Fast Free Returns to Mars and Venus with Applications to Inspiration Mars

Abstract

Mars free-return trajectories are investigated both with and without the use of Venus for gravity assist. Launch dates are searched from 2015 to 2060, and focus is placed on identifying opportunities that have a short total time of flight (that is, that are “fast” among the available free-return opportunities) so that they may be used for a human mission to flyby Mars. Constraints on Earth launch and Earth arrival are based on those used for the nominal Inspiration Mars opportunity in 2018. All attractive Mars free-return candidates found are shown to be rare, with launch opportunities only repeating (approximately) every 15 years, or every 32 years if a Venus flyby is used. A set of near-term candidate trajectories are found using the gravity-assist path Earth–Venus–Mars–Earth, which may be suitable for backup to (or replacement for) the nominal Inspiration Mars free return. One such candidate, with a launch date on 22 November 2021, has an Earth launch of ( of ) and an arrival of (entry speed of ), both of which are lower than the nominal Inspiration Mars trajectory, with a total flight time of 582 days. Venus free-return opportunities are also found, with promising application for a human flyby mission to Venus. An entry analysis is done for select cases (including the 2018 and 2021 opportunities) and shown to be feasible using present-day or near-term technology. An opportunity in 2023 is also found, which may be feasible if aerocapture is available.