Improving the spacecraft attitude control performance with on-off thruster actuator and fractional-order pulse width pulse- frequency modulator

In this article, the problem of controlling the attitude of a spacecraft with integral pulse width and frequency integrator is investigated and the said integrator is developed as a fractional order. The spacecraft is controlled by a two-state on-off thruster actuator with a combination of proportional-derivative law and integrator. In order to focus more on studying the behavior of the proposed integrator, the operator model is ideally considered, although it is due to the use of a nonlinear control system integrator. Average fuel consumption and operator activity are included as two main evaluation indicators, and on the other hand, the absolute average value of the sign error on spacecraft status is also included as another important indicator in the study of the behavior of the proposed integrator. In order to compare the results fairly, the situation control problem has been done for the same assumed conditions and for the integrator of integer order and fractional order. The comparative results for changing the fractional power of the fractional order integrator filter and checking the three performance criteria have been done. Also, the influence of the uncertainty of the moment of inertia of the spacecraft, the uncertainty of the reference entry angle and the range of external disturbances have also been studied. The obtained results indicate the change of the performance criterion for changing the order of the fractional combiner filter and show the more appropriate performance of the proposed combiner for a range of fractional powers.