With the exploration of space, the number of orbiting spacecrafts has been accumulating. A considerable part of them are non-cooperative targets such as the rocket end-stages or disposed satellites, which seriously threaten active spacecrafts. So the reasonable disposal of space non-cooperative targets is very urgent. On-orbit capture is the premise of most on-orbit operations. As non-cooperative objects are unable to supply any prior information and its inertial parameters are not available, the capture process owns the feature of complex time varying, strong coupling and nonlinearity, and thereby the space operation via space robotic system requires better adaptive and real-time property. This chapter focuses on the inertial parameter identification of a non-cooperative object, the adaptive reactionless path planning strategy for the robot arm during the identification and stability control strategy for the whole system. The relative content is organized as follows: The first section establishes the basic dynamic model of the space robotic system that operates in the post-capture stage. According to the system's kinematics and dynamics equations, the two basic equations of identification for the non-cooperative object are constructed: the equation of Momentum Conservation as well as the equation of Newton-Euler, to obtain the basis of two-step identification and the error mechanism analysis. The second section proposes the theory of error mechanism analysis and designing an improved inertial parameter identification method via the contact force measure. To deal with the strong coupling existing in the conventional identification equation, the two-step scheme is proposed, and the sufficient condition for identification as well as the error mechanism analysis is deduced for the improved identification method, which employs the contact force information to deal with the error accumulation and thus can improve the accuracy. The third section designs an adaptive reactionless path planning method for the manipulator to deal with the motion disturbance and proposes a robust adaptive control strategy for joints' controllers and feedforward control strategy for the spacecraft's controller to ensure the stability of the whole system. The Slide-windowed Recursive Least Square (RLS) algorithm is employed to identify and compensate the momentum coefficient matrix that updates online, and thus the Adaptive Reaction Null Space (ARNS) algorithm is constructed and the dynamic path planning is completed for the manipulator. The robust adaptive control strategy for the manipulator is proposed to track the planned path, and the feedforward control strategy via coupling torque compensation for the spacecraft ensures the attitude stabilization in the process of capturing and parameter identification.

Chapter Contents:

• 6.1 Introduction
• 6.1.1 Relative work and development status
• 6.1.1.1 Method for identifying inertial parameters of space non-cooperative targets
• 6.1.1.2 Reactionless path planning for non-cooperative objects capture
• 6.1.1.3 Attitude stable control method of spacecraft-manipulator-target system
• 6.2 Joint kinetic model of spacecraft and unknown object
• 6.2.1 System kinematic analysis
• 6.2.1.1 System position vector analysis
• 6.2.1.2 System velocity vector analysis
• 6.2.1.3 Velocity Jacobian matrix
• 6.2.1.4 System linear and angular momentum calculation
• 6.2.2 System kinetic analysis
• 6.3 Unknown object inertial parameter identification
• 6.3.1 Basic theory of identification
• 6.3.2 Identification scheme incorporating information of contact force together with force/torque of end-effector
• 6.3.3 Solution of the modified identification equation using the hybrid RLS-APSA algorithm
• 6.4 Adaptive reactionless control strategy during manipulation of unknown object
• 6.4.1 Adaptive reactionless path planning via SW-RLS
• 6.4.2 Robust adaptive control strategy via the PSO-ELM algorithm
• 6.4.2.1 Adaptive control term via PSO-ELM algorithm
• 6.4.2.2 Robust control strategy
• 6.4.2.3 Stability analysis of the proposed control strategy
• 6.5 Numerical simulation
• 6.5.1 Inertial parameter identification simulation
• 6.5.2 Path planning and control simulation
• 6.6 Experimental results
• 6.7 Recommendations and future work
• References

Inspec keywords: adaptive control; position control; mobile robots; space vehicles; attitude control; manipulator dynamics; motion control; artificial satellites; feedforward; end effectors; robust control; torque control; least squares approximations; path planning; parameter estimation; stability; aerospace robotics

Other keywords: planned path; attitude stabilization; on-orbit operations; ARNS algorithm; orbiting spacecrafts; spacecraft; adaptive reactionless path planning strategy; orbital robotic capturing; adaptive reactionless path planning method; space noncooperative targets; inertial parameters; coupling torque compensation; noncooperative object; feedforward control strategy; Newton-Euler equation; parameter identification process; robot arm; stability control strategy; post-capture stage; adaptive reaction null space; rocket end-stages; error mechanism analysis; robust adaptive control strategy; space robotic system; adaptive reaction null space algorithm; reasonable disposal; contact force information; RLS algorithm; active spacecrafts; capturing process; dynamic path planning; two-step identification; inertial parameter identification method; error accumulation; conventional identification equation; slide-windowed recursive least square; space operation

Subjects: Interpolation and function approximation (numerical analysis); Mobile robots; Stability in control theory; Robot and manipulator mechanics; Spatial variables control; Mechanical variables control; Manipulators; Numerical analysis; Self-adjusting control systems; Aerospace control