The thermal conversion system contains a large number of rotating machines. If all the machines are oriented to have the individual momentum vectors additively aligned, a total momentum of approximately 6.14 x 108 N-m-s is present on the SPS. A brief study was made of the effect of this state on an uncontrolled SPS in the presence of gravity gradient torques. The three cases studied were for zero momentum, nominal momentum, and a momentum 1000 times the nominal. The results indicate that the SPS performed identically with the zero and nominal momentum values. Therefore, no special machinery orientation is required to provide cancellation of the individual momentum vectors. The large momentum case provided a significant increase in the stability of two axes because of gyroscopic stiffness. Also, the large momentum case indicated the need for a control law that conforms to gyroscopic torque relations. Figure 7-38 provides plots of the angular rotations versus time for each of the cases studied. 7. 2. 7. 5 PROPELLANT CONSUMPTION 7. 2. 8 REQUIRED TECHNOLOGY ADVANCEMENTS Technology advancements are required on each major component of the solar thermal SPS. 7.2.8.1 CONCENTRATOR The last solar concentrator technology work was done in the 1960's for the Sunflower program [20] and the solar Brayton (LeRC) work. Concentrators were made of foam-backed, aluminized, polyester film ''Japanese Fan" with petals of ALZAK aluminum and rigid glass substrate mirrors. Sizes up to approximately 9 m in diameter were constructed and tested. None of these approached the lightweight requirements of SPS. Some work was done by Goodyear in the same time frame on lightweight inflatable antennas approximately 9 m in diameter. Ground tests, but no flight tests, were performed. The closest
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