Mars free returns via gravity assist from Venus

The safety of the crew is the top priority for human exploration of Mars. If an unexpected emergency occurs, a free-return trajectory can bring the spacecraft back to the Earth without a large trajectory correction maneuver. Such mission-abort scenarios are analyzed by searching for various Mars free-return trajectories, including gravity assist from Venus en route. Thorough investigations of Earth-Mars-Earth, Earth-Mars-Venus-Earth, and Earth-Venus-Mars-Earth sequences are made for the 15-year launch window beginning in 2010. Out of this study, a Mars-Venus free-return abort option, which satisfies the energy and time-of-flight constraints of NASA's Design Reference Mission in January 2014, is discovered. If aerogravity assist (consistent with the capability of the Design Reference Mission vehicle) is employed at Mars, the abort option can be improved over pure gravity assist at Mars in terms of more launch opportunities and lower time of flight. The planned mission date in January 2014 is remarkably fortuitous because the Mars-Venus abort trajectory only repeats every 32 years.