0191 -9067/81 /030203-04$02.00/0 Copyright ® 1981 SUNSAT Energy Council LETTERS TO THE EDITOR To the Editor: Ruth and Westphal, in “Solar Power Satellites for Europe” (SSPR 1, 351, 1980), correctly point out that the area of the rectenna increased with longitude offset. Figure 3 also correctly indicates that the azimuth of the microwave beam, and consequently the major axis of the rectenna ellipse, varies with longitude offset, although this is not mentioned in the text. The second point may prove to be of greater importance than the first, in that the rectenna must be installed so as to take account of any planned offset; conversely, the rectenna installation, once completed, fixes the longitude of the satellite servicing it. Some early SPS work contemplated, at least implicitly, a degree of flexibility in satellite/rectenna pairing. To my knowledge, this flexibility has not been specifically denied in subsequent work. Rectennas are still generally visualized with a north-south orientation, although this is not the case in general. This will be of more concern in the United States than in Europe, since the variation of azimuth with longitude offset is greater at lower latitudes. The effects of azimuth variation are not entirely unfavorable. It is possible, if not probable, that a rectenna site that had been considered unacceptable because of limited north-south extent might be completely adequate if the rectenna axis could be rotated 40° or 50°. Such rotation can be accomplished by longitude offsets of 25° to 35°, while increasing the land area required by only 15% to 18%. Louis E. Livingston Head, Systems Analysis Office Program Development Office Lyndon B. Johnson Space Center Houston, Texas 77058 The following table summarizing nongovernmental space activities was provided by Theo Pirard, Space Information Center, Route de la Croix Maga, 54, B-4860 Pepin- ster, Belgium. Editor
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