TABLE 31 NATURAL AND ARTIFICIAL FLUX OF NO INTO THE STRATOSPHERE Source Flux (106 metric tons/year) Natural^' 0.2 to 2.0 SST Fleets^ U.S. Type1.2 to 3.6 Concorde^ 0.16 to 0.4 Shuttle Boosters (360 launches/year) 1.4 a. From Johnson (57), Crutzen (59), Nicolet and Vergison (60), and McElroy and McConnell (61). b. Each SST is assumed to cruise at approximately 20 km for 7 hours per day. c. U.S. type SST's consume 66 tons of fuel per hour and emit 13 to 42 pounds of NO per 1000 pounds of fuel. d. Concordes consume 9 to 16 tons of fuel per hour and emit 13 to 15 pounds of NO per 1000 pounds of fuel. Tropospheric Pollution. —The effects of HC1, NO, or CO in the lower troposphere in the regions of the launch site have not been considered. During the first 30 seconds after launch when the vehicle travels from the ground to an altitude of about 5000 feet, it emits about 138 tons of CO, 126 tons of HC1, and 18 tons of NO. Although these quantities are low compared to other large sources of these components, we feel that somewhat closer analysis of their effects is warranted, and that other constituents of the exhaust should be considered. Key Economic Issues Key Cost Considerations. — Capital cost projections for a system as complex as an SSPS must at this time be recognized as preliminary because of the limited detailed engineering effort that has gone into the design of the components and subsystems. It is possible to assign cost ranges to the most significant parts of the system which include silicon solar cells, microwave generation, transmission and rectification, and the space transportation. The following section reviews the basis for capital cost projections for specific elements of the SSPS. a. Solar Energy Conversion The present cost of silicon solar cells for use in spacecraft — about $175/W — is prohibitive. New methods for producing single-crystal silicon and mass-production assembly techniques will have to be developed to reach the goal of less than $1/W. Based on the experience of present
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