Boeing X-51

In early 2003, the Air Force Research Laboratory (AFRL) established a program called EFSEFD (Endothermically Fueled Scramjet Engine Flight Demonstrator), a name since changed to SED-WR (Scramjet Engine Demonstrator - WaveRider). This program effectively continued earlier studies made under the waverider part of DARPA's ARRMD (Advanced Rapid Response Missile Demonstrator) program. In January 2004, AFRL selected a team of Boeing (airframe) and Pratt & Whitney (engine) to build the SED-WR flight test vehicle. In September 2005, this vehicle was officially designated as X-51A.

Image: Pratt & Whitney

X-51A (design concept)

The X-51A will be an air-launched expendable missile powered by a hydrocarbon-fueled scramjet engine. This engine has been in development by P&W since at least 2000 under the AFRL's HySET (Hypersonic Scramjet Engine Technology) program, a part of the USAF's overall HyTech (Hypersonic Technology) effort. A prototype, the GDE-1 (Ground Demonstration Engine 1), has already been ground-tested between September 2002 and June 2003 at simulated air speeds between Mach 4.5 and 6.5. Originally the AFRL had planned to fly the P&W engine on NASA's X-43C vehicle, but that program was cancelled in March 2004. It's possible that the SED-WR program was started early to have a follow-on project up and running in the case of a (possibly anticipated) cancellation of the X-43C.

The X-51A will be launched by a B-52 at about 10700 m (35000 ft), and accelerated to the Mach 4.5 scramjet ignition speed by the solid-propellant rocket motor of a surplus MGM-140 ATACMS missile. Estimated target speed for the X-51A is between Mach 6 and 7. The first flight is tentatively scheduled for late 2008, but the total number of planned flights (and number of vehicles to be built) has not been announced.

Specifications

No detailed design data for the X-51A has been published so far.

Main Sources

[1] Stanley W. Kandebo: "Landmark Tests Boost Scramjet's Future", Aviation Week & Space Technology, 26 March 2001
[2] Stanley W. Kandebo: "Researchers plan civil and military scramjet flight tests", Aviation Week & Space Technology, 4 June 2003
[3] "Scramjet Demonstrator Get X-Plane Designation", AFRL Propulsion Directorate Monthly Accomplishment Report, September 2005
[4] Pratt & Whitney Website

Back to Directory of U.S. Military Rockets and Missiles, Appendix 4