Low Equatorial and Polar and Other Orbit Markets The market for power in LEO will be driven by systems such as space stations and other free- flying platforms for commercial and government activities. Past plans for these systems were very ambitious and many vehicles were envisioned. The power hungry environment needed to conduct all of these diverse missions could be augmented by beamed power. However, since a ground based laser is in practice limited to beaming within 60” of zenith [Landis 92], providing coverage over all longitudes for low earth orbit satellites would require many ground stations along the orbital ground track. A 500 km altitude orbit reaches an azimuth of 60” with respect to a point on the ground when only 900 km away laterally, and around 40 ground stations would be required for continuous illumination of an equatorial orbit at this altitude. For the Space Station Freedom orbit, however, (or any inclined orbit spacecraft) the 28“ orbital inclination renders totally impractical the supply of ground based laser energy on a continuous basis, since the ground track of the orbit is so varied. The region between 28“ north and 28“ south would have to be populated with ground stations every 1800 km around the entire circumference of the world for continuous coverage, and even during direct overflight of a ground facility, the space station would remain within 60° azimuth for less than 3 minutes. Therefore, the servicing of inclined orbit LEO spacecraft must wait for the medium term, when space based laser power stations may become viable (see below). Shuttle tended payloads fall into this category, as do polar orbiting customers whose orbital inclination is even higher. Small satellites may also be a potential market for beamed energy. The most significant limitation on small satellite capabilities is the power they are able to generate, which is normally of the order of 100W or less (100kg class spacecraft) due to the limited surface area on which to mount photovoltaic (PV) cells. Power beaming to small satellites in higher equatorial orbits could more than double their power supply since with body mounted PV cells they could receive solar as well as laser energy simultaneously (heat rejection problems will limit the amount of power that can be received). This would significantly increase the range of missions and applications such cheap satellites could undertake. Many small satellite applications involve high inclination orbits however, and the total market for power to small satellites is likely to remain limited to a handful of such space-craft, even if greater numbers were launched to take advantage of such a power supply system. Summary of Market Analysis for Near Term Applications in Space The market in the near term is essentially limited to aiding an occasional malfunctioning high value satellite in geostationary orbit, and few limited high equatorial orbit missions, such as small satellite power boosting. The net value of this market is unlikely to be large, but the commercial viability of a near term ground to space power beaming system is analyzed in section 11.1.1. Earth Applications Identifying the near term Earth applications of space solar power for Earth use, we consider the time frame unto 2020. It is our assumption that Space Solar Power delivery to the electricity grid will not yet be done on a large scale. As a consequence, we tried to identify market niches which could facilitate the gradual establishment of solar based power systems. A basic assumption for this analysis is that the cost of conventional energy resources will have a stable present value, and that cost for environmental impact is not yet included. The following market cases meet this profile: • remote locations with a developed energy demand, that have generator power now and could use solar power as an alternative • locations that use little power now and that are not connected to any grid, like villages in developing nations • power relay from resource-rich areas on Earth (in stead of in space) to an area with high power demands • electricity grids with high peak power demands.
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