KEYWORDS: Satellites, Adaptive control, Space operations, Control systems, Aerospace engineering, Robotics, Nonlinear control, Space telescopes, Safety, Robotic systems
Autonomous satellite on-orbit servicing is a very challenging task when the satellite to be serviced is tumbling and
has an unknown dynamics model. This paper addresses an adaptive control approach which can be used to assist the
control of a servicing satellite to rendezvous and dock with a tumbling satellite whose dynamics model is unknown. A
proximity-rendezvous and docking operation can be assumed to have three steps: 1) pre-dock alignment, 2) soft docking
and latching/locking-up, and 3) post-docking stabilization. The paper deals with the first and third steps. Lyapunovbased
tracking law and adaptation law are proposed to guarantee the success of the nonlinear control procedures with
dynamics uncertainties. A dynamics simulation example is presented to illustrate the application of the proposed control
approach. Simulation results demonstrated that the adaptive control method can successfully track any required angular
velocity trajectory even when the dynamics model of the target satellite is unknown.
KEYWORDS: Computer simulations, Space operations, Motion models, Computing systems, Control systems, Space robots, Kinematics, Human-machine interfaces, Systems modeling, Atrial fibrillation
This paper presents the concept of a cable-manipulator based 6-DOF hardware-in-the-loop (HIL) dynamics simulation system for testing and verification of microgravity contact-dynamics behavior of a space system. It then focuses on the inverse dynamics problem of the 6-DOF cable-driven manipulator which is designed for the simulation system. Accurate modeling and solution of the inverse dynamics is a key requirement for the control and high-fidelity performance of the complex simulation system. The inverse dynamics problem is solved completely under the basic operational conditions of a cable manipulator - all the cables must be always in tension for any possible end-effector motion of the manipulator. It is the first time that a systematic method of determining whether or not the inverse dynamics problem has a solution is proposed with full mathematical proof. Based upon this proven method, two numerical examples are presented to demonstrate the inverse dynamics solution of a 6-DOF cable manipulator. The study results support the feasibility of using such a manipulator for hardware-in-the-loop simulation of microgravity contact-dynamics.
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