conclusions may be drawn regarding the economic viability of the systems. The economic results do not include the relative social and environmental impacts that would be associated with the systems that were compared. Differences between terrestrial generation systems and the SSPS may be significant. • The SSPS may be cost effective with respect to terrestrial systems by 1995. Since most terrestrial concepts depend upon non-renewable energy sources, the economic viability of SSPS may be enhanced relative to terrestrial systems beyond 1995. Given the time period before SSPS may be cost effective (1995), a decision to enter into a development-to- operations program or large-scale prototype is not economically justifyable at this time. However, given the potential economic benefits of SSPS in the 1995 time period, the many concepts that are currently being studied, the new design approaches that are being advanced and the number of possible approaches to development and operations the study results suggest that a significant research and assessment program is warranted over the next four to five years. The purpose of this program would be to provide reliable information on the economic and technical viability of SSPS. * SSPS might repay its total $44 billion DDT&E by CY 2013 with less than 60 units, were alternative terrestrial systems' generation cost 35 mills/kwh and were the unit cost of SSPS to be $7.6 billion. This result requires an SSPS buildup rate that provides at least ten percent of incremental U.S. installed generation capacity. • The PRS concept that has been studied has a decisive economic disadvantage over alternative terrestrial systems up to distances of 3500 nautical miles. Beyond this distance, were it deemed.in the national interest to engage in international transmission of power, the PRS appears to be preferred to alternative concepts . 4.0 Technology Areas Eight major sub-program areas have been identified which need to be resolved for the development, operation and maintenance
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