Coordinated Control of Spacecraft's Attitude and End-Effector for Space Robots

Abstract

This paper addresses the coordinated control of the spacecraft's attitude and the end-effector pose of a manipulatorequipped space robot. A controller is proposed to simultaneously regulate the spacecraft's attitude, the global center-ofmass (CoM), and the end-effector pose. The control is based on a triangular actuation decomposition that decouples the endeffector task from the spacecraft's force actuator, increasing fuel efficiency. The strategy is validated in hardware using a robotic motion simulator composed of a seven degrees-of-freedom (DOF) arm mounted on a 6DOF base. The trade-off between control requirements and fuel consumption is discussed.

Coordination of thrusters, reaction wheels, and arm in orbital robots

“…Furthermore, the experiments confirmed that in the pre-contact phase the control is realized without any use of thrusters, whereas in the post-contact phase the thrusters are automatically activated to restore the proper inertial location of the system and to dump the angular momentum injected by the impulse. This minimalistic use of the thrusters is the main advantage of the proposed method and leads to reduced fuel consumption and improved performance, as preliminary observed in [30], and further analyzed in Section 6.…”

“…For orientation, the vector part of the error quaternion is used [36]. The exact expressions ofx c ,x e ,x b , Jx e , and Jx b can be found in [30,Sect.IV].…”

“…Thrusters-only coordinated control strategies were proposed in the literature to simultaneously control the arm, the attitude of the spacecraft, and to stabilize the translational motion [25][26][27][28][29][30]. However, when momentum exchange devices, e.g.…”

“…However, the requirement of controlling the translation of the spacecraft leads to increased fuel consumption during the pre-contact phase of the robotic operation. A different and more fuel-efficient requirement of controlling the translation of the center-of-mass (CoM) of the whole space robot may be enforced for stabilizing the translational motion, as observed in [30,32]. Compared to a base-control strategy such as [31], a CoM-control approach employs ideally 1 no thrusters during the pre-contact phase, because the CoM naturally conserves.…”

“…Note that the transformation of the dynamics is different than the one derived in [30] and [32] because in [30] the attitude and end-effector control inputs are assigned to the thrusters torques; furthermore, [30] results in an inertially-coupled attitude and end-effector dynamics. In [32] the attitude cannot be controlled.…”