Guidance and control for cooperative tether-mediated orbital rendezvous

The tether-mediated rendezvous procedure involves a free-flying pursuit vehicle that docks with a tether tip vehicle suspended at the end of a tether. The tether tip vehicle is equipped with small thrusters, and its maneuvers, along with the tether length, are controlled in such a way that they assist with the rendezvous. Presented in this paper is an algorithm that optimizes the location of the rendezvous state such that the minimum total maneuvering effort is required of the two vehicles performing the cooperative tether-mediated rendezvous. A variation to this algorithm that permits the maximum proximity time between the two vehicles is also described. The guidance algorithm was tested by simulating perturbations of the pursuit vehicle from its nominal rendezvous trajectory and then by observing the capability of the algorithm to determine corrective maneuvers to allow a successful rendezvous. Results indicate that the algorithm performs well even with large pursuit vehicle perturbations, and the resulting total fuel cost for both vehicles is less than what would be required by having one vehicle alone perform the rendezvous maneuvers.