On Feasibility of Interplanetary Travel: the Flight from Earth to Mars and Back

This paper deals with the major issues of round-trip Mars missions, namely: flight time, characteristic velocity, andmassratio. Two classes of trajectories are considered: (i) slow transfer trajectories, for which the round-trip angular travel of Earth exceeds that of the spacecraft by 360 degrees; (ii) fast transfer trajectories, for which the round-trip angular travels of Earth and spacecraft are the same.For robotic spacecraft, the best trajectory is the minimum energy trajectory, which is of type (i). For manned spacecraft, the comfort of the crew might require a trajectory of type (ii), in which a substantial decrease in flight time is achieved at the expense of a large increase in characteristic velocity and an even larger increase in mass ratio.At this time, it appears that the best policy is to continue the exploration of Mars via robotic spacecraft, since the present state of the art is not consistent with the safe and economic exploration of Mars via manned spacecraft. Major advances have yet to be achieved in three areas: spacecraft structural factors, engine specific impulses, and life support systems.