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

Precise Attitude Control Techniques: Performance Analysis From Classical to Variable Structure Control

Small satellites have begun to play an important role in space research, especially about new technology development and attitude control. The main objective of this research is the design of a robust flight software, in which the key feature is suitably designed control laws to guarantee the robustness to uncertainties and external disturbances. To accomplish the desired mission task and to design the robust software, a classical Proportional Integrative Derivative (PID) method and two robust control system technologies are provided, focusing on applications related to small satellites and on the real-time implementability. Starting from PID approach, simulations are performed to prove the effectiveness of the proposed control systems in different scenarios and in terms of pointing stability and accuracy, including uncertainties, measurement errors, and hardware constraints. Different control techniques are analyzed: (i) a tube-based robust model predictive control (MPC) and (ii) a variable gain continuous twisting (CT) sliding mode controller. Both controllers are compared with loop shaping PID controller

A Novel Concept for Guidance and Control of Spacecraft Orbital Maneuvers

e purpose of this paper is the design of guidance and control algorithms for orbital space maneuvers. A 6-dof orbital simulator, based on Clohessy-Wiltshire-Hill equations, is developed in C language, considering cold gas reaction thrusters and reaction wheels as actuation system. e computational limitations of on-board computers are also included. A combination of guidance and control algorithms for an orbital maneuver is proposed: (i) a suitably designed Zero-E ort-Miss/Zero-E ort-Velocity (ZEM/ZEV) algorithm is adopted for the guidance and (ii) a linear quadratic regulator (LQR) is used for the attitude control. e proposed approach is veri ed for di erent cases, including external environment disturbances and errors on the actuation system

An Innovative Cloud-based Supervision System for the Integration of RPAS in Urban Environments

This paper proposes the outline of a Cloud-based supervision system for Remotely Piloted Aircraft Systems (RPAS), which are operating in urban environments. The novelty of this proposed concept is dual: (i) a Cloud-based supervision system focusing on safety and robustness, (ii) the definition of technical requirements allowing the RPAS to fly over urban areas, as a possible evolution of drone use in future smart cities. A new concept for the regulatory issues is also proposed, compared with existing worldwide regulations. The Cloud framework is intended to be an automated system for path planning and control of RPAS flying under its coverage, and not limited to conventional remote control as if supervised by a human pilot. Future works will be based on the experimental validation of the proposed concept in an urban area of Turin (Italy)

Reusable space tug concept and mission

The paper deals with the conceptual design of a space tug to be used in support to Earth satellites transfer ma-noeuvres. Usually Earth satellites are released in a non-definitive low orbit, depending on the adopted launcher, and they need to be equipped with an adequate propulsion system able to perform the transfer to their final operational location. In order to reduce the mass at launch of the satellite system, an element pre-deployed on orbit, i.e. the space tug, can be exploited to perform the transfer manoeuvres; this allows simplifying the propulsion requirements for the satellite, with a consequent decrease of mass and volume, in favour of larger payloads. The space tug here presented is conceived to be used for the transfer of a few satellites from low to high orbits, and vice versa, if needed. To support these manoeuvres, dedicated refuelling operations are envisaged. The paper starts from on overview of the mission scenario, the concept of operations and the related architecture elements. Then it focuses on the detailed definition of the space tug, from the requirements' assessment up to the budgets' development, through an iterative and recursive design process. The overall mission scenario has been derived from a set of trade-off analyses that have been performed to choose the mission architecture and operations that better satisfy stakeholder expectations: the most important features of these analyses and their results are described within the paper. Eventually, in the last part of the work main conclusions are drawn on the selected mission scenario and space tug and further utilizations of this innovative system in the frame of future space exploration are discussed. Specifically, an enhanced version of the space tug that has been described in the paper could be used to support on orbit assembly of large spacecraft for distant and long exploration missions. The Space Tug development is an activity carried on in the frame of the SAPERE project (Space Advanced Project Excellence in Research and Enterprise), supported by Italian Ministry of Research and University (MIUR), and specifically in its STRONG sub-project (Systems Technology and Research National Global Operations) and related to the theme of space exploration and access to space

A Comprehensive RVD Simulation Environment for GNC Algorithms Design and Implementation

This paper proposes a strategy for the Chaser position tracking during the approaching maneuver to a passive vehicle (Target), oriented to the development of a comprehensive simulator and guidance algorithms for rendezvous (RVD) maneuvers, starting from far range rendezvous to the final approach. The simulator is designed to reproduce space flight operations along Low Earth Orbits (LEO) for Chaser-Target systems. The simulation environment includes accurate and realistic models of sensors and actuators (thrusters and reaction wheels), which allow a complete simulation of autonomous spacecraft behavior orbiting in LEO. A simplified model of the external disturbances is also considered. Different guidance algorithms are considered for the guidance, navigation and control (GNC) subsystem of the Chaser vehicle. An optimal proportional navigation (PN) algorithm for the far range rendezvous and, in the final phase, a cone approach based on a continuous thrust straight-line maneuver are implemented. In addition, a comparison with ZEM-ZEV (Zero Effort Miss-Zero Effort Velocity) algorithms have been accomplished. Extensive simulations, that include different phases of the approaching maneuver, mainly identified on the Chaser distance from the Target, are performed to validate the feasibility and the tracking performance of the proposed guidance algorithms

PERFORMANCE ANALYSIS OF AN ATTITUDE CONTROL SYSTEM FOR SMALL SATELLITES

Attitude Determination and Control (ADC) algorithms may implement different solutions depending on computational performance and sensor accuracy. Pointing requirements may be very restrictive and the ADC System (ADCS) shall be compliant with these strict requirements, ensuring their satisfaction through the implementation of robust control algorithms and design of a proper actuation system. The objective of this paper is the design of a robust flight software, in which the key features are (i) suitably designed control laws to guarantee the robustness to uncertainties and (ii) detailed model of the external disturbances, focusing on Low Earth Orbit (LEO) missions. In this paper, a first-order and a second order sliding mode controllers are proposed. Extensive simulations are performed to prove the effectiveness of the proposed control system in a LEO mission scenario, including uncertainties of the spacecraft configuration, measurement errors and errors in torque actuation. Moreover, a detailed model of external disturbances is taken into account, since this controller is proposed for LEO missions

Obstacle Avoidance with Potential Field Applied to a Rendezvous Maneuver

This paper outlines a method based on the theory of artificial potential fields combined with sliding mode techniques for spacecraft maneuvers in the presence of obstacles. Guidance and control algorithms are validated with a six degree-of-freed (dof) omorbital simulator. The idea of this paper is to provide computationally efficient algorithms for real time applications, in which the combination of Artificial potential field (APF) and sliding mode control shows the ability of plan trajectories, even in the presence of external disturbances and model uncertainties. A reduced frequency of the proposed controllers and a pulse width modulation (PWM) of the thrusters are considered to verify the performance of the system. The computational performance of APF as a guidance algorithm is discussed and the algorithms are verified by simulations of a complete rendezvous maneuver. The proposed algorithm appears suitable for the autonomous, real-time control of complex maneuvers with a minimum on-board computational effort