Aerojet is proposing development of a novel combined-cycle propulsion system for reusable hypersonic vehicles which packages current technology to achieve a seamless transition from a standing start to Mach 7 plus.
The concept tackles key problems that developers face in trying to accelerate aircraft to high enough speed for a scramjet to begin operating. Although rocket boosters have been used to accelerate experimental scramjet-powered vehicles like the X-51A to the take-over point, this approach is not suitable for reusable platforms that would operate from a runway.
Major hurdles in the path to successful aircraft-like operation include producing sufficient thrust to punch through the high drag encountered at transonic speeds around Mach 1. Even if this can be overcome, designers also face a “thrust gap” between around Mach 2.5, where current turbine engine power falls off, and Mach 3.5-4, where the transition to a dual-mode ramjet/scramjet takes place. To date, all attempts to develop a viable high-speed turbine engine to bridge this gap have failed.
Aerojet’s TriJet concept builds on the advantages of two traditional air-breathing propulsion systems extensively studied for this role—the turbine- and rocket-based combined cycles (T/RBCC). However, in isolation, both have disadvantages. TBCCs require turbine engines that are often heavy and large, taking up space for fuel, and have poor transonic acceleration, while RBCCs have significantly lower fuel efficiency than turbine engine-powered concepts. The TriJet combines the two options into one by melding a turbine engine and rocket-augmented ejector ramjet (ERJ) with a dual-mode ramjet (DMRJ) to achieve the final push to hypersonic flight.
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