Modified Lyapunov Vector Fields Based Approach Plane Constrained Spacecraft Docking Guidance for Non-cooperative Tumbling Targets

Space debris removal and on-orbit servicing missions require docking spacecraft guidance that not only enables reaching the target spacecraft but also avoids collisions with appendages protruding from it. In this paper, two modified guidance laws are proposed for spacecraft docking on non-cooperative tumbling targets, with collision avoidance, using Lyapunov Vector Fields. In the literature, a two-stage thrust-constrained guidance strategy has been proposed, with the first stage used for a station-keeping approach trajectory and the second for contraction towards the docking port. Our proposed strategy follows a similar approach but additionally ensures that the chaser spacecraft enters and stays on a safe approach plane during both stages so that collisions with protruding appendages of the target spacecraft can be avoided. This is done by introducing a third component of motion in the target's body frame away from the initial approach plane, towards a plane free from intersections with undesirable appendages. It is shown that with these modified guidance laws, asymptotic convergence is guaranteed to the respective goal locations of each stage. A maneuver design example, along with numerical simulations, is presented to demonstrate the effectiveness of the proposed guidance strategy on a real mission.