


Degree granted by The University of Texas at Arlington