site. There are several possible shapes for this beam. An ideal Gaussian distribution is the least attractive, because it has a relatively high microwave power density at its center. But even at this density, the beam has a lower power density than sunlight. Therefore, this beam cannot cause damage, and can be well controlled. At the edges of the antenna site we can meet the most stringent international standards for continuous exposre to microwaves. We have already learned how to direct microwave beams to earth with microwave interferometers, as used in the ATS-F spacecraft. Thus, the beam can be accurately directed from the SSPS in synchronous orbit back to earth. In addition, in our concept, we use a low power control signal transmitted from the center of the receiving antenna towards the satellite, which forces the microwave beam to travel down the signal, thus eliminating any possibility of beaming to the wrong target. Should anything happen and that signal not be received, the microwave beam will demodulate, because we no longer effectively control the phase front, and the beam reading the earth would be at communication signal levels, such as that received from present satellites. The receiving antenna is stationary. It always looks toward the same spot in synchronous orbit, where the satellite is located. The device which allows us to convert microwaves directly into electricity is a dipole rectifier. This is one of the early models which Mr. Brown of the Raytheon Co., has devised. There are the kind' of dipole rectifiers which could be produced in huge quantities, as would be required for the receiving antenna. This summer a very significant experiment was carried out at Goldstone, Calif., under the direction of the Jet Propulsion Laboratory. In this experimentat the site of the Venus antenna—we mounted a portion of the receiving antenna on top of a tower 1 mill' distant from the transmitting antenna. There are the dipole rectifier elements in the receiving antenna. The 86-foot-diameter dish transmitting antenna then sent a microwave beam across a 1-mile distance. Thirty kilowatts of microwave power were received at the receiving antenna and converted directly into electricity. Lamps lighting up just below the antenna indicate that electricity was actually being produced. The conversion of the microwave beam directly into electricity was achieved with an 82-percent efficiency, which is a major achievement for this part of the SSPS system. The satellites will have to be deployed in orbit. There are transportation systems which can be developed for this purpose. This Nation already is embarked on the development of the Space Shuttle. A modified Space Shuttle is adequate to let us pursue the technology verification steps as well as to place a prototype SSPS into orbit. Heavy-lift launch vehicles which are being studied by NASA are the preferred second-generation system, because they could have lift capacities in excess of 400,000 pounds to low Earth orbit. If the SSPS were just a matter of developing the technology, we would be very confident that this project can start now. But we know that we have to access the SSPS on the basis of several criteria to decide whether the SSPS is indeed beneficial to society beyond just being technically or even economically feasible.
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