Trajectory options for a Mars sample return mission

This paper discusses several EP-trajectory options to accomplish the heliocentric legs of a Mars sample-return mission and compares the different strategies in terms of time-length and payload delivered to Mars and/or Earth. In particular, direct, Earth-Gravity-Assist (EGA), Mars-Gravity-Assist (MGA), and Earth-Mars-Cravity-Assist (EMGA) trajectories are considered for the outbound leg. Direct and MGA trajectories are considered for the return leg. Attention is paid to the different options that are available for the capture by Mars (electric propulsion, chemical propulsion, or aerobraking), as they greatly influence the mission strategy for the outbound heliocentric leg.