Figure 2.1-2. Configuration Alternatives (worst case) produced on a single frame of the SPS structure. Finally five structural shapes were compared (normalized to have equal cap area and equal perimeter) to determine which shape would be most effective structurally for the reference SPS configuration. The general properties sought were high allowable stresses per unit mass where column, local crippling, general instability and fatigue allowables are equal. The structural shape must also be capable of mass production such that all structural centroids would be concentric at all levels of assembly. Finally all interconnections of structural elements were to have end-fixidity coefficients from 1.4 to 1.6 using quick-connect assembly concepts. Physical Description Rockwell SPS Structure The reference configuration is a two-trough, solar photovoltaic SPS. The overall size is 2.15 km wide, 1.386 km deep, and 26.7 km long. Each trough contains two aluminized polished Mylar/Kapton mirrors set at 60 degrees to base of the trough which is the photovoltaic solar cell collector surface. The solar cell surface receives one solar sun of energy by direct exposure and one solar sun of energy from the inclined mirror surfaces. The resultant two solar sun energy level is uniformly incident to all areas of the photovoltaic surface when orientation of the SPS is normal to solar rays. The troughs are supported by a central hexagonal structure as shown in Figure 2.1-3. Figure 2.1-4 illustrates the locational arrangement of the basic roll-formed sheet metal structural element, the next larger tri-beam girder, and the longitudinal and lateral location of the girder structure. This structure is comprised of 11.longitudinal main structural columns and 14 interconnecting tribeams which form the frame support structure for the longitudinal tribeam columns.
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