Stabilised LQR Control and Optimised Spin Rate Control for Nanosatellites

This paper presents the design and study of cross product control, Linear-Quadratic Regulator (LQR)optimal control and high spin rate control algorithms for ESTCube-2/3 missions. The three-unit CubeSat is required to spin up in order to centrifugally deploy a 300-m long tether for a plasma brake deorbiting experiment. The algorithm is designed to spin up the satellite to one rotation per second which is achieved in 40 orbits. The LQR optimal controller is designed based on closed-loop step response with controllability and stability analysis to meet the pointing requirements of less than 0.1° for the Earth observation camera and the high-speed communication system. The LQR is based on linearised satellite dynamics with an actuator model. The preliminary simulation results show that the controllers fulfil the requirements set by payloads. While ESTCube-1 used only electromagnetic coils for high spin rate control, ESTCube-2 will make the use of electromagnetic coils, reaction wheels and cold gas thrusters to demonstrate technologies for a deep-space mission ESTCube-3. The attitude control algorithms will be demonstrated in low Earth orbit on ESTCube-2 as a stepping stone for ESTCube-3 which is planned to be launched to lunar orbit where magnetic control is not available.

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