NASA has selected a Williams International high-speed turbojet as the turbine element of its Turbine Based Combined Cycle (TBCC) engine test rig, which will be used to evaluate technologies for potential future two-stage to orbit launcher concepts.

The 30-foot-long TBCC rig is under construction for runs at Mach 2 to 4 in a supersonic wind tunnel at NASA's Glenn Research Center, Ohio, starting next year. The Williams WJ38 turbojet is adapted to run at Mach 3-plus and is a predecessor of more advanced high-speed turbine designs being developed separately under the Air Force Research Laboratory/Defense Advanced Research Projects Agency (DARPA) Mach 4-plus turbine Histed (high-speed turbine engine demonstration) program.

Although not a Histed engine, the WJ38 was acquired by NASA as part of that program, and will be integrated into the TBCC rig next year.

The TBCC is designed to integrate a turbine and ramjet/scramjet into a unified propulsion system that could be used to power the first-stage of a two-stage launch vehicle from a standing start on a runway to speeds in excess of Mach 7. The concept also is being evaluated by Lockheed Martin and Pratt & Whitney Rocketdyne as the ongoing Mode Transition (MoTr) program, which aims to fill the void left by the DARPA HTV-3X/Blackswift hypersonic demonstrator canceled in 2008. Unlike the NASA effort, MoTr is aimed at a propulsion system for potential high-speed strike/reconnaissance vehicles, and will include a running scramjet.

The NASA TBCC rig incorporates a simulated hydrocarbon-fueled scramjet on the upper side of the combined propulsion system, with the turbine housed below, both of which will be fed with a common inlet and both exiting through a common nozzle. Testing will be divided into four main phases, beginning with inlet performance work in 2010, followed by unsteady inlet system work.

The third phase will demonstrate mode control transitions in 2011 and will include testing the ability of the engine to recover from "unstarts." The nozzle and turbine will be added for full integrated flowpath tests in 2012.

TBCC photo: NASA