Thruster Pointing Constrained Fuel Optimal 6-DOF Proximity Operations using Indirect Methods

Future space missions, such as in-space telescope assembly and on-orbit servicing, require rendezvous and proximity operations that avoid thruster-induced contamination and plume impingement on sensitive components of the client spacecraft. In this paper, we introduce a novel thruster pointing constraint into the six degrees-of-freedom (6DOF) optimal rendezvous problem and solve it using indirect techniques. A thruster pointing constraint limits the angular range over which a spacecraft's thrusters may operate, thereby avoiding plume contamination while still minimizing the desired objection function (e.g. fuel consumption or time-of-flight). By embedding this constraint directly into the dynamical model, our solution method eliminates the need for prior knowledge of the burn sequence or the precise times at which the constraint transitions to active/inactive. The spacecraft's 6-DOF motion is controlled by a set of fixed translational thrusters and an attitude control system that can provide instantaneous torque. Our solution method is demonstrated for an orbit rendezvous problem considering the Clohessy-Wiltshire relative dynamics for the translational motion and modified Rodrigues parameters for the attitude motion. A validation is presented through comparison with solutions to the simpler 3DOF problem.