| Popis: |
Theme CONCEPT for a large, lightweight, parabolic antenna A which relies on the equilibrium of internal forces to achieve dimensional stability has been realized in a model 10 ft in diameter weighing only 1.7 lb. The model was constructed to verify the feasibility of the structural concept and to determine the gross features of the electrical performance. Contents The structure consists of a central mast, a torus, three tension wire systems, and a fine wire mesh to form the reflecting surface. The two compression members, the mast and torus, are interconnected by a guy wire system which establishes the plane of the torus and stabilizes the mast against buckling. Wires located in the plane of the torus to form a grid of equilateral triangles constitute the facet wire system. The nodes of the facet wire system are attached to the rear portion of the mast by 163 tension elements of the tie-back wire system. The facet wire system and connection pattern for facet wire nodes is shown in Fig. 1. The tie-back wires are adjusted to produce a controlled deformation of the triangular grid. The paraboloidal surface is approximated by 294 plane equilateral triangles, or facets. The facets are filled with a fine wire mesh. Figure 2 shows the guy wire and tie-back wire systems in a side view of the antenna concept. The torus is 10 ft in diameter and the central mast is 12 ft long. These two members are composed of various lengths of inflated (8-10 psi), 0.001 in. Mylar 1 in. tubing. The question of the integrity of the Mylar compression members in a meteoroid environment is dealt with in Ref. 1. Special fittings are required at the junctions of the inflated Mylar tubes to transmit forces from the tension wire systems and to maintain pressurization. These fittings alone comprise 34% of the weight of the model. Five mil beryllium-copper wire is used throughout for tension wires. Approximately 2400 ft of wire, contributing 12% of the weight, is used in the model. The reflecting surface is formed from 0.003 in. beryllium-copper expanded metal mesh with & in. x & in. diamond-shaped openings. The effective reflecting area is equivalent to a paraboloid 8.4 ft in diameter. The reflecting surface contributes 43% of the total weight. The remaining weight is associated with the Mylar tubes, (5%), and the feedhorn, waveguide and pressure seal, (6%). |
