Analysis and experimentation of control strategies for underactuated spacecraft

Abstract

A laboratory spacecraft simulator testbed is first introduced to examine the problem of multiple spacecraft interacting in close proximity. This testbed enables validation of guidance, navigation and control (GNC) algorithms by combining 6-Degrees of Freedom (DoF) computer simulation with 3-DoF Hardware-In-the-Loop (HIL) experimentation. The presented 3-DoF spacecraft simulator employs a novel control actuator configuration consisting of a Miniature Single Gimbaled Control Moment Gyroscope (MSGCMG) and dual on/off cold-gas in-plane vectorable thrusters. The dual vectorable thruster design enables simultaneous translation and attitude control allowing it to act both in conjunction with the MSGCMG as well as provide sole actuator control throughout a commanded closed-path maneuver. Small-time local controllability (STLC) of this uniquely actuated system via Lie Algebra methods is formally demonstrated and results of experiments conducted on the described testbed are included. From this study in 3-DoF, a 6-DoF minimally control actuated asymmetric spacecraft design is proposed. Six-DoF control of this underactuated mechanical system is achieved via two oppositely mounted hemispherically vectorable thrusters. In order to capitalize on the unique nature of this system with only two control torques, a quaternion feedback regulator is developed to yield three-axis stabilization of its attitude. This regulator capitalizes on recent advancements in generalized inversion and perturbed feedback linearizing control to stabilize the dynamics of an underactuated asymmetric spacecraft and extends this to include stabilization of the kinematics of the system. Two control design methodologies are derived. The first is Lyapunov based, yielding a globally stable system, while the second yields local stability within a domain of attraction through perturbed feedback linearization. Results of several numerical simulations are presented for an asymmetric spacecraft with two bounded body-fixed control torques. The proposed attitude control method is not intended to provide attitude maintenance for attitude tracking or in the presence of relatively large disturbance torques; however, it may prove widely applicable for detumbling and reorientation maneuvers of spacecraft with only two available control torques.