excursion of the microwave beam, life will routinely be exposed to microwaves in two ways: (1) all life forms that live around the perimeter of the rectenna, receiving a microwave flux that represents a small fraction of the maximum beam intensity (less than 1 mw/cm2). (2) airborne life forms (i.e., birds, bats and insects) which fly through the beam and receive the full beam intensity. Although the experimental data in reference 8 does have some uncertainties in the microwaves flux, the data should be taken as indicative of the types of problems that may be encountered. For example, the data suggest that the survival of some species may be directly effected at maximum beam intensity, while other species may show only slight short-term effects. Therefore, there is the possibility that certain species of airborne life may be effected in the time required to fly across the microwave beam. Although there may be a natural avoidance of microwaves by birds, as exemplified by using microwaves to clear runways of birds, there may also be a natural attraction, such as heat during colder climatic conditions. These possibilities must be looked at in detail. The effects of microwaves may extend below thermogenic intensities (i.e., below 10 mw/cm2), ranging from decreased weight, slower reflexes, decreased birth rate, and increased! abnormal offspring to changes in the rate of transport of K+ and Na+ ions across membranes, decreased reproductive functions, and changes in immunobiologic resistance (at intensities of lmw/cm2 or less). In addition, there is some controversy regarding a decrease in eye lens translucency of workmen routinely exposed to microwaves. Some authors report no difference between workmen exposed and those not exposed, while others report an increase in the lens aging process. The resolution may be that a definite threshold is required for producing lens opacity; however, it has only been consistently produced in the rabbit. This data contains uncertainties, and at times is contradictory. In order to avoid controversy, it is important that exact safe levels be established. Such work is already being done by the Food and Drug Administration, Bureau of Radiological Health, and the University of Washington. This work should be followed closely, as well as new studies started. 2. Ionospheric Heating - see section IV-A-2 Although only a small fraction of the microwave beam would be absorbed by the ionosphere, the beam could cause, measurable changes in the temperature. This would, in turn, lead to changes in the ionosphere chemistry, effecting the ion density, and short wave communications. Although these effects would probably be of insignificant consequence they should be looked at closer. Most previous experiments at ionosphere modification have been at RF frequencies and power densities different than proposed for the SPS (ref. 9); therefore more studies would be required to determine the exact effects on the ionosphere.
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