SPACE TRANSPORTATION FOR THE 21ST-CENTURY

The Congressional committees that authorize NASA funding requested tha t the National Research Council (NRC) assess future requirements for s pace transportation as well as the benefits, technological feasibility , and roles of various Earth-to-orbit transportation system options. T he study, ''From Earth to Orbit - An Assessment of Transportation Opti ons,'' was completed by a blue ribbon panel March 1992.1 Launch requir ements considered include assembly and operation of Space Station Free dom, Mission to Planet Earth, human exploration of space, and the laun ch requirements of space science missions and experiments. Launch vehi cles for national security purposes were factored in as well. Launch v ehicle systems studied include existing and proposed expendable launch vehicles, the National Launch System, other potential followons to th e Shuttle system, single-stage-to-orbit vehicles, and systems designed for very heavy lift. Past, present, and potential propulsion systems, as well as international propulsion systems were also investigated. T his paper: 1) summarizes the principal conclusions of the NRC study, ' 'From Earth to Orbit - An Assessment of Transportation Options, '' 2) includes several comments by the authors referring to the NRC report i n hindsight, and 3) discusses the determination of future requirements for larger launch vehicles for Space Exploration Initiative applicati ons (SEI).