Steering Law of Control Moment Gyros using Optimization of Initial Gimbal Angles for Satellite Attitude Control

Abstract

Control Moment Gyroscope (CMG) has been expected to be applied to a spacecraft such as an earth observation satellite in recent years. However it is not easy to control it because CMG has a singularity condition and a major source of disturbance. Although there are many singularity avoidance logics, these optimal methods from the viewpoint of singularity avoidance may cause inner disturbance by fast and furious motion of gimbals in avoiding singularity. This paper presents a new but simple CMG steering law using preferred initial gimbal angles and null motion for high accurate attitude control system on an agile spacecraft. The preferred initial gimbal angles are decided by evaluating function considering inner state of CMG. From the simulation results, the effectiveness of the proposed method was verified.

Optimal Attitude Control of Agile Spacecraft Using Combined Reaction Wheel and Control Moment Gyroscope Arrays

“…Nanamori [22] expanded on the work of Wie to implement preferred gimbal angles to multiple target collection. These preferred gimbal angles were only set at the beginning of the multiple target mission for the first target.…”

“…Following the work of Wie, Nanamori [22] developed a method of optimizing initial SGCMG gimbal angles prior to a multiple target agile s/c trajectory mission. Nanamori recognized that a SR method of solving the torque equation can cause chatter in the gimbals as the algorithm attempts to navigate past a singularity.…”

“…The second metric defined in [22] was the inner disturbance S 2 which is described as being due to mechanical and electromagnetic factors by…”

“…The design points for the optimization were limited to those gimbal angles which could be achieved through thirty seconds of null motion, starting from each gimbal initially set to zero degrees. The optimization for initial gimbal angles in [22] Nanamori's concept of using null motion to seek preferred gimbal angles before an agile spacecraft mission starts is expanded in the RWCMG system such that the null motion is performed for every target during the mission. Further discussion of RWCMG null motion and preferred gimbal angles is found in Sections 2.6 and 2.8.…”

Steering Law of Control Moment Gyroscopes for Agile Attitude Maneuvers

“…In the literature [3,4], it is assumed that gimbals are positioned at desirable initial angles using solo null motion, namely, a state where gimbals produce no net torque on the spacecraft. Vadali et al [3] demonstrated the existence of "preferred sets of initial gimbal angles" that avoid singularities, accomplishing singularity-free steering by using a simple pseudo inverse law with initial null motion to position gimbals at their preferred angles.…”