Trajectory Options for Manned Mars Missions

Abstract

Manned missions to Mars have been the subject of studies for more than 50 years. Trajectory options examined include opposition and conjunction class missions, a direct landing on Mars with in situ propellant production, and a dash to Mars by the crew coupled with a hyperbolic rendezvous at Mars, and possibly at the Earth. This study examines the effect of trajectory choice on the initial mass in low Earth orbit and illustrates the important decisions that must be made when balancing risk and cost. Three different propulsion systems are used in the comparison, including chemical, nuclear thermal, and gas core nuclear. Of the three, nuclear thermal propulsion appears to be the good choice because the mass launched into Earth orbit is low, and because of the testing in the late 1960s, the technological risk associated with nuclear thermal propulsion appears to be small. Of the trajectories examined, the lowest cost trajectory appears to be a dash mission, but for this trajectory a hyperbolic rendezvous is required, which greatly increases the mission risk. The choice of the trajectory is crucial to success because decisions to reduce the cost to a manageable level must be carefully balanced against the risk to the crew.