Abstract
This study proposes a method of selecting a set of gimbal angles in the final state and applies the method to the mode-scheduling steering law of variable-speed control moment gyros intended for multi-target pointing manoeuvres in the three-axis attitude control of a spacecraft. The proposed method selects reference final gimbal angles, considering the condition numbers of the Jacobian matrix of the reaction wheel mode in the final state of a single manoeuvre and that of the constant-speed control moment gyro mode at the start of the upcoming manoeuvre to keep away from the singularities. To improve the reachability of reference final gimbal angles, the nearest set of gimbal angles among nominated sets according to the Euclidean norm is selected as the reference final set at the middle of the single manoeuvre, and then realised by adopting gimbal angle feedback steering logic using null motion. In addition, the manoeuvre profile is designed such that the second half of the single manoeuvre is more gradual and takes longer than the first. Numerical simulation confirms the validity of the proposed method in consecutive manoeuvres.
Highlights
A remote sensing satellite used in an emergency response requires high observation frequency as shown in Figure 1, which is achieved by making highly accurate and large-angle agile manoeuvres consecutively [1,2,3]
The authors previously proposed a mode-scheduling steering law for variable-speed control moment gyros (VSCMGs), where the suitable set of initial gimbal angles is selected in the constant-speed control moment gyro (CSCMG) mode considering singularity avoidance during an agile attitude manoeuvre, and the steering mode is transited to the reaction wheel (RW) mode smoothly according to the attitude error of the spacecraft during highly accurate pointing control in the final state of the manoeuvre [6]
For the multi-target pointing and agile manoeuvring of a spacecraft with VSCMGs, the present study proposed a method of selecting reference final gimbal angles of a single manoeuvre and its application to the mode-scheduling steering law of VSCMGs
Summary
A remote sensing satellite used in an emergency response requires high observation frequency as shown in Figure 1, which is achieved by making highly accurate and large-angle agile manoeuvres consecutively [1,2,3]. A remote sensing satellite used in an emergency response requires high observation frequency as shown, which is achieved by making highly accurate and large-angle agile manoeuvres consecutively [1,2,3] To satisfy this requirement, the application of variable-speed control moment gyros (VSCMGs) to an attitude control actuator of a spacecraft and the steering law of the gyros have been studied [4,5]. The present study proposes a method of selecting reference final gimbal angles considering the condition numbers of both the CSCMG mode and RW mode during multi-target pointing manoeuvres, and applies the method to the mode-scheduling steering law of VSCMGs. Through numerical analysis, it is confirmed that the condition number of the wheel Jacobian does not always need to take a minimum value, and a certain value retains the torque generation capability. This paper presents the design of the proposed method and carries out numerical simulations to verify the feasibility of the method
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