service life. Although it is possible to select structural design approaches which will minimize the effect of such thermal exposure, more detailed evaluations of these effects are warranted. FIGURE 4 SSPS BASELINE CONFIGURATION The large structure required for the SSPS will be subjected to orbital perturbations, see Figure 5, of which the gravity gradient will be the most significant. A reaction control system based on the use of ion engines (Argon is one candidate propellant) will be required to keep the SSPS in the appropriate orbit and to assure that the solar collector panels point towards the sun within one degree, while the microwave antenna is directed towards the receiving antenna on Earth. To achieve the desired stationkeeping and attitude control for the SSPS about 100,0001b of propellant will be required per year, depending upon specific orbital characteristics. The mass of the SSPS, assuming that 5000 MW are delivered to the bus bar on Earth, is:
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