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This report investigates various methods of reducing the cost in space transportation systems for human Mars missions. The reference mission for this task is a mission currently under study at NASA. called the Mars Design Reference Mission, characterized by In-Situ propellant production at Mars. This study mainly consists of comparative evaluations to the reference mission with a view to selecting strategies that would reduce the cost of the Mars program as a whole. One of the objectives is to understand the implications of certain Mars architectures, mission modes, vehicle configurations, and potentials for vehicle reusability. The evaluations start with year 2011-2014 conjunction missions which were characterized by their abort-to-the-surface mission abort philosophy. Variations within this mission architecture, as well as outside the set to other architectures (not predicated on an abort to surface philosophy) were evaluated. Specific emphasis has been placed on identifying and assessing overall mission risk. Impacts that Mars mission vehicles might place upon the Space Station, if it were to be used as an assembly or operations base, were also discussed. Because of the short duration of this study only on a few propulsion elements were addressed (nuclear thermal, cryogenic oxygen-hydrogen, cryogenic oxygen-methane, and aerocapture). Primary ground rules and assumptions were taken from NASA material used in Marshall Space Flight Center's own assessment done in 1997.