requirement is the most significant consideration, with little or no data to support a selection. Vac Kote lubricants have proven highly reliable in OSO and other spacecraft slip ring, gear and motor applications. Greases have the same basic characteristics as the oils with appropriate thickening agents added. Greases should be used only where leakage is too high to retain an oil. Solids would have application for slip ring and motor brushes. 3.2.3 Primary/Secondary Antenna Structure The basic structure consists of 20 major beams perpendicular to each other to form a grid of squares 108 meters on each side. The secondary structure located within these grids form a denser grid of squares 18 meters on each side. The major beam "upper" caps are girder/columns consisting of three longitudinal members equidistant apart. At appropriate intervals, cross bracing and tension wires are added to balance the shear loads. The "lower" cap of the primary structure is identical to the secondary structure which is a beam consisting of girder/columns five meters apart. These are of similar construction to the primary members but scaled down. All beams are given shear capability by virtue of wire/ cables connected in the manner of a drag truss. Horizontal shear capability is obtained in a like manner by attaching cables at the upper beam caps across the 108 meter bays. See Fig. 3.2-13 for a typical 108 meter bay structural arrangement. 3.2.4 Structure/Wa Teguide Interface Two methods of attaching the waveguide assembly to the secondary structure have been identified: • The Single Point Pickup (Fig. 3.2-14) consists of a two-axis motor driven gi abal located at each 18 meter intersection. Lugs on this unit attach to composite structural members which support the waveguide assembly and effectively present any conductive heat transfer. The gimbal provides means of varying the Anting attitude of the waveguide assembly to account for structural/thermal deformations ii the structure. • The Three Point Support (Fig. 3.2-15) requires three motor driven screw jacks at each 18 meter intersection. Each one is mounted or a two axis gimbal which, when coupled to the screw jack action, provides rotationaal and translational adjustment. Conductive heat transfer is minimized by the use of composite fittings to interface with the screw jacks.
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