SRS-’79: Ground Segment. The nominal ground receiver for the Reference System concept is a single 13 km diameter (approximately) rectenna site with direct electrical feed into the commercial power utilities interface. For primary power, no long-duration ground-based energy storage system would be required, however there would be periodic shadowing of the array by the Earth, requiring alternate energy (possible stored) during these periods. Markets. A single, targeted major industrialized country electrical energy markets (on a global basis) could be served by a single SRS-’79 satellite. Major block incremental increases in power services with increasing coverage are possible due to expansion of the space segment to a constellation of up to 60 satellites. 33, Sun Tower The “SunTower” space solar power concept exploits several innovative approaches to reduce the development and life cycle cost of SSP, while at the same time broadening market flexibility. The system concept involves an extensively evolvable and modular space segment, initially deployed in low Earth orbit (LEO) and later migrating to its operational orbit, which may either be: a sun-synchronous (nearpolar) LEO orbit (600 - 1400 km altitude); or an inclined (30 - 50 degree) middle Earth orbit (MEO) in a medium altitude range of6,000 - 20,000 km Figure 3-3 provides a schematic of the SunTower space segment concept. For MEO-based Sun Tower systems, a single satellite/ground receiver ‘pair’ would be sized to approximately 250 MW scale, with multiple satellites required to maintain constant power at that level A Sun Tower system operating from LEO sun-synchronous orbit, with more limited satellite to ground site contact times, would be sized somewhat smaller than its MEO counterpart - typically on the order of 50 MW - to provide peaking service to customers at the dawn terminator. Figure 3-4 illustrates a typical MEO orbital architecture, and Figure 3-5 a typical LEO sun-synchronous architecture into which the SunTower system concept could be integrated. SunTower: Development & Manufacturing. This concept, owing to its extensive modularity, will entail relatively small individual system components which can be developed at a moderate price, ground tested with no new facilities, and demonstrated in a flight environment with a sub-scale test. Manufacturing can be ‘mass production’ style from the first satellite system. Earth-to-Orbit Transportation. No concept-unique ETO transportation system is required, beyond that necessary to achieve extremely low launch costs (on the order of $200 per kg), with payloads of greater than 10 MT; this is consistent with Highly Reusable Space Transportation (HRST) system concepts. In-Space Transportation. No in-space transportation is required for initial system deployment, which takes place in LEO. After the system grows to more than 10-100 MW transmitted power (depending on ground receiver sizing), three functions must be met by in-space transportation: (1) transport of the SunTower to its new orbit (this may be an inherent function of the SSP - e.g., using SEPS), (2) transport of later SSP elements/modules to the new orbital location, and (3) transport of replacement elements to the operational orbit and return for de-orbit of replaced elements. SunTower: Space Segment. The “SunTower” concept is a constellation of medium-scale, gravity gradient-stabilized, RF-transmitting space solar power systems. Each satellite resembles a large, Earthpointing sunflower in which the face of the flower is the transmitter array, and the ‘leaves’ on the stalk are solar collectors. The simpler LEO-based concept is assumed to transmit at 5.8 GHz from an initial
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