This study presents the overall design of a 3U CubeSat equipped with commercial-off-the shelf hardware, Teflon-fueled micro-Pulsed Plasma Thrusters (µPPT) and an attitude determination and control system. The µPPT is sized by the impulse bit and pulse frequency required for continuous compensation of expected maximum disturbance torques at altitudes between 400 and 1000 km, and to perform stabilization of up to 20 deg/s and slew maneuvers of up to 180 degrees. The study involves realistic power constraints anticipated on the 3U CubeSat. Attitude estimation is implemented using the q-method for static attitude determination of the quaternion using pairs of the spacecraft-sun and magnetic field vectors. The quaternion estimate and the gyroscope measurements are used with an extended Kalman filter to obtain the attitude estimates. Proportional and derivative control algorithms use the static attitude estimation in order to calculate the angular momentum required to compensate for the disturbance torques and to achieve specified stabilization and slewing maneuvers or combinations. Two control methods are developed: paired firing method, and separate control algorithm and thruster allocation methods which determines the optimal utilization of the available thrusters and introduces redundancy. Simulations results are presented for a 3U CubeSat under stabilization, pointing, and pointing and spinning scenarios.

"One of the general processes of interest in Pulsed Plasma Thrusters is the ablation of the solid fuel. In general, ablation occurs when a short pulse of applied energy removes a portion of the fuel surface. Although this ablation process is relatively straight-forward in simple materials that sublimate, ablation in Pulsed Plasma Thrusters is significantly more complicated. This is caused by the transient conditions and the complex behavior of Teflon that does not sublimate but rather undergoes both physical and chemical changes prior to leaving the surface. These two effects combine to make Teflon ablation a highly nonlinear function of heat flux, material property variations, changing molecular weight, and phase transformation behavior. To gain greater insight into the ablation process, a one-dimensional ablation model is developed that addresses the more detailed thermal and thermodynamic behavior of Teflon during simulated operation of a Pulsed Plasma Thruster. The mathematical model is based on the work of Clark (1971), which focused on two-phase, one-dimensional Teflon ablation in the context of thermal protection systems. The model is modified for use in simulated PPT operations and implemented numerically using an adaptive non-uniform grid, explicit finite-difference techniques, and a volume fraction method to capture the interface between the crystalline and amorphous Teflon phases. The ablation model is validated against analytical heat transfer and ablation solutions and compared with previous experimental results. The Teflon ablation model is used to analyze several general ablation scenarios in addition to specific PPT conditions to gain greater insight into long-duration thruster firing, post-pulse material ablation, variable heat flux effects, variable material property effects, and the impact of surface re-crystallization on particulate emission. These simulations are considered in the context of prior experimental investigations of Pulsed Plasma Thrusters. The results of these simulations demonstrate the success of the numerical ablation model in predicting experimental trend and suggest potential paths of moderately improving thruster efficiency and operational repeatability in the future. "