Dynamics, Simulation & Control of Orbital Modules for On-Orbit Assembly

Abstract

In the context of in-orbit assembly, modular building blocks offer the advantage of distributed launches. After the orbit-injection, the overall motion control requires the individual modules to approach each other while regulating their relative shape and the total formation. This kind of formation control has already been addressed for rigid body modules. However, in practical cases, each module might be a multibody (with rotors) system. To address the control problem for such a fleet of fixed-inertia multibody modules, we propose a novel dynamics formulation that is inertia-decoupled, singularity-free, and invariant of their absolute poses. We extend the passive decomposition theory for deriving new representative systems corresponding to the total momentum (locked) and relative shape variations. We exploit the dynamics to design two distinct control laws with complementary mission benefits to regulate the locked and relative motions. We also leverage the proposed formulation to design a Hardware-in-the-Loop (HIL) framework, in which the facility reproduced the relative motions while total momentum was propagated in software. Furthermore, the proposed HIL framework and the motion control are experimentally validated.