0191 -9067/82/010009-21 $03.00/0 Copyright ® 1982 SUN SAT Energy Council METEOROLOGICAL EFFECTS ON LASER PROPAGATION FOR POWER TRANSMISSION R. E. BEVERLY III Consulting Physicist 1891 Fishinger Road Columbus, Ohio 43221 Abstract — Potential mitigation techniques which can minimize the deleterious effects of inclement weather on space-to-Earth power transmission using lasers have been examined, including the choice of laser wavelength, propagation zenith angle, receptor-site elevation, and the potential of laser hole boring. An extensive series of propagation calculations have been performed to estimate the attenuation due to molecular absorption and aerosol absorption and scattering. All commonly encountered meteorological conditions have been modelled, including haze, fog, clouds, rain, and snow. Spectral windows at 2 and 11 gm were identified which permit the highest transmission efficiency for low- and high-elevation receptor sites, respectively, under various meteorological conditions. A new method of hole boring is proposed which is environmentally innocuous and which meets safety standards imposed for accidental specular or diffuse reflection of the beam within the atmosphere and the concomitant random-pointing hazard. A repetitively-pulsed (~ 100 pulses/sec), high peak-power-density (~ 105 W/cm2) laser beam is superimposed on the low-power-density, continuous-wave primary beam resulting in shattering of the obscuring aerosol but with a beam having a combined average power density of only — 10 W/cm2. INTRODUCTION Lasers are presently being evaluated as an alternate power beaming technique to microwaves for space-to-Earth power transmission. Although preliminary studies (1) indicate that laser power transmission has the advantages of negligible environmental damage and small land requirements associated with the receptor sites, meteorological conditions influence the transmission efficiency to a much greater extent than with microwaves. With proper selection of laser wavelength, clear-air propagation can be very efficient; however, haze, fog, clouds, and rain can severely attenuate the beam. This study investigates potential mitigation techniques which may minimize this effect by a judicious choice of laser operating parameters. In particular, the influence of laser wavelength and receptor elevation on transmission efficiency under realistic meteorological conditions is examined. The viability of hole boring through obstructing aerosol formations is quantitatively evaluated consistent with safety and environmental concerns. Finally, laser operating conditions are recommended which will afford the largest receptor power availability for typical mid-latitude sites. Research supported by Rockwell International Corporation, Space Operations and Satellite Systems Division (NASA/MSFC Prime Contract No. NAS 8-32475).
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