Guidance, Navigation, and Control of Small Satellite Attitude Using Micro-Thrusters

M.S. University of Hawaii at Manoa 2016.Includes bibliographical references.In this study, a new and automated Navigation, Guidance and Control system is designed, analyzed, simulated and tested for small satellites. As is known, this system represents the primary unit of on-board control of a flight vehicle. It consists of a set of system software algorithms and hardware elements, including various sets of sensors and electronics depending on the type of the vehicle. This study is focused on small satellites, which are becoming one of the primary tools for a wide range of low Earth and deep space missions. The Navigation subsystem has been described in terms of its sensors and filtering technique, known as the Extended Kalman Filter. This subsystem provides the estimates of the satellite’s state vector. It is assumed that this vehicle’s Navigation subsystem includes GPS receiver, and accelerometer and gyro, which are considered as Inertial measurement Unit (IMU) component subsystems. The Guidance subsystem provides guidance commands for satellite’s actuators, which are assumed to include a set of micro-thrusters. The Control subsystem provides control commands for increments of torque of actuation. This study deals with the development, design and integration of the Navigation, Guidance and Control (known as GNC) subsystems into a unique framework that can be executed on-board in real time to perform satellite attitude maneuvers. The main focus is on the development of Guidance subsystem functions and algorithms. These functions, in particular, include attitude angles, angular rates and coefficients. The Guidance subsystem provides commanded angular acceleration based on a fourth-order polynomial with respect to time, which was used for lunar-descent trajectory guidance during the Moon landing maneuvers of Apollo Landers. The difference in the utility of this polynomial law in Apollo missions and this work is that in those missions this polynomial was used for trajectory guidance using numerically integrated trajectories as reference solutions. In this work, this polynomial is used to compute attitude guidance commands using a simple PD controller as an analytic reference attitude profile. The novelty of this work is that this polynomial law is formulated and implemented for the first time for real-time and on-board attitude guidance and control using a set of microthrusters as part of the integrated GNC system. Another element of novelty is associated with targeting. A real-time targeting procedure implies on-board computations of the target states and the time remaining to achieve the target state from the current state. In this work, the target state includes Euler angles and their rates. As such, the targeting is considered as an integral and critical part of the guidance function. The guidance command is computed only after computations of the target state and is the explicit function of this state. Therefore, the proposed guidance function is considered as the ob-board target-relative attitude guidance. The performance of the proposed GNC system has been demonstrated by two illustrative examples. In the first example, the satellite is guided to orient itself to its target position. In the second example, the satellite is guided to perform two consecutive rotational maneuvers, detumbling and reorientation, to achieve a desired attitude. The numerical simulation parameters and its results are illustrated by various plots and qualitative analysis of the relationships between the satellite’s state and guidance parameters. The list of references and appendix with necessary formulas and figures are provided