A renewed sense of urgency spurred by rivals Russia and China has pushed the U.S. military to speed up the development of hypersonic technology. The Army, Navy and Air Force are all closely involved in the campaign with more test flights coming in 2020.
The systems are characterized by their maneuverability and ability to reach speeds of Mach 5 and greater.
Michael Griffin, undersecretary of defense for research and engineering, has been an outspoken advocate for hypersonic weapon research and development.
"Hypersonic capabilities remain a major department-wide modernization focus, and DoD is accelerating hypersonic systems development and demonstration," he said in March during testimony before the House Armed Services Committee's subcommittee on intelligence and emerging threats and capabilities.
The Defense Department requested $2.6 billion toward hypertonics in President Donald Trump's fiscal year 2020 budget request and is nearly doubling its long-term investments from $6 billion to $11.2 billion over the next five years, Griffin noted.
"We have significantly increased flight testing, as we intend to conduct approximately 40 flight tests over the next few years, to accelerate the delivery of capability to our warfighters years earlier than previously planned," he said in his prepared testimony.
For example, the Defense Advanced Research Projects Agency and the Air Force are developing two hypersonic vehicle prototypes that are due to fly by the end of the year, said Steven Walker, DARPA's director.
One vehicle is part of the hypersonic air-breathing weapon concept, or HAWC, program. The other is the tactical boost-glide, or TBG, effort, Walker told reporters during a meeting in Washington, DC in May.
"We're on track for both to have flights... before the calendar year ends," he said. However, that might be questionable because once "you actually get into the building of these things and qualifying the hardware,... things tend to slip."
Walker said there is a chance the vehicles could fly in early 2020 instead, but was hopeful that would not be the case. DARPA has been working on both efforts alongside the Air Force since 2012, he noted.
These initiatives were focused on tactical theater-level operations, he said.
Tactical boost-glide is meant to develop an advanced system that can be launched from a rocket, he said. The vehicle reaches high speeds as it glides back toward Earth.
The air-breathing concept takes advantage of work DARPA has previously done in scramjet technology to create a system that can be self-powered after being launched from an aircraft such as a B-52.
According to the agency, the effort is focusing on three technology challenge areas including air-vehicle feasibility, effectiveness and affordability.
"Two very different concepts, but when you're talking hypersonics it's good to have what I consider intended redundancy," Walker said. It's difficult to manufacture "materials and propulsion systems that last in 3,000-degree Fahrenheit...