Multi-axis thruster-only fine pointing control strategies for nanosatellites

Abstract

Many satellites are required to be pointed at a target with high accuracy, a task which can in some scenarios be either better or only performed using thrusters. Control algorithms are well studied for solving this problem around a single axis using on/off thrusters, but not for cases where significant inter-axis coupling is present in the moment of inertia or thruster torque matrices, as is often the case when using commercial-off-the-shelf components in nanosatellites. This work proposes a linear programming-based method for applying single-axis phase plane control techniques in a multi-axis environment, while minimizing fuel usage and obeying constraints on minimum impulse bit and pointing accuracy. A multi-axis extension of a feedback pulse-width pulse-frequency modulation scheme is also developed. Simulations are performed where these methods are compared to existing multi-axis control techniques in the presence of realistic disturbances and non-ideal thruster behaviour.