Autonomous thruster failure recovery for underactuated spacecraft

Abstract

Thruster failures historically account for a large percentage of failures that have occurred on orbit. Therefore, autonomous thruster failure detection, isolation, and recovery (FDIR) is an essential component to any robust space-based system. This thesis focuses specifically on developing thruster failure recovery techniques as there exist many proven thruster FDI algorithms. Typically, thruster failures are handled through redundancy-if a thruster fails, control can be allocated to other operational thrusters. However, with the increasing push to using smaller, less expensive satellites there is a need to perform thruster failure recovery without additional hardware, which would add extra mass, volume, and complexity to the spacecraft. This means that a thruster failure may cause the spacecraft to become underactuated, requiring more advanced control techniques. Therefore, the objective of this thesis is to develop and analyze thruster failure recovery techniques for the attitude and translational control of underactuated spacecraft. To achieve this objective, first, a model of a thruster-controlled spacecraft is developed and analyzed with linear and nonlinear controllability tests. This highlights the challenges involved with developing a control system that is able to reconfigure itself to handle thruster failures. Several control techniques are then identified as potential candidates for solving this control problem. Solutions to many issues with implementing one of the most promising techniques, Model Predictive Control (MPC), are described such as a method to compensate for the large delays caused by solving an nonlinear programming problem in real time. These control techniques were implemented and tested in simulation as well as in hardware on the SPHERES testbed. These results show that MPC provided superior performance over a simple path planning technique in terms of maneuver completion time and number of thruster failure cases handled at the cost of a larger computational load and slightly increased fuel usage. Finally, potential extensions to this work as well as alternative methods of providing thruster failure recovery are provided.