0191-9067/80/040317-28S02.00/0 Copyright ® 1980 SUNSAT Energy Council LASER-SPS SYSTEMS ANALYSIS AND ENVIRONMENTAL IMPACT ASSESSMENT* R. E. BEVERLY III Columbus, Ohio Abstract — The laser alternative for power transmission from space to earth is investigated from both an environmental and systems viewpoint. Twenty independently controllable, CO electric-discharge lasers are retrofitted onboard an existing SPS point design replacing the microwave transmitters. Each 110-MW beam is separately directed to clustered or geographically separated heat-engine receptors using adaptive Cassegrain telescopes. Propagation calculations, including the effects of molecular and aerosol absorption and scattering, turbulence, and thermal blooming, indicate a clear-air transmission efficiency of 84% to 97% for a receptor-site elevation of 0.5 to 3.5 km, respectively. For a primary mirror diameter of 25 m, =99% of the available power at the terrestrial site will be captured in a 50-m-diameter spot. The land area required by each site is approximately 0.3 to 2.0 km2, depending upon the number of receptor devices in a cluster and the safety margin allowance. The estimated specific mass of the laser transmitters and associated subsystems but excluding the photoelectric collector array is 13.3 kg/kW and the power delivered to the utility interface is 1.47 GW. The present satellite concept is far too massive and inefficient to be considered economically viable; significant technological breakthroughs in advanced laser concepts will be necessary for the laser SPS to become cost-effective. One promising class of candidates is the direct solar pumped laser. The safety issues associated with laser power transmission, however, appear tractable. Furthermore, no effects could be identified which present a real danger of serious injury to the environment, although certain phenomena deserve closer scrutiny, including possible highly localized perturbation to the D-layer, induced turbulence in the lower troposphere, and the impact on insects and birds traversing the beam. INTRODUCTION Laser power transmission is being seriously considered as a viable technological alternative to microwaves for the Satellite Power System (SPS) due to concerns about the environmental implications and potential biological hazards of long-term, low-level microwave radiation and the possible utility of laser-SPS systems of lower base-load power and smaller receptor land area (1-3). The primary emphasis of this research is on the environmental impact of space-to-earth power transmission using lasers; the system concept presented here is not intended to portray an optimized design. Using an existing microwave-based satellite concept (4) we examined the systems feasibility and environmental impact of replacing the microwave transmitters with laser transmitters using current or near-term state-of-the-art laser technology. Although the environmental hazards associated with space-to-earth laser propagation are minimal, the results of this study are discouraging from an economic and systems engineering point of view. Laser technology, however, is progressing at a rapid pace and, indeed, laser power transmission from satellites may become viable in the near future using more advanced solar conversion schemes and laser devices. *Research supported by Rockwell International Corporation, Space Division (NASA/MSFC Prime Contract No. NAS 8-32475).
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