Solar sail missions to Mercury with Venus gravity assist

Missions towards Mercury are expensive in terms of propellant mass, especially when conventional propulsion systems are considered. Significant propellant mass saving may be obtained with the use of complex multiple intermediate flyby maneuvers, but the corresponding mission time increase is substantial. An interesting option is offered by solar sails that are potentially able to fulfil a Mercury rendezvous mission within reasonable time intervals, without the need of any propellant. In this paper we investigate the solar sail performance for a minimum time mission towards Mercury with a single Venus flyby. This allows us to quantify the improvement (in terms of mission time saving) that such a flyby offers with respect to a classical direct transfer. Also, with the aid of a suitable simplified model of spacecraft mass distribution, we quantify the significant increase in payload mass fraction associated with the flyby maneuver.