Design and Analysis of the Attitude Control System for the S2TEP Mission

Abstract

This thesis describes the design, implementation and simulation process of the attitude control system for DLRs next compact satellite mission S2TEP, which is a three-axis actively stabilized satellite. Based on the requirements arisen during phases A/B, different pointing modes have been established in order to achieve the scientific objectives of this mission. An analytical estimation of the worst-case disturbance torques is obtained for the whole mission, as well as detailed reconstruction for different fine pointing sub-modes for one orbit. This information was later used for the definition of theminimal requirements in attitude determination and attitude control hardware. Some controllers are consequently proposed for every pointing mode. First, an enhanced B-dot controller is used to detumble the satellite after the separation from the launcher. Secondly, a spin controller is defined for coarse attitude acquisition during LEOP, and to maintain the satellite in a stable status in case of any failure. Finally, a LQR-based controller is used for the fine pointing manoeuvres. The mathematical models for the satellite dynamics, actuators, sensor, and environmental models are also derived along this work. At the end, the capabilities of the control system are demonstrated by running someMonte-Carlo simulations under nominal and non-nominal conditions.