The final flight of the X-51A Waverider test program has accomplished a breakthrough, reaching Mach 5.1 over the Pacific Ocean on May 1 a little after 10 a.m. Pacific Time.
The cruiser traveled over 230 nautical miles in just over six minutes over the Point Mugu Naval Air Warfare Centre Sea Range. It was the longest of the four X-51A test flights and the longest air-breathing hypersonic flight ever.
The X-51A took off from the Air Force Test Centre at Edwards AFB, California under the wing of a B-52H Stratofortress. It was released at approximately 50,000 feet and accelerated to Mach 4.8 in about 26 seconds powered by a solid rocket booster. After separating from the booster, the cruiser’s scramjet engine then lit and accelerated to Mach 5.1 at 60,000 feet.
After exhausting its 240-second fuel supply, the vehicle continued to send back telemetry data until it splashed down into the ocean and was destroyed as designed. All told, 370 seconds of data was collected from the experiment.
This was the last of four test vehicles originally conceived when the $300 million technology demonstration program began in 2004. The program objective was to prove the viability of air-breathing, high-speed scramjet propulsion.
The X-51A is unique primarily due to its use of a hydrocarbon fuel in its supersonic combustion ramjet, or Scramjet, engine. Other vehicles have achieved hypersonic – generally defined as speeds above Mach 5 – flight with the use of hydrogen fuel. Without any moving parts, hydrocarbon fuel is injected into the scramjet’s combustion chamber where it mixes with the air rushing through the chamber and is ignited in a process likened to lighting a match in a hurricane.
The use of logistically supportable hydrocarbon fuel is widely considered vital for the practical application of hypersonic flight.
As a technology demonstration program, there is no immediate successor to the X-51A program. However, the Air Force will continue hypersonic research and the successes of the X-51A will pay dividends to the High Speed Strike Weapon program currently in its early formation phase with AFRL.