microwave beam phase front control. The results of this effort indicate that mechanical steering of the antenna to accuracies better than 1 arc-min are readily achieved without substantial increase in control system torque or horsepower requirements. Figure 3. 3-7 summarizes control system design used in preliminary assessment. The initial response of the motor drive will be to relieve torque loads on the antenna induced by spacecraft (SSPS) disturbances. These spacecraft disturbances include gravity gradients, bending modes, and normal satellite limit cycling with a time constant of 12 hours. Spacecraft bending modes couple through the rotary joint and are of the form: due to spacecraft bending dynamics which is coupled into the antenna only in elevation. This occurs because the antenna system uses only a 2-axis gimbal system. This coupled inertial load into the antenna is relatively small. The gravity gradient disturbance has been neglected in this study because it is orders of magnitude less than the coupling disturbance and friction torque. The 1° satellite limit cycle is also neglected with the rationale that the 12-hour period is sufficiently long to assume that steady state conditions exist. The preliminary system design is modeled as a motor directly driving the antenna through a shaft. Gearing dynamics and selection can be made with detail analysis at a later date. A study of control torque requirements and power requirements indicate that they are insensitive to variations of control frequency within the range studied. The system size requirements to achieve 1 arc-min are: 3.3.2 Thermal Evaluation During Task 1, the analyses were centered about studies of the sensitivity of temperature level and temperature gradient within the antenna supporting structure (Fig. 3. 3-8) to parameters such as antenna size, power transmitted, efficiency of microwave converter, thermal radiation properties of structure, and spacing of structural elements.
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