such as Saturn's rings, is similar to the values derived in CCIR 224-4 for spectral line radio astronomy in this wavelength region. If the SPS noise power density can in fact be limited to that shown in Figure 26 of Satel1ite Power System: System Report, DOE/ER - 0023, October 1978, then the noise from 60 power satellites lies at the harmful interference threshold for planetary radar research. The third area of particular concern to Arecibo is the impact of direct and scattered sunlight on airglow research. Because of the weakness of most (non-auroral) airglow emission features, airglow observing is traditionally a "dark moon" activity. It is almost impossible to obtain useful measurements with direct moonlight in the field of view of an instrument. In fact, many automatic photometers incorporate protection devices to guard against possible detector damage caused by exposure to direct moonlight. In investigations of spatial variations, north-south meridian scanning is a common mode of operation. A chain of satellites across a meridian could seriously limit studies of the dynamic behavior of the airglow. The problem of moonlight scattered into the field of view is rather difficult to quantify, as it depends on local tropospheric conditions. Adequate measurements of strong emission features can probably be obtained when the moon is less than 1/4 full. However, recent developments on instrument design and detector technology have made it possible to observe very weak airglow features. Work of this type is seriously compromised by an increase in background brightness by a factor of 5, such as is caused by the presence of the Milky Way in the field of view. At Arecibo, an increase in sky brightness of this order is observed at the zenith when a moon about 1/8 full (by area) is present near the horizon. Scattered light from the SPS of this amount would seriously compromise present airglow research at Arecibo. The discussion has thus far assumed that a rectenna array is not placed in Puerto Rico. In fact, the extrapolated power requirements in Puerto Rico match the 5-GW capability of an SPS, and the island imports 100% of its energy. For these and other reasons, it may be selected for a rectenna site early in the program. If it is selected, the interference criteria may be much more difficult to meet, both because the observatory will lie in the near-pattern of
RkJQdWJsaXNoZXIy MTU5NjU0Mg==