Orbital payload delivery using hydrogen and hydrocarbon fuelled scramjet engines

This paper compares the performance of two different launch systems; one with a hydrogen fuelled scramjet stage and one with a hydrocarbon fuelled scramjet stage. The two launch systems are optimized with respect to payload delivery capability and then compared, assuming a fixed launch mass. A rocket powered booster is used to achieve the required scramjet ignition conditions and a rocket powered orbital stage is used to accelerate the payload from scramjet shut-down to low earth orbit. The trajectory simulator includes a full spheroidal, rotating earth model, a fourth order gravitation model and an MSISE93 atmosphere model. A gradient projection optimization routine is used to achieve an optimal solution using a set of time referenced vertical accelerations as optimization parameters. Hypersonic engine performance is determined using a quasi-one-dimensional scramjet model. Results show that a hydrogen powered scramjet launch system outperforms a hydrocarbon powered system due to its higher specific impulse and peak Mach number. While payload mass fractions are shown to be favorable, the high structural requirements of the scramjet imply that reusability is a key characteristic to make them financially viable. Trajectories were found to be dominated by their lift requirements, which outweighed any performance advantage for hydrocarbon fuels in terms of their better storage capability