Technology and staging effects on two-stage-to-orbit systems

Horizontal takeoff and landing two-stage systems with an airbreathing first stage and rocket second stage are evaluated for staging Mach numbers that range from 5 to 14. With advanced technologies, the two-stage systems are heavier than the single stage. Using a rocket on the first stage to accelerate from the turboramjet limit of Mach 6-Mach 10 significantly decreases dry weight as compared to the Mach 6 staged system. The optimum dry weight staging Mach number for the scramjet two-stage system is Mach 12. With current technology, the scramjet two-stage systems are half the weight of the single stage, but still require substantial technology development in the areas of inlets, nozzles, ramjet propulsion, active cooling, and high-temperature structures.