1. Fuzzy Controller for Spacecraft Attitude Control CHIN-HSING CHENG SHENG-LI SHU Dept. of Electrical Engineering Feng-Chia University IEEE TRANSACTIONS ON AEROSPACE AND ELECTRONIC SYSTEMS VOL. 45, NO. 2 APRIL 2009

2. spacecraft A spacecraft is a craft or machine designed for spaceflight.craft spaceflight On a sub-orbital spaceflight, a spacecraft enters space then returns to the Earth.sub-orbital spaceflight spaceEarth For an orbital spaceflight, a spacecraft enters a closed orbit around the planetary body.orbital spaceflight closed orbit Spacecraft used for human spaceflight carry people on board as crew or passengers.human spaceflight Spacecraft used for robotic space missions operate either autonomously or telerobotically.robotic space missionsautonomouslytelerobotically

3. Applications Spacecraft are used for a variety of purposes, including, communicationscommunications, earth observation, meteorology, navigation, planetary exploration and space tourism.earth observation meteorologynavigationplanetary explorationspace tourism Spacecraft and space travel are common themes in works of science fiction.space travelscience fiction

4. Spacecraft subsystems A spacecraft system comprises various subsystems, dependent upon mission profile. Spacecraft subsystems comprise the spacecraft "bus" and may include:bus attitude determination and control, guidance, navigation and control, communications, command and data handling, power, thermal control, propulsion, and structures. Attached to the bus are typically payloads.payloads

5. Attitude control A Spacecraft need an attitude control subsystem to be correctly oriented in space and respond to external torques and forces properly.attitude controltorques The attitude control subsystem consists of sensors and actuators, together with controlling algorithms.sensorsactuators The attitude control subsystem permits proper pointing for the science objective, sun pointing for power to the solar arrays and earth-pointing for communications.

6. Spacecraft Control Spacecraft control is usually synonymous with “Attitude Control,” the engineering discipline of keeping a satellite or spacecraft pointed in the right direction. Spacecraft control embodies five distinct areas: 1. Control system design 2. Dynamics and modeling of systems 3. Software design 4. User interface design 5. Spacecraft operations

7. Basic diagram

8. Dynamics The dynamical equations for the spacecraft are Euler’s equations where I is the inertia matrix of the spacecraft, w is the body rate measured about the body axes with respect to the inertial frame and T is the sum of all external torques on the spacecraft. w x is the equivalent of the cross product wx.Written out it is The vector form is not tied to a particular coordinate frame but the matrix form is tied to a frame. In this case the equations are written in the body frame so the two forms are equivalent. The spacecraft is nominally earth pointing and our control system will correct small deviations from that pointing.

9. Spacecraft reference frame

10. The attitude kinematics come from the small angle approximation

11. Classical controller PI pitch controller. PID roll/yaw controller

12. Design of fuzzy controller The proposed controller receives the inputs of angular error and differential angular error; the fuzzy logic controller outputs control commands to stabilize the attitude of the satellite.

13. Two Fuzzy Controllers

14. The variables are as follows. The input and output variables of fuzzy systems are the linguistic variables. The variables E1, CE1, E2, and CE2 represent roll angle error, differentiation of roll angle error, pitch angle error, and differentiation of pitch angle error respectively. H3 and H2 are the commands to control the yaw axis attitude and pitch axis attitude, respectively.

15. Consolidated Fuzzy Controller

16. FSW simulation of angular error.

17. Dynamical model simulation of angular error.

18. Conclusion A new approach using a fuzzy controller has been proposed for satellite attitude control. The two fuzzy controllers can be used to supersede two classical controllers for attitude stabilization of the satellite and to obtain a faster convergence time and lower steady-state error.

19. Advantage over classical controller it does not require gain settings and complicated computation, making it more easily implemented on a microcomputer.