analysis and experiments. The thermal environment for an SPS is dominated by solar radiation and waste heat rejection by the antenna, in the example configuration. Thermal distortion can significantly reduce the buckling stability for a compression column as illustrated in Figure 9. This can be avoided by structural configuration design, appropriate thermal control, use of a low coefficient of thermal expansion (CTE) material or a combination of these. The daily solar cycle of the antenna could also lead to unacceptable thermal distortion if similar techniques were not employed. The significant parameters to the distortion of an antenna is illustrated in Figure 10. An in-depth assessment of the achievable flatness for the reference system antenna was studied by General Dynamics, Convair. As given in Figure 11, the results of this study indicate that the desired flatness of 2 arc minutes could be achieved by state-of-the-art manufacturing tolerance, within maneuvering distortions and within thermal distortion if a low CTE material is used. An existing graphite/epoxy (GY-70/X-30 pseudoisotropic) was used to provide a realistic assessment of material properties and variations in properties. The transient thermal environment associated with biannual occulations can induce dynamic distortions of the overall system depending on the detailed thermal response characteristics and configuration. The dynamic response of the example configuration can be held to a minimum if the structural material is a low CTE material. The prime findings of the SPS studies to date in the areas of structures and controls are listed in Figure 12. Although the SPS has a significant need for engineering and development work by analysis and experiment in the structures, controls and materials areas, there do not appear to be any insurmountable problems in these areas. There is a definite need for technology development in these areas, however. An in-depth assessment of the control system design and associated system performance is still needed. The significant interrelationships between control sensors, actuators and structural response are not well understood. The limitations of structural and dynamic modeling and their significance to control and system performance require assessment. First order analysis indicate that a 7% scale system (.4% full scale energy) in low earth orbit can provide a reasonable similitude for verification testing of the structure and control systems. There is also a need to develop an understanding of the long term behavior of materials and coatings in the SPS operating environment. The behavior of materials under the particulate, UV radiation and plasma exposure with low level stress and thermal cycling needs quantification. The significance of construction and assembly to structural design, material selection and control requirements cannot be underemphasized. Overall, the SPS system is an intriguing challenge to the control, structures and materials specialists.
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