The format of this report consists of a brief summary of the reference system (section 2), a presentation of general conclusions by the panel (section 3) followed by specific conclusions in each of the major topic areas (sections 4 through 7). In this report, the discussion of solid-state microwave devices has been included under the heading of Microwave Amplifiers. Section 8 is a summary. 2. SUMMARY OF THE REFERENCE SYSTEM According to the DOE/NASA reference system report DOE/ER-0023, October 1978, the SPS Microwave Power Transmission System (MPTS) could consist of a large array (about 100,000) of high power klystrons grouped into subarrays and feeding an array of slotted waveguides (spacetenna). Solid-state microwave amplifiers have also been investigated. The high power klystrons would be powered by 40 kV power lines from a series/parallel solar cell array. The klystrons would be phase controlled at the subarray or individual klystron level in such a manner as to produce as nearly as possible a parallel beam, plane wavefront launched from the 1 km diameter spacetenna and directed at a 10 km diameter rectenna located on the surface of the earth. Phase control would be accomplished by a retrodirective pilot beam launched from the center of the rectenna and phase conjugated with the help of an onboard phase reference signal to provide the proper phase angle for each subarray or klystron. Main beam conversion to DC electricity at the ground would be accomplished by rectifier-filter circuits attached to each dipole antenna in the rectenna array. The DC power output from the rectenna would be about 5 GW. The primary constraining factors on the beam power are the 21 kW/m2 heat dissipation limit on the spacetenna and the hypothetical 23 mW/cm2 power density limit on heat balance disturbances to the ionosphere. The main beam operating frequency of 2.45 GHz has been chosen. The overall MPTS efficiency for the reference system is estimated by NASA to be 61.1%. Microwave power levels at the rectenna edge are constrained to 1 mW/cm2 and are less than 0.1 mW/cm2 beyond 0.7 km from the rectenna edge. For further details on the reference system, see D0E/ER-OO23 or the Workshop summaries edited by R.H. Dietz. 3. GENERAL CONCLUSIONS First and foremost, the review panel wishes to indicate that it is impressed with the large quantity of excellent work which has been done on the SPS Microwave Power Transmission System. Given the relatively short time that the system has been under study and the modest funding available, the results to date are impressive. The dedication of a number of individuals is clearly apparent. The panel believes that a microwave power transmission system for the SPS is probably technically feasible, given sufficient resources in terms of funding and time. Perhaps the best phrase to describe the panel’s attitude is “cautious optimism.” It is likely, however, that the final system will bear little resemblance to the present reference system. The panel feels that it is imperative that NASA not become locked on to the reference system as a basis for all future design. In some areas, such as the retrodirective phase control system and rectenna design, the review panel questions the present reference system approach. The panel believes that top priority should be given to determining a hard upper
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