The structural cross section geometry utilized for the baseline solar cell array structure is shown in Figure 7-6 and is based upon the structural concept developed by the Grumman Aerospace Corp. The lateral truss geometry conforms to the required geometry of the reflectors and solar cell blanket, eliminating the need for secondary structural members. The length of the individual members provides adequate structural depth for bending stiffness. These characteristics are necessary to achieve very low structural planform area densities of 0. 05 to 0.15 kg/m2. This structural concept was incorporated into an elliptical planform to achieve minimum overall SPS weights and to accommodate power distribution through some structural members. A listing of the primary characteristics and requirements of the solar array structural configuration is presented in Table 7-4. These characteristics and requirements are the primary drivers in determining and defining major structural parameters such as beam sizing, tensioning cable sizing, materials selection, etc. Structural assembly considerations such as beam end joining concepts and tensioning wire attachment concepts were excluded, since their influence on the size and mass of the total configuration is considered to be minimal. A comparison of rectangular and elliptical planform shapes indicates a structural mass advantage for the elliptical shape. The longeron cross sectional area is an indicator of the size of the structural elements used to construct all major structural members and, hence, is an indicator of total structural mass. A comparison of the candidate shapes based on the first mode bending period is shown in Figure 7-7. For given stiffness sizing criteria, the comparison of structural mass of an elliptical planform to a rectangular planform, either of equal length or equal length-to-width ratio, is indicated. A systems comparison of the weight differences must also consider other mass drivers, such as shear and bending moment loads occurring during orbital transfer maneuvering and attitude control propellant requirements. Current comparisons indicate propellant mass advantages for the elliptical planform shape. Further comparisons were made between the elliptical and rectangular planform configurations by evaluating the effects of orbital transfer propulsion systems in different locations. The location options considered in the study are: 1. A 66 720 N thrust transfer propulsion system located on the microwave antenna 2. Two 33 360 N thrust transfer propulsion systems located on the ends of the configuration
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