Orbital Delivery of Small Payloads Using Hypersonic Airbreathing Propulsion

Scramjet engines promise significantly higher specific impulse than rockets during the hypersonic phase of low- Earth-orbit insertion trajectories. Despite this, scramjets are not used on any current systems due to the difficulty of operating over the large Mach number envelope required by this accelerating trajectory. The key to taking advantage of airbreathing hypersonic engines for low-Earth-orbit insertion is to develop a multistage system that makes use of the scramjet only within its high-performance regime. Amultistage rocket-scramjet-rocket system that accepts this limitation has therefore been examined. This system includes a solid rocket boost to Mach 6, a near-term Mach 6–12 hydrogen-fueled scramjet engine to propel a reusable second stage, and a liquid-fueled final-stage rocket. Trajectory calculations for a system scaled to deliver approximately 100 kg to a 200 km equatorial orbit indicate payload mass fractions of approximately 1.5% with the use of a scramjet stage designed for low drag and efficient packaging. The goal of this work is to guide the future development of scramjets by identifying the areas that will make the most significant improvement to their use for space access.