Comparing optimum operation of Pulse Width-Pulse Frequency and Pseudo-Rate modulators in spacecraft attitude control subsystem employing thruster

摘要

The Aim of this paper is to verify which modulator will extend the life time of a spacecraft attitude control system utilizing thrusters. For this purpose, the optimal region of operation for Pulse Width-Pulse Frequency modulator and Pseudo-Rate modulator is defined where they are used as a compensator in the control subsystem. The optimal region is where the modulator behavior is close to linear and simultaneously, fuel consumption and thruster activity is at the lowest. Because of nonlinear nature of the modulator, an analytic approach is difficult so as an alternative, system simulations are carried out. Optimal region of parameters is determined through Static and dynamic analysis. Modulators are compared by employing them in a spacecraft model for minimum fuel use once for same parameters and once for their optimal parameters. Results give valuable information about control system fuel usage and reliability and effects of modulators in control effort. Trustworthiness and accuracy of results are increased by employing nonlinear attitude dynamics in system simulations. Results can be utilized for practical designs in order to select proper modulator for different missions.