Access to space is in the early stages of commercialization. Private enterprises have been making headway into low-Earth orbit launch systems for small-weight-class payloads of approximately 1,000 1b. These modest gains have emboldened the launch industry, which is now poised to move into the middle-weight class (approximately 5000 lb). The majority of these commercially successful systems are based on relatively straightforward two-stage, liquid propellant rocket technology developed by the United States Government 40 years ago, accompanied by many technology improvements. Configurations that incorporate airbreathing, reusable carrier vehicles for the first launch stage are the next paradigm in developing game-changing access-to-space technologies. While many conceptual deisgns exist, technological advancement in key areas such as combined-cycle engines is predicated upon successful flight research. In this study, airbreathing access-to-space is addressed from the specific perspective of bringing combined-cycle engine technology to flight research and the next level of readiness. The engines considered are based on or extrapolated from known performance parameters of rocket-based combined cycle (the Marquardt Corporation ejector ramjet) and turbine-based combined cycle (the Pratt & Whitney J-58 engine used in the Lockheed SR-71 Blackbird). Validated engine models are coupled with trajectory simulation and analysis in multiple software tools to explore viable launch scenarios using a hypothetical aerospaceplane platform conforming to the aerodynamic model of the SR-71. This aerodynamic model is augmented to simulate an attached orbital insertion vehicle by including the drag increment of the Linear Aerospike SR-71 Experiment. Finally, recommendations are made in support of advocacy of successful adoption of combined-cycle engine systems for space access. The recommended pathway is founded on the principle of concentrating on the technologies of specific interest, while reducing risk and complexity in every other aspect of such a program. In this sense, leaping to fully-integrated conceptual systems is rejected in favor of focused flight research in key technologies.
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