Simulation study of a robotics-based method for on-orbit identification of spacecraft inertia properties

This paper presents the results of a simulation based study of a method for identifying the inertia parameters of a spacecraft on orbit. The method makes use of an onboard robotic arm to change the inertia distribution of the spacecraft system. As the result of the inertia redistribution, the velocity of the spacecraft system changes correspondingly. Since the velocity change is measurable and the inertia change of the robotic arm 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, the problem 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 the whole onboard mechanical subsystem involved is energized by solar power; 2) it requires measuring steady-state velocities only, but not acceleration and force; 3) it is not affected by any internal energy dissipation, which is very difficult to predict otherwise. The paper investigates the sensitivity of the method with respect to different arm/spacecraft mass ratios, arm motion trajectories, and velocity errors. The possible extension of the method by using a pair of two degrees of freedom solar panel mechanisms instead of a robotic arm is also discussed.