Automatic rendez-vous scheme proposed for an unmanned (or manned) vehicle with a space station

Abstract

A method for automatic rendez-vous between an active vehicle, and a passive orbiting vehicle (typically a space station on a circular orbit) is presented. The main interest of the method is the simplicity of system implementation, and the small requirements on vehicle maneuvres and on-board computations, rather than in the mathematical optimization of fuel expenditure or elapsed time. The chaser is at first put on a circular orbit, lower and nearly coplanar to the orbit of the target (space station). An open-loop transfer of the chaser is performed, in order to put it in a window appropriated for automatic rendez-vous. When the relative distance of the two vehicles is small enough, a radar is used on the chaser for continuous determination of relative position and speed. An on-board computer is used then to derive the moments of application of corrective thrusts and their orientation. The scheme leads to a series of corrections nearly equally spaced in time, and the chaser approaches the target exponentially. Out of plane errors are also corrected. When the vehicles are close, the docking phase is initiated, which can be performed either automatically or manually. Even in manual control, an automatic loop is used in order to give the pilot simple motions in response to the control.