Design and Simulation of an Attitude Control System for a Microsatellite

Abstract

This thesis offers an open-source alternative tool for the implementation and assessment of various attitude control systems for microsatellites. Spacecraft GNC Toolbox, a software toolbox written in Scilab environment was created for that purpose. The toolbox provides an Application Programming Interface (API) and simulation block palette to be used in Xcos environment. Spacecraft dynamics, sensors, actuators, external disturbances, and controllers were modeled as Xcos blocks and their source code was written in Scilab from the ground up. Owing to the fact that Scilab provides an interface for code blocks in Fortran and C languages, the source code of environmental models could be conveniently imported into the toolbox. The disturbance analysis was carried out to estimate the worst environmental conditions for the Attitude and Orbital Control System (AOCS). Attitude control modes were determined according to the reference mission requirements. Considering control modes and disturbance analysis results, adequate sensors (Gyroscope, magnetometer, and star tracker) and actuators (reaction wheels and magnetorquers) for AOCS were selected. Quaternion-based attitude controllers were developed using Linear Quadratic Regulator (LQR) technique and its integral controller augmented form. The robustness of these controllers was examined with Monte-Carlo simulations and worst-case analyses. After obtaining the robust controllers, mode transition scenarios were conducted, in order to deduce whether the designed controllers were practical and accurate. In the end, Spacecraft GNC Toolbox, which was developed in Scilab/Xcos environment, was proven to be sufficient for AOCS design since it allows engineers to develop controllers from the ground up and evaluate them.