be effected by argon jets. Transport of equipment and materials would be by the Shuttle, which can carry a payload of 30 tons. A more effective “Space Freighter” capable of delivering 400 tons will probably be developed. The transmitting antenna will have a diameter of about 1000 meters and will consist of approximately 7000 subarrays, each 100 square meters in area. It will contain nearly 100,000 klystrons, which will be distributed nonuniformly so as to transmit the 2.45 MHz waves in a Gaussian pattern with its maximum located at the center. This maximum will have an intensity of 23 mW/cm2 in order to satisfy environmental limitations. A study of methods to measure antenna performance was presented by Dr. D. J. Kozakoff of Georgia Institute of Technology, Atlanta GA. The receiving antenna will have elliptical shape (10 x 13 km, if located near 35° latitude). Transmission of energy by microwave is close to 70% effective. Eventual rectification of the microwaves to DC is well within presently used technology and has an efficiency of about 90%. Details of the integration of the SPS with the utility network were given by G. Woodcock of Boeing Aerospace Corporation, Seattle WA, who discussed a paper to be presented by B. M. Kaupang of General Electric Company. He concluded that the SPS can be made compatible with the power network. One of the important requirements for this compatibility is the capability of the SPS to control its power output. While virtually all the discussion of power transmission from SPS to earth centered about microwaves, the possibility of transmission by laser beams was considered carefully by Professor A. Orszag of the Ecole Polytechnique at Palaiseau, France. The theoretical efficiency of laser transmission would be unusually high but many engineering and materials problems are yet to be solved. The problem of ecological impact was approached from the points of view of microwave effects on animal life and of microwave and rocketry interference with communications in the ionosphere. Group Captain 1. R. Lindsay of the Royal Air Force, Alverstoke, Hants., gave a full account of the known effects of microwaves on the animal body. These can be divided into thermal and nonthermal effects. The lens in the eye appears to be most susceptible to thermal damage, and cataract formation in humans can ensue after exposure to microwave radiation densities of at least 100 mW/cm2. This threshold density is, of course, dependent on exposure time. Nonthermal effects, which are said to manifest themselves by headaches, sleeplessness, irritability, fatigue, etc., are still a cause of controversy. NATO standards for exposure time are based on the formula time in minutes/hour = „ , W~ where W, the power density, is given in mW/cm2. For the maximum density at the center of the rectenna of 23 mW/cm2, permitted exposure time would be 11.3 minutes in every one-hour period. Experimental observations show that an envirionment of 23 mW/cm2 is unlikely to disturb birdlife. (Experiments in this are just getting underway in the U.S., however.) It was concluded that thresholds for biological effects from short-term microwave radiation are well above the maximal power density of 1 mW/cm2 estimated to prevail outside the rectenna. The effects of the SPS on the upper atmosphere were taken up by Dr. L. M. Duncan, Los Alamos National Laboratory, New Mexico. During the construction of the SPS, propellant emission from heavy lift-launch vehicles (HLLV) may cause depletion of charge densities in the ionosphere. This aspect is presently being investigated. Also, electron temperatures may be raised in the lower ionosphere by their
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