dilemmas of hypersonic vehicle design is illustrated in Figure 3.27. Using reasoning based on subsonic aircraft, a smaller aircraft should be easier to fabricate and operate than a larger one. However, for a SSTO demonstrator, that is, a demonstrator that can actually achieve orbital speed and altitude, the opposite is the case. The minimum sized, zero payload demonstrator is on the ICI boundary, and at the maximum value of tau. A operational vehicle with a 7.0-ton payload, as analyzed by Vanderckhove and Czysz, has a significant reduction of the ICI value needed. As the payload increases, the tau value at the ICI boundary decreases, so that for a 10-ton payload the minimum value of tau is 0.14. Please note it would be possible to build a hypersonic demonstrator that could achieve Mach 12 for, say, just 5 minutes flight time, but the mass ratio for that mission might be on the order of 1.8, far from the 8.1 ratio required to reach orbital speed and altitude.
Figure 3.27 presents the solution map for the rocket plus ejector ram/scramjet operating as an airbreathing system to Mach number 8. The bottom scale is for ICI in English units for Ip and Istr and the top scale is for ICI in SI (IS) units. The left scale is in English units and the right scale is in SI units for the planform area. The vertical bar is the ICI boundary for the rocket plus ejector ram/scramjet operating as an airbreathing system to Mach number 8 and it is at the 9.0 to 9.5 value, the same as for the all-rocket launcher. In terms of industrial capability required, this analysis points to an equality of requirements. As with the previous case, most of the design space is to the right of the ICI boundary, that is, beyond the current state of the art. Both the operational example and the demonstrator example have the same ICI
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