Ph.D. Dissertation Defense by Erika A. Ooten Biediger
Thursday, February 24, 2005
(Dr. William Singhose, Co-Chair)
"Vibration Reduction Using Command Generation in Formation Flying Satellites"
The precise control of spacecraft with flexible appendages is extremely difficult. The complexity of this task is magnified many times when several flexible spacecraft must be controlled precisely and collaboratively as in formation flying. Formation flying requires a group of spacecraft to fly in a desired trajectory while maintaining both relative positions and velocities with respect to each other. This work enhances two current state-of-the-art formation flying algorithms, specifically a leader-follower and virtual structure architecture. First, a flexible satellite model is integrated into each of these architectures. Second, input shaping is used to generate the satellites' desired trajectories, thereby enhancing the performance of the system.
Input shaping is a relatively simple technique that is used to generate system commands. When used on a flexible system, these commands allow the system to move without inducing residual vibration, limit transient deflection, and move in a fuel-efficient manner. For this case, input shaping is used to generate the desired trajectories for the formation satellites. Applying input shaping to formation flying control architectures creates several additional challenges. The input-shaping scheme, must not only eliminate vibration, it must also maintain the required formation positions and velocities. The temporal tracking and trajectory tracking are the primary performance measures evaluated.
This dissertation addresses key issues regarding the application of command generation techniques to flexible satellites controlled with formation flying control architectures. The temporal tracking and the trajectory tracking of each architecture was examined as well as the vibration characteristics of the formation satellites. Guidelines for applying trajectory shaping for the leader-follower and virtual structure architecture were developed, and experiments performed on a flexible satellite testbed verify key simulated results.