TABLE 1 COST AND MASS ESTIMATING FACTORS FROM BASELINES and microwave power transmitter systems replaced by a (laser) subsystem that combines their functions. This system also has a somewhat reduced thermal problem. Although the CO2 lases in a supersonic flow condition at about 60°K, its heat rejection occurs at a much higher temperature after the gas is decelerated by the diffuser. The effective radiating temperature is about 480°K. The studies referenced above do not appear to have made a substantial analysis of the thermodynamics of the gas cycle. The optically pumped systems combine all the features of the baseline SPS into a single subsystem assembly consisting of an optical concentrator and a laser. The laser performs a direct conversion of concentrated sunlight to coherent laser light, thus eliminating a requirement for solar arrays and power distribution. The lasing gas, in this case CF3I or CO2, must be maintained at a relatively low temperature (such as 375°K) and converts sunlight to laser light with a comparatively low efficiency; 15% is used as a representative figure for indirect system although quite an uncertainty exists as to what might be achieved in practice. Taussig estimates 10 to 20% and this appears to be a reasonable representation of the range of uncertainty. Results of these parametric models are displayed in Figures 1 and 2. Several explanatory remarks are in order: (1) Optimistic projections of laser efficiencies were used in order to allow for the probable improvements in that technology and not penalize those systems unfairly. It may turn out that the authors were somewhat too optimistic on several laser options, particularly the gas dynamic laser. However, these biases do not appear to be great enough to change the limited conclusions drawn from this analysis. (2) The mass of thermal radiators is highly temperature-dependent. Whereas
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