lations in this study demonstrate that much smaller separations are necessary to overcome the overcrowding conditions. Even a 1° spacing, it has been shown, does not yield sufficient slots for the proposed SPS numbers, and so spacings of 0.5°, or even 0.3°, have to be considered. There are obviously vast areas of uncertainty here — basically because the various RF1 effects and their magnitudes are still largely undefined — but it seems to be generally accepted that 0.5° spacing can be achieved. This seems to be the optimum case at present, although a 0.3° spacing has not been completely ruled out — obvious advantages occuring here from the many extra available slots. One very relevant factor is the development of geostationary platforms and multifunction satellites. Such developments are the only way to expand satellite communication capabilities substantially and thus accommodate the anticipated traffic in coming decades. It has been assumed by the author that such developments will be forthcoming. The major recommendations and conclusions from this study are summarised below: 1. Clarification is needed to ensure that the SPS fulfills the condition that space exploration must be carried out for the benefit and in the interests of all countries, as defined in the Outer Space Treaty. 2. A ruling is required as to whether the projected 30-year occupancy of a geostationary slot by an SPS constitutes national appropriation. 3. A formal definition of the geostationary orbit as outer space is required, to rule out any present or future claims of sovereignty by equatorial countries over the portions of the orbit lying above their territories. 4. An international entity — either existing or new — must be given responsibility for protecting national and international wants and needs for the efficient, economic, and equitable use of geostationary orbit. Particular attention needs to be paid to the developing countries, whose orbital needs lie generally in the future. 5. A detailed study and analysis of all potential RFI effects associated with the SPS must be carried out, where relevant to orbital spacing. 6. Design variables such as antenna polarisation, modulation techniques, common frequency usage, reversal of frequency assignments, and antenna discrimination techniques must be developed to optimise the use of the electromagnetic spectrum. 7. The development of geostationary platforms and multifunction satellites is essential in view of the projected future demands on the orbit. 8. The flexibility of a 0.3° satellite separation condition must be carefully studied in the light of probable developments outlined in points 5-7. 9. A more detailed analysis of collision risks from inactive geostationary satellites is needed. If risks are too high, there may be a need to “clear” the orbit before the SPS programme commences. 10. Reliable estimates are needed of geostationary satellite launches and locations for the period 1990-2030, as these have a direct bearing on slot availability for SPSs. 11. Development of techniques for offshore rectenna construction must be accelerated should longitude offsets become a mandatory requirement for implementation. If so, cheaper and more efficient ways of transporting electrical energy over large land distances will need to be developed, as many rectenna sites will thus be constrained to be situated at large distances from main consumption areas.
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