MARS FREE RETURN TRAJECTORIES

For human missions to Mars, the top priority is a safe return of the c rew to Earth. In the case of an emergency, trajectories that naturally return to the Earth with no intervention are preferred. We use automa ted design software to compute all possible Mars free return trajector ies from 1995 to 2020, given constraints on the total time of Right an d on the launch energy. The resulting data file contains all of the pr eviously known types of returns. Because Earth and Mars return to the same inertial positions every 15 years, these results are representati ve of all Mars free returns. Of particular interest are two families o f fast free returns (having times of flight of about 1.4 years) that o ccur in 2000 and 2002 and repeat in 2015 and 2017.