forms; military observation, communications, and command/control systems), low-to- medium altitude polar and/or Sun-synchronous orbits (remote sensing, scientific, and military reconnaissance/surveillance satellites), and high-inclination, low-to-medium altitude orbits (military reconnaissance, surveillance, and weapon-carrying platforms). Other system considerations are the level and type of electric power demand required by the system's customers and the constraints imposed on the power delivery system by the customer's spacecraft; e.g. mass, volume, launch-vehicle constraints, operational needs, communications, maneuvering requirements, microgravity limits, field-of-view requirements, sensitivity to environmental contaminants, etc. For military satellites, survivability in the face of both natural environmental hazards (radiation and debris) and potential enemy action (electromagnetic pulse, high-power microwaves, lasers, kinetic-energy weapons, etc) is a major consideration in powersystem use. For investment decisions, costs and schedules for research, design, development, deployment qualification, prototype demonstration, and full-scale operations are key elements. Although these can only be estimated very roughly at this time, such estimates do shed some light on the real near-term and far-term economic potential of space-based central-station power systems. Orbital Constraints. The three regions of potential interest for central-station power systems in space are the various geocentric (Earth) orbits, the Moon, and Mars. Orbital constraints for lunar or Martian space power systems would not be a problem. Power satellites positioned at appropriate locations in the Clarke orbits of each of these bodies, using beam power transmission to the surface, would be very similar to Earthorbiting power stations, since neither the Moon nor Mars have dense atmospheres like that of Earth. Mars power stations, however, are not likely to utilize solar energy sources because of their distance from the Sun. For Earth-orbiting customers, however, which are likely to comprise the bulk of the space power market for at least the next few decades, orbital constraints are more important. The easiest customers to supply would be those that co-orbit in clusters; for example, the space station is likely to be accompanied in future years by a number of free-flying science, research, and commercial platforms in relatively close orbits so that they can be serviced by the station's crew. Here a commercial power depot satellite, conceivably even using tethers to deliver power, would involve few, if any, transmission problems. Geostationary-orbit satellites, too, because they remain fixed relative to each other, also pose few power-system delivery problems. A single geosynchronous (probably not geostationary) power depot could cover each of the three largest clusters of such satellites; i.e. those over South America, Africa, and the Pacific archipelago. Three power satellites with transmission capabilities of the order of 25 000 km, which are quite feasible for either laser or submillimeter-wave power transmission, could cover the bulk of these high-density regions. There could be a problem of interference due to low-frequency harmonics of the submillimeter-wave transmission beams, but their primary frequency (100-300 GHz) would not affect normal C-band, Ku-band, or even Ka-band communications traffic. Non-colocated customers in the lower Earth orbits do present some problems to the central-station power concept. It is of course impossible for a single central-station spacecraft to maintain line-of-sight contact with all customer spacecraft in all geocentric orbits due to eclipse by the Earth; hence one of three alternatives must be employed: (a) multiple central-station powerplants in orbits that assure all customers being in line-of-sight of at least one powerplant at all times, (b) multiple relay
RkJQdWJsaXNoZXIy MTU5NjU0Mg==