use in a modified Glaser type configuration as shown in figure IV-B-3-7. This is a 5 GW configuration with a centrally located microwave antenna. The number of structural members requiring dielectric material has been reduced to just the outside members. This is in contrast to the original Glaser structure in which all longitudinal members were carried into the transmission space. The deepening of the structure makes this possible with no increase in weight. The linear amount of truss required in this planar truss structure is constant and independent of depth. The added number of joints in a shallow structure increases the structural weight and provides less stiffness. The antenna cradle for this 5 GW configuration is shown in figure IV-B-3-8. Translational inertia from rotation of the microwave antenna should be kept to a minimum during normal operations. The function of this cradle is to allow 360° rotation without translational movement. Two pivot points allow rotation about the X axis for adjustment to rectenna latitude. A rotary joint on either end of the cradle allows continuous rotation and passage of electrical current. A large variety of structural configurations is possible through a combination of these two structural concepts. For example, the "picnic table" configuration shown in figure IV-B-3-9 could use a combination of distributed and concentrated load paths to achieve an isotropic moment of inertia tensor. This would minimize attitude control problems and be amenable to current loop control about two axes. d. Technology and Testing Requirements The design, development, transport, fabrication and assembly of a solar power station structure requires a refined blend of analysis and testing. Although this represents a technological challenge, it can also be viewed as a logical development proceeding from the technology foundation associated with current aircraft and space vehicles. The main difficulty associated with the design and development of a structure for the solar power station, as currently envisioned, is the impossibility of ground test simulation. The measurement of even tolerance capability for a structural element is not possible in the earth's gravitational environment. The situation is somewhat analogous to the impossibility of experimentally duplicating the reentry flow field environment for a spacecraft such as the Space Shuttle Orbiter. In this case, a numerical flow field analysis, which was calibrated by comparison of wind tunnel data and numerical analysis of wind tunnel flow fields, is used to establish the design environment for the Orbiter. By analogy, numerical analysis of the SPS structural design characteristics can be calibrated through carefully planned orbital tests and associated measurements and then applied with confidence to the final design. Necessary elements to this process are the adequate comprehension of the material characteristics, fabrication and assembly limitations, the detailed loads and temperature distribution, and integrated analyses of other significant subsystems such as the control system, power distribution system, and the electronic components. To support this design and development process, a synergetic balance of analysis and test requirements is needed. e. Consideration of Materials for Solar Power Stations Introduction: In considering candidate materials suitable for use in the SPS, one must first consider the environmental extremes and load requirements of the system. These requirements are related to the following major parameters:
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