Investigation of Two-Stage-to-Orbit Airbreathing Launch-Vehicle Configurations

Abstract

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.