On the Airbreathing/Rocket Propulsion Relationship: For Advanced Spaceflight Systems, It's the Combination that Counts

Too often joint considerations of the two major classes of aerospace propulsion are thus addressed: Airbreathing versus Rocket Propulsion. But, prospectively, these two mot ive -power fields can yield a highly synergistic, combined means for enabling the high ambitions set for tomorrow’s space transport fleets to be realistically achieved. These goals foresee that true airline -like flight safety, dependability and cost aspirat ions are to be met in routine Earth -to -orbit and “highest speed” transglobal terrestrial transportation service. While spaceflight achievements to date have, in fact, been uniquely conducted through rocket propulsion, the compelling performance and operabi lity attributes of airbreathing propulsion continue to be heeded for their potential contributions to advanced transportation systems applications. This has led to considerations of combined airbreathing/rocket propulsion systems. The leading engineering c haracteristics of both airbreathing and rocket subsystems and technologies are discussed in this context of combined systems. In this, a distinction is made between combination propulsion systems (several vehicle -installed separate, non -interactive engine types), and combined -cycle engines (single flowpath, with several interactive subsystems). The latter choice is illustrated in terms of its characteristic hardware makeup and multimode operation by a description of the Ejector Scramjet combined -cycle engin e. This engine is depicted in powering a non -staged (SSTO)* orbital vehicle through its ascent phase. Key points of this overall presentation are compiled ahead of a set of concluding remarks.