Space Transportation Systems, Launch Systems, and Propulsion for the Space Exploration Initiative

This Note analyzes a number of transportation and propulsion options for Mars exploration missions. For space transportation options, the operational figures of merit that are of interest are (1) initial mass in low Earth orbit (IMLEO) and (2) transit times to and from the destination planet. It is desirable for both these parameters to have low values. Of the space transportation options examined, two approaches are most interesting: split missions, which use cargo spacecraft that follow low-energy trajectories to pre-position in Mars orbit the mass needed for Mars exploration and Earth return; and the use of in-situ propellants, which offer the potential for large reductions in IMLEO. To reduce IMLEO and trip time substantially, nuclear systems should be considered; a range of such systems is described. Almost all of the space transportation options evaluated would benefit from orbital transfer systems that can economically transfer large masses from low Earth orbit to high Earth orbits and Lunar space. In addition, all of these options would benefit from the development of propellant sources either on the Moon, on Martian systems, or both.