Development of Innovative GNC Algorithms for Aerospace Applications

The main context of the present dissertation is the SAPERE STRONG (Space Advanced Project for Excellence in Research and Enterprise – Sistemi, Tecnologie e Ricerche per l’Operatività Nazionale Globale) project, founded by Italian Ministry of University and Research (MIUR) with the goal to improve Italian access to Space and Space Exploration. For this purpose, extension of the launch capability of the Vega launcher is included in the project, realized with a Space-Tug which is used to deploy in the nominal orbit a payload spacecraft. This thesis has the objective to develop an advanced orbital simulator as a tool which makes the designer able to develop and test the Guidance, Navigation and Control (GNC) software for the Space-Tug spacecraft. The GNC software is developed in collaboration with the leader industrial company of the project, Thales Alenia Space. Thales Alenia Space (TAS) is in charge of developing the Navigation and Control Function and the main structure of flight software, while Politecnico di Torino collaborates with the development of the Guidance function and the orbital simulator. During the whole project has been planned an internship of 1500 hours inside the offices of TAS in Torino. The project includes also a visiting period of international institution. In the specific frame of this Ph. D. thesis, has been spent three months at the University of Sevilla, with the purpose of study and design of a Galileo receiver as an additional input for determination of position in advanced navigation systems, since the Galileo constellation is near to be fully operative in the next future. Details related to all the activities executed during this internship will be presented in Appendix B. The main objective of this dissertation is the development of innovative GNC algorithms, focusing mainly on the Guidance problem, for aerospace application. An extensive literature review of existing guidance law, control techniques, actuators for attitude and trajectory control, sensors and docking mechanism and techniques has been performed. The Guidance topic has been analyzed focusing on the missile-derived Proportional Navigation Guidance (PNG) algorithm, Zero-Effort-Miss/Zero-Effort-Velocity (ZEM/ZEV) algorithm and Lambert guidance. Feasibility, performance, pros and cons have been extensively studied in this work, especially in an experimental fashion, and new solutions and implementation strategies have been proposed. The literature review has been completed for Control and Navigation issues, as well. Control strategies, actuation systems and algorithm have been investigated, starting from the classical proportional/Integrative/Derivative (PID) controllers, to more recent and innovative control law, such as Linear Quadratic Regulator (LQR). As for the Control function, the Navigation topic, intended as navigation filters and algorithms, has been studied in the last period of this work, while the navigation problem form the hardware side (i.e. sensors) has been deeply analyzed in the present work. In addition to the GNC investigation, the simulation topic has been studied as well, since one of the goals of this dissertation is the realization of an orbital simulator. The orbital simulator is a complete 6 degrees-of-freedom simulator, based on the relative equation of motion (Hill’s equations) for the trajectory computation and based on the classical rigid body equation, including the quaternion notation, for the computation of the attitude dynamics. The orbital environment is well defined, including all common disturbances found in Low Earth Orbits (LEO) and affecting the dynamics of an orbiting body. A complete set of sensors is implemented, including an accurate model of common measurement errors affecting the sensors included in the spacecraft configuration (Inertial Measurement Unit, Star Tracker, GPS, Radio Finder, Lidar and Camera). Actuators are carefully modeled, including a reaction wheels system and a reaction control thrusters system. Errors derived for misalignment of the wheels system and non-nominal inertia and shooting and misalignment errors for the thrusters systems are modeled as well.