Theoretical and Experimental Investigation of Attitude Control for Underactuated Spacecraft

This thesis investigates the detumbling and attitude control capabilities of an underactuated 3U-CubeSat used for ESSENCE mission developed by York University. Three different types of actuatorsexternal thrusters, magnetorquers, and reaction wheelsare considered in the nonlinear rigid-body control problem. According to Brocketts theorem, a smooth or continuous feedback law does not exist in the attempt to stabilize the attitude dynamics, hence robust discontinuous control algorithms such as sliding mode control (SMC) and model predictive control (MPC) are considered. First, two thrusters are used to study the ability to detumble the spacecraft using SMC and nonlinear model predictive control (NMPC). Second, a comparison between the B-dot controller and NMPC in detumbling a spacecraft equipped with two magnetorquers is explored. SEET library in STK is utilized to obtain an accurate geomagnetic field model to model the space environment. Then, the use of two reaction wheels along the principal axes of the spacecraft to perform an attitude correction maneuver is studied using quaternion-based nonlinear control (QBNC) and NMPC. Finally, an air-bearing testbed with a floating satellite simulator that closely mimics the dynamics of a spacecraft is used to validate the use of NMPC for attitude control through experimentation. Air thrusters and a reaction wheel is used to perform two separate experiments to observe the performance of NMPC with each actuator. Design recommendations and challenges posed by underactuated configuration of the ESSENCE 3U-CubeSat are presented as a result of this thesis.