Autonomous Proximity Operations of Small Satellites with Minimum Numbers of Actuators

A novel testbed is introduced to examine the problem of multiple spacecraft interacting in close proximity in a laboratory setting. This testbed enables validation of guidance, navigation and control (GNC) algorithms by combining six-degrees of freedom (DoF) computer simulation and three-degrees of freedom hardware-in-the-loop experimentation. The 3-DOF spacecraft simulator enables real-time hardware-in-the-loop testing of GNC algorithms by employing the principle of air-flotation along a flat floor to duplicate the frictionless and weightlessness inherent to orbital flight. This 3-DoF spacecraft simulator fuses sensor data from pseudo-GPS and a fiber-optic gyroscope in order to provide precise state estimation while employing a novel single gimbaled miniature control moment gyroscope and rotating thruster actuator for attitude and translational control. With its inherent high torque to required power ratio, the miniature CMG enables a high slew-rate capability for the spacecraft simulator which is a key measure of performance in spacecraft proximity operations. Furthermore, the rotating thruster design enables simultaneous translation and attitude control, allowing for efficient CMG desaturation when required. This paper presents the basic components and key parameters of the robotic vehicle with specific focus on the small time local controllability of this uniquely actuated system. The small time local controllability and input-output linearizability of the nonlinear Multi-Input Multi-Output system are demonstrated through both analytical means using Lie algebra methods as well as numerical simulations. Utilization of the designed input-output linearization controller with a standard Linear Quadratic Regulator for computation of the requisite linear gains provides a promising control system for a minimally actuated small spacecraft during autonomous proximity operations