The concept of a coherent Space Exploration Initiative (SEI) architecture is defined and is shown to be largely unsatisfied by the conventional Earth-orbital assembly/Mars orbital rendezvous mission plan that has dominated most recent analysis. Coherency's primary requirements of simplicity, robustness, and cost effectiveness are then used to derive a secondary set of mission features that converge on an alternative mission architecture known as "Mars Direct." In the Mars Direct plan two launches of a heavy lift booster optimized for Earth escape are required to support each 4 person mission. The first booster launch delivers an unfueled and unmanned Earth Return Vehicle (ERV) to the martian surface, where it fills itself with methane/oxygen bipropellant manufactured primarily out of indigenous resources. After propellant production is completed, a second launch delivers the crew to the prepared site, where they conduct extensive regional exploration for 1.5 years and then return directly to Earth in the ERV. No on- orbit assembly or orbital rendezvous is required in any phase of the mission, and the same set of booster, crew hab, and ERV used to support Mars missions can also be used to support a lunar base. This paper discusses both the martian and lunar forms of implementation of the Mars Direct architecture. Candidate vehicle designs are presented, and the means of performing the required in-situ propellant production is explained. The in-situ propellant process is also shown to present very high leverage for a Mars Rover Sample Return mission flown as a scaled down precursor version of the manned Mars Direct. Methods of coping with the radiation and zero gravity problems presented by a manned Mars mission are discussed. Prime objectives for Mars surface exploration are outlined, and the need for substantial surface mobility is made clear. Combustion powered vehicles utilizing the in-situ produced methane/oxygen are proposed as a means for meeting the surface mobility requirement. While the Mars Direct plan can be implemented utilizing only chemical propulsion, it is found that substantial improvement in mission capability can be achieved through the introduction of nuclear thermal rocket propulsion, and that the architecture is highly amenable to the introduction of such technology whenever it becomes available. It is concluded that the Mars Direct architecture offers an attractive means of rapidly realizing a coherent SEI, thereby opening the doors of the solar system to humanity.

Mars Mission Planning and Engineering