Orbital delivery of small payloads using hypersonic airbreathing propulsion

Abstract

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 air-breathing hypersonic engines for low earth orbit insertion is to develop a multi-stage system that makes use of the scramjet only within its high performance regime. A multi-stage rocket-scramjet-rocket system that accepts this limitation has therefore been examined. The current paper describes the development of a scramjet propulsion module with the fidelity to properly model the performance constraints of a near-term hydrogen fuelled Mach 6-12 scramjet engine. This module was used to calculate a baseline trajectory involving the boost of a 3000 kg scramjet powered vehicle to Mach 6 and an altitude of 27 km, an airbreathing acceleration phase to Mach 12, and then release of a final rocket powered stage to deliver approximately 100 kg to a 200km orbit. 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.