the receiver cavity walls. Also, since the energy produced by the SDPM is a function of the concentrator reflecting area, placing the SDR in front of the concentrator either reduces the power delivered to the receiver for a given concentrator size or requires additional reflective area (and associated mass) to compensate. Solar Dynamic Radiator Alternative Configurations Dynamic disturbances initiated by the rotation of the beta gimbal or by propagation along the transverse boom from an external source (e.g. docking) will perturb the SD module including the concentrator and radiator structures. Beta gimbal control along with the fine pointing and tracking system is required to provide concentrator pointing and tracking within 0.1 degree accuracy. In order to meet this requirement, structural vibations must be above the frequencies to which the FP&T control system responds. Since the bandwidth of the SD FP&T control system is 0.5 Hz, the structure components need to have a higher natural frequency to minimize control/structure interaction. It appears, in view of the required control function algorithms for the FP&T system, that a natural frequency of 1.0 Hz or higher may be required for the SDPM. The necessity of this requirement is currently under study at Rocketdyne. Due to dynamic coupling between the radiator and the concentrator, radiator vibrations may also excite the concentrator, reducing pointing and tracking performance. Therefore, it would appear that the fundamental frequency for the SDR should be in the order of 1.0 Hz or higher. To achieve a 1.0 Hz minimum deployed natural frequency, three SDR alternative configurations have been studied. All three options are depicted in Fig. 3. In all three options tension rods have been added to increase the stiffness of the scissors mechanism. The modified baseline vertical configuration also differs from the baseline design via additional stiffening of the top panel and the radiator supporting plate. In the second alternative configuration, known as the ‘bow-tie' configuration, the radiator is located in the transverse direction, parallel to the Space Station Freedom transverse boom, such that the SDR deploys symmetrically towards port and starboard sides. All of the radiator panels are in the same plane and the normal vector is parallel to the beta gimbal axis of rotation. The radiator is divided into two halves each half containing a supporting base plate and four panels. The third studied alternative is a variation of the ‘bow-tie' configuration. This option is known as the ‘butterfly' configuration and is obtained by rotating each ‘side' of the ‘bow-tie' configuration about the point of attachment to the radiator supporting plate, as seen in Fig. 3. Advantages and Disadvantages of the SDR Alternative Configurations Each of the alternatives studied present advantages and disadvantages worth considering in the determination of the best SDR option for the Space Station Freedom EPS. These advantages and disadavantages have been grouped into the five areas of physical characteristics, thermal performance, drag and concentrator shading and mass, as described below. Physical Characteristics Two physical constraints must be considered in the design of the SDR. The first relates to the maximum possible dimensions that the SDR may have in its stowed configuration in order to fit in the space shuttle's cargo bay with the rest of the
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