The U.S. military may be able to deploy unmanned hypersonic weapons as early as 2025, an official said.
The Air Force on May 1 successfully flew the X-51 WaveRider, an experimental "scramjet" made by Boeing Co., reaching up to five times the speed of sound for a record three and a half minutes. The service called it "the longest air-breathing hypersonic flight ever."
The fourth and final mission was the culmination of a nine-year, $300 million project designed to test the viability of using more common jet fuels for hypersonic flight. The demonstration may lead to a program to develop weapons based on the technology by 2020 and usable systems by 2025, according to Charlie Brink, manager of the Air Force Research Laboratory's X-51A program.
"The goal is to be ready in the 2020 time frame so we could go to the war fighter and say, 'We're ready to go with this,' and then Air force leadership will make the decision if we want to go forward with a hypersonic weapon," he said last week during a conference call with reporters. It "probably would not start in the battlefield until at least the 2025-2030 time frame."
The technology has the potential to improve the ability of a weapon to enter enemy territory and shorten the time necessary for U.S. troops to respond to targets, Brink said.
"Today's cruise missiles might go 500 to 600 miles per hour and they might fly one or more hours to go after a very far away target," he said. "If you could get something that flies six times that speed, instead of taking it an hour to hit that target, it might only take you 10 minutes. That kind of capability to take out an enemy's air defenses or high-value target could be of great benefit to the war fighter as we move forward."
The technology is also unlikely to be confused with a nuclear weapon because its trajectory is unlike the bell-shaped curve of a ballistic missile.
The missile-like vehicle was dropped at 50,000 feet from the wing of a B-52H Stratofortress flown by Maj. Andrew Murphy, according to the Air Force. Powered by a solid-rocket booster, it accelerated to Mach 4.8 in less than 30 seconds. After it separated from the booster, the scramjet engine ignited and pushed it to a top speed of Mach 5.1 at 60,000 feet.
The propulsion system was built by Pratt & Whitney Rocketdyne, a unit of United Technologies Corp. that is being sold to GenCorp.
In all, the X-51 traveled more than 230 nautical miles in more than six minutes above the Point Mugu Naval Air Warfare Center Sea Range, according to the Air Force. After running out of fuel, it crashed into the ocean, as planned. The service released a video of the flight taken by a NASA pilot who flew alongside the bomber in a modified F-15 fighter jet.
"It was a very, very good day," Brink said. "We got all the data that we wanted on our last flight test vehicle, so we were ecstatic with the results."
The U.S. military has previously flown aircraft at hypersonic speeds of Mach 5 and above using hydrogen fuel. The X-51 is unique in that it uses a hydrocarbon-based jet fuel known as JP-7, a type of fuel derived from kerosene that also powered the SR-71 Blackbird, Brink said. The X-51's engine was started with a small amount of ethylene, then transitioned to JP-7, he said.
Hydrocarbon-based fuels are easier to store and more practical for military use, according to Joe Vogel, manager of the program at Chicago-based Boeing.
"The hydrocarbon fuel is a much easier storable type of a fuel, where hydrogen, though you can get more energy out of it, it's more energetic, it's also very difficult to store," he said during the conference call. "So from a practical standpoint, having a hydrocarbon fuel is a lot easier to work with."
The project was managed by the Air Force and funded by the Defense Advanced Research Projects Agency.
The service didn't say whether the X-51 will be followed by a similar project, only that research from the effort will be incorporated into the High Speed Strike Weapon, a program led by Lockheed Martin's Skunk Works division to develop a hypersonic missile for future bomber and fighter aircraft.