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 $100 per pound), with payloads of greater than 20,000 lbs; this is consistent with Highly Reusable Space Transportation (HRST) system concepts. In-Space Transportation A unique in-space transportation Is required for initial system deployment, which takes place in LEO. Because of its size, an extremely affordable LEO-to-GEO in-space transportation system is vitally important to this concept. It is also assumed that the launched systems will include modular assembly support systems. These must consist of both a clever mechanical scheme inherent in the structure as well as sophisticated and mobile, self-contained robotics approach - a la 'spiders'. SolarDisc: Space Segment The “SolarDisc" concept is a single, large-scale GEO-based, RF-transmitting space solar power system Each satellite resembles a large disc, which can range from approximately 4-to-9 kilometers in diameter, to deliver the required power for its customary markets, he. cities and mega-cities. The outer portion of the disc is a thin-film PV array, rotationally stabilized and continually Sun-pointing. The center of the disc is occupied by a free-turning transmitting antenna and feed system that is electromagnetically coupled but mechanically decoupled from the rotating outer disc so that it can maintain a continuous Earth-pointing orientation. The concept schematic of Figure 3-12 shows that in order to eliminate periods of transmitted beam blockage by the outer disc over the 24-hour orbit, two separate transmitting arrays (or reflectors if an RF rather than DC feed is employed) are used. Each transmitting area is approximately 0.5 to 1.5 kilometers in diameter, again depending on the market power requirement. These arrays (or reflectors) are offset from the central axis by a long (approximately 1 kilometer) tether that provides a degree of gravity gradient stabilization for the inner, Earth-pointing structure. The transmitter feed is located on the central axis of the inner structure, and continually provides power to one of the two transmitting areas; switching from one to the other prior to beam blockage by the solar array disc. The concept is assumed to transmit at 5.8 GHz from operational GEO location, at a transmitted power level of 1000-5000 MW at the output of a ground-based rectenna. Total beam-steering capability is 20 degrees (±10 degrees) which provides greater than full hemispheric coverage from GEO. Although the transmitting arrays/reflectors must initially be assembled at their final projected size, the transmitter assembly and RF feeds are modular and can be expanded as the customer base increases. Sunlight-to-electrical power conversion is via thin-film PV array. This system is anticipated to be largely modular at the sub-element level and deployable in "units" that represent a single concentric ring of uniform width. These solar collection systems are rotationally stabilized to be always sun facing (with the system in a GEO orbit) and to be attached regularly to "tether anchors" that radiate from a central power distribution loop slightly more than 3 km in diameter to accommodate the inner assembly. Heat rejection for power conversion and conditioning systems is assumed to be largely passive, but where active cooling is needed, to be modular and integrated with power transmission systems along the back of the SolarDisc.
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