The attitude control system designates all the equipment and algorithms implemented autonomously on a spaceship. In satellites, the accuracy of the missions depends on the reliability and robustness of the controller it is one of the most important subsystems. The purpose of this paper is to design and apply a fractional-order controller specifically for the attitude stabilization of a Low Earth Orbit (LEO) satellite using reaction wheels. Real microsatellite parameters are used to test and run the fractional order controller, designed with MATLAB software which accurately stabilizes the attitude of the satellite system.

This study compares the result of the PID controller to the LQR controller when used in the on-orbit stabilization of a satellite in the low earth orbit. The results from the PID controller show that the controller is too weak when used alone as the controller could not stabilize the system after 500 s which is not even allowable in practical application. For the LQR controller, a performance metric was set which is: i. the settling time is to be ≤ 10 seconds, ii. Maximum power consumption ≤ 1.5 Watts and iii. Zero (0) steady-state error / final value. The LQR controller meets system performance by achieving a settling time of roll (peak amplitude=0.26 s, settling time=10.0 s), Pitch (peak amplitude=0.395 s, settling time=5.52 s), Yaw (peak amplitude=0.350 s, settling time=5.52 s) and Total power consumption are 1.26 watt with a maximum torque of 3.22 mNm. Because power consumption and precision are critical in satellite applications, particularly military surveillance satellites. As a result, for an aerospace engineer to achieve their space mission, for instance, space mission like low earth orbit surveillance satellites, flexible solar panels, a high accuracy pointing accuracy, it will be impossible to adopt a PID controller except the engineer is ready for the complexity of design filters and compensators. An LQR design in this study can take care of all this complexity with minimum power consumption.

Utilization of satellites to meet the needs of various missions requires a reliable Attitude Determination and Control System (ADCS). In this paper, we presents a robust design of the ADCS for the ESTCube-2 nanosatellite. The primary aim of the ADCS is to provide angular momentum to deploy a 300-meter tether used in a plasma brake deorbiting experiment. This is achieved by spinning up the three-unit CubeSat to 360 degrees per second about the short axis, deploying the tether and repeating the spin-up-deployment sequence until the whole tether is deployed. The system also provides accurate pointing for an Earth observation camera and a high-speed communication system. In addition to basic sensors and actuators commonly used on nanosatellites, the design includes a cold-gas propulsion system and a star tracker which will be tested for the future use in deep space. In order to operate the Earth observation and high-speed communication payloads, the satellite will use reaction wheels and the star tracker to achieve pointing the accuracy better than 0.25 degrees and the stability better than 0.125 degrees per second. To achieve the control requirements, a Lyapunov-based stability function and an optimal linear-quadratic regulator control is implemented. The attitude determination is handled by an unscented Kalman filter, which is deployed on a Cortex-M7 microcontroller. The ESTCube-2‘s plasma brake experiment in low Earth orbit serves as a precursor of ESTCube-3 which will test similar technology - the electric solar wind sail - for interplanetary propulsion in lunar orbit.

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.