Testing is under way atNASA's Langley Research Center on a jet-fueled, air-breathing engine like theone that will power the U.S. Air Force's X-51 WaveRider vehicle as it sets outin late 2009 to set new records in hypersonic flight.
Aiming for top speedsapproaching Mach 7 (around 5,000 miles or 8,050 kilometers per hour), X-51 is not intended tobe the fastest air-breathing vehicle the United States has built. But it is themost complicated, designed to achieve five or six minutes of powered flightbefore doing a controlled glide into the ocean.
Six minutes might notsound like much, but the X-43A, the NASA-led project that set a speed record of7,545 miles (12,144 kilometers) per hour (Mach 9.8) in November 2004 on the vehicle's thirdand final flight, fired its supersonic-combustion ramjet for all of about 10seconds.
James Pittman, NASAprincipal investigator for the U.S. space agency's $75 million-a-yearhypersonics program, called the success of X-43A one of NASA's and the nation's"proudest moments" in the development of hypersonicvehicles.
"But [X-43A] wasonly for a few seconds," Pittman told reporters during a Sept. 3 mediabriefing at Langley Research Center, Hampton, Va. "This was a landmarkachievement in hypersonics. But in order for us to continue the development ofhypersonics, we've got to move along several different paths. One path is to gofrom seconds of operation to minutes of operation."
Another path, accordingto Pittman, is to develop a combined-cycle engine that can allow a vehicle totake off from a runway and accelerate to Mach 3 or Mach 4 before transitioningto the scramjet-powered flight necessary to achieve truly hypersonic speeds.Future applications for such a vehicle include next-generation space launch andvarious fast-reaction military systems.
X-51 goes part of thatdistance by incorporating the thermal-control systems and other technologiesneeded to demonstrate sustained hypersonic flight. Its Pratt & WhitneyRocketdyne-built engine also burns fairly conventional jet propellant ratherthan the comparatively hard-to-store hydrogen fuel that the X-43A burned on itsrecord-breaking flights. Pittman and other program officials said jet propellantis a better fit for the type of combined-cycle engines that are necessary forproducing operational vehicles of the sort NASA and the Air Force envision.
NASA is the juniorpartner in the $246 million X-51 program, with the Air Force putting up roughlythree-quarters of the funding. Nearly all of the rest comes from the U.S.Defense Advanced Research Projects Agency (DARPA),which views X-51 as a steppingstone to Blackswift, a flight demonstrator thatis slated to take off from a runway around 2012.
The goal of theBlackswift program is to accelerate the vehicle to a speed of more than Mach 6,maneuver it and then return to a runway landing. DARPA currently is said to bein pre-negotiation with a Lockheed Martin Skunk Works-led team that includesBoeing and Alliant Techsystems. A contract award is expected in September,according to sources.
Charlie Brink, the X-51program manager at the Air Force Research Laboratory's propulsion directorateat Wright Patterson Air Force Base outside Dayton, Ohio, said NASA had madeimportant contributions toward proving the flight readiness of X-51's engine.
Brink told reporters atthe Langley briefing that X-51 was in many ways a continuation of X-43C, aplanned NASA-Air Force follow-on to X-43A that NASA, he said, was forced toabandon when President George W. Bush refocused the agency in 2004 on returningto the Moon.
"Because of the Bushadministration's plan to go to Moon and Mars and other things that went on withNASA's budget, that program did not go through," Brink said of X-43C. Butby the time it became clear NASA was not going to go forward with X-43C, Brinksaid, the engine the Air Force was developing for the program "waseffectively 95 percent built."
NASA and the Air Forcewent ahead with the engine testing, conducting scores of cold-flow and hot-firetests in the high-speed tunnels at Langley.
Brink said the success ofthe tests encouraged the Air Force and DARPA to press on with X-51, theoverriding goal of which is to take the engines from the test stand and showthat they are ready to support military applications.
Testing at Langley is expected to continue through September. Pratt & Whitney Rocketdyne,meanwhile, is getting ready to ship the first of four flight-ready engines toX-51 prime contractor Boeing, which will integrate them into the WaveRidervehicle with an eye toward conducting the first of four planned flightsstarting in late 2009.
Brink said the flightswill take place out of Edwards Air Force Base in California. X-51 will becarried aloft by a B-52bomber.
The wedge-shapedhypersonic vehicle will be mounted atop a U.S. Army tactical missile systemsolid-rocket booster that will propel the X-51 to speeds in excess of Mach 4before its scramjet engine takes over. After five or six minutes of poweredflight, Brink said, X-51 will glide into the Pacific Ocean. Brink said the AirForce will coordinate with the Federal Aviation Administration to make surethat flights between Los Angeles and Hawaii and Australia are rerouted duringthe four-hour window for each X-51 flight. NASA and the Air Force asked theFederal Aviation Administration for similar flight restrictions when X-43Aflew, he said.
Also like X-43A, each oneof the X-51s are designed as single-use vehicles. "We would love torecover the vehicles," he said, adding that each flight model already isfilled with so much avionics and instrumentation that trying to install aparachute or any type of flotation device is prohibitively expensive and "design-wisevery tough."