• Requirement for propellant resupply • Contamination of waveguide functions. Figure 2-3 lists mechanical system options considered in Task 1 and identifies configurations recommended for Task 2 Concept Definition. Also included in Fig. 2-3 are recommended technology studies which could provide a more optimum design. Power clutches or rotary transformers are power transfer advanced space techniques that could lead to a reduction in interface friction, and increased life. Spur gears are recommended for the gear train, but a direct drive motor system would eliminate gears and may be easier to implement, provided sufficient accuracy could be achieved. Individual rollers are recommended as baseline because of ease of implementation. Ball bearings offer an advantage in terms of lower friction torques and should be considered as an alternate. DC brush torque motors are recommended; however, linear induction motors may show advantages in terms of life and inherent capability to isolate the spacecraft dynamics from the antenna dynamics. 2.1.2 Thermal/Structural Analysis A thermal/structural analysis has been carried out to determine deformations to be used in establishment of requirements for phase front control, and to determine cost and weight factors for overall system selection. 2.1.2.1 Preliminary Design Options Figure 2-4 is a weight comparison of principal structural design layouts. The rectangular grid approach was found to be lighter than the radial spoke arrangement. Two compression member designs were considered; a singular tube, 100 m long, and a triangular girder with thin walled circular tubes at the apex with cross tubes and diagonal wire bracing. The triangular girder approach was found to be significantly lighter than the singular tube. Assessment of structural deflections included analysis of load, thermal and assembly tolerance induced deformations. The assembly tolerances were found to be the largest source of deformation with a worst case tip deflection of 0.17 degree. Deflections due to thermal bending can be kept below 1 arc-min if thermal gradients between the upper and lower primary structural caps can be controlled to less than 4°K. Deflections due to loads were found to be insignificant.
RkJQdWJsaXNoZXIy MTU5NjU0Mg==