6-DOF Formation Keeping Control for Three-Craft Electromagnetic Formation with Triangular Invariant Shape

Spacecraft relative motion control with inter-craft electromagnetic force has distinct advantages, and its invariant shapes which are convenient for formation keeping ensure some significant potential applications. However, the electromagnetic actuators affect both the relative trajectory and attitude motion, complicating related studies on issues of invariant shape design and formation control. This paper mainly focuses on the formation keeping control for three-craft electromagnetic formation with triangular invariant shape on the basis of a 6-DOF full nonlinear dynamic model. Considering the high nonlinearity, strong coupling, model uncertainties and external disturbances, a combined control scheme involving feed-forward and feedback control components is proposed. The feed-forward component is obtained through desired invariant shape design which is complicated by the superposition and coupling effects of any two distinct magnetic dipoles. The feedback component is realized utilizing linear feedback controller based on the LQR method and active disturbance rejection control based on the extended state observer. Finally, the numerical simulation is presented to verify the feasibility and validity of the proposed 6-DOF control scheme.