Figure 3.2 Battery Masses for Communications Satellites [Pidgeon, 1991] As an example of a potential LEO client, lets look at Space Station Freedom. Though Freedom is not currently in flight, one might expect that it would be in orbit in the time frame considered here, and good data is available concerning its orbit and battery power system. To supply the station's 56 kW of power during an eclipse the station uses 24 ORU's, each containing 36 nickelhydrogen cells for a total mass of almost 4 metric tons. Taking the launch cost per kilogram as $12,000, the savings gained by a battery-independent design would be $48 million. As these batteries would have to be replaced every 10 years or so years, one can calculate a market worth of about $5 million/year. As $5 million/year does not seem to be an adequate market to support a single power satellite, much less a constellation, one might look at the possibility of providing a space platform with a power increase. Here the savings would not come from replacing the weight of the solar panels, but from the fuel savings which would result from the reduced drag of the platform by eliminating the need to add new panels. By using beamed power, the platform gains the benefit of being able to place its most bulky components where the drag penalty due to their size is minimal while keeping the accessibility of the LEO location. Using Space Station Freedom as a baseline design for calculating this market, it has been estimated that the possible revenues from fuel savings would be on the order of $150-300 million/year if an Ariane type launcher was used for fuel resupply. [Eurospace, 1992] One must remember, however, that such a power increase would require a dedicated power satellite. Another possible market which has been suggested for the mid term is providing baseline power to satellites. The reduced mass required for laser-receiving photovoltaics or rectennas for microwave power reception is pointed to as a potential revenue source. The main problem with this concept, however, is that each power satellite, or rather each transmitter on a power satellite, would be fully occupied with providing power to the client satellite, instead of servicing 20 or more satellites as in the eclipse servicing case. With current transmission technology, it seems unlikely that the revenues from support of only a single satellite would be adequate to pay for a separate power satellite. This may change with technology, however; it may be that within 30 years transmitters will improve enough so that a single satellite could beam power to one or two
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