The wide variety of orbit-to-orbit missions in support of the SPS demonstration, construction and operation need to be better defined before the vehicle concepts can be identified. Chemical Orbital Transfer Vehicles (OTVs) need further analysis and technology work and a reasonably early start on development to provide a capability that is needed in the present STS. Orbit-to-orbit including intra-orbit requirements of the 1980s should be coordinated with SPS requirements for chemical rocket OTVs in the 1990s and beyond. In-orbit propellant processing needs to be fully assessed. Much work is needed on the concepting and research and technology work for electric rocket propulsion systems. Mission analyses including optimized high and low thrust acceleration trajectories are needed that serve the SPS requirements. High-power ion thrusters and magneto-plasma-dynamic (MPD) thrusters need urgent development attention to ascertain their characteristics. Much better coordination is needed between the electric rocket propulsion system technology planning and support and the overall NASA need for this kind of propulsion including the SPS. More advanced propulsion systems such as dual-mode solid-core nuclear fission systems, gas-core nuclear rocket stages and mass-driver reaction engines (MDRE) need sustained attention. Orbit-to-orbit propulsion using high-power lasers should also be given attention. The present ground based exploratory development (GBED) program in space transportation for SPS is entirely inadequate and such content as it has misses the target completely. Its primary aim should be to strengthen the present concepts but, at the same time and just as importantly, be careful not to close off any promising concepts or technologies. If the GBED is intended to be the next phase for SPS, it needs to be reconceived from the ground up with an order of magnitude increase in funding. A greatly increased program of SPS space transportation analysis, research and technology is clearly needed. Efforts must be devoted to areas of systems analysis and technology readiness (including ground and space testing) that will reduce space transportation cost uncertainties in the next five to ten years. Although the consensus of the Workshop supported the future prospects of the SPS, it was generally believed that much work is needed before space transportation choices could be made.
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