• The initial and variable (per flight) costs of the vehicle used for transport to LEO. • The potential and actual proposed number of flights per vehicle. • The total production run (cost span) for the vehicles required. While all of these issues are discussed at length in various references, there are few, if any, systematic treatments of transportation costs that make all of them clear and therefore permit the exercise of equations (9), (10), and (11) in the conceptual cost model (see Exhibit 22 ). Those references that deal most explicitly with the economic analysis of transportation tend not to be the ones with comprehensive treatment of other costs, while the more comprehensive references, in terms of point estimates of component costs, tend to summarize transportation costs in a form that does not lend itself to systematic reconstruction. Nevertheless, there are certain general conclusions that can be drawn from an overview of the various references: • Target levels of $40-$100/lbm ($88-$220/kg) will probably have to be achieved to make the SSPS concept feasible. • Although this cost level is substantially below current costs, e.g., approximately $300-$350/lbm ($660-$770/kg) for the space shuttle, excluding fleet costs and DDT&E, there appears to be a general concensus that the necessary cost reductions can be achieved if there is sufficient demand for frequent heavy load launches and concomitant government R&D support. • Achievement of the desired goals will almost inevitably require the development of a new Heavy Lift Launch Vehicle, capable of lifting as much as 500,000 Ibm (225,000 kg) into LEO and susceptible to extensive reuse. • A critical ingredient in achieving the necessary cost reductions, even with the HLLV, will be a large number
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