Magnetic Attitude Control of Dynamically Unbalanced Spinning Spacecraft during Orbit Raising

Abstract

In this article, the use of a magnetic attitude control system (MACS) in preparing a spacecraft for orbit circularization without the use of high-level torque-restoring actuators is investigated. The main task of the attitude control subsystem is to maneuver the spacecraft so that its spin axis direction aligns with the direction of its velocity at the apogee place and to execute the spacecraft spin up for orbit circularization. The attitude control system is required to provide a desired attitude for maneuvering, such that the relevant maneuvers can be accomplished sequentially and successively at the apogee point. The nutation angle control system has been designed to maintain the nutation angle to less than 10° during orbital maneuvers. The magnitude of thrust force, duration of thrust application in each maneuver, and spin rate are chosen in such a way that the desired attitude of the satellite is not affected by maneuver-induced disturbances. This selection has been finalized through repeated simulations and by considering all the relevant factors and disturbances. The final selection is a thrust of 3 N using a cold gas propulsion system with an application duration of 100 s at the apogee point and a satellite spin rate of 20 rpm. The whole scenario required for the execution of orbit circularization from the initial stage of spacecraft separation from the carrier rocket has been simulated. Moreover, a scenario has been designed and implemented for control of the spin axis direction so that if the objective becomes the control of the spin axis in a short time, in addition to the magnetorquer of the longitudinal axis, one of the magnetorquers of the transverse axis can also be used. In this situation, the other magnetorquer of the transverse axis is simultaneously used for control of the spin rate. Also, for accelerating and optimizing control of the spin axis direction in the power acquisition mode, a scheme has been presented, in which spin axis maneuvering is minimized between two given attitudes. In addition, the wobble angle that is produced due to the existence of a dynamic imbalance in the spacecraft is never eliminated by this active damping method. Computer simulation results of attitude, pointing, and orbital maneuver controls are provided to demonstrate the validity of the design capability.