REDUCING THRUSTER PLUME CONTAMINATION FOR SATELLITE SERVICING USING CONVEX OPTIMIZATION

Commercialization of space has opened the door to a multitude of possibilities for on-orbit servicing, assembly and manufacturing missions. Rendezvous, proxim- ity operations and docking are key elements of such missions, and extreme care must be taken to avoid thruster plume contamination of delicate sensors or pay- loads onboard either vehicle. In this paper we present a thorough investigation into the key sources of contamination for chemical and electric thrusters operat- ing in close proximity to another vehicle. We develop first order plume models, to approximate thruster induced contamination, for use in our trajectory planning simulations. Fuel-optimal approach trajectories from the chaser/servicer satellite to the target/client satellite are computed using convex optimization, where the Clohessy-Wilteshire equations are used to represent the system dynamics. We then re-solve the problem while restricting the thruster pointing region by formulating a non-convex pointing constraint. This constraint is incorporated using a successive approximations method and leads to converged trajectories that reduce contami- nation of designated areas on the target vehicle, while keeping the required ∆V for the maneuver relatively low compared with the unconstrained problem. As ex- pected, results confirm that incorporating this pointing constraint into the convex optimization problem leads to trajectories that are significantly more fuel efficient than those where an arbitrary non-optimal pointing constraint is simply enforced at specific times to avoid contamination.