Figure 3.1 Eclipse Lengths in Geostationary Orbit During Eclipse Season Of course, several things must be considered when examining the simple calculation above. First of all, the power satellite itself will be in eclipse for some portion of this time and will be unable to transmit, though for a constellation this factor may be ignored as presumably one power satellite would always be in view. Secondly, it should be noted that geostationary communications satellites tend to orbit in clusters over strategic areas of the globe. As satellites in groups of this sort would sometimes be in eclipse at the same time, the 27 satellites serviced would have to be relatively spread out. Also it should be noted that the 1.2 hour maximum eclipse occurs only twice each year. For the majority of the time eclipse servicing would not take up a power satellite's full duty cycle. The question of capacity is quite important in assessing the real worth of this market. The above calculations assumed a constellation of satellites each servicing on average 27 other satellites. Taking a minimum constellation size of three power satellites, it would take at least 81 satellites expiring due to battery failure to fill the market for those three power satellites. As the number of communications satellites failing for this reason in the last decade could be counted on the fingers of one hand, it seems that this market would be extremely unlikely to fill, even when one considers the rapidly growing communications network enveloping the world. At best this market could provide a profitable sideline for satellites already in place and serving another market of larger volume. Another important question to answer concerning this calculation is whether or not the communications company will need the extra satellite lifetime. Table 3.1 shows something of the recent trends in communications satellite mass, power, capacity, and lifetime. Clearly we can expect that communications satellites may reach lifetimes of 20 years by the year 2000. When extending the lifetime of a satellite which has been working for 20 years, one must wonder how outmoded that satellite has become. Will it have the capacity and bandwidth to compete in the market of 25-30 years after it was developed?
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