aluminum transmission lines is necessary to minimize line size and weight requirements and still maintain the necessary electrical conductivity for efficient energy transmission. Coatings may also be required on electrical transmission lines to provide the necessary thermal control properties to maintain sufficiently low temperatures. Summary: Tn considering the candidate materials from which the SPS may be constructed, there does appear to be an adequate technology base present as a beginning. The use of graphite composite materials for the primary structure appear to be promising. The unknown of a thirty-year life in a space environment does raise questions since the material is relatively new. Aluminum alloys, on the other hand, have an extensive history of use in previous years which add confidence that aluminum will do the job. The fact that the 30-year operational stresses on the SPS will be primarily the result of thermal cycles and thermal gradients tend to favor a materials with a low coefficient of thermal expansion, such as graphite composites. As a result, graphite composites appear to meet the major requirements of the SPS structural members, although a thorough evaluation of radiation damage, outgassing and thermal effects is needed to prove the usefulness of these materials. Available data indicate these problems may be overcome and lend optimism that in-space fabrication techniques may be simpler than with metals. Nonmetal lie films and fibers for supporting solar cells appear to be available providing the design does not introduce local loads at low temperature where low temperature brittleness could lead to failure. Adhesive films provide simple techniques for joining and repair. Existing materials for low temperature, vacuum stable seals and elastomers may not be satisfactory. This may require material development or thermal control techniques for successful application. Many specific materials problems will surface when the design matures. Overviews such as this summary should be evaluated in this light. It is concluded that a sufficient number of candidate materials exist to warrant further design study so that development problems can be defined and solved prior to SPS initiation and commitment. f. References 1. Glaser, Peter E., et al: Feasibility Study of a Satellite Solar Power Station, NASA CR-2357, February 1974. 2. Woodcock, G. R. and Gregory, D. L.: Derivation of a Total Satellite Energy System, AIAA paper 75-640, AIAA/AAS Solar Energy for Earth Conference, Los Angeles, April 24, 1975. 3. JSC Six-Week Study, Space Solar Power Development Laboratory, NASA JSC-09991. 4. Quinn, R.: Selection of the Baseline Attitude Control System for the SSPS and a Stability and Performance Analysis of the Elastic Coupling Between the Control System and the Spacecraft's Structural Modes, Grumman Aerospace Corporation, Bethpage, New York, ASP-611-M-l009 (NASA 74X76993).
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