workshops are being reported and will be discussed during this conference, but I would like to give a very brief summary of their findings as a capstone to this discussion of the systems studies effort which NASA has conducted. In the microwave power transmission area, the workshop panel reported that there was cautious optimism that the SPS microwave power transmission system is probably technically feasible; however, a long-term R&T program will be needed in order to prove the capabilities of this complex operation of transmitting power from space to Earth. In structures and controls, the workshop panel report indicates that substantial work remains to be done in modeling and in techniques of active control for structures the size of SPS. In the construction and materials workshop, the findings were that the assembly concepts appear credible but much more R&D work is needed in this area. One important lack is the insufficient data on the long-term behaviour of composite materials in geosynchronous orbit. The panel recommended that, in addition to the composite structural materials in the reference system, aluminum structures also be given continued consideration. In space transportation it was recognized that the propulsion systems for the reference heavy lift launch vehicle are achievable without high risk. It was also thought necessary to keep open many of the propulsion options before a firm choice is made. Reusable thermal structures will require a major development program and the key issues in space transportation remain the solution of problems related to repeated operations of space vehicles. This technology will be developed, in part, through the operation of the Shuttle. Under energy conversion and power management it was noted that key technology advances are needed, for example, in the solar blankets, the solar cell encapsulants, waste heat radiators, and the high speed switch gear. There can also be a major concern in the area of operation of satellite systems at the extremely high voltages required by the reference system. The question at this time must be, "What are the major findings of the systems studies activity in the Concept Development and Evaluation Program?" Those of us close to the program feel that the concept of transmitting power from space to Earth is not faced with insurmountable technical problems; however, this judgment is based in large part on studies that rely on assumptions and projections of critical technology disciplines. It is only through further research and experiments that we can change these assumptions to hard data, and it is only with hard data that we will be able to give an unqualified statement as to the technical and economic viability of any SPS concept.
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