INTRODUCTION

A major goal of the manned Mars missions is to expand human presence in space. Typical mission objectives
associated with this goal are extended visits to the Moon and exploration of Mars. However, in order to fully realize
the goal of a sustainable human presence in space, it must be necessary for spacefarers to eventually live off of the
land and perhaps even bring something back. This implies that the reasons for going to space and staying must lie
within space itself since the payoffs of a space program for science, national pride, etc. are becoming difficult to
justify. 

The high cost of space transportation has traditionally dominated decisions regarding mankind's exploration and
utilization of space. Launch costs are constraining the ability for humans to expand their activities into the solar
system and beyond. Whether designing a communications satellite or conceptualizing manned missions to other
planets, the amount of mass to be launched and delivered to its final destination has typically been a major
consideration or actual show stopper. With the discovery of near-Earth objects (NEOs) that contain rocket
propellant materials, the concept of providing effectively limitless amounts of propellant in Earth orbit for
subsequent usage could become a dream come true. In addition, other valuable commodities made available at
desired destinations in the solar system could have large potential payoffs. This paper discusses an approach to
providing inexpensive space transportation, for manned Mars missions specifically, and the possible implications
that other NEO resources may hold for the future. 

An expanding space program will most likely need to be self-sustaining. Utilization of nonterrestrial resources
from NEOs may have large payoffs encouraging private company involvement and the ability of space activities to
pay for themselves. The dream of commercialization and privatization of certain space activities will certainly
depend upon economic means of transporting material(s) and/or personnel from place to place. Structural materials
and life-sustaining compounds such as water, carbon dioxide, ammonia and oxygen will have large value at a
manned planetary base or terraforming site. The availability of these materials as well as inexpensive transportation
costs from their source to their usage destination could enable a sustainable space program and fulfill the dream of a
true human presence in space.