Table 2. AC&SK System Mass Summary Figure 7. AC&SK Dual Solid-State Configuration Figure 6. Frequency Distribution The symmetrical “dual" configuration is preferable to an unsymmetrical "single" energy conversion system spacecraft because of the large propellant requirements (41.1% of spacecraft mass over 30 years) due to additional large gravity gradient and solar pressure torques which arise from the asymmetry. In summary, the dominant control requirements of SPS change appreciably relative to small contemporary spacecraft. The trade studies and analyses have illustrated preferred control approaches and that the AC&SK requirements are tractable. No major feasibility issues are visible at this time. Supporting conclusions include: 1. Geosynchronous equatorial orbit is preferred over the alternative orbits considered. 2. The solar pressure orbit perturbation dominates stationkeeping propulsion requirements. High-performance propulsion is necessary to avoid large propellant resupply costs. 3. A combined AC&SK system using ion electric propulsion can satisfy the attitude control requirements with very small propellant increases over that required to correct solar pressure orbit perturbation. 4. Gravity gradient and solar pressure disturbance torques can cause large attitude control propellant penalties for asymmetric configurations. 5. Control system/structural dynamic interaction stability can be obtained through frequency separation with reasonable structural requirements. Modern controllerscan potentially ease structural dynamic requirements and simplify spacecraft design.
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