degrees relay power to ground stations on a periodic (not continuous) basis, serving approximately 20 town-class or smaller markets. Each market is served by a single rectenna producing 10 MW. The deployment scenario includes emplacing 1 SunTower and 1 rectenna site during the first year, 11 Relays and 9 rectennas in second year and the final LEO SunTower and 10 Rectennas in the third year (for 20 rectennas total). Case 11 was designed to allow a reasonable comparison of a LEO-MEO relay architecture with the baseline MEO constellation presented in Cases 5 and 6. Due to the significantly greater masses associated with the active RF ReflectArray, the total cost for Case 11 are much greater than those of comparable architectures without relay links. For example, the total cost for a pair of LEO SunTower SPS phis 12 PRS is $105 B for the town market, versus $14 B for a single MEO SunTower (Case 6) sized to serve a much larger Mega-town market. This case never achieved a positive NPV and is not a viable candidate for further study. Case 12 SunTower (x2) with 7 GEO Relays Case 12 includes a pair of SunTowers in a LEO sun- synchronous orbit and seven PRS operating in GEO. The system provides electrical energy to seven Town-class or smaller markets. Each market is served by a single rectenna producing 10 MW. The deployment scenario inchides emplacing 2 SunTowers 7 GEO Relays, and rectenna sites during a period of 15 years. Case 12 was designed to allow a comparison of a LEO-GEO relay architecture with the baseline GEO SSP presented in Case 1. As in Case 11, the greater masses associated with the active RF ReflectArray result in a much higher total system cost than for the comparable architecture without PRS. For example, the total cost for-a pair of LEO SunTower SPS phis 7 PRS is $525 B for the town market, versus $64 B for a single GEO SolarDisc (Case 1) serving the larger Mega-city market. This case was found to never achieve a positive NPV and is not a viable candidate for further study. (Here again, alternate PRS approaches must be assessed.) Case 13 Sun Synchronous SunTower (x 72) Case 13 represents a LEO sun-synchronous, 72-SPS architecture involving the SunTower system concept deployed at an altitude of 1,500 km. The orbital inclination of about 95 degrees allows the constellation to provide intermittent cycling and peak electrical energy to approximately 500 town-class markets. Each town is served by a single rectenna producing 50 MW, with the total constellation producing 400 MW. The deployment scenario includes emplacing 72 SunTowers deployed uniformly over 8 years, with 50 Rectennas deployed per year for 10 years (resulting in 500 rectennas total). Case 13 examines the potential for viability at larger scales for the ground infrastructure — in which a very large number of sites (500) is served intermittently by a substantial number of smaller SPS — and to do so at a scale similar to a single GEO SPS producing total power approaching 5 GW. (Case 13 generates approximately 3.5 GW.) This case achieves an overall internal rate of return of approximately 13%, with total revenues of approximately $306 B, costs of $81 B, and an undiscounted net present value of about $225 B (or $4.1 B when discounted at a rate of 10%). This basic LEO constellation approach to SSP represents a remarkable improvement in start-up costs when compared to GEO approaches. The 72 SunTower SPS system analyzed yielded an investment-to- first-power requirement of less than 4% that in the updated 1979 Reference presented in Case 1 ($4.36 B versus more than $250 B) and about 6% that of the GEO SolarDisc approach (Case 4). In addition, the
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