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A summary is given of the concept definition phase of NASA's Orbital Transfer Vehicle (OTV) program. The mission requirements are threefold: (1) the ability to deliver payloads well beyond the capability of any current system at low acceleration levels, (2) the extension of the cost effectiveness from reusability and operational flexibility provided by the Shuttle at LEO to the geosynchronous altitude, and (3) the provision of the round trip capability needed to service and maintain this expanded and more valuable resource at GEO. The initial Shuttle-matched, reusable OTV is shown to be cost effective with low development cost, relatively short development period and high projected reliability. The performance enhancement provided by aero-assist is discussed, which will enable the difficult round trip to be flown in a single Shuttle launch. Two methods of reducing vehicle velocity are available: (1) aeromaneuvering, which uses vehicle lift to climb or descend and thereby correct for density variations, and (2) aerobraking which varies vehicle drag directly to correct for density.

The requirements for extended-duration space missions in earth orbit beyond those anticipated for the 7- to 30-day Shuttle Spacelab system have been examined. It has been determined that a continuously manned, free-flying orbital facility provides a realistic and cost-effective space platform for multidiscipline payloads designed to support research, applications, and system implementation programs such as the assembly of large space structures, and on-orbit space manufacturing. A conceptual description of such a manned facility (early Space Station) and the accommodations that it can provide using agencies and organizations is presented in this paper.

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Propulsion module consisting of Nerva-2-class engine and Saturn V stage would permit wide spectrum of space missions including near-Earth, cislunar and manned interplanetary flight