make the satellites appear as individual stationary radio sources, unlike natural radio sources. Emissions originating at the power receiving (rectenna) arrays could be much like other terrestrial sources of interference. Emissions in the allocated radio astronomy bands are subject to constraints under international treaty. Emissions at other frequencies can also harm a substantial number of important radio astronomy observations that occur at spectral lines and frequencies of opportunity outside the protected radio astronomy bands. While the potential effects of SPS on astronomical research are quite diverse, particularly as they apply to the radio and optical regimes of the electromagnetic spectrum, there are two important effects of common origin that would affect both areas of research. The satellites would be in geostationary orbits and occupy the same portion of the sky at all times. Therefore, a fixed region of the sky would not be usable for astronomical research. The size of the region depends on the design of the satellites, the particular observation being made, and the kind of instrumentation being used. The second effect is that the source of electromagnetic interference and light pollution would be high in the sky. As a result, the general strategy of placing observatories in remote locations to avoid local interference and light pollution effects would be very little help in mitigating SPS effects on astronomical observations. Finally, optical effects resulting in increased sky brightness would affect not only optical astronomy, but aeronomy as well. Aeronomers study the physics and chemistry of the upper atmosphere by observing naturally occurring optical emissions such as airglow. This is difficult to distinguish from other increases in night sky brightness. It was concluded that a substantial fraction of faint airglow studies are incompatible with the current SPS Reference System.
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