Dynamic Control of a Space Robot System with No Thrust Jets Controlled Base

Abstract

In this paper we discuss dynamic control of a free-flying space robot system where the base attitude is not controlled by thrust jets. Without external forces and moments, the system is governed by linear and angular momentum conservation laws. We first derive the system dynamic formulations in joint space and in inertia space, based on Lagrangian dynamics. Then we discuss the fact the dynamics of a space robot system can not be linearly parameterized, as opposed to the case of a fixed-based robot. Revealing this property is significant since the linearity of parameterization has been used as a prerequisite for various adaptive and nonlinear control schemes currently used in the robot control. Based on the dynamic model of the space robot system, a simple linear control scheme is presented for the normal regulation problem for tasks in space, such as holding lights for illuminating objects or handing an astronaut tools in extra-vehicular activity. A globally stable dynamic control scheme is proposed for trajectory tracking applications, such as catching moving objects or structure inspection for the space station. The dynamic control algorithm exhibits a fast and accurate motion response even when the mass/inertia ratio of the base with respect to the robot is low. The effectiveness of the proposed algorithms are demonstrated by simulation studies.