Third test flight of X-51A hypersonic missile ends in failure
By David Szondy
August 15, 2012
Wright Patterson AFB has confirmed in an official press release that Tuesday’s test of the Waverider X-51A unmanned hypersonic missile has failed. Launched from a B-52 bomber over Point Mugu Naval Air Warfare Center Sea Range at 11:36 AM PST, the separation from the bomber and ignition of the X-51A’s rocket booster went as planned. However, 16 seconds into the flight a fault occurred in one of the missile’s control fins before the scramjet could start, resulting in the craft losing control, and the X-51A was today officially reported as "lost." At present, there are no further official details as to the fate of the craft, but the New York Daily News reports that the missile crashed into the Pacific Ocean while NBC News states that the X-51A broke up in flight and fell into the ocean in "pieces."
"It is unfortunate that a problem with this subsystem caused a termination before we could light the Scramjet engine," said Charlie Brink, X-51A Program Manager for Air Force Research Laboratory. "All our data showed we had created the right conditions for engine ignition and we were very hopeful to meet our test objectives."
This was the third test of the unmanned Waverider X-51A. The first in May, 2010 set a new record for hypersonic flight of 140 seconds. However, the second flight in June, 2011 ended in failure when the engine cut out before reaching Mach 5 (3,307 knots, 3,806 mph, 6,125 km/h) and couldn’t restart itself before the missile crashed into the ocean.
A joint effort by the U.S. Air Force Research Laboratory, the Defense Advanced Research Projects Agency (DARPA), Pratt and Whitney Rocketdyne and Boeing, the Waverider X-51A is a testbed for the new SJY61 Supersonic Combustion Ramjet (scramjet) developed by Pratt and Whitney. Like a ramjet, a scramjet is a jet engine with no moving parts. Instead of compressing air before burning by using turbines, as in a conventional jet engine, the scramjet compresses the air with the vehicle’s own speed. The difference between a ramjet and a scramjet is that, where the ramjet slows down the flow of air inside it to subsonic speeds, the scramjet runs the air through it at supersonic velocity. This allows a scramjet-equipped vehicle to fly at hypersonic speeds.
Unfortunately, it also means that the craft can’t operate at much below hypersonic speed or at low altitude where the air is so thick that it would be like jamming a breeze block through the engine. This means that the 14-foot (4.26 m) Waverider X-51A has to be dropped from a B-52 and lofted to its operational speed of Mach 6 (3,969 knots, 4,567 mph, 7,350 km/h) by a rocket that’s almost half as long as Waverider itself. Once underway, the missile operates autonomously until it consumes its 270 pounds (122.47 kg) of JP-7 jet fuel and then executes a pre-programmed ditching in the ocean.
Because the Waverider X-51A is a technology demonstrator rather than a prototype, Tuesday's flight was intended to test the underlying technology, such as the performance of the scramjet engine. Having already broken endurance records on the first flight, the third would not only have put the failure of the second behind, but would have seen the X-51A reach new endurance and speed records with the first flight's Mach 5 run bested by the third's Mach 6. The test would also have used Waverider's signature ability to ride its own shockwave at hypersonic speeds from which it derives its name. After completing its test run in about four minutes, the craft would then have made a controlled ditching in the Pacific Ocean about 400 nautical miles (460 mi, 741 km) downrange from the drop zone.
The Waverider X-51A is part of the U.S. Pentagon’s program to develop a hypersonic missile capable of striking with conventional weapons anywhere in the world within a matter of minutes. Currently, the only systems with that capability are ballistic missiles designed to carry nuclear warheads. All other ordnance, such as cruise missiles, can take hours to reach their targets. ICBMs can’t be used in conventional strikes for fear of being mistaken for a nuclear attack, so the U.S. Air Force wants an air-breathing missile capable of speeds of Mach 6 (3,969 knots, 4,567 mph, 7,350 kph) or better. The technology also has application for reconnaissance, orbital launches and commercial aviation.
A fourth test flight of the X-51A is planned, though when will likely depend on the official results of Tuesday’s test.