(An) experimental study on attitude control of spacecraft using two-axis hardware testbed

Abstract

This primary objective of this study is to demonstrate ground-based experiment for the attitude control of spacecraft. A two-axis rotational simulator with a flexible arm is constructed with on-off air thrusters and reaction wheel as actuation. The simulator is also equipped with payload pointing capability by simultaneous thruster and DC servo motor actuation. The experiment of spacecraft attitude control is per-formed using the thruster and the reaction wheel. First, using the thruster the azimuth angle is controlled by on-off thruster command while the payload elevation angle is controlled by a servo-motor. A thruster modulation technique PWM (Pulse Width Modulation) em-ploying a time-optimal switching function plus integral error control is proposed. An optical camera is used for the purpose of pointing as well as on-board rate sensor calibration. Attitude control performance based upon the new closed-loop control law is demonstrated by ground experiment. The modified switching function turns out to be effective with improved pointing performance under external disturbance. The rate sensor calibration technique by Kalman Filter algorithm led to reduction of attitude error caused by the bias in the rate sensor output. Second, using the reaction wheel the performance of the PID and the three proposed neural network controllers is illustrated by simulation and experimental results for a two-axis rotational simulator.