Dynamics and control of a spacecraft-mounted robot capturing a spinning satellite

Issues associated with dynamical modelling and control of a spacecraft-mounted robotic manipulator capturing a spinning satellite are investigated in this research. The formulation of the post-capture dynamical equations of the system was carried out by writing the individual Lagrange's equation for the mother spacecraft, the two-link robotic manipulator, and the captured payload. These equations were then assembled to obtain the constrained dynamical equations of the system as a whole. This method, however, introduces the non-working constraint forces and moments which substantially complicate the dynamical analysis and therefore have to be eliminated. A novel technique that involves the use of the natural orthogonal complement of the velocity-constraint matrix was used in order to obtain a set of unconstrained independent equations. A computer code was written using FORTRAN and the IMSL subroutine DIVPAG was used to integrate the equations of motion. The pitch angle of the mother spacecraft, the joint angles of the manipulator, and their rates just after capture were calculated by solving the inverse kinematics problem and using impact dynamics principles. These were then used as initial conditions for the post-capture dynamics. A dynamical simulation of the system for the uncontrolled case was carried out to study the effect of the disturbance, resulting from the capture of the satellite, on the spacecraft/manipulator system. In light of the results corresponding to the uncontrolled system, a control algorithm, whose objective is to produce a set of feedback-linearized, homogeneous, and uncoupled equations, was designed and implemented. The effect of structural flexibility in the robot links on the response of the system was also investigated for both the uncontrolled and controlled cases.