GUY NORRIS / LOS ANGELES
General Electric (GE) has revealed design details of the turbofan ramjet at the heart of one of NASA's long-term third-generation Space Shuttle replacement proposals. The Revolutionary Turbine Accelerator (RTA-1) engine is based on GE's YF120 variable cycle engine developed for the Advanced Tactical Fighter programme which spawned the Lockheed Martin F/A-22.
The RTA is being studied under NASA's Turbine Based Combined Cycle (TBCC) project aimed at providing aircraft-like spaceflight operations, as the first element of NASA's Next Generation Launch Technology initiative. The TBCC is competing against a rocket-based combined cycle alternative with a downselection expected in 2009.
Any full-scale production version of the RTA would be based on a versatile core derived from CFM International's Tech56 technology project and US government-industry versatile affordable advanced turbine engine development initiatives.
The RTA-1 is designed to accelerate from a standing start to around Mach 4.1 at 56,000ft (17,000m) in eight minutes. Following a normal take-off and acceleration to Mach 2 with afterburner in single bypass mode, the RTA will transition to double bypass mode for acceleration to M3. A key feature of the RTA is a combined ramjet/afterburner dubbed the "hyperburner". Above M3 the hyperburner transitions from an afterburner to a ramjet burner for the final jump to M4-plus, after which the second-stage space vehicle will separate from the RTA-powered vehicle, the former landing as a conventional aircraft. At M4 GE says the engine core is at flight idle and all the thrust is generated by the hyperburner.
Design work is under way at GE on a new fan and fan frame for the YF120 which is being refurbished, and a new core-driven fan stage and hyperburner are being developed.