CONCLUDING REMARKS AND RECOMMENDATIONS Structure and Control Techniques Conclusions. — State-of-the-art analytical techniques and tools are adequate for the structural and dynamic analyses needed for the SSPS structure. Desirable material characteristics can be identified and technology developments specified to provide inputs leading to the design of structure and attitude control systems for the very large area, light-weight space structures represented by the SSPS. The flight control performance of the SSPS baseline design can be established and parametric studies performed to determine the influence of structural flexibility upon attitude control performance. An interrelated structure/attitude control dynamic model, including such parameters as structural stiffness (frequency), steady-state attitude error, control gains and thrust levels, response time, damping ratios, and control frequencies, can be used to predict SSPS flight control performance. The flight control performance evaluation indicated that the pointing accuracy of the SSPS fell well within the ± 1-deg limit specified by the baseline requirements for the pitch, roll, and yaw axes. In addition, the system's response time and percent overshoot were found to be acceptable for control about all three axes. Using a digital simulation, we generated time-history response plots for the rigid-body and flexible-body dynamics of the SSPS. A comparison of the results indicated structural flexibility tended to decrease the damping characteristics of the rigid-body dynamic characteristics. The parametric studies showed that the spacecraft's attitude errors and response times decreased as the structural. frequency (stiffness) increased. For as much as a 50% decrease in structural weight (25% decrease in structural frequency) the system's pointing accuracy was still well within a ± 1-deg attitude control specification about the pitch, roll, and yaw axes. The analyses indicated that structurally the baseline design is sufficiently stiff to allow excellent attitude control. Control of the system can be achieved to maintain the required attitude of the SSPS in orbit with a limited expenditure of propellants. Recommendations. — A summary of efforts recommended for further study in this area follows: ® Evaluate the structure/control implications imposed by orbital assembly, including assessments of alternative assembly modes; • Analyze the implications of thermal transients induced by eclipse periods;
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