Attitude determination of a pico-satellite

Abstract

Attitude determination is a crucial component of all satellite systems. It aims to provide accurate estimates of a satellite’s orientation (attitude) in space, to be used by the Attitude Determination and Control System (ADCS), to actively control the satellite’s motion to achieve a desired attitude.

This dissertation presents a thorough design of the three-axis attitude determination system for the UoMBSat-1 satellite. This satellite is a 5x5x5cm, PocketQube pico-satellite, weighing 250 grams, that is currently being designed by the astrionics research group, ASTREA, at the University of Malta.

This dissertation focuses on the design and implementation of an attitude determination system based on Kalman filtering. A number of sensors, each measuring different phys-ical quantities, are considered as inputs to the filter. The combination of these readings within the filtering algorithm, termed sensor fusion, forms a considerable part of this project. The use of these measurements also requires the design of an accurate mathemat-ical model for each of these sensors.

A comprehensive model of the satellite in orbit is also developed, including the modelling of numerous reference frames, the modelling of the satellite’s dynamics and kinematics and the modelling of the various predictive models to determine the satellite’s position and velocity. Further models of the Earth’s magnetic field and the incident solar irradi-ance, at any orbit position, are developed to provide the required input to the various sensors on the satellite.

These systems are implemented in simulation to enable the validation and testing of the complete system under realistic conditions. In these simulated conditions, the attitude determination system achieves a pointing accuracy of 5.42 outside of solar eclipse and 64.66 in eclipse. Furthermore, the filter is shown to significantly reduce the angular velocity measurement noise and bias drift introduced due to inherent sensor characteristics, improving the accuracy of this important parameter.