From the work of the original Reference Mission (Version 1.0), the strategy for the human exploration of Mars has evolved from its original form to one of reduced system mass, use of a smaller, more reasonable launch vehicle, and use of more current technology. The steps which have been taken by the Exploration Team are motivated by the need to reduce the mass of the payload delivery flights, as well as the overall mission cost, without introducing additional mission risk. By eliminating the need for a large heavy-lift launch vehicle and deleting the redundant habitat delivery flight in Version 3.0 , two launches from the Earth were eliminated. The net result is a current Version 3.0 Reference Mission which requires an injected mass of approximately one-half that of the 1993/94 Reference Mission (Table A4-1).

The modifications which have been made to the Reference Mission have resulted in significant reductions in total initial mass in low-Earth-orbit without significantly altering the overall mission architecture. A complete overview of the current Reference Mission Version 3.0 architecture is provided in Figure A4-1.

A comparison of the mass breakdown for the various flights are provided in Table A4-2 through Table A4-4. The masses of Reference Mission 1.0 and 3.0 are provided for comparison.

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