Guidance, navigation and control for 6DOF rendezvous in Cislunar multi-body environment

Recent studies highlighted the benefits of a support infrastructure located in Cislunar environment, which would ease the design of forthcoming space missions with a favorable access from and to the lunar surface, the Earth and many interplanetary destinations. Multi-body orbits rose a peculiar interest and were selected to stage a human-robotic exploration outpost; the family of Near Rectilinear Halo Orbits (NRHO), in particular, appears specifically suitable in these regards. Among the different capabilities that such outpost will tend to, the docking with other crewed or autonomous vehicles is a key feature that shall be present. Although low Earth orbit (LEO) rendezvous and docking is well assessed, no mission has performed such task in a multi-body gravitational environment. The paper presents a guidance, navigation and control (GNC) framework for 6 degrees of freedom (6DOF) coupled Cislunar rendezvous and docking. A feasible operational rendezvous scenario is detailed and exploited to define open-loop and closed-loop GNC functions for far-range and close-range. Then, the final approach is analyzed, proposing a closed-loop GNC that encompasses coupled translational-rotational dynamics. Vision-based only relative navigation techniques are applied to Cislunar multi-body dynamics to guarantee a coupled state estimation with a simple suite of sensors and a broad applicability range, ranging from passively cooperative to non-cooperative or unknown target spacecraft.