318 J. ENERGY VOL. 2, NO. 5 Technical Notes TECHNICAL NOTES are short manuscripts describing new developments or important results of a preliminary nature. These Notes cannot ex- ceed 6 manuscript pages and 3 figures; a page of text may be substituted for a figure and vice versa. After informal review by the editors, they may be published within a few months of the date of receipt. Style requirements are the same as for regular contributions (see inside back cover). An Aperture-Augmented Prototype Power Satellite K.E. Drexler* and B.R. Sperber* Massachusetts Institute of Technology, Cambridge, Mass. T O demonstrate the feasibility of power satellites at a minimum of cost and risk, most agree that the development program should include a subscale prototype. A prototype which would test the technically risky parameters of the microwave power transmission system at their full-scale values while greatly relaxing other parameters to reduce total system cost could prove attractive. Such a prototype requires a new system element with wide application in power satellite design—a microwave optical element used to augment the transmitting aperture area. This could be either reflector l ' 4 or refractor 3 ' 4 area. To demonstrate safety and to test interactions with the ionosphere, the prototype should deliver a full-intensity microwave beam to the receiving antenna on the ground. That is, all of the microwave power transmission system elements should operate at a full-scale power density to demonstrate safe microwave power transmission through the ionosphere. With the degree of freedom offered by aperture augmen- tation, this demonstration will not require full-scale mass or power for the prototype. Current power satellite designs launch the microwave beam directly from a slotted waveguide antenna. Microwave reflectors (and possibly also microwave lenses) may be made roughly ten times less massive than waveguide on a per-unit- area basis. Aperture augmentation captializes on this fact by using a small area of conventional transmitting antenna to illuminate a large reflector (or lens) which serves as the final transmitting aperture (see Fig. 1.) In this fashion many of the advantages of the standard transmitting antenna design (retrodirective phase control, optimally distributed dc-to- microwave power conversion devices, etc.) may be combined with the low mass per unit area of the reflector (or lens) to yield a versatile power transmitting system. If we model the prototype as a power generating and transmitting system with mass proportional to power output, together with a reflector (or lens) with mass proportional to area, total system mass Mis where C P R -mass per unit delivered power of the power generating and transmitting system - delivered power -reflector (or lens) mass per unit area = reflector (or lens) area Received Feb. 24, 1978; revision received Aug. 4, 1978. Copyright © American Institute of Aeronautics and Astronautics, Inc., 1978. All rights reserved. Index categories: Microwaves; Photovoltaic Power. *Graduate student, Dept. of Aeronautics and Astronautics. The constraint of geometric scaling of the received power intensity distribution yields A R =A 0 P 0 P-' where A 0 = transmitting antenna area for a reference design P 0 = delivered power from the reference design Thus M=CP + RA 0 P 0 P- ! We want to minimize M with respect to P. At the minimum, dM =0 =C-RA 0 P 0 P- 2 so P=(RA 0 P 0 C-') For typical reference designs R = 0.5 kg-m ~ 2 (Ref. 1, reflector area/mass of power relay satellite) A 0 =7r(500m) 2 =7.85xl0 5 m 2 P 0 = 5xl0 6 kW C =10kg-kW- J yielding with P min = 4.4 x 10 5 kW = .44 GW M min =2P min C=8.8xl0 6 kg The above calculation is quite approximate in that it does not consider the configuration changes required to in- corporate a reflector (or lens) as massive as the rest of the TRANSMITTER •I I I ) a) DIRECTION OF MICROWAVE -> PROPAGATION TRANSMITTER Fig. 1 The augmented aperture concept using a) refractor and b) reflector. Downloaded by UNIVERSITY OF ARIZONA on February 3, 2015 | http://arc.aiaa.org | DOI: 10.2514/3.47984