A critical review of the principal issues governing the feasibility of reusable space launch vehicle systems, i.e., propulsion, structural weights, heat protection, and costs, is presented from the vantage point of 1965. The dependence on flight Mach number of the fuel specific impulse of airbreathing propulsion systems, i.e., turbo.-jets, ramjets, and scramjets, is reduced to a dependence on staging velocity of effective specific impulse values, including flight losses, to provide performance relations for preliminary design use. Reasonable configurations of rocket and airbreathing reusable vehicles are selected and the structural weights are characterized in terms of specific surface weights. Well-established simple laminar and turbulent heat-transfer correlations and transition criteria are used to calculate the temperature histories and distributions on the windward side of slab delta wings during reentry. The performance and weight relations are joined to detailed cost calculations to provide a framework for internally consistent comparisons among rocket and airbreathing reusable vehicles, an advanced expendable vehicle, and current vehicles. The worth of technological improvements is evaluated quantitatively in terms of the cost savings produced in different reusable launch vehicle programs.
Salient results of the analysis and comparison include the following: Operationally and economically, a 10,000-lb-payload reusable HTO vehicle with an airbreathing first stage and a rocket second stage is very attractive, but a scramjet second stage to orbit is relatively unattractive economically. Mixed HTO and all-rocket VTO vehicles exhibit total 10-year program costs that do not differ by more than 10 percent for realistic launch rates. The 10-year program costs of the reusable systems considered will be greater than those of existing boosters at a traffic rate of 300,000 lb of payload to orbit per year, but doubling the traffic rate would make it possible to justify the development of reusable vehicles on an economic basis alone. The reusable vehicles are always significantly less expensive if research and development costs are excluded. The aerodynamic heating and materials problems are less critical than suggested in previous studies.