The principal technology issue is the de switching problem arising from the high voltage and current levels. 3. Structure Operating structural loads on the SPS are very low, increasing the significance of transportation, assembly, and maintenance loads. The large scale of the SPS emphasizes the dynamic characteristics of the structure that must be addressed in design. The primary natural load in synchronous orbit is gravity gradient torque; at low altitudes aerodynamic drag is also a consideration. Induced loads include propulsion/RCS thrust, current loop interactions with the Earth's magnetic field, microwave recoil from the antennas, and nonuniform antenna motion. Thermal transients and gradients arising from eclipses will produce differential expansion loads. Two fundamentally different approaches have been considered. Two of the most efficient structural members are tension members (cables) and buckling-limited compression members. This fact is the basis of the column/cable structural concept, which consists of a small number of compression members that are held in position by a large number of cables. An alternative approach is to maintain component alinement by providing local stiffness at the minimum level consistent with dynamic stability, such as in the truss configuration. This structure is less efficient from a weight standpoint but may offer advantages in assembly and modularization. For either configuration, conventional aerospace structural concepts will be inadequate to achieve the low weight required. One possible approach applicable to the truss configuration is to accept occasional elastic buckling of individual members due to random loadings (e.g., docking), from which the member would recover after removal of the load (such as deformation of a Venetian blind). Following this concept, the low operational stresses make it possible to design columns with L/p = 200. The most significant dynamic loading frequency is the 12-hour (2.3 x 10 Hz) gravity gradient cycle. In selecting a minimum -4 natural frequency of 2.3 x 10 Hz to keep the dynamic response to a reasonable level, it was found that the membrane stress in the array of the column/cable configuration should be on the order of 0.3 N/m (0.02 Ib/ft), and that the minimum depth of the truss configuration should be on the order of 600 m.
RkJQdWJsaXNoZXIy MTU5NjU0Mg==