Performance analysis of rocket-ramjet propelled SSTO-vehicles

Winged single-stage-to-orbit (SSTO) vehicles designed for vertical or horizontal takeoff and horizontal landing with both rocket and rocket-ramjet propulsion concepts are analyzed and their performance and costs are compared. For this purpose, LOX/LH2 rocket baseline vehicles with payload and mission requirements similar to the Space Shuttle system are modified to accommodate hydrogen-fueled ramjet engines. The use of the airbreathing engines results in a substantial decrease in propellant consumption but is heavily penalized by the added weights of the ramjet engine and structural reinforcements to resist higher aero-thermodynamic loads. The results suggest that for vehicles of the same gross lift-off weight the total system costs of the airbreathing vehicles are 19 percent higher compared to rocket systems; however, due to increased payload capabilities, the specific transportation costs are lower.