Trajectories for human missions to Mars, part 1: Impulsive transfers

Earth-Mars trajectories with low energy requirements that also limit the (transfer) time a crew spends in interplanetary space are essential to the design of cost-effective, minimal-risk missions. We compute optimal Delta V trajectories with constraints on the transfer time of flight for launch years 2009 through 2022. We further explore the consequences of specifying different time of flight limits (from 120 to 270 days) for human missions to Mars. In addition to conjunction class trajectories, we calculate free-return, Mars-Earth semicycler, Earth-Mars semicycler, and cycler trajectories. The trades between powered and aeroassisted planetary capture for each trajectory type are also examined. We find that as the number of flybys increase (i.e., free returns have one flyby, semicyclers may have from two to four flybys, and cyclers have an unlimited number of flybys), the V-infinity increase, but the mission mass decreases because less maneuvers are performed by the crew transfer vehicle. The energy requirements of the trajectories decrease with increasing flight times, and the optimal Delta V is reduced by up to 50% when the flight time limit is increased from the NASA-recommended 180 days, to 270 days. Our results are compiled into sets of plots that describe the optimal, constrained time of flight trajectories for use in Mars mission studies.