The effects of external and internal disturbances will be sensed by the phase control subsystem. These sensed pointing errors will then be used to modify the preprogrammed antenna motions to maintain pointing acquisition to the desired accuracy. 7. 3. 8. 3 OPERATIONAL ATTITUDE IMPACTS The two operational attitude alternates were discussed in subsection 7.1. 6. 3 for the photovoltaic conversion system. Table 7-10 summarizes the predominant antenna motions that result from each of the two attitudes. The basic 360° per day rotation is required for either attitude. However, the Z-solar orientation requires large angular vertical and roll motion. Since the large motions for the Z-solar attitude must be controlled to the specified pointing accuracy requirements, the pointing task for this attitude is critical. The X-POP orientation greatly simplifies the pointing task, since the requirements are for a 360° per day rotation with the antenna tilted at the fixed angle required to point to the ground rectenna. Therefore, even though additional solar panel mass is required for the X-POP mode, the simplified antenna motions appear to make the X-POP mode the desirable attitude orientation. 7. 3. 8.4 GIMBAL CONFIGURATIONS The antenna gimbal system (rotary joint) must provide the following functions: • Rotate the antenna 360° per day with respect to body coordinates. • Tilt the antenna as a function of the geographical location of the ground rectenna. • Maintain the desired orientation of the antenna with respect to the rectenna about the microwave beam line of sight. • Correct for any perturbations of the microwave beam pointing direction. • Minimum loss power transfer. The mechanical assembly requires the equivalent of two or three gimbals depending on the geometry of the mounting structure and the SPS attitude orientation. If the active area of the solar conversion system is maintained normal to the solar vector, structural offsets of 23. 5° can be supplied
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