POTENTIAL IMPACT OF OUT-OF-BAND RADIATION FROM THE SATELLITE POWER SYSTEM AT ARECIBO OBSERVATORY M. M. Davis Arecibo Observatory, operated as a national research center by Cornell University, has the world's largest radio/radar telescope. Its S-band radar system at 2380 MHz is the source of the most powerful collimated signal leaving the Earth; at the same time, its 20-acre collecting area and maser receivers provide the highest instantaneous sensitivity anywhere for the reception of faint signals. The observatory carries out a wide range of research in astronomy, planetary radar and atmospheric physics over its usable frequency range of 5 to 5000 MHz. In addition, an active optical program of airglow research is underway as part of the atmospheric physics program. All of these programs could be severely affected by out-of-band radiation or optical scattering from the satellite power system. The harmful interference levels for radio astronomy in the protected frequency bands are adequately covered by the discussion and tables in CCIR 224-4. It should be noted, however, that these tables are based on an isotropic side lobe level, and assume that the main beam and near-in side lobes are pointed well away from the interfering source. At Arecibo, the available sky coverage is limited to a maximum of 20° zenith angle. The relationship between the Arecibo coverage and the power satellite locations is shown in Figure 1. The figure makes clear that at southern declinations the beam must necessarily come close to the power satellites. In general, the need to accurately correct for spherical aberration has as a byproduct a remarkably "clean" beam pattern at Arecibo, but it is nevertheless clear that the sensitivity at southern declinations may be particularly affected by SPS out-of-band radiation. Three areas are of particular concern at Arecibo: second harmonic radiation, the effect on the planetary radar system at 2380 MHz, and the impact on airglow observations. Second harmonic SPS radiation is of special concern at Arecibo because it falls in our highest frequency band. The Arecibo reflector
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