The purpose of this report is to provide the reader with a readily accessible reference volume and history for the Integrated In-Space Transportation Plan (IISTP) phase I effort. This report was prepared by Gray Research, Inc. as a partial fulfillment of the Integrated Technology Assessment Center subcontract No. 4400037135 in support of the IISTP phase I effort within the In-Space Investment Area of the Advanced Space Transportation Program managed at Marshall Space Flight Center, Huntsville, Alabama. Much of the data used in the preparation of this report was taken from analyses, briefings, and reports prepared by the vast number of dedicated engineers and scientists who participated in the IISTP phase I effort. The opinions and ideas expressed in this report are solely those of the authors and do not necessarily reflect those of NASA in whole or in part. Reaching the outer solar system is a struggle against time and distance. The most distant planets are 4.5 to 6 billion kilometers from the Sun and to reach them in any reasonable time requires much higher values of specific impulse than can be achieved with conventional chemical rockets. In addition, the few spacecraft that have reached beyond Jupiter have used gravity assist, mainly by Jupiter, that is only available for a few months' period every 13 or so years. This permits only very infrequent missions and mission planners are very reluctant to accept travel times greater than about ten years since this is about the maximum for which one can have a realistic program plan. Advanced In-Space Propulsion (ISP) technologies will enable much more effective exploration of our Solar System and will permit mission designers to plan missions to "fly anytime, anywhere and complete a host of science objectives at the destinations' with greater reliability and safety. With a wide range of possible missions and candidate propulsion technologies with very diverse characteristics, the question of which technologies are

Reaching the outer solar system is a struggle against time and distance. The most distant planets are 4.5 to 6 billion kilometers from the Sun and to reach them in any reasonable time requires much higher values of specific impulse than can be achieved with conventional chemical rockets. In addition, the few spacecraft that have reached beyond Jupiter have used gravity assist, mainly by Jupiter, that is only available for a few months' period every 13 or so years. This permits only very infrequent missions and mission planners are very reluctant to accept travel times greater than about ten years since this is about the maximum for which one can have a realistic program plan. Advanced In-Space Propulsion (ISP) technologies will enable much more effective exploration of our Solar System and will permit mission designers to plan missions to "fly anytime, anywhere and complete a host of science objectives at the destinations" with greater reliability and safety. With a wide range of possible missions and candidate propulsion technologies with very diverse characteristics, the question of which technologies are "best" for future missions is a difficult one. The primary focus of the IISTP Phase I efforts were to: Develop, iterate and baseline future NASA requirements for In-Space Transportation; Define preliminary integrated architectures utilizing advanced ISP technologies; Identify and prioritize ISP technologies.

NASA's Integrated Space Transportation Plan and Orbital Space Plan [i.e. Plane] program : hearing before the Subcommittee on Space and Aeronautics, Committee on Science, House of Representatives, One Hundred Eighth Congress, first session, May 8, 2003.