Minimum vibration maneuvers using input shaping and pulse-width, pulse frequency modulated thruster control

Minimizing the modal vibration induced by on-off thrusters is a challenging problem for designers of flexible spacecraft. This thesis presents the first study of PulseWidth, Pulse-Frequency (PWPF) modulated thruster control using the method of command input shaping. Input shaping for systems with linear actuators has been successfully developed to reduce modal vibrations. Recently, this method has been extended to systems with on-off actuators to some degree. However, existing approaches require complicated non-linear optimization and result in bang-bang control action. Bangbang thruster operation on flexible spacecraft is propellant-intensive and causes frequent thruster switches. In this thesis, a new approach integrating command input shaping with PWPF -modulated thruster control is developed to minimize residual vibration in maneuvers and to reduce propellant consumption. To realize this approach, an in-depth analysis of the PWPF modulator is first conducted to recommend parameter settings. Next, command input shapers are designed and integrated with the PWPF modulator. Simulation verifies the efficacy of this technique in reducing modal vibration. Lastly, robustness analyses are performed and demonstrate the method's insensitivity to frequency and damping uncertainty.