Investigation of two-stage-to-orbit airbreathing launch-vehicle configurations

A conceptual design study was performed to assess and compare the parameters of two-stage-to-orbit airbreathing launch-vehicle systems in an effort to identify optimal configurations for improved access to space. The following vehicle configuration categories were considered: horizontal takeoff ramjet-scramjet boosters with upper-stage reusable rockets, horizontal takeoff turbine boosters with ramjet-scramjet upper stages, and vertical takeoff rocket boosters with ramjet-scramjet upper stages. Ramjet-scramjet upper stages utilize integrated rockets for final orbital ascent. Ramjet-scramjet booster stages make use of either integrated turbines or rockets for takeoff and acceleration to ramjet start. The payload requirement for each vehicle system is 20,000 lb delivered to a 100-n mile low Earth orbit. The vehicle solutions were-evaluated utilizing several figures of merit including empty weight, wetted area, actively cooled area, gross weight, staging considerations, and design and technology traceability to future development of single-stage-to-orbit hypersonic airbreathing vehicles. The application of these criteria to the closed vehicle solutions reveals that the vertically launched rocket booster with an upper-stage ramjet-scramjet is the best two-stage airbreathing launch vehicle configuration. Of all of the two-stage vehicles investigated, those which place the hypersonic propulsion elements as part of the upper stage surpass those with first-stage placement and exhibit more design traceability with single-stage-to-orbit airbreathing launch vehicles.