A Robotic System as an Alternative to the Air-Bearing System for Spacecraft Simulator

A system emulation that can be used for testing a spacecraft control system with all of its hardware in place, in a 1-g laboratory environment, is presented. The system is comprised of a manipulator whose end-effector rigidly grasps a functional spacecraft, a six-axis force/moment (F/M) sensor placed at the interface of the spacecraft and the manipulator, and a control system. The controller takes the values of the force/moment as well as the manipulator's joint angles and velocities and issues torque command to drive the manipulator so that the motion of the spacecraft model in the presence of external forces replicates 0-g motion dynamics of a flight spacecraft. The control system can also modify the inertial properties of the spacecraft so as to match those of an actual spacecraft, even if the latter is flexible and the former is rigid. The stability of the overall system is analytically investigated, and the results show that the system remains stable provided that the inertial properties of two spacecraft are different. Important practical issues such as calibration and analysis of the sensitivity to noise and disturbance are also presented. Finally, the concept of the 0-g emulation of spacecraft is demonstrated by conducting an experiment using a robotic testbed at the Canadian Space Agency (CSA).