  This paper presents a trajectory optimization and control approach for the
guidance of an orbital four-arm robot in extravehicular activities. The robot
operates near the target spacecraft, enabling its arm's end-effectors to reach
the spacecraft's surface. Connections to the target spacecraft can be
established by the arms through specific footholds (docking devices). The
trajectory optimization allows the robot path planning by computing the docking
positions on the target spacecraft surface, along with their timing, the arm
trajectories, the six degrees of freedom body motion, and the necessary contact
forces during docking. In addition, the paper introduces a controller designed
to track the planned trajectories derived from the solution of the nonlinear
programming problem. A weighted controller formulated as a convex optimization
problem is proposed. The controller is defined as the optimization of an
objective function that allows the system to perform a set of tasks
simultaneously. Simulation results show the application of the trajectory
optimization and control approaches to an on-orbit servicing scenario.
