Constrained Rendezvous and Mating with Gateway using Nonlinear Control Techniques

Gateway will represent a logistic outpost with a vital role for the future lunar and deep space exploration. Orbit dynamics in the proximity of Gateway is strongly perturbed, and in this research it is modeled in a high-fidelity multibody dynamical framework, with the inclusion of all the relevant orbit perturbations, by using a modified Battin-Giorgi approach. The rendezvous and mating maneuver is accomplished through low-thrust propulsion and is split in three phases: (1) close-range rendezvous, starting from a relatively short distance, (2) terminal approach, and (3) final drift and mating. In phase (1), a novel hybrid predictive nonlinear control approach is proposed and tested. Phase (2) includes coordinated trajectory and attitude control, and is aimed at driving the spacecraft toward the Gateway interface system, with correct alignment and modest relative velocity. In this phase, trajectory control uses feedback linearization. Phase (3) regards the last few meters in which the spacecraft naturally drifts toward Gateway, with no propulsion. Strict collision avoidance constraints, with the definition of a suitable exclusion region, are included in the real-time iterative update of the tracked trajectory. In powered arcs, the time-varying thrust components identify the commanded pointing direction of the spacecraft, and a nonlinear control algorithm, which enjoys global stability properties, is used. Actuation is demanded to an array of momentum exchange devices. Near the end of rendezvous and mating, attitude maneuvering is carried out (while trajectory naturally drifts, with no propulsion), and correct alignment is pursued, with reference to two distinct scenarios, i.e. (a) docking and (b) berthing. Numerical simulations, in both nominal and nonnominal flight conditions, show that the nonlinear control techniques developed in this study are effective for spacecraft rendezvous and mating with Gateway.