to nerve tissues in rabbits and rats subjected to power densities of 20 mW/cm2 for 30 minutes. Another data point is that commercial microwave ovens typically leak RF at the door seals or window at densities of 1 to 20 mW/cm2. In summary, detailed investigations need to be conducted to insure complete understanding of biological and ecological effects for both short term and long-term exposures. On a scale from 1 to 5, the criticality is 5. c. Ionospheric effects also require investigation; from the effects on the ionosphere of the MW beam> to the effects of the ionosphere on the phase front control system to be used on the SPS. The effects are presently believed to be small; however, other user effects will also have to be taken into consideration, such as earth-based long- haul communi cations and earth/space communications. Although the theoretical approaches to this problem are known, the resulting limits which may be imposed on the design of the SPS are not known. On a scale from 1 to 5, the criticality is estimated as between 3 and 4. d. There may be some concern on the thermal heating effects of the atmosphere immediately above and adjacent to the rectenna site. With an overall RF/DC conversion efficiency of 85 percent, approximately 750 MW of heat will be continuously radiated from the rectenna. Whether this will have any adverse affect on the troposphere is not known at this time. It is not expected that this will be a difficult analytical assessment. On a scale of 1 to 5, the criticality is 2. Test Plan: Three types of tests are envisioned for further understanding of the rectenna development problems. a. One is associated with the acceptable power densities at the rectenna site with regard to biological and ecological effects. These tests appear to be comprehensive in scope if enough detailed data is to be obtained to evaluate the short-term and long-term effects on plant and animal life. These tests could be accomplished on the ground; however, the availability of equipment, duration of tests, and size of the test facility are driving factors in conduct and quantitative effectiveness of the tests. b. Another type of test is that associated with determining optimum efficiency versus development costs of more efficient diodes for the low power density rectenna elements. These tests could be ground tests also. These should be closely coordinated with the present investigations into the high efficiency, low cost Schottky barrier diode. c. The other type of test is that associated with testing microwave transmission concepts from space. Any tests associated with development of power amplifiers, RFI effects of the MW beam, transmitting antenna design, or phase control will require corresponding rectennas on the ground.
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