satellites (to reflect and guide laser or microwave/submillimeter-wave beams from the central-station powerplant to the customer), in orbits that assure customer line-of- sight contact with at least one relay satellite or the power satellite at all times, or (c) adequate storage capability onboard each customer satellite to provide power during the maximum projected eclipse cycle. One of the major advantages of laser power transmission, despite its low efficiency and less advanced technological state-of-the-art than microwave power transmission, is the coherence of the power beam at very long range due to the very short laser wavelength. This makes it possible, for example, to cover the entire geocentric region with three power satellites located in equally spaced geosynchronous orbits. Even more interesting, perhaps (and practical only with lasers), would be coverage of the entire geocentric region by a single geostationary power satellite and two geosynchronous- orbit relay satellites. Transmissions with this configuration would span total distances of the order of 100000-130000 km, which could be accomplished in the vacuum of space with laser wavelengths in the 0.5 /zm range, but would be wholly impractical even with submillimeter waves due to the enormous antenna sizes required by beam diffraction at such great distances. Another important orbital constraint is the interruption in insolation that would occur during Earth eclipse for power satellites that employ solar energy sources. The alternatives here would be to equip the power satellites with onboard storage (maximum eclipse period for geosynchronous satellites is about 20 min at the equinoxes), or employ Sun-synchronous orbits for the power satellites, which would reduce their completeness of coverage of the other geocentric orbit regions. System options for most effective customer coverage are as follows: (1) Supply only high-density co-orbiting low Earth orbit customers, using either tethers or microwave power transmission. This is the lowest-risk option. (2) Supply customers as in Option (1), and also high-density geostationary platforms using geosynchronous central-station power satellites in the center of each geostationary cluster with submillimeter-wave power transmission. (3) Supply customers in the entire geocentric space using either three geosynchro- nous-orbit central-station power satellites or one power satellite and two relay satellites, employing submicron-wavelength laser power transmission. (4) Supply lunar and Mars settlements using Clarke-orbit power stations and either microwave or submillimeter-wave power transmission. Type of Demand. The overall demand for space power in the next few decades is not uniform. Unlike terrestrial power grids, which are built around the use of singlefrequency AC with inductive transformers used to adjust voltage to one of a number of standardized levels, satellite customers have grown accustomed to individually tailored power supplies optimized for the requirements of the particular type of payload carried. However, there is little technical or cost risk involved in simply conditioning the central-station power as necessary for each customer. That conditioning is best accomplished onboard the customer's spacecraft, since it would not be economical (except perhaps in the case of cable transmission via tether) to operate beam transmission systems off optimum. Hence for microwave and submillimeter-wave systems the customer-located receiving antenna would simply incorporate power conditioning apparatus as necessary to meet the customer's specifications; for laser transmission the customer-located power reconversion system would be similarly equipped. Hence individual customer specifications, which could include 24 V DC,
RkJQdWJsaXNoZXIy MTU5NjU0Mg==