Fig. 2. Effect of AV distribution. Fig. 3. Effect of first stage configuration. Fig. 4. Effect of learning curve. Fig. 5. Effect of development cost, Co. the present shuttle mission model must be compared with the two to three thousand operations a year for a typical jet transport, or the 20 million operations a year for the worldwide air transportation system. The SPS will generate a demand for space transportation which, in turn, could generate a level of space operations leading to cost reductions such as those demonstrated by the air transport systems. It is important to recognize that the energy costs of transportation to LEO are only about four times higher than the energy costs required for round trip transportation from, for example, Los Angeles to London: this latter transportation is available with full passenger amenities for about $5/kg. The importance of scale of demand is evident from Figure 1 where the cost of transportation is shown as a function of payload mass per launch. At low demands the learning curve drives the optimum to relatively low payload masses similar to those of the Space Shuttle. The effect of varying some of the basic assumptions on which these curves are based is shown in Figures 2 to 5.
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