Last spring, representatives from the Defense Advanced Research Projects Agency, or DARPA, came to the office of then-Deputy Secretary of Defense Bob Work and laid out some hard truths about U.S. development of hypersonic weapons — the ones meant to travel more than five times faster than sound. The message from the military scientists: U.S. hypersonics aren’t keeping up with Russia and China.
Early on Thursday, national-security professionals across Washington, D.C., awoke to news that Russian President Vladimir Putin was claiming to have created an air-defense-beating, “invincible” hypersonic missile — though offering no particular proof. New DARPA director Steven Walker declined to comment on Putin’s assertion but told defense reporters that his teams are working as they can to test a hypersonic missile before 2020 — and that they need more help.
“Most of our programs at DARPA [related to hypersonic research] are testing at one facility,” Walker said: NASA’s Langley Research Center in Virginia, where research and testing is happening around the clock.
He says he needs more testing infrastructure.
“If you look at some of our peer competitors, China being one, the number of facilities that they’ve built to do hypersonics… surpasses the number we have in this country. It’s quickly surpassing it by 2 or 3 times. It is very clear that China has made this one of their national priorities. We need to do the same,” he said.
DARPA and the U.S. Air Force are working on two hypersonic weapon concepts. One is the Tactical Boost Glide weapon. A rocket accelerates the craft to very high speeds and altitudes, then glides back to earth. The other is the hypersonic air-breathing weapon concept, or HAWC, whose scramjet engine takes in air at supersonic speeds, compresses it, and pushes it through a nozzle out the back.
The military is requesting a lot more money for hypersonic research following some technological breakthroughs within the last few years. The trend began in 2010 with the achievement of 200 seconds of supersonic combustion in the air, on the X-51 Waverider experimental aircraft.
Current efforts, Walker said, are keenly focused not just on achieving new research breakthroughs, but on putting those into weapons and figuring out how much those weapons will cost.
“Things are moving,” he said. “This is becoming not just [a science and technology] thing. The services are interested in moving forward with real capabilities.”
The military will increase spending for testing and for secondary (or “follow-on”) programs as part of its FY 19 budget request, which includes some $14.3 million for the Tactical Boost Glide effort.
Walker announced on Thursday that the fruits of the research will also further the development of long-range precision weapons for the Army. The military is requesting $53 million for that, part of a program called Operational Fires. And it’s requesting another $50 million to demonstrate a ground-launched hypersonic system that incorporates tech from the Tactical Boost Glide program.
There’s growing support and interest from the leadership as well, said Walker, who reported that Michael Griffin, the new undersecretary of defense for research and engineering and a former NASA administrator, was making hypersonics one of his “top priorities.”
The Air Force program for the boost-glide system is focused on “an operational prototype in the 2022 period,” Walker said. There’s also work on a $140 million program to create a hypersonic craft capable of multiple flights, using tech that has come out of the HAWC.
“We have a program we are working with NASA … called the advanced full range engine. It’s basically developing the combined cycle propulsion system you would need for a reusable platform. We’re making good progress on that. We expect to test the engine in  or  on the ground” at a NASA facility that boasts a 100-square-foot wind tunnel. “Whether we actually go to a flight demo, that’s not part of the program right now,” he said.
The goal is to get a conventional turbine engine that can get up to Mach 2 and then transition seamlessly to a scramjet engine to transition to higher speeds. “You can actually take off like an airplane, fly up to Mach 6, do your mission, and come back down,” said Walker.
In hypersonics, optimism and disappointment are in a constant push and pull, just like the physical forces that act on airplanes flying faster than sound. It’s nearly impossible to predict how a bunch of interconnected metal and electronica are going to behave moving at those speeds. The laws of physics still apply, but at that point, you start getting into the laws’ very fine print.
Why Designing Hypersonic Aircraft Is So Hard
“The tricky thing about hypersonics is that equilibrium flows become non-equilibrium,” said Walker, referring to the effects of air pressure on the physical structure of solid objects at high speeds.
“Lots of friction [and] separation, potentially in the flows [of air, energy and physical materials]” happen in such a way that very good calculations about the material effects become “more guesses than actual reality,” he said.
Different mathematical tools and techniques can make that guesswork easier, such as the Reynolds-Averaged Navier Stokes, or RAND, formula, which allows you to predict what will happen as air moves across object surfaces.
Nicholas Bisek, a research aerospace engineer at the hypersonic sciences branch of the Air Force Research Lab’s Aerospace Systems Directorate, says that Navier Stokes is one of many different mathematical models you can use to figure out solid material interaction at high speeds. But when you apply those formulas to something as big as an aircraft, you have to do it again and again, chewing over the problem millimeter by millimeter to better calculate the effects of air, pressure, and other phenomenon at the most minute level.
“We have to move away from even RAND to particle-based methods that allow us to model individual particles as opposed to fluid treated as a continuum,” he says.
The Air Force is looking toward supercomputers to help with those tiny but numerically herculean math problems. In February, it awarded some $57 million to Hewlett Packard Enterprise, or HPE.
It’s a bit like doing a jigsaw puzzle with highly complex equations. Getting everything to fit together is beyond what humans can do with Sharpies and blackboards, according to Kevin Newmeyer, chief of staff for the high-performance computing modernization program for defense at the military’s High Performance Computing Modernization Program. “Instead of modeling a single aircraft, you have to model the surface and air in blocks as small as centimeters, millimeters. You join these calculations together in a cascading set of calculations,” he said.
But even here, at the cutting edge of big data and big computing, you still get a very small and very brief window into how air and solid surface are interacting. “One of these calculations may take days or even up to a couple of weeks to model,” Newmeyer said. That model will run 15 to 20 seconds, “if it goes that long.”
Supercomputers are useful; but physical testing facilities are essential, said Walker.
“Another complicating factor in hypersonics is you can only simulate so much on the ground. It’s hard to get the velocity, the temperature, the Mach number all correct as the vehicle would experience [them] in the air. We do component testing on the ground. We’ll do this engine testing on the ground. With hypersonics, you really have to fly,”
Fly they will. In 2019, he says, expect “lots of tests.”