On-Orbit Identification of Inertia Properties of Spacecraft Using a Robotic Arm

This paper presents a robotics-based method for on-orbit identification of inertia properties of spacecraft. The method makes use of an onboard robotic arm to change the inertia distribution of the spacecraft system. As a result of the inertia redistribution, the velocity of the spacecraft system will change correspondingly. Because the velocity change is measurable and the inertia redistribution of the robotic arm itself is precisely computable, the inertia parameters of the spacecraft body become the only unknown in the momentum equations and, hence, can be identified from the momentum equations of the spacecraft system. To treat the problem as a linear identification problem, it has to be solved in two steps. The first step is to identify the mass and mass center of the spacecraft; and the second step is to identify the inertia tensor of the spacecraft. The advantages of this method are 1) it does not consume fuel because a robotic subsystem is energized by solar power; 2) it requires measuring velocities only, but not accelerations and forces; and 3) it is not affected by internal forces, which are difficult to accurately measure. The paper investigates the sensitivity of the method with respect to different arm/spacecraft mass ratios, arm motion trajectories, and velocity-measurement errors.