structure in varying degrees. The largest forces to be considered are the vibration and acoustic noise incurred at launch. Next, would be the gravitational and handling force the structure is subjected to on Earth. The least would be the operational forces on the structure from the space environment. However, if the designed structure were to respond exactly to the loads incurred at launch, the structure would be over designed. This is due to the fact that deployables are a packaged payload on the Spacecraft, therefore the loads incurred by each individual member during launch is not as great because of the distribution of the forces over the entire package and not to the individual members. Deployable structures are also subjected to external space forces. The effects of gravitational forces as well as atmospheric drag have large elastic deflection effects and cause instability of the structure [Natori, 1987]. Thermal effects of solar radiation, cause thermoelastic deformation. In addition to thermal solar radiation effects, the structure is subjected to three types of pressure, absorbed radiation, diffusely reflected, and most importantly specularly reflected. These forces are important in the consideration and the choice of the technology as well as the design configuration of the structure. Although, these forces are negligible compared to the terrestrial manufacturing and transportation loads due to the 1G force on the structure as well as the stresses incurred by handling and testing. Therefore, the primary environment that a deployable must be designed for is the terrestrial manufacturing environment. Deployable Structures Deployable structures use many different technologies and employ different structural concepts to achieve their mission objective. The following is a brief description of the different technologies and their appropriate applications. The most near term referenced structural shape is linear (the boom). Deployable truss structures have played an important role in satellite development for antennas and booms in the last 35 years. High stiffness properties have triggered much interest and research. Truss structures fall under two types of headings, one dimensional beam structures and two dimensional planar structures. Extendible beams have been used as supporting members for substructures and instruments as well as main structures. Some deployment concepts of beams include telescopic masts, coilable "astromast", collapsible mast, and variable geometry trusses (fig. 9.7a). These trusses utilize geometric forms of polyhedra in various combinations. The basic building block for a typical geodesic beam is the octahedron. Geometrical transformations of polyhedra to collapsed configurations by folding and/or changing the length of the members allows for efficient packaging (Figure 9.7b). Applications of these structures would be as a substructure to a solar array, or rectenna Figure 9.7 (a) Beam Deployment Concepts (b) Tetrahedral Fold [Natori and Miura, 1985] [Natori et al, 1986]
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