Figure 3. Erectable Momentum Wheel Conceptual Design •UFLRMIIINU Lire Ot LMinkJMLJ/ - JUW I IIX Figure 5. Baseline A ttitude Control and Stationkeeping System Figure 4. Propellant Requirements for Various RCS Propulsion Types system is given in Table 2 and is 0.08% of the spacecraft mass (dry) and 0.37% with annual propellant requirement. The average operating power is 34 megawatts. Dynamic stability is a concern because of low SPS structural frequencies in the order of 6 cycles/hour. Preliminary simplified analyses have been performed^ to establish control bandwidth requirements and system stability. Quasi-linear control torques are obtained with a combination of throttling and on-off thruster commands. The results indicate that substantial separation between control bandwidth and structural frequencies exists (Figure 6) and that stability is achievable using classical control techniques. This is due primarily to the low SPS bandwidth requirements for the sun-staring application. Small increases in depth of the structure can appreciably increase structural frequencies with only minor increases in structural mass. However, technology advancement in control of large space structures is recommended to support potential structural mass savings and spacecraft design simplifications. A variety of SPS configurations have evolved, with significantly different AC&SK requirements. The solid-state SPS configuration depicted in Figure 7 has a larger solar pressure stationkeeping propellant requirement than the reference spacecraft due to larger area/mass and area/power ratios.
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