detailed analysis of W. European orbital slot availability was carried out. This analysis reveals that predicted available orbital slot numbers over the 340°-25° E range are 116 for 0.3° spacing, and 56 for 0.5° spacing (6). Calculations were not carried out for the 1° and 2° spacing conditions, as the previous estimates had indicated that these are completely impractical for the postulated SPS numbers. A study into W. European orbital limitation characteristics (8) considered two distinct future scenarios. These maintain slightly different conservative projections to predict the power density demands of the 9 identified consumption sectors. The effects of varying SPS numbers and separations have been considered, but the presence of other geostationary satellites has been ignored. The first scenario (A), considers three different energy mix fractions of the SPS system in providing 20% (24 SPSs), 40% (48 SPSs), and 60% (70 SPSs) of the 2025 estimated W. European electrical energy demand. The second scenario (B), is specifically junctioned to 48 SPSs with a uniform 0.5° separation. The power density demands of the various consumption sectors, as described by the two scenarios, were compared with the predicted power density levels produced by the three distribution cases (6). These latter values are dependent on, and limited by, the other geostationary satellites in the vicinity. With allowance for longitudesharing and offset-longitude contributions, it seems that there is a reasonable correlation between the power demands, as presented in the two scenarios, and the potential power availability, as presented in the three distribution cases. If we consider 0.5° spacing— the favoured situation — conditions for scenarios A and B, with 48 SPSs, can reasonably be met. Some redistribution of longitudinally- offset power is needed (it was uniformly distributed with longitude in the calculations) to meet the individual requirements of the consumption sectors, but this seems practical. If allowances for sharing and offset contributions are ignored, the 0.5° power density distribution is safely above the 24-satellite accepted minimum, but is well below both of the 48-satellite scenarios. Using a 0.3° spacing, there seems little problem meeting the scenario conditions even for the maximum 70-satellite scenario A case. The scenarios have only considered a 0.5° average minimum spacing condition, and have not included longitude-offset contributions in their estimates. However, these effects will be counterbalanced to some extent when consideration is taken of the fact that the presence of other geostationary satellites has been ignored. However, vast problems will occur if many orbital allocations are made to nonWestern European countries. These problems could well be critical if 0.5° spacing is the optimum condition, but should virtually disappear if a 0.3° spacing condition can be achieved. Similar calculations could be performed for the U.S.A, if equivalent information defining consumption sector characteristics were considered. The next step in the W. European case would be to try and analyse individual national energy allocations from the overall picture. Attempts have been made to perform such calculations for the U.K. (6), but the accuracy is very debatable due to the very uncertain present situation regarding international allocations over the relevant longitudinal areas. CONCLUSIONS In spite of some of the large separating angles quoted in the RF1 section, it is believed that a 2° satellite separation is the most pessimistic sensible estimate bearing in mind the long timescale before implementation of the SPS programme (3). Calcu-
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