As a result of the structural dynamic analysis, four vertical bending modes were identified for the baseline structure. The mode shapes for each of the vertical modes are shown in Figures 17 through 20. As indicated. Figures 17 and 19 show symmetric modes while the anti-symmetric modes are shown in Figures 18 and 20. The modal characteristics for these modes are identified in Table 7. The normalized modal displacements,0, and the normalized modal slopes, o, corresponding to each mode, are only identified at the ends of the axis where the control actuators and sensors are located on the baseline system (Reference 36). These data are only given for one side of the structure since structural symmetry is assumed. A more detailed discussion of these mode shapes is given in Reference 36. Nominally the X axis of the SSPS is perpendicular to the orbit plane. An assessment of the Y axis disturbance torques in this orientation has determined that there is a constant torque, Tdy due to solar pressure as well as a gravity gradient torque, Kdy which is proportional to the off-nominal deviation angle, Nominally this latter term is zero. The magnitude of these effects was evaluated in Reference 31 and is repeated in Table 8. TABLE 8 PITCH AXIS DISTURBANCE TORQUES Tdy Kdy 5550 N-M 176 x 10“ N-M/rad 4100 ft lb 131.8 x 104 ft - Ib/rad As a result of the controllability study (Reference 35) it was determined that the system's transient response characteristics could be approximately measured in terms of the system's rigid body damping ratio, f, and undamped natural frequency, . Parametric expressions for each of these terms are given in Reference 35 and are repeated in Equations (1) and (2) below:
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